Sound reduction by metamaterial-based acoustic enclosure

Directory of Open Access Journals (Sweden)

Shanshan Yao

2014-12-01

Full Text Available In many practical systems, acoustic radiation control on noise sources contained within a finite volume by an acoustic enclosure is of great importance, but difficult to be accomplished at low frequencies due to the enhanced acoustic-structure interaction. In this work, we propose to use acoustic metamaterials as the enclosure to efficiently reduce sound radiation at their negative-mass frequencies. Based on a circularly-shaped metamaterial model, sound radiation properties by either central or eccentric sources are analyzed by numerical simulations for structured metamaterials. The parametric analyses demonstrate that the barrier thickness, the cavity size, the source type, and the eccentricity of the source have a profound effect on the sound reduction. It is found that increasing the thickness of the metamaterial barrier is an efficient approach to achieve large sound reduction over the negative-mass frequencies. These results are helpful in designing highly efficient acoustic enclosures for blockage of sound in low frequencies.

Sound reduction by metamaterial-based acoustic enclosure

Energy Technology Data Exchange (ETDEWEB)

Yao, Shanshan; Li, Pei; Zhou, Xiaoming; Hu, Gengkai, E-mail: hugeng@bit.edu.cn [Key Laboratory of Dynamics and Control of Flight Vehicle, Ministry of Education and School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081 (China)

2014-12-15

In many practical systems, acoustic radiation control on noise sources contained within a finite volume by an acoustic enclosure is of great importance, but difficult to be accomplished at low frequencies due to the enhanced acoustic-structure interaction. In this work, we propose to use acoustic metamaterials as the enclosure to efficiently reduce sound radiation at their negative-mass frequencies. Based on a circularly-shaped metamaterial model, sound radiation properties by either central or eccentric sources are analyzed by numerical simulations for structured metamaterials. The parametric analyses demonstrate that the barrier thickness, the cavity size, the source type, and the eccentricity of the source have a profound effect on the sound reduction. It is found that increasing the thickness of the metamaterial barrier is an efficient approach to achieve large sound reduction over the negative-mass frequencies. These results are helpful in designing highly efficient acoustic enclosures for blockage of sound in low frequencies.

Reduction of Altitude Diffuser Jet Noise Using Water Injection

Science.gov (United States)

Allgood, Daniel C.; Saunders, Grady P.; Langford, Lester A.

2011-01-01

A feasibility study on the effects of injecting water into the exhaust plume of an altitude rocket diffuser for the purpose of reducing the far-field acoustic noise has been performed. Water injection design parameters such as axial placement, angle of injection, diameter of injectors, and mass flow rate of water have been systematically varied during the operation of a subscale altitude test facility. The changes in acoustic far-field noise were measured with an array of free-field microphones in order to quantify the effects of the water injection on overall sound pressure level spectra and directivity. The results showed significant reductions in noise levels were possible with optimum conditions corresponding to water injection at or just upstream of the exit plane of the diffuser. Increasing the angle and mass flow rate of water injection also showed improvements in noise reduction. However, a limit on the maximum water flow rate existed as too large of flow rate could result in un-starting the supersonic diffuser.

Applications of aero-acoustic analysis to wind turbine noise control

International Nuclear Information System (INIS)

Lowson, M.V.

1992-01-01

Wind turbine noise generation mechanisms are essentially equivalent to the aero-acoustic mechanisms of other rotors, which have been studied in depth for many years. Basic sources for the wind turbine noise radiation process are defined, and their significance assessed. From the analysis, areas of potential improvement in wind turbine noise prediction are defined. Suggestions are made for approaches to wind turbine noise control which separate the noise problems at cut-in from those at rated power. Some of these offer the possibility of noise reduction without unfavourable effects on performance. (author)

Applications of aero-acoustic analysis to wind turbine noise control

International Nuclear Information System (INIS)

Lowson, M.

1993-01-01

Wind turbine noise generation mechanisms are essentially equivalent to the aero-acoustic mechanisms of other rotors, which have been studied in depth for many years. Basic sources for the wind turbine noise radiation process are defined, and their significance assessed. From the analysis, areas of potential improvement in wind turbine noise prediction are defined. Suggestions are made for approaches to wind turbine noise control which separate the noise problems at cut-in from those at rated power. Some of these offer the possibility of noise reduction without unfavourable effects on performance. (author)

Blade-Mounted Flap Control for BVI Noise Reduction Proof-of-Concept Test

Science.gov (United States)

Dawson, Seth; Hassan, Ahmed; Straub, Friedrich; Tadghighi, Hormoz

1995-01-01

This report describes a wind tunnel test of the McDonnell Douglas Helicopter Systems (MDHS) Active Flap Model Rotor at the NASA Langley 14- by 22-Foot Subsonic Tunnel. The test demonstrated that BVI noise reductions and vibration reductions were possible with the use of an active flap. Aerodynamic results supported the acoustic data trends, showing a reduction in the strength of the tip vortex with the deflection of the flap. Acoustic results showed that the flap deployment, depending on the peak deflection angle and azimuthal shift in its deployment schedule, can produce BVI noise reductions as much as 6 dB on the advancing and retreating sides. The noise reduction was accompanied by an increase in low frequency harmonic noise and high frequency broadband noise. A brief assessment of the effect of the flap on vibration showed that significant reductions were possible. The greatest vibration reductions (as much as 76%) were found in the four per rev pitching moment at the hub. Performance improvement cam results were inconclusive, as the improvements were predicted to be smaller than the resolution of the rotor balance.

Propulsion Noise Reduction Research in the NASA Advanced Air Transport Technology Project

Science.gov (United States)

Van Zante, Dale; Nark, Douglas; Fernandez, Hamilton

2017-01-01

The Aircraft Noise Reduction (ANR) sub-project is focused on the generation, development, and testing of component noise reduction technologies progressing toward the NASA far term noise goals while providing associated near and mid-term benefits. The ANR sub-project has efforts in airframe noise reduction, propulsion (including fan and core) noise reduction, acoustic liner technology, and propulsion airframe aeroacoustics for candidate conventional and unconventional aircraft configurations. The current suite of propulsion specific noise research areas is reviewed along with emerging facility and measurement capabilities. In the longer term, the changes in engine and aircraft configuration will influence the suite of technologies necessary to reduce noise in next generation systems.

Field-Deployable Acoustic Digital Systems for Noise Measurement

Science.gov (United States)

Shams, Qamar A.; Wright, Kenneth D.; Lunsford, Charles B.; Smith, Charlie D.

2000-01-01

Langley Research Center (LaRC) has for years been a leader in field acoustic array measurement technique. Two field-deployable digital measurement systems have been developed to support acoustic research programs at LaRC. For several years, LaRC has used the Digital Acoustic Measurement System (DAMS) for measuring the acoustic noise levels from rotorcraft and tiltrotor aircraft. Recently, a second system called Remote Acquisition and Storage System (RASS) was developed and deployed for the first time in the field along with DAMS system for the Community Noise Flight Test using the NASA LaRC-757 aircraft during April, 2000. The test was performed at Airborne Airport in Wilmington, OH to validate predicted noise reduction benefits from alternative operational procedures. The test matrix was composed of various combinations of altitude, cutback power, and aircraft weight. The DAMS digitizes the acoustic inputs at the microphone site and can be located up to 2000 feet from the van which houses the acquisition, storage and analysis equipment. Digitized data from up to 10 microphones is recorded on a Jaz disk and is analyzed post-test by microcomputer system. The RASS digitizes and stores acoustic inputs at the microphone site that can be located up to three miles from the base station and can compose a 3 mile by 3 mile array of microphones. 16-bit digitized data from the microphones is stored on removable Jaz disk and is transferred through a high speed array to a very large high speed permanent storage device. Up to 30 microphones can be utilized in the array. System control and monitoring is accomplished via Radio Frequency (RF) link. This paper will present a detailed description of both systems, along with acoustic data analysis from both systems.

Noise Reduction Potential of Cellular Metals

Directory of Open Access Journals (Sweden)

Björn Hinze

2012-06-01

Full Text Available Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 °C only metallic or ceramic structures can be used. Due to fatigue loading and the notch effect of the pores, mechanical properties of porous metals are superior to the ones of ceramic structures. Consequently, cellular metals like metallic foams, sintered metals, or sintered metal felts are most promising materials. However, acoustic absorption depends highly on pore morphology and porosity. Therefore, both parameters must be characterized precisely to analyze the correlation between morphology and noise reduction performance. The objective of this study is to analyze the relationship between pore morphology and acoustic absorption performance. The absorber materials are characterized using image processing based on two dimensional microscopy images. The sound absorption properties are measured using an impedance tube. Finally, the correlation of acoustic behavior, pore morphology, and porosity is outlined.

Noise reduction with complex bilateral filter.

Science.gov (United States)

Matsumoto, Mitsuharu

2017-12-01

This study introduces a noise reduction technique that uses a complex bilateral filter. A bilateral filter is a nonlinear filter originally developed for images that can reduce noise while preserving edge information. It is an attractive filter and has been used in many applications in image processing. When it is applied to an acoustical signal, small-amplitude noise is reduced while the speech signal is preserved. However, a bilateral filter cannot handle noise with relatively large amplitudes owing to its innate characteristics. In this study, the noisy signal is transformed into the time-frequency domain and the filter is improved to handle complex spectra. The high-amplitude noise is reduced in the time-frequency domain via the proposed filter. The features and the potential of the proposed filter are also confirmed through experiments.

Potential for Landing Gear Noise Reduction on Advanced Aircraft Configurations

Science.gov (United States)

Thomas, Russell H.; Nickol, Craig L.; Burley, Casey L.; Guo, Yueping

2016-01-01

The potential of significantly reducing aircraft landing gear noise is explored for aircraft configurations with engines installed above the wings or the fuselage. An innovative concept is studied that does not alter the main gear assembly itself but does shorten the main strut and integrates the gear in pods whose interior surfaces are treated with acoustic liner. The concept is meant to achieve maximum noise reduction so that main landing gears can be eliminated as a major source of airframe noise. By applying this concept to an aircraft configuration with 2025 entry-into-service technology levels, it is shown that compared to noise levels of current technology, the main gear noise can be reduced by 10 EPNL dB, bringing the main gear noise close to a floor established by other components such as the nose gear. The assessment of the noise reduction potential accounts for design features for the advanced aircraft configuration and includes the effects of local flow velocity in and around the pods, gear noise reflection from the airframe, and reflection and attenuation from acoustic liner treatment on pod surfaces and doors. A technical roadmap for maturing this concept is discussed, and the possible drag increase at cruise due to the addition of the pods is identified as a challenge, which needs to be quantified and minimized possibly with the combination of detailed design and application of drag reduction technologies.

Measuring the background acoustic noise in the BN-600 steam generator

International Nuclear Information System (INIS)

Yugaj, V.S.; Zhukovets, V.N.; Ivannikov, V.I.; Vylomov, V.V.; Ryabinin, F.; Chernykh, P.G.; Flejsher, Yu.V.

1987-01-01

Acoustic noises in the lower chambers of evaporation and intermediate overheating moduli of the BN-600 reactor steam generator are measured. Bachground noises are registered in the whole range of frequencies studied, from 0.63 to 160 kHz. The comparison of noise spectra in evaporator and overheater has revealed a certain difference. However the general tendency is the reduction of the noise level at high frequencies > 8 kHz. The increase of the noise level at low steam content is observed only in a narrow of frequency range of 3-6 kHz

Experimental demonstration of wind turbine noise reduction through optimized airfoil shape and trailing-edge serrations

Energy Technology Data Exchange (ETDEWEB)

Oerlemans, S. [National Aerospace Laboratory NLR, Emmeloord (Netherlands); Schepers, J.G. [Unit Wind Energy, Energy research Centre of the Netherlands ECN, Petten (Netherlands); Guidati, G.; Wagner, S. [Institut fuer Aerodynamik und Gasdynamik IAG, Universitaet Stuttgart (Germany)

2001-07-15

The objective of the European project DATA (Design and Testing of Acoustically Optimized Airfoils for Wind Turbines) is a reduction of trailing-edge (TE) noise by modifying the airfoil shape and/or the application of trailing-edge serrations. This paper describes validation measurements that were performed in the DNW-LLF wind tunnel, on a model scale wind turbine with a two-bladed 4.5 m diameter rotor which was designed in the project. Measurements were done for one reference- and two acoustically optimized rotors, for varying flow conditions. The aerodynamic performance of the rotors was measured using a torque meter in the hub, and further aerodynamic information was obtained from flow visualization on the blades. The acoustic measurements were done with a 136 microphone out-of-flow acoustic array. Besides the location of the noise sources in the (stationary) rotor plane, a new acoustic processing method enabled identification of dominant noise source regions on the rotating blades. The results show dominant noise sources at the trailing-edge of the blade, close to the tip. The optimized airfoil shapes result in a significant reduction of TE noise levels with respect to the reference rotor, without loss in power production. A further reduction can be achieved by the application of trailing-edge serrations. The aerodynamic measurements are generally in good agreement with the aerodynamic predictions made during the design of the model turbine.

Prediction of interior noise due to random acoustic or turbulent boundary layer excitation using statistical energy analysis

Science.gov (United States)

Grosveld, Ferdinand W.

1990-01-01

The feasibility of predicting interior noise due to random acoustic or turbulent boundary layer excitation was investigated in experiments in which a statistical energy analysis model (VAPEPS) was used to analyze measurements of the acceleration response and sound transmission of flat aluminum, lucite, and graphite/epoxy plates exposed to random acoustic or turbulent boundary layer excitation. The noise reduction of the plate, when backed by a shallow cavity and excited by a turbulent boundary layer, was predicted using a simplified theory based on the assumption of adiabatic compression of the fluid in the cavity. The predicted plate acceleration response was used as input in the noise reduction prediction. Reasonable agreement was found between the predictions and the measured noise reduction in the frequency range 315-1000 Hz.

Effects of directional microphone and adaptive multichannel noise reduction algorithm on cochlear implant performance.

Science.gov (United States)

Chung, King; Zeng, Fan-Gang; Acker, Kyle N

2006-10-01

Although cochlear implant (CI) users have enjoyed good speech recognition in quiet, they still have difficulties understanding speech in noise. We conducted three experiments to determine whether a directional microphone and an adaptive multichannel noise reduction algorithm could enhance CI performance in noise and whether Speech Transmission Index (STI) can be used to predict CI performance in various acoustic and signal processing conditions. In Experiment I, CI users listened to speech in noise processed by 4 hearing aid settings: omni-directional microphone, omni-directional microphone plus noise reduction, directional microphone, and directional microphone plus noise reduction. The directional microphone significantly improved speech recognition in noise. Both directional microphone and noise reduction algorithm improved overall preference. In Experiment II, normal hearing individuals listened to the recorded speech produced by 4- or 8-channel CI simulations. The 8-channel simulation yielded similar speech recognition results as in Experiment I, whereas the 4-channel simulation produced no significant difference among the 4 settings. In Experiment III, we examined the relationship between STIs and speech recognition. The results suggested that STI could predict actual and simulated CI speech intelligibility with acoustic degradation and the directional microphone, but not the noise reduction algorithm. Implications for intelligibility enhancement are discussed.

Acoustic plane waves normally incident on a clamped panel in a rectangular duct. [to explain noise reduction curves for reducing interior noise in aircraft

Science.gov (United States)

Unz, H.; Roskam, J.

1979-01-01

The theory of acoustic plane wave normally incident on a clamped panel in a rectangular duct is developed. The coupling theory between the elastic vibrations of the panel (plate) and the acoustic wave propagation in infinite space and in the rectangular duct is considered. The partial differential equation which governs the vibration of the panel (plate) is modified by adding to its stiffness (spring) forces and damping forces, and the fundamental resonance frequency and the attenuation factor are discussed. The noise reduction expression based on the theory is found to agree well with the corresponding experimental data of a sample aluminum panel in the mass controlled region, the damping controlled region, and the stiffness controlled region. All the frequency positions of the upward and downward resonance spikes in the sample experimental data are identified theoretically as resulting from four cross interacting major resonance phenomena: the cavity resonance, the acoustic resonance, the plate resonance, and the wooden back panel resonance.

Binaural noise reduction via cue-preserving MMSE filter and adaptive-blocking-based noise PSD estimation

Science.gov (United States)

Azarpour, Masoumeh; Enzner, Gerald

2017-12-01

Binaural noise reduction, with applications for instance in hearing aids, has been a very significant challenge. This task relates to the optimal utilization of the available microphone signals for the estimation of the ambient noise characteristics and for the optimal filtering algorithm to separate the desired speech from the noise. The additional requirements of low computational complexity and low latency further complicate the design. A particular challenge results from the desired reconstruction of binaural speech input with spatial cue preservation. The latter essentially diminishes the utility of multiple-input/single-output filter-and-sum techniques such as beamforming. In this paper, we propose a comprehensive and effective signal processing configuration with which most of the aforementioned criteria can be met suitably. This relates especially to the requirement of efficient online adaptive processing for noise estimation and optimal filtering while preserving the binaural cues. Regarding noise estimation, we consider three different architectures: interaural (ITF), cross-relation (CR), and principal-component (PCA) target blocking. An objective comparison with two other noise PSD estimation algorithms demonstrates the superiority of the blocking-based noise estimators, especially the CR-based and ITF-based blocking architectures. Moreover, we present a new noise reduction filter based on minimum mean-square error (MMSE), which belongs to the class of common gain filters, hence being rigorous in terms of spatial cue preservation but also efficient and competitive for the acoustic noise reduction task. A formal real-time subjective listening test procedure is also developed in this paper. The proposed listening test enables a real-time assessment of the proposed computationally efficient noise reduction algorithms in a realistic acoustic environment, e.g., considering time-varying room impulse responses and the Lombard effect. The listening test outcome

Acoustic Performance of Novel Fan Noise Reduction Technologies for a High Bypass Model Turbofan at Simulated Flights Conditions

Science.gov (United States)

Elliott, David M.; Woodward, Richard P.; Podboy, Gary G.

2010-01-01

Two novel fan noise reduction technologies, over the rotor acoustic treatment and soft stator vane technologies, were tested in an ultra-high bypass ratio turbofan model in the NASA Glenn Research Center s 9- by 15-Foot Low-Speed Wind Tunnel. The performance of these technologies was compared to that of the baseline fan configuration, which did not have these technologies. Sideline acoustic data and hot film flow data were acquired and are used to determine the effectiveness of the various treatments. The material used for the over the rotor treatment was foam metal and two different types were used. The soft stator vanes had several internal cavities tuned to target certain frequencies. In order to accommodate the cavities it was necessary to use a cut-on stator to demonstrate the soft vane concept.

Acoustics. Measurement of sound insulation in buildings and of building elements. Laboratory measurements of the reduction of transmitted impact noise by floor coverings on a heavyweight standard floor

CERN Document Server

British Standards Institution. London

1998-01-01

Acoustics. Measurement of sound insulation in buildings and of building elements. Laboratory measurements of the reduction of transmitted impact noise by floor coverings on a heavyweight standard floor

Aero-acoustic noise of wind turbines. Noise prediction models

Energy Technology Data Exchange (ETDEWEB)

Maribo Pedersen, B. [ed.

1997-12-31

Semi-empirical and CAA (Computational AeroAcoustics) noise prediction techniques are the subject of this expert meeting. The meeting presents and discusses models and methods. The meeting may provide answers to the following questions: What Noise sources are the most important? How are the sources best modeled? What needs to be done to do better predictions? Does it boil down to correct prediction of the unsteady aerodynamics around the rotor? Or is the difficult part to convert the aerodynamics into acoustics? (LN)

A Background Noise Reduction Technique Using Adaptive Noise Cancellation for Microphone Arrays

Science.gov (United States)

Spalt, Taylor B.; Fuller, Christopher R.; Brooks, Thomas F.; Humphreys, William M., Jr.; Brooks, Thomas F.

2011-01-01

Background noise in wind tunnel environments poses a challenge to acoustic measurements due to possible low or negative Signal to Noise Ratios (SNRs) present in the testing environment. This paper overviews the application of time domain Adaptive Noise Cancellation (ANC) to microphone array signals with an intended application of background noise reduction in wind tunnels. An experiment was conducted to simulate background noise from a wind tunnel circuit measured by an out-of-flow microphone array in the tunnel test section. A reference microphone was used to acquire a background noise signal which interfered with the desired primary noise source signal at the array. The technique s efficacy was investigated using frequency spectra from the array microphones, array beamforming of the point source region, and subsequent deconvolution using the Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) algorithm. Comparisons were made with the conventional techniques for improving SNR of spectral and Cross-Spectral Matrix subtraction. The method was seen to recover the primary signal level in SNRs as low as -29 dB and outperform the conventional methods. A second processing approach using the center array microphone as the noise reference was investigated for more general applicability of the ANC technique. It outperformed the conventional methods at the -29 dB SNR but yielded less accurate results when coherence over the array dropped. This approach could possibly improve conventional testing methodology but must be investigated further under more realistic testing conditions.

Engine-propeller power plant aircraft community noise reduction key methods

Science.gov (United States)

Moshkov P., A.; Samokhin V., F.; Yakovlev A., A.

2018-04-01

Basic methods of aircraft-type flying vehicle engine-propeller power plant noise reduction were considered including single different-structure-and-arrangement propellers and piston engines. On the basis of a semiempirical model the expressions for blade diameter and number effect evaluation upon propeller noise tone components under thrust constancy condition were proposed. Acoustic tests performed at Moscow Aviation institute airfield on the whole qualitatively proved the obtained ratios. As an example of noise and detectability reduction provision a design-and-experimental estimation of propeller diameter effect upon unmanned aircraft audibility boundaries was performed. Future investigation ways were stated to solve a low-noise power plant design problem for light aircraft and unmanned aerial vehicles.

Acoustic guide for noise-transmission testing of aircraft

Science.gov (United States)

Vaicaitis, Rimas (Inventor)

1987-01-01

Selective testing of aircraft or other vehicular components without requiring disassembly of the vehicle or components was accomplished by using a portable guide apparatus. The device consists of a broadband noise source, a guide to direct the acoustic energy, soft sealing insulation to seal the guide to the noise source and to the vehicle component, and noise measurement microphones, both outside the vehicle at the acoustic guide output and inside the vehicle to receive attenuated sound. By directing acoustic energy only to selected components of a vehicle via the acoustic guide, it is possible to test a specific component, such as a door or window, without picking up extraneous noise which may be transmitted to the vehicle interior through other components or structure. This effect is achieved because no acoustic energy strikes the vehicle exterior except at the selected component. Also, since the test component remains attached to the vehicle, component dynamics with vehicle frame are not altered.

DFT-Domain Based Single-Microphone Noise Reduction for Speech Enhancement

DEFF Research Database (Denmark)

C. Hendriks, Richard; Gerkmann, Timo; Jensen, Jesper

As speech processing devices like mobile phones, voice controlled devices, and hearing aids have increased in popularity, people expect them to work anywhere and at any time without user intervention. However, the presence of acoustical disturbances limits the use of these applications, degrades...... their performance, or causes the user difficulties in understanding the conversation or appreciating the device. A common way to reduce the effects of such disturbances is through the use of single-microphone noise reduction algorithms for speech enhancement. The field of single-microphone noise reduction...

Experimental identification of noise reduction properties of honeycomb panels using a small cabin

OpenAIRE

D'Ortona, Vittorio; Vivolo, Marianna; Pluymers, Bert; Vandepitte, Dirk; Desmet, Wim

2013-01-01

A procedure to identify the noise reduction properties of panels by means of a single cabin test setup is discussed. The complexity of the sound pressure field that builds up in the acoustic volume requires the support of advanced numerical techniques allowing for the evaluation of noise and vibration performances. Numerical models are used to predict the structural dynamics and the vibro-acoustic behaviour of the tested panel. Both Finite Element and Boundary Element simulations are validate...

Aero-acoustics noise assessment for Wind-Lens turbine

International Nuclear Information System (INIS)

Hashem, I.; Mohamed, M.H.; Hafiz, A.A.

2017-01-01

This paper introduces an aero-acoustic computational study that investigates the noise caused by one of the most promising wind energy conversion concepts, namely the 'Wind-Lens' technology. The hybrid method - where the flow field and acoustic field are solved separately, was deemed to be an appropriate tool to compute this study. The need to investigate this phenomenon increased gradually, since the feasibility of utilizing Wind-Lens turbine within densely populated cities and urban areas depends largely on their noise generation. Ffowcs Williams-Hawkings (FW-H) equation and its integral solution are used to predict the noise radiating to the farfield. CFD Simulations of transient three-dimensional flow field using (URANS) unsteady Reynolds-averaged Navier-Stokes equations are computed to acquire the acoustic sources location and sound intensity. Then, the noise propagates from the before-mentioned sources to pre-defined virtual microphones positioned in different locations. ANSYS-FLUENT is used to calculate the flow field on and around such turbines which is required for the FW-H code. Some effective parameters are investigated such as Wind-Lens shape, brim height and tip speed ratio. Comparison of the noise emitted from the bare wind turbine and different types of Wind-Lens turbine reveals that, the Wind-Lens generates higher noise intensity. - Highlights: • Aero-acoustic noise generated by wind turbines are one of the major challenges. • Noise from wind turbine equipped with a brimmed diffuser is investigated. • A computational aero-acoustic study using the hybrid method is introduced. • Effective parameters are studied such Wind-Lens shape, brim height and speed ratio. • The optimal shape has a moderate power coefficient and the less noise generation.

A PWM strategy for acoustic noise reduction for grid-connected single-phase inverters

Energy Technology Data Exchange (ETDEWEB)

Shao, R.; Guo, Z.; Chang, L. [New Brunswick Univ., Fredericton, NB (Canada). Dept. of Electrical and Computer Engineering

2006-07-01

This paper presented a newly proposed and improved pulse width modulation (PWM) strategy for grid-connected single-phase inverters. Small distributed generators using energy from renewable resources such as PV and wind systems typically use grid-connected single-phase inverters as voltage source inverters for good acoustic performance. PWM is generally applied in these inverters in order to achieve good waveforms of output current as required by interconnection standards. In routine simultaneous switching PWM methods, the current ripples through the inverter output filter inductor are at the carrier switching frequency, which is one of the major causes for inverter acoustic noise. The new PWM strategy effectively alleviates acoustic noise and improves output power quality. It is based on the principle of evenly splitting the switching of Insulated Gate Bipolar Transistors (IGBT) in each switching cycle among all IGBTs of the full bridge, thereby using a non-simultaneous mode of PWM which doubles the output current ripple frequency. This increases the inductor current ripple frequency to twice the carrier frequency. It is therefore possible to increase the current ripple frequency, or noise frequency into the range of ultrasonic which is inaudible to the human ear, without increasing the inverter's switching frequency to which the inverter's switching loss is proportional. In addition, this new PWM scheme can reduce the output current harmonics distortion and dc link current ripples. As such, lower capacitance in dc link capacitors and lower inductance of output inductor are needed. The improved PWM scheme was verified in a 3 kW grid-connected single-phase inverter. It was shown that the PWM strategy can be readily implemented with a digital signal processing microcontroller. 8 refs., 11 figs.

Acoustic ambient noise recorder

Digital Repository Service at National Institute of Oceanography (India)

Saran, A.K.; Navelkar, G.S.; Almeida, A.M.; More, S.R.; Chodankar, P.V.; Murty, C.S.

with a robust outfit that can withstand high pressures and chemically corrosion resistant materials. Keeping these considerations in view, a CMOS micro-controller-based marine acoustic ambient noise recorder has been developed with a real time clock...

Structural Acoustic Prediction and Interior Noise Control Technology

Science.gov (United States)

Mathur, G. P.; Chin, C. L.; Simpson, M. A.; Lee, J. T.; Palumbo, Daniel L. (Technical Monitor)

2001-01-01

This report documents the results of Task 14, "Structural Acoustic Prediction and Interior Noise Control Technology". The task was to evaluate the performance of tuned foam elements (termed Smart Foam) both analytically and experimentally. Results taken from a three-dimensional finite element model of an active, tuned foam element are presented. Measurements of sound absorption and sound transmission loss were taken using the model. These results agree well with published data. Experimental performance data were taken in Boeing's Interior Noise Test Facility where 12 smart foam elements were applied to a 757 sidewall. Several configurations were tested. Noise reductions of 5-10 dB were achieved over the 200-800 Hz bandwidth of the controller. Accelerometers mounted on the panel provided a good reference for the controller. Configurations with far-field error microphones outperformed near-field cases.

Four-jet impingement: Noise characteristics and simplified acoustic model

International Nuclear Information System (INIS)

Brehm, C.; Housman, J.A.; Kiris, C.C.; Barad, M.F.; Hutcheson, F.V.

2017-01-01

Highlights: • Large eddy simulation of unique four jet impingement configuration. • Characterization of flow features using POD, FFT, and wavelet decomposition. • Noise source identification utilizing causality method. • Development of simplified acoustic model utilizing equivalent source method. • Comparison with experimental data from BENS experiment. - Abstract: The noise generation mechanisms for four directly impinging supersonic jets are investigated employing implicit large eddy simulations with a higher-order weighted essentially non-oscillatory scheme. Although these types of impinging jet configurations have been used in many experiments, a detailed investigation of the noise generation mechanisms has not been conducted before. The flow field is highly complex and contains a wide range of temporal and spatial scales relevant for noise generation. Proper orthogonal decomposition is utilized to characterize the unsteady nature of the flow field involving unsteady shock oscillations, large coherent turbulent flow structures, and the sporadic appearance of vortical flow structures in the center of the four-jet impingement region. The causality method based on Lighthills acoustic analogy is applied to link fluctuations of flow quantities inside the source region to the acoustic pressure in the far field. It will be demonstrated that the entropy fluctuation term plays a vital role in the noise generation process. Consequently, the understanding of the noise generation mechanisms is employed to develop a simplified acoustic model of the four-jet impingement device by utilizing the equivalent source method. Finally, three linear acoustic four-jet impingement models of the four-jet impingement device are used as broadband noise sources inside an engine nacelle and the acoustic scattering results are validated against far-field acoustic experimental data.

Mobile Communication Devices, Ambient Noise, and Acoustic Voice Measures.

Science.gov (United States)

Maryn, Youri; Ysenbaert, Femke; Zarowski, Andrzej; Vanspauwen, Robby

2017-03-01

The ability to move with mobile communication devices (MCDs; ie, smartphones and tablet computers) may induce differences in microphone-to-mouth positioning and use in noise-packed environments, and thus influence reliability of acoustic voice measurements. This study investigated differences in various acoustic voice measures between six recording equipments in backgrounds with low and increasing noise levels. One chain of continuous speech and sustained vowel from 50 subjects with voice disorders (all separated by silence intervals) was radiated and re-recorded in an anechoic chamber with five MCDs and one high-quality recording system. These recordings were acquired in one condition without ambient noise and in four conditions with increased ambient noise. A total of 10 acoustic voice markers were obtained in the program Praat. Differences between MCDs and noise condition were assessed with Friedman repeated-measures test and posthoc Wilcoxon signed-rank tests, both for related samples, after Bonferroni correction. (1) Except median fundamental frequency and seven nonsignificant differences, MCD samples have significantly higher acoustic markers than clinical reference samples in minimal environmental noise. (2) Except median fundamental frequency, jitter local, and jitter rap, all acoustic measures on samples recorded with the reference system experienced significant influence from room noise levels. Fundamental frequency is resistant to recording system, environmental noise, and their combination. All other measures, however, were impacted by both recording system and noise condition, and especially by their combination, often already in the reference/baseline condition without added ambient noise. Caution is therefore warranted regarding implementation of MCDs as clinical recording tools, particularly when applied for treatment outcomes assessments. Copyright © 2017 The Voice Foundation. Published by Elsevier Inc. All rights reserved.

An Overview of Virtual Acoustic Simulation of Aircraft Flyover Noise

Science.gov (United States)

Rizzi, Stephen A.

2013-01-01

Methods for testing human subject response to aircraft flyover noise have greatly advanced in recent years as a result of advances in simulation technology. Capabilities have been developed which now allow subjects to be immersed both visually and aurally in a three-dimensional, virtual environment. While suitable for displaying recorded aircraft noise, the true potential is found when synthesizing aircraft flyover noise because it allows the flexibility and freedom to study sounds from aircraft not yet flown. A virtual acoustic simulation method is described which is built upon prediction-based source noise synthesis, engineering-based propagation modeling, and empirically-based receiver modeling. This source-path-receiver paradigm allows complete control over all aspects of flyover auralization. With this capability, it is now possible to assess human response to flyover noise by systematically evaluating source noise reductions within the context of a system level simulation. Examples of auralized flyover noise and movie clips representative of an immersive aircraft flyover environment are made in the presentation.

Acoustic textiles

CERN Document Server

Nayak, Rajkishore

2016-01-01

This book highlights the manufacturing and applications of acoustic textiles in various industries. It also includes examples from different industries in which acoustic textiles can be used to absorb noise and help reduce the impact of noise at the workplace. Given the importance of noise reduction in the working environment in several industries, the book offers a valuable guide for companies, educators and researchers involved with acoustic materials.

A numerical study of the effects of design parameters on the acoustics noise of a high efficiency propeller

Science.gov (United States)

Yang, Liu; Huang, Jun; Yi, Mingxu; Zhang, Chaopu; Xiao, Qian

2017-11-01

A numerical study of a high efficiency propeller in the aerodynamic noise generation is carried out. Based on RANS, three-dimensional numerical simulation is performed to obtain the aerodynamic performance of the propeller. The result of the aerodynamic analysis is given as input of the acoustic calculation. The sound is calculated using the Farassat 1A, which is derived from Ffowcs Williams-Hawkings equation, and compared with the data of wind tunnel. The propeller is modified for noise reduction by changing its geometrical parameters such as diameter, chord width and pitch angle. The trend of variation between aerodynamic analysis data and acoustic calculation result are compared and discussed for different modification tasks. Meaningful conclusions are drawn on the noise reduction of propeller.

Acoustic noise simulation for switched reluctance motors with audible output p

Energy Technology Data Exchange (ETDEWEB)

Rasmussen, P.O.; Blaabjerg, F.; Pedersen, J.K.; Kjaer, P.C. [Aalborg Univ., Inst. of Energy Technology (Denmark); Miller, T.J.E. [Univ. of Glasgow, SPEED Lab., Dep. of Electronics and Electrical Engineering (United Kingdom)

1999-07-01

Acoustic noise in switched reluctance motors is one of the last problems which have to be solved before a more widespread use will come. In order to design a low noise Switched Reluctance Motor drive, simulation tools are needed, and this paper describes a design programme where acoustic noise of electromagnetic origin can be estimated and even be heard by the motor-designer. The design program is based on a new, simple developed vibrational and acoustic model where the parameters can be calculated based on the geometry of the motor. The vibrational and acoustic model is verified in both time and frequency domain where vibrations and acoustic noise have been considered. (au)

Noise can affect acoustic communication and subsequent spawning success in fish.

Science.gov (United States)

de Jong, Karen; Amorim, M Clara P; Fonseca, Paulo J; Fox, Clive J; Heubel, Katja U

2018-06-01

There are substantial concerns that increasing levels of anthropogenic noise in the oceans may impact aquatic animals. Noise can affect animals physically, physiologically and behaviourally, but one of the most obvious effects is interference with acoustic communication. Acoustic communication often plays a crucial role in reproductive interactions and over 800 species of fish have been found to communicate acoustically. There is very little data on whether noise affects reproduction in aquatic animals, and none in relation to acoustic communication. In this study we tested the effect of continuous noise on courtship behaviour in two closely-related marine fishes: the two-spotted goby (Gobiusculus flavescens) and the painted goby (Pomatoschistus pictus) in aquarium experiments. Both species use visual and acoustic signals during courtship. In the two-spotted goby we used a repeated-measures design testing the same individuals in the noise and the control treatment, in alternating order. For the painted goby we allowed females to spawn, precluding a repeated-measures design, but permitting a test of the effect of noise on female spawning decisions. Males of both species reduced acoustic courtship, but only painted gobies also showed less visual courtship in the noise treatment compared to the control. Female painted gobies were less likely to spawn in the noise treatment. Thus, our results provide experimental evidence for negative effects of noise on acoustic communication and spawning success. Spawning is a crucial component of reproduction. Therefore, even though laboratory results should not be extrapolated directly to field populations, our results suggest that reproductive success may be sensitive to noise pollution, potentially reducing fitness. Copyright © 2017 Elsevier Ltd. All rights reserved.

Acoustics of fish shelters: background noise and signal-to-noise ratio.

Science.gov (United States)

Lugli, Marco

2014-12-01

Fish shelters (flat stones, shells, artificial covers, etc., with a hollow beneath) increase the sound pressure levels of low frequency sounds (noise ratio (SNR) in the nest. Background noise amplification by the shelter was examined under both laboratory (stones and shells) and field (stones) conditions, and the SNR of tones inside the nest cavity was measured by performing acoustic tests on stones in the stream. Stone and shell shelters amplify the background noise pressure levels inside the cavity with comparable gains and at similar frequencies of an active sound source. Inside the cavity of stream stones, the mean SNR of tones increased significantly below 125 Hz and peaked at 65 Hz (+10 dB). Implications for fish acoustic communication inside nest enclosures are discussed.

Extraction of Overt Verbal Response from the Acoustic Noise in a Functional Magnetic Resonance Imaging Scan by Use of Segmented Active Noise Cancellation

Science.gov (United States)

Jung, Kwan-Jin; Prasad, Parikshit; Qin, Yulin; Anderson, John R.

2013-01-01

A method to extract the subject's overt verbal response from the obscuring acoustic noise in an fMRI scan is developed by applying active noise cancellation with a conventional MRI microphone. Since the EPI scanning and its accompanying acoustic noise in fMRI are repetitive, the acoustic noise in one time segment was used as a reference noise in suppressing the acoustic noise in subsequent segments. However, the acoustic noise from the scanner was affected by the subject's movements, so the reference noise was adaptively adjusted as the scanner's acoustic properties varied in time. This method was successfully applied to a cognitive fMRI experiment with overt verbal responses. PMID:15723385

Flap Side Edge Liners for Airframe Noise Reduction

Science.gov (United States)

Jones, Michael G. (Inventor); Khorrami, Mehdi R. (Inventor); Choudhari, Meelan M. (Inventor); Howerton, Brian M. (Inventor)

2014-01-01

One or more acoustic liners comprising internal chambers or passageways that absorb energy from a noise source on the aircraft are disclosed. The acoustic liners may be positioned at the ends of flaps of an aircraft wing to provide broadband noise absorption and/or dampen the noise producing unsteady flow features, and to reduce the amount of noise generated due to unsteady flow at the inboard and/or outboard end edges of a flap.

Active3 noise reduction

International Nuclear Information System (INIS)

Holzfuss, J.

1996-01-01

Noise reduction is a problem being encountered in a variety of applications, such as environmental noise cancellation, signal recovery and separation. Passive noise reduction is done with the help of absorbers. Active noise reduction includes the transmission of phase inverted signals for the cancellation. This paper is about a threefold active approach to noise reduction. It includes the separation of a combined source, which consists of both a noise and a signal part. With the help of interaction with the source by scanning it and recording its response, modeling as a nonlinear dynamical system is achieved. The analysis includes phase space analysis and global radial basis functions as tools for the prediction used in a subsequent cancellation procedure. Examples are given which include noise reduction of speech. copyright 1996 American Institute of Physics

An improved probe noise approach for acoustic feedback cancellation

DEFF Research Database (Denmark)

Guo, Meng; Jensen, Søren Holdt; Jensen, Jesper

2012-01-01

The perhaps most challenging problem in acoustic feedback cancellation using adaptive filters is the bias problem. It is well-known that a probe noise approach can effectively prevent this problem. However, when the probe noise must be inaudible and the steady-state error of the adaptive filter...... expressions for its system behavior, and through a simulation experiment in an acoustic feedback cancellation system....

Wing Leading Edge Concepts for Noise Reduction

Science.gov (United States)

Shmilovich, Arvin; Yadlin, Yoram; Pitera, David M.

2010-01-01

This study focuses on the development of wing leading edge concepts for noise reduction during high-lift operations, without compromising landing stall speeds, stall characteristics or cruise performance. High-lift geometries, which can be obtained by conventional mechanical systems or morphing structures have been considered. A systematic aerodynamic analysis procedure was used to arrive at several promising configurations. The aerodynamic design of new wing leading edge shapes is obtained from a robust Computational Fluid Dynamics procedure. Acoustic benefits are qualitatively established through the evaluation of the computed flow fields.

Noise reduction performance of thermobonded nonwovens

OpenAIRE

Carvalho, R.; Rana, S.; Fangueiro, Raúl; Soutinho, Hélder Filipe Cunha

2012-01-01

Acoustic insulation is an important requirement for the human life today, since noise affects the efficiency of day-to-day activities and even cause various health problems Materials based on fibrous structures show very good acoustic insulation properties, which however strongly depends on the type of structures used. The present paper reports the qualitative analysis of the acoustic insulation behavior of various thermo-bonded nonwoven fabrics. The results showed that the acoust...

Effect of Two Advanced Noise Reduction Technologies on the Aerodynamic Performance of an Ultra High Bypass Ratio Fan

Science.gov (United States)

Hughes, Christoper E.; Gazzaniga, John A.

2013-01-01

A wind tunnel experiment was conducted in the NASA Glenn Research Center anechoic 9- by 15-Foot Low-Speed Wind Tunnel to investigate two new advanced noise reduction technologies in support of the NASA Fundamental Aeronautics Program Subsonic Fixed Wing Project. The goal of the experiment was to demonstrate the noise reduction potential and effect on fan model performance of the two noise reduction technologies in a scale model Ultra-High Bypass turbofan at simulated takeoff and approach aircraft flight speeds. The two novel noise reduction technologies are called Over-the-Rotor acoustic treatment and Soft Vanes. Both technologies were aimed at modifying the local noise source mechanisms of the fan tip vortex/fan case interaction and the rotor wake-stator interaction. For the Over-the-Rotor acoustic treatment, two noise reduction configurations were investigated. The results showed that the two noise reduction technologies, Over-the-Rotor and Soft Vanes, were able to reduce the noise level of the fan model, but the Over-the-Rotor configurations had a significant negative impact on the fan aerodynamic performance; the loss in fan aerodynamic efficiency was between 2.75 to 8.75 percent, depending on configuration, compared to the conventional solid baseline fan case rubstrip also tested. Performance results with the Soft Vanes showed that there was no measurable change in the corrected fan thrust and a 1.8 percent loss in corrected stator vane thrust, which resulted in a total net thrust loss of approximately 0.5 percent compared with the baseline reference stator vane set.

Compact, Lightweight, Ceramic Matrix Composite (CMC) Based Acoustic Liners for Reducing Subsonic Jet Aircraft Engine Noise

Science.gov (United States)

Kiser, J. Douglas; Grady, Joseph E.; Miller, Christopher J.; Hultgren, Lennart S.; Jones, Michael G.

2016-01-01

Recent developments have reduced fan and jet noise contributions to overall subsonic aircraft jet-engine noise. Now, aircraft designers are turning their attention toward reducing engine core noise. The NASA Glenn Research Center and NASA Langley Research Center have teamed to investigate the development of a compact, lightweight acoustic liner based on oxide/oxide ceramic matrix composite (CMC) materials. The NASA team has built upon an existing oxide/oxide CMC sandwich structure concept that provides monotonal noise reduction. Oxide/oxide composites have good high temperature strength and oxidation resistance, which could allow them to perform as core liners at temperatures up to 1000C (1832F), and even higher depending on the selection of the composite constituents. NASA has initiated the evaluation of CMC-based liners that use cells of different lengths (variable-depth channels) or effective lengths to achieve broadband noise reduction. Reducing the overall liner thickness is also a major goal, to minimize the volume occupied by the liner. As a first step toward demonstrating the feasibility of our concepts, an oxide/oxide CMC acoustic testing article with different channel lengths was tested. Our approach, summary of test results, current status, and goals for the future are reported.

Wake Management Strategies for Reduction of Turbomachinery Fan Noise

Science.gov (United States)

Waitz, Ian A.

1998-01-01

The primary objective of our work was to evaluate and test several wake management schemes for the reduction of turbomachinery fan noise. Throughout the course of this work we relied on several tools. These include 1) Two-dimensional steady boundary-layer and wake analyses using MISES (a thin-shear layer Navier-Stokes code), 2) Two-dimensional unsteady wake-stator interaction simulations using UNSFLO, 3) Three-dimensional, steady Navier-Stokes rotor simulations using NEWT, 4) Internal blade passage design using quasi-one-dimensional passage flow models developed at MIT, 5) Acoustic modeling using LINSUB, 6) Acoustic modeling using VO72, 7) Experiments in a low-speed cascade wind-tunnel, and 8) ADP fan rig tests in the MIT Blowdown Compressor.

Computational Acoustic Beamforming for Noise Source Identification for Small Wind Turbines.

Science.gov (United States)

Ma, Ping; Lien, Fue-Sang; Yee, Eugene

2017-01-01

This paper develops a computational acoustic beamforming (CAB) methodology for identification of sources of small wind turbine noise. This methodology is validated using the case of the NACA 0012 airfoil trailing edge noise. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of noise sources generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz.

Aircraft interior noise models - Sidewall trim, stiffened structures, and cabin acoustics with floor partition

Science.gov (United States)

Pope, L. D.; Wilby, E. G.; Willis, C. M.; Mayes, W. H.

1983-01-01

As part of the continuing development of an aircraft interior noise prediction model, in which a discrete modal representation and power flow analysis are used, theoretical results are considered for inclusion of sidewall trim, stiffened structures, and cabin acoustics with floor partition. For validation purposes, predictions of the noise reductions for three test articles (a bare ring-stringer stiffened cylinder, an unstiffened cylinder with floor and insulation, and a ring-stringer stiffened cylinder with floor and sidewall trim) are compared with measurements.

Utilisation of polyurethane composit with 50% composition of roystonea regia fiber as noise reduction panel on car hood

Science.gov (United States)

Ikhwansyah; Mulia; Gunawan, S.; Lubis, R. D. W.

2018-02-01

The objective is to get the characteristics of noise reduction, noise reduction level, variety of measurement spaces, and knowing the process in making acoustic material of natural fiber becomes noise reduction on a car hood. The process of making noise reduction material used casting method and pressed by using molded press. The composition of noise reduction material consist of 50% roystonea regia by 32 mesh and 50% combined by gypsum and polyurethane. The result shows that the average result of noise reduction at X1- side is 5,7% and X2- side is 3,9%, X1+ side is 0,9% and X2+ side is 6,2%, Z1- side is 8,9% and Z2- side is 10,1%, Z1+ side is 9,7% and Z2+ side is 10,01%. The main conclusion of the study shows that a noise reduction which made of roystonea regia with 32 mesh mixed by matrix of polyurethane and gypsum is appropriate for noise reduction on car hood.

Theory of the Auger effect in an intense acoustic noise field

International Nuclear Information System (INIS)

Doan Nhat Quang.

1995-10-01

A study is given of the effect on Auger processes produced by an intense acoustic noise flux affecting charge carriers via deformation-potential interaction. The calculation of Auger coefficients is carried out within a semiclassical approach to the acoustic noise field and non-degenerate carrier statistics. Simple analytic expressions are then obtained, which expose an exponential dependence of the Auger coefficients on flux intensity. The Auger recombination is found, in analogy with the case of piezoelectric noise field, to be strongly enhanced as compared to that in no-noise conditions by up to several orders of magnitude at high flux intensity, short acoustic wavelength, small carrier concentration and low temperature. (author). 29 refs, 4 figs, 1 tab

Prediction and Reduction of Aerodynamic Noise of the Multiblade Centrifugal Fan

Directory of Open Access Journals (Sweden)

Shuiqing Zhou

2014-08-01

Full Text Available An aerodynamic and aeroacoustic investigation of the multiblade centrifugal fan is proposed in this paper, and a hybrid technique of combining flow field calculation and acoustic analysis is applied to solve the aeroacoustic problem of multiblade centrifugal fan. The unsteady flow field of the multiblade centrifugal fan is predicted by solving the incompressible Reynolds-averaged Navier-Stokes (RANS equations with conventional computing techniques for fluid dynamics. The principal noise source induced is extracted from the calculation of the flow field by using acoustic principles, and the modeled sources on inner and outer surfaces of the volute are calculated with multiregional boundary element method (BEM. Through qualitative analysis, the sound pressure amplitude distribution of the multiblade centrifugal fan in near field is given and the sound pressure level (SPL spectrum diagram of monitoring points in far field is obtained. Based on the analysis results, the volute tongue structure is adjusted and then a low-noise design for the centrifugal fan is proposed. The comparison of noise tests shows the noise reduction of improved fan model is more obvious, which is in good agreement with the prediction using the hybrid techniques.

Effects of acoustic noise on the auditory nerve compound action potentials evoked by electric pulse trains.

Science.gov (United States)

Nourski, Kirill V; Abbas, Paul J; Miller, Charles A; Robinson, Barbara K; Jeng, Fuh-Cherng

2005-04-01

This study investigated the effects of acoustic noise on the auditory nerve compound action potentials in response to electric pulse trains. Subjects were adult guinea pigs, implanted with a minimally invasive electrode to preserve acoustic sensitivity. Electrically evoked compound action potentials (ECAP) were recorded from the auditory nerve trunk in response to electric pulse trains both during and after the presentation of acoustic white noise. Simultaneously presented acoustic noise produced a decrease in ECAP amplitude. The effect of the acoustic masker on the electric probe was greatest at the onset of the acoustic stimulus and it was followed by a partial recovery of the ECAP amplitude. Following cessation of the acoustic noise, ECAP amplitude recovered over a period of approximately 100-200 ms. The effects of the acoustic noise were more prominent at lower electric pulse rates (interpulse intervals of 3 ms and higher). At higher pulse rates, the ECAP adaptation to the electric pulse train alone was larger and the acoustic noise, when presented, produced little additional effect. The observed effects of noise on ECAP were the greatest at high electric stimulus levels and, for a particular electric stimulus level, at high acoustic noise levels.

SPATIAL DISTRIBUTIONS OF ABSORPTION, LOCAL SUPPRESSION, AND EMISSIVITY REDUCTION OF SOLAR ACOUSTIC WAVES IN MAGNETIC REGIONS

International Nuclear Information System (INIS)

Chou, D.-Y.; Yang, M.-H.; Zhao Hui; Liang Zhichao; Sun, M.-T.

2009-01-01

Observed acoustic power in magnetic regions is lower than the quiet Sun because of absorption, emissivity reduction, and local suppression of solar acoustic waves in magnetic regions. In the previous studies, we have developed a method to measure the coefficients of absorption, emissivity reduction, and local suppression of sunspots. In this study, we go one step further to measure the spatial distributions of three coefficients in two active regions, NOAA 9055 and 9057. The maps of absorption, emissivity reduction, and local suppression coefficients correlate with the magnetic map, including plage regions, except the emissivity reduction coefficient of NOAA 9055 where the emissivity reduction coefficient is too weak and lost among the noise.

Environment noise reduction study. The effect of acoustical ceramics

International Nuclear Information System (INIS)

Nakayasu, Fumio

2007-01-01

Asbestos was used to improve acoustical and thermal conditions in the working environment. The purpose of this study is to investigate ceramics properties as the alternative material for asbestos. The acoustical properties of ceramics designed to absorb sound were investigated in this study. The properties of the concerned ceramics show the characteristics of an excellent sound absorber. Concrete is a good sound barrier but reflect more than 90% of the incident sound striking it. The thickness of conventional acoustical materials, like fibers, has a great impact on the material sound absorbing qualities. However, the acoustical effect of the thickness of the concerned ceramics was found to be reasonably small. A acoustical analysis of a working environment was done to determine the level of reverberation influenced by the different materials used to construct the space. It was found that the concerned ceramics has a potential to be good thermal shield material. (author)

Identification of Turbomachinery Noise Sources Using Acoustical Holography, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — Evaluation and enhancement of the acoustical performance of turbomachinery requires knowledge of the acoustic sources. However, the noise generation mechanisms...

Open noise barriers based on sonic crystals. Advances in noise control in transport infraestructures

Energy Technology Data Exchange (ETDEWEB)

Peiro Torres, M.P.; Redondo Pastor, J.; Bravo Plana-Sala, J.M.; Sanchez Perez, J.V.

2016-07-01

Noise control is an environmental problem of first magnitude nowadays. In this work, we present a new concept of acoustic screen designed to control the specific noise generated by transport infrastructures, based on new materials called sonic crystals. These materials are formed by arrangements of acoustic scatterers in air, and provide a new and different mechanism in the fight against noise from those of the classical screens. This mechanism is usually called multiple scattering and is due to their structuring in addition to their physical properties. Due to the separation between scatterers, these barriers are transparent to air and water allowing a reduction on their foundations. Tests carried out in a wind tunnel show a reduction of 42% in the overturning momentum compared to classical barriers. The acoustical performance of these barriers is shown in this work, explaining the new characteristics provided in the control of noise. Finally, an example of these barriers is presented and classified according to acoustic standardization tests. The acoustic barrier reported in this work provides a high technological solution in the field of noise control. (Author)

Noise disturbance in open-plan study environments: a field study on noise sources, student tasks and room acoustic parameters.

Science.gov (United States)

Braat-Eggen, P Ella; van Heijst, Anne; Hornikx, Maarten; Kohlrausch, Armin

2017-09-01

The aim of this study is to gain more insight in the assessment of noise in open-plan study environments and to reveal correlations between noise disturbance experienced by students and the noise sources they perceive, the tasks they perform and the acoustic parameters of the open-plan study environment they work in. Data were collected in five open-plan study environments at universities in the Netherlands. A questionnaire was used to investigate student tasks, perceived sound sources and their perceived disturbance, and sound measurements were performed to determine the room acoustic parameters. This study shows that 38% of the surveyed students are disturbed by background noise in an open-plan study environment. Students are mostly disturbed by speech when performing complex cognitive tasks like studying for an exam, reading and writing. Significant but weak correlations were found between the room acoustic parameters and noise disturbance of students. Practitioner Summary: A field study was conducted to gain more insight in the assessment of noise in open-plan study environments at universities in the Netherlands. More than one third of the students was disturbed by noise. An interaction effect was found for task type, source type and room acoustic parameters.

The ecological and evolutionary consequences of noise-induced acoustic habitat loss

Science.gov (United States)

Tennessen, Jennifer Beissinger

Anthropogenic threats are facilitating rapid environmental change and exerting novel pressures on the integrity of ecological patterns and processes. Currently, habitat loss is the leading factor contributing to global biodiversity loss. Noise created by human activities is nearly ubiquitous in terrestrial and marine systems, and causes acoustic habitat loss by interfering with species' abilities to freely send and receive critical acoustic biological information. My dissertation investigates how novel sounds from human activities affect ecological and evolutionary processes in space and time in marine and terrestrial systems, and how species may cope with this emerging novel pressure. Using species from both marine and terrestrial systems, I present results from a theoretical investigation, and four acoustic playback experiments combining laboratory studies and field trials, that reveal a range of eco-evolutionary consequences of noiseinduced acoustic habitat loss. First, I use sound propagation modeling to assess how marine shipping noise reduces communication space between mother-calf pairs of North Atlantic right whales (Eubalaena glacialis ), an important unit of an endangered species. I show that shipping noise poses significant challenges for mother-calf pairs, but that vocal compensation strategies can substantially improve communication space. Next, in a series of acoustic playback experiments I show that road traffic noise impairs breeding migration behavior and physiology of wood frogs (Lithobates sylvaticus ). This work reveals the first evidence that traffic noise elicits a physiological stress response and suppresses production of antimicrobial peptides (a component of the innate immune response) in anurans. Further, wood frogs from populations with a history of inhabiting noisy sites mounted reduced physiological stress responses to continuous traffic noise exposure. This research using wood frogs suggests that chronic traffic noise exposure has

Low-Frequency Noise Reduction by Earmuffs with Flax Fibre-Reinforced Polypropylene Ear Cups

Directory of Open Access Journals (Sweden)

Linus Yinn Leng Ang

2018-01-01

Full Text Available Soldiers and supporting engineers are frequently exposed to high low-frequency (<500 Hz cabin noise in military vehicles. Despite the use of commercial hearing protection devices, the risk of auditory damage is still imminent because the devices may not be optimally customised for such applications. This study considers flax fibre-reinforced polypropylene (Flax-PP as an alternative to the material selection for the ear cups of commercial earmuffs, which are typically made of acrylonitrile butadiene styrene (ABS. Different weaving configurations (woven and nonwoven and various noise environments (pink noise, cabin booming noise, and firing noise were considered to investigate the feasibility of the proposed composite earmuffs for low-frequency noise reduction. The remaining assembly components of the earmuff were kept consistent with those of a commercial earmuff, which served as a benchmark for results comparison. In contrast to the commercial earmuff, the composite earmuffs were shown to be better in mitigating low-frequency noise by up to 16.6 dB, while compromising midfrequency acoustical performance. Consequently, the proposed composite earmuffs may be an alternative for low-frequency noise reduction in vehicle cabins, at airports, and at construction sites involving heavy machineries.

Acoustic fMRI noise : Linear time-invariant system model

NARCIS (Netherlands)

Sierra, Carlos V. Rizzo; Versluis, Maarten J.; Hoogduin, Johannes M.; Duifhuis, Hendrikus (Diek)

Functional magnetic resonance imaging (fMRI) enables sites of brain activation to be localized in human subjects. For auditory system studies, however, the acoustic noise generated by the scanner tends to interfere with the assessments of this activation. Understanding and modeling fMRI acoustic

Acoustic Noise Prediction of the Amine Swingbed ISS ExPRESS Rack Payload

Science.gov (United States)

Welsh, David; Smith, Holly; Wang, Shuo

2010-01-01

Acoustics plays a vital role in maintaining the health, safety, and comfort of crew members aboard the International Space Station (ISS). In order to maintain this livable and workable environment, acoustic requirements have been established to ensure that ISS hardware and payload developers account for the acoustic emissions of their equipment and develop acoustic mitigations as necessary. These requirements are verified by an acoustic emissions test of the integrated hardware. The Amine Swingbed ExPRESS (Expedite the PRocessing of ExperimentS to Space) rack payload creates a unique challenge to the developers in that the payload hardware is transported to the ISS in phases, making an acoustic emissions test on the integrated flight hardware impossible. In addition, the payload incorporates a high back pressure fan and a diaphragm vacuum pump, which are recognized as significant and complex noise sources. In order to accurately predict the acoustic emissions of the integrated payload, the individual acoustic noise sources and paths are first characterized. These characterizations are conducted though a series of acoustic emissions tests on the individual payload components. Secondly, the individual acoustic noise sources and paths are incorporated into a virtual model of the integrated hardware. The virtual model is constructed with the use of hybrid method utilizing the Finite Element Acoustic (FEA) and Statistical Energy Analysis (SEA) techniques, which predict the overall acoustic emissions. Finally, the acoustic model is validated though an acoustic characterization test performed on an acoustically similar mock-up of the flight unit. The results of the validated acoustic model are then used to assess the acoustic emissions of the flight unit and define further acoustic mitigation efforts.

Effects of cavity resonances on sound transmission into a thin cylindrical shell. [noise reduction in aircraft fuselage

Science.gov (United States)

Koval, L. R.

1978-01-01

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model is presented for the effects of internal cavity resonances on sound transmission into a thin cylindrical shell. The 'noise reduction' of the cylinder is defined and computed, with and without including the effects of internal cavity resonances. As would be expected, the noise reduction in the absence of cavity resonances follows the same qualitative pattern as does transmission loss. Numerical results show that cavity resonances lead to wide fluctuations and a general decrease of noise reduction, especially at cavity resonances. Modest internal absorption is shown to greatly reduce the effect of cavity resonances. The effects of external airflow, internal cabin pressurization, and different acoustical properties inside and outside the cylinder are also included and briefly examined.

Noise and room acoustic conditions in a tertiary referral hospital in Seoul, Korea

DEFF Research Database (Denmark)

Jeong, Cheol-Ho; Cho, Wan-Ho; Chang, Ji-ho

2018-01-01

Noise levels and room acoustic parameters at a tertiary referral hospital, Seoul National University Hospital in Korea, are investigated. Through a questionnaire, acoustically problematic rooms are identified. Noise levels in emergency rooms (ERs) and intensive care units (ICUs) are measured over...... level for the first night was 66 dBA, which came down to 56 dBA for the next day. The reason for the higher noise level for the first night in the ICU was frequent alarm sound and treatment noise related to a critical patient. The noise level in the measured ERs is about 10 dB lower than those measured...... about three days. Acoustically critical and problematic rooms in the otolaryngology department are measured: examination rooms, operating rooms, nurse stations, patient rooms, and audiometric rooms. The equivalent A-weighted noise level, LAeq, ranges from 54 to 56 dBA in two ERs. In an ICU, the noise...

A survey of acoustic conditions and noise levels in secondary school classrooms in England.

Science.gov (United States)

Shield, Bridget; Conetta, Robert; Dockrell, Julie; Connolly, Daniel; Cox, Trevor; Mydlarz, Charles

2015-01-01

An acoustic survey of secondary schools in England has been undertaken. Room acoustic parameters and background noise levels were measured in 185 unoccupied spaces in 13 schools to provide information on the typical acoustic environment of secondary schools. The unoccupied acoustic and noise data were correlated with various physical characteristics of the spaces. Room height and the amount of glazing were related to the unoccupied reverberation time and therefore need to be controlled to reduce reverberation to suitable levels for teaching and learning. Further analysis of the unoccupied data showed that the introduction of legislation relating to school acoustics in England and Wales in 2003 approximately doubled the number of school spaces complying with current standards. Noise levels were also measured during 274 lessons to examine typical levels generated during teaching activities in secondary schools and to investigate the influence of acoustic design on working noise levels in the classroom. Comparison of unoccupied and occupied data showed that unoccupied acoustic conditions affect the noise levels occurring during lessons. They were also related to the time spent in disruption to the lessons (e.g., students talking or shouting) and so may also have an impact upon student behavior in the classroom.

Perceptual learning of acoustic noise generates memory-evoked potentials.

Science.gov (United States)

Andrillon, Thomas; Kouider, Sid; Agus, Trevor; Pressnitzer, Daniel

2015-11-02

Experience continuously imprints on the brain at all stages of life. The traces it leaves behind can produce perceptual learning [1], which drives adaptive behavior to previously encountered stimuli. Recently, it has been shown that even random noise, a type of sound devoid of acoustic structure, can trigger fast and robust perceptual learning after repeated exposure [2]. Here, by combining psychophysics, electroencephalography (EEG), and modeling, we show that the perceptual learning of noise is associated with evoked potentials, without any salient physical discontinuity or obvious acoustic landmark in the sound. Rather, the potentials appeared whenever a memory trace was observed behaviorally. Such memory-evoked potentials were characterized by early latencies and auditory topographies, consistent with a sensory origin. Furthermore, they were generated even on conditions of diverted attention. The EEG waveforms could be modeled as standard evoked responses to auditory events (N1-P2) [3], triggered by idiosyncratic perceptual features acquired through learning. Thus, we argue that the learning of noise is accompanied by the rapid formation of sharp neural selectivity to arbitrary and complex acoustic patterns, within sensory regions. Such a mechanism bridges the gap between the short-term and longer-term plasticity observed in the learning of noise [2, 4-6]. It could also be key to the processing of natural sounds within auditory cortices [7], suggesting that the neural code for sound source identification will be shaped by experience as well as by acoustics. Copyright © 2015 Elsevier Ltd. All rights reserved.

Aerodynamic Measurements of a Gulfstream Aircraft Model With and Without Noise Reduction Concepts

Science.gov (United States)

Neuhart, Dan H.; Hannon, Judith A.; Khorrami, Mehdi R.

2014-01-01

Steady and unsteady aerodynamic measurements of a high-fidelity, semi-span 18% scale Gulfstream aircraft model are presented. The aerodynamic data were collected concurrently with acoustic measurements as part of a larger aeroacoustic study targeting airframe noise associated with main landing gear/flap components, gear-flap interaction noise, and the viability of related noise mitigation technologies. The aeroacoustic tests were conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Wind Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the measurements were obtained with the model in landing configuration with the flap deflected at 39º and the main landing gear on and off. Data were acquired at Mach numbers of 0.16, 0.20, and 0.24. Global forces (lift and drag) and extensive steady and unsteady surface pressure measurements were obtained. Comparison of the present results with those acquired during a previous test shows a significant reduction in the lift experienced by the model. The underlying cause was traced to the likely presence of a much thicker boundary layer on the tunnel floor, which was acoustically treated for the present test. The steady and unsteady pressure fields on the flap, particularly in the regions of predominant noise sources such as the inboard and outboard tips, remained unaffected. It is shown that the changes in lift and drag coefficients for model configurations fitted with gear/flap noise abatement technologies fall within the repeatability of the baseline configuration. Therefore, the noise abatement technologies evaluated in this experiment have no detrimental impact on the aerodynamic performance of the aircraft model.

Aircraft Noise Reduction Subproject Overview

Science.gov (United States)

Fernandez, Hamilton; Nark, Douglas M.; Van Zante, Dale E.

2016-01-01

The material presents highlights of propulsion and airframe noise research being completed for the Advanced Air Transport Technology Project. The basis of noise reduction plans along with representative work for the airframe, propulsion, and propulsion-airframe integration is discussed for the Aircraft Noise reduction Subproject.

Efficient prediction of ground noise from helicopters and parametric studies based on acoustic mapping

Directory of Open Access Journals (Sweden)

Fei WANG

2018-02-01

Full Text Available Based on the acoustic mapping, a prediction model for the ground noise radiated from an in-flight helicopter is established. For the enhancement of calculation efficiency, a high-efficiency second-level acoustic radiation model capable of taking the influence of atmosphere absorption on noise into account is first developed by the combination of the point-source idea and the rotor noise radiation characteristics. The comparison between the present model and the direct computation method of noise is done and the high efficiency of the model is validated. Rotor free-wake analysis method and Ffowcs Williams-Hawkings (FW-H equation are applied to the aerodynamics and noise prediction in the present model. Secondly, a database of noise spheres with the characteristic parameters of advance ratio and tip-path-plane angle is established by the helicopter trim model together with a parametric modeling approach. Furthermore, based on acoustic mapping, a method of rapid simulation for the ground noise radiated from an in-flight helicopter is developed. The noise footprint for AH-1 rotor is then calculated and the influence of some parameters including advance ratio and flight path angle on ground noise is deeply analyzed using the developed model. The results suggest that with the increase of advance ratio and flight path angle, the peak noise levels on the ground first increase and then decrease, in the meantime, the maximum Sound Exposure Level (SEL noise on the ground shifts toward the advancing side of rotor. Besides, through the analysis of the effects of longitudinal forces on miss-distance and rotor Blade-Vortex Interaction (BVI noise in descent flight, some meaningful results for reducing the BVI noise on the ground are obtained. Keywords: Acoustic mapping, Helicopter, Noise footprint, Rotor noise, Second-level acoustic radiation model

Holistic optimization of noise barriers from acoustical and non-acoustical parameters

NARCIS (Netherlands)

Defrance, J.; Leissing, T.; Grannec, F.; Jean, P.; Lutgendorf, D.; Heinkele, C.; Clairbois, J.P.

2012-01-01

We present the last results obtained within WP5 "Holistic optimizations" of the QUIESST European Project dedicated to the assessment of Noise Reducing Devices' acoustical performances. A first task was a state of the art of existing methods followed by choices of best solutions for holistic

Parallel feedback active noise control of MRI acoustic noise with signal decomposition using hybrid RLS-NLMS adaptive algorithms.

Science.gov (United States)

Ganguly, Anshuman; Krishna Vemuri, Sri Hari; Panahi, Issa

2014-01-01

This paper presents a cost-effective adaptive feedback Active Noise Control (FANC) method for controlling functional Magnetic Resonance Imaging (fMRI) acoustic noise by decomposing it into dominant periodic components and residual random components. Periodicity of fMRI acoustic noise is exploited by using linear prediction (LP) filtering to achieve signal decomposition. A hybrid combination of adaptive filters-Recursive Least Squares (RLS) and Normalized Least Mean Squares (NLMS) are then used to effectively control each component separately. Performance of the proposed FANC system is analyzed and Noise attenuation levels (NAL) up to 32.27 dB obtained by simulation are presented which confirm the effectiveness of the proposed FANC method.

Active control of the noise

International Nuclear Information System (INIS)

Rodriguez V, Luis Alfonso; Lopez Q, Jose German

2001-01-01

The problems of acoustic noise are more and more preponderant in the measure in that the amount of equipment and industrial machinery is increased such as fans, transformers, compressors etc. the use of devices passive mechanics for the reduction of the noise is effective and very appreciated because its effects embrace a wide range of acoustic frequency. However, to low frequencies, such devices become too big and expensive besides that present a tendency to do not effective. The control of active noise, CAN, using the electronic generation anti-noise, constitutes an interesting solution to the problem because their operation principle allows achieving an appreciable reduction of the noise by means of the use of compact devices. The traditional techniques for the control of acoustic noise like barriers and silenced to attenuate it, are classified as passive and their works has been accepted as norm as for the treatment of problems of noise it refers. Such techniques are considered in general very effective in the attenuation of noise of wide band. However, for low frequency, the required passive structures are too big and expensive; also, their effectiveness diminishes flagrantly, that which makes them impractical in many applications. The active suppression is profiled like a practical alternative for the reduction of acoustic noise. The idea in the active treatment of the noise it contemplates the use of a device electro-acoustic, like a speaker for example that it cancels to the noise by the generation of sounds of Same width and of contrary phase (anti-noise). The cancellation phenomenon is carried out when the ant-noise combines acoustically with the noise, what is in the cancellation of both sounds. The effectiveness of the cancellation of the primary source of noise depends on the precision with which the width and the phase of the generated ant-noise are controlled. The active control of noise, ANC (activates noise control), it is being investigated for

Review of noise reduction methods for centrifugal fans

Science.gov (United States)

Neise, W.

1981-11-01

Several methods for the reduction of centrifugal fan noise are presented, the most of which are aimed at a lower blade passage frequency level. The methods are grouped into five categories: casing modifications to increase the distance between impeller and cutoff, the introduction of a phase shift of the source pressure fluctuations, impeller modifications, radial clearance between impeller eye and inlet nozzle, and acoustical measures. Resonators mounted at the cutoff of centrifugal fans appear to be a highly efficient and simple means of reducing the blade passage tone, and the method can be used for new fan construction and existing installations without affecting the aerodynamic performance of the fan.

Acoustic noise in functional magnetic resonance imaging reduces pain unpleasantness ratings.

Science.gov (United States)

Boyle, Y; Bentley, D E; Watson, A; Jones, A K P

2006-07-01

Functional magnetic resonance imaging (fMRI) is increasingly used in cognitive studies. Unfortunately, the scanner produces acoustic noise during the image acquisition process. Interference from acoustic noise is known to affect auditory, visual and motor processing, raising the possibility that acoustic interference may also modulate processing of other sensory modalities such as pain. With the increasing use of fMRI in the investigation of the mechanisms of pain perception, particularly in relation to attention, this issue has become highly relevant. Pain is a complex experience, composed of sensory-discriminative, affective-motivational and cognitive-evaluative components. The aim of this experiment was to assess the effect of MRI scanner noise, compared to white noise, on the affective (unpleasantness) and the sensory-discriminative (localisation) components of pain. Painful radiant heat from a CO(2) laser was delivered to the skin of the right forearm in 24 healthy volunteers. The volunteers attended to either pain location or pain unpleasantness during three conditions: i) no noise, ii) exposure to MRI scanner noise (85 dB) or iii) exposure to white noise (85 dB). Both MRI scanner noise and white noise significantly reduced unpleasantness ratings (from 5.1 +/- 1.6 in the control condition to 4.7 +/- 1.5 (P = 0.002) and 4.6 +/- 1.6 (P white noise respectively), whereas the ability to localise pain was not significantly affected (from 85.4 +/- 9.2% correct in the control condition to 83.1 +/- 10.3% (P = 0.06) and 83.9 +/- 9.5% (P = 0.27) with MRI scanner and white noise respectively). This phenomenon should be taken into account in the design of fMRI studies into human pain perception.

Experiment and Simulation Analysis on Noise Attenuation of Al/MF Cylindrical Shells

Directory of Open Access Journals (Sweden)

Bin Li

2017-01-01

Full Text Available For the issue concerning internal noise reduction of Al-made cylindrical shell structure, the noise control method of laying melamine foam (MF layer is adopted for in-shell noise attenuation experiments of Al and Al/MF cylindrical shells and corresponding internal noise response spectrograms are obtained. Based on the Virtual.Lab acoustics software, a finite element model is established for the analysis of noise in the Al/MF cylinder shell and numerical simulation computation is conducted for the acoustic mode and in-shell acoustic response; the correctness of the finite element model is verified via comparison with measured data. On this basis, influence rules of different MF laying rate and different laying thickness on acoustic cavity resonance response within the low and medium frequency range of 100–400 Hz are studied. It is indicated that noise reduction increases with MF laying rate, but the amplification decreases along with the rising of MF laying rate; noise reduction per unit thickness decreases with the increase of laying thickness, while noise reduction per unit area increases.

Filtering out the noise: evaluating the impact of noise and sound reduction strategies on sleep quality for ICU patients.

Science.gov (United States)

Bosma, Karen J; Ranieri, V Marco

2009-01-01

The review article by Xie and colleagues examines the impact of noise and noise reduction strategies on sleep quality for critically ill patients. Evaluating the impact of noise on sleep quality is challenging, as it must be measured relative to other factors that may be more or less disruptive to patients' sleep. Such factors may be difficult for patients, observers, and polysomnogram interpreters to identify, due to our limited understanding of the causes of sleep disruption in the critically ill, as well as the challenges in recording and quantifying sleep stages and sleep fragmentation in the intensive care unit. Furthermore, most research in this field has focused on noise level, whereas acousticians typically evaluate additional parameters such as noise spectrum and reverberation time. The authors highlight the disparate results and limitations of existing studies, including the lack of attention to other acoustic parameters besides sound level, and the combined effects of different sleep disturbing factors.

Quantum Noise Reduction with Pulsed Light in Optical Fibers.

Science.gov (United States)

Bergman, Keren

Optical fibers offer considerable advantages over bulk nonlinear media for the generation of squeezed states. This thesis reports on experimental investigations of reducing quantum noise by means of squeezing in nonlinear fiber optic interferometers. Fibers have low insertion loss which allows for long interaction lengths. High field intensities are easily achieved in the small cores of single mode fibers. Additionally, the nonlinear process employed is self phase modulation or the Kerr effect, whose broad band nature requires no phase matching and can be exploited with ultra-short pulses of high peak intensity. All these advantageous features of fibers result in easily obtained large nonlinear phase shifts and subsequently large squeezing parameters. By the self phase modulation process a correlation is produced between the phase and amplitude fluctuations of the optical field. The attenuated or squeezed quadrature has a lower noise level than the initial level associated with the coherent state field before propagation. The resulting reduced quantum noise quadrature can be utilized to improve the sensitivity of a phase measuring instrument such as an interferometer. Because the Kerr nonlinearity is a degenerate self pumping process, the squeezed noise is at the same frequency as the pump field. Classical pump noise can therefore interfere with the desired measurement of the quantum noise reduction. The most severe noise process is the phase noise caused by thermally induced index modulation of the fiber. This noise termed Guided Acoustic Wave Brillouin Scattering, or GAWBS, by previous researchers is studied and analyzed. Experiments performed to overcome GAWBS successfully with several schemes are described. An experimental demonstration of an interferometric measurement with better sensitivity than the standard quantum limit is described. The results lead to new understandings into the limitations of quantum noise reduction that can be achieved in the

The effects of noise reduction technologies on the acceptance of background noise.

Science.gov (United States)

Lowery, Kristy Jones; Plyler, Patrick N

2013-09-01

Directional microphones (D-Mics) and digital noise reduction (DNR) algorithms are used in hearing aids to reduce the negative effects of background noise on performance. Directional microphones attenuate sounds arriving from anywhere other than the front of the listener while DNR attenuates sounds with physical characteristics of noise. Although both noise reduction technologies are currently available in hearing aids, it is unclear if the use of these technologies in isolation or together affects acceptance of noise and/or preference for the end user when used in various types of background noise. The purpose of the research was to determine the effects of D-Mic, DNR, or the combination of D-Mic and DNR on acceptance of noise and preference when listening in various types of background noise. An experimental study in which subjects were exposed to a repeated measures design was utilized. Thirty adult listeners with mild sloping to moderately severe sensorineural hearing loss participated (mean age 67 yr). Acceptable noise levels (ANLs) were obtained using no noise reduction technologies, D-Mic only, DNR only, and the combination of the two technologies (Combo) for three different background noises (single-talker speech, speech-shaped noise, and multitalker babble) for each listener. In addition, preference rankings of the noise reduction technologies were obtained within each background noise (1 = best, 3 = worst). ANL values were significantly better for each noise reduction technology than baseline; and benefit increased significantly from DNR to D-Mic to Combo. Listeners with higher (worse) baseline ANLs received more benefit from noise reduction technologies than listeners with lower (better) baseline ANLs. Neither ANL values nor ANL benefit values were significantly affected by background noise type; however, ANL benefit with D-Mic and Combo was similar when speech-like noise was present while ANL benefit was greatest for Combo when speech spectrum noise was

Two Methods of Mechanical Noise Reduction of Recorded Speech During Phonation in an MRI devic

Czech Academy of Sciences Publication Activity Database

Přibil, J.; Horáček, Jaromír; Horák, Petr

2011-01-01

Roč. 11, č. 3 (2011), s. 92-98 ISSN 1335-8871 R&D Projects: GA ČR GA102/09/0989 Institutional research plan: CEZ:AV0Z20760514; CEZ:AV0Z20670512 Keywords : speech processing * noise reduction * NMR imaging Subject RIV: BI - Acoustics Impact factor: 0.418, year: 2011

A PIV Study of Slotted Air Injection for Jet Noise Reduction

Science.gov (United States)

Henderson, Brenda S.; Wernet, Mark P.

2012-01-01

Results from acoustic and Particle Image Velocimetry (PIV) measurements are presented for single and dual-stream jets with fluidic injection on the core stream. The fluidic injection nozzles delivered air to the jet through slots on the interior of the nozzle at the nozzle trailing edge. The investigations include subsonic and supersonic jet conditions. Reductions in broadband shock noise and low frequency mixing noise were obtained with the introduction of fluidic injection on single stream jets. Fluidic injection was found to eliminate shock cells, increase jet mixing, and reduce turbulent kinetic energy levels near the end of the potential core. For dual-stream subsonic jets, the introduction of fluidic injection reduced low frequency noise in the peak jet noise direction and enhanced jet mixing. For dual-stream jets with supersonic fan streams and subsonic core streams, the introduction of fluidic injection in the core stream impacted the jet shock cell structure but had little effect on mixing between the core and fan streams.

Core Noise: Overview of Upcoming LDI Combustor Test

Science.gov (United States)

Hultgren, Lennart S.

2012-01-01

This presentation is a technical summary of and outlook for NASA-internal and NASA-sponsored external research on core (combustor and turbine) noise funded by the Fundamental Aeronautics Program Fixed Wing Project. The presentation covers: the emerging importance of core noise due to turbofan design trends and its relevance to the NASA N+3 noise-reduction goal; the core noise components and the rationale for the current emphasis on combustor noise; and the current and planned research activities in the combustor-noise area. Two NASA-sponsored research programs, with particular emphasis on indirect combustor noise, "Acoustic Database for Core Noise Sources", Honeywell Aerospace (NNC11TA40T) and "Measurement and Modeling of Entropic Noise Sources in a Single-Stage Low-Pressure Turbine", U. Illinois/U. Notre Dame (NNX11AI74A) are briefly described. Recent progress in the development of CMC-based acoustic liners for broadband noise reduction suitable for turbofan-core application is outlined. Combustor-design trends and the potential impacts on combustor acoustics are discussed. A NASA GRC developed nine-point lean-direct-injection (LDI) fuel injector is briefly described. The modification of an upcoming thermo-acoustic instability evaluation of the GRC injector in a combustor rig to also provide acoustic information relevant to community noise is presented. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The reduction of aircraft noise is critical to enabling the anticipated large increase in future air traffic. The Quiet Performance Research Theme of the Fixed Wing Project aims to develop concepts and technologies to dramatically reduce the perceived community noise attributable to aircraft with minimal impact on weight and performance.

Separating underwater ambient noise from flow noise recorded on stereo acoustic tags attached to marine mammals

NARCIS (Netherlands)

Benda-Beckmann, A.M. von; Wensveen, P.J.; Samarra, F.I.P.; Beerens, S.P.; Miller, P.J.O.

2016-01-01

Sound-recording acoustic tags attached to marine animals are commonly used in behavioural studies. Measuring ambient noise is of interest to efforts to understand responses of marine mammals to anthropogenic underwater sound, or to assess their communication space. Noise of water flowing around the

Vibration and acoustic noise emitted by dry-type air-core reactors under PWM voltage excitation

Science.gov (United States)

Li, Jingsong; Wang, Shanming; Hong, Jianfeng; Yang, Zhanlu; Jiang, Shengqian; Xia, Shichong

2018-05-01

According to coupling way between the magnetic field and the structural order, structure mode is discussed by engaging finite element (FE) method and both natural frequency and modal shape for a dry-type air-core reactor (DAR) are obtained in this paper. On the basis of harmonic response analysis, electromagnetic force under PWM (Pulse Width Modulation) voltage excitation is mapped with the structure mesh, the vibration spectrum is gained and the consequences represents that the whole structure vibration predominates in the radial direction, with less axial vibration. Referring to the test standard of reactor noise, the rules of emitted noise of the DAR are measured and analyzed at chosen switching frequency matches the sample resonant frequency and the methods of active vibration and noise reduction are put forward. Finally, the low acoustic noise emission of a prototype DAR is verified by measurement.

Adaptive EMG noise reduction in ECG signals using noise level approximation

Science.gov (United States)

Marouf, Mohamed; Saranovac, Lazar

2017-12-01

In this paper the usage of noise level approximation for adaptive Electromyogram (EMG) noise reduction in the Electrocardiogram (ECG) signals is introduced. To achieve the adequate adaptiveness, a translation-invariant noise level approximation is employed. The approximation is done in the form of a guiding signal extracted as an estimation of the signal quality vs. EMG noise. The noise reduction framework is based on a bank of low pass filters. So, the adaptive noise reduction is achieved by selecting the appropriate filter with respect to the guiding signal aiming to obtain the best trade-off between the signal distortion caused by filtering and the signal readability. For the evaluation purposes; both real EMG and artificial noises are used. The tested ECG signals are from the MIT-BIH Arrhythmia Database Directory, while both real and artificial records of EMG noise are added and used in the evaluation process. Firstly, comparison with state of the art methods is conducted to verify the performance of the proposed approach in terms of noise cancellation while preserving the QRS complex waves. Additionally, the signal to noise ratio improvement after the adaptive noise reduction is computed and presented for the proposed method. Finally, the impact of adaptive noise reduction method on QRS complexes detection was studied. The tested signals are delineated using a state of the art method, and the QRS detection improvement for different SNR is presented.

Efficacy of passive acoustic screening: implications for the design of imager and MR-suite.

Science.gov (United States)

Moelker, Adriaan; Vogel, Mika W; Pattynama, Peter M T

2003-02-01

To investigate the efficacy of passive acoustic screening in the magnetic resonance (MR) environment by reducing direct and indirect MR-related acoustic noise, both from the patient's and health worker's perspective. Direct acoustic noise refers to sound originating from the inner and outer shrouds of the MR imager, and indirect noise to acoustic reflections from the walls of the MR suite. Sound measurements were obtained inside the magnet bore (patient position) and at the entrance of the MR imager (health worker position). Inner and outer shrouds and walls were lined with thick layers of sound insulation to eliminate the direct and indirect acoustic pathways. Sound pressure levels (SPLs) and octave band frequencies were acquired during various MR imaging sequences at 1.5 T. Inside the magnet bore, direct acoustic noise radiating from the inner shroud was most relevant, with substantial reductions of up to 18.8 dB when using passive screening of the magnetic bore. At the magnet bore entrance, blocking acoustic noise from the outer shroud and reflections showed significant reductions of 4.5 and 2.8 dB, respectively, and 9.4 dB when simultaneously applied. Inner shroud coverage contributed minimally to the overall SPL reduction. Maximum noise reduction by passive acoustic screening can be achieved by reducing direct sound conduction through the inner and outer shrouds. Additional measures to optimize the acoustic properties of the MR suite have only little effect. Copyright 2003 Wiley-Liss, Inc.

Reduction of centrifugal fan noise by use of resonators

Science.gov (United States)

Neise, W.; Koopmann, G. H.

1980-11-01

A method by which an acoustic resonator can be used to reduce at source the aerodynamic noise generated by turbomachinery has been investigated experimentally. The casing of a small, centrifugal blower was modified by replacing the cut-off of the scroll with the mouth of a quarter-wavelength resonator. The mouth of the resonator was constructed from a series of perforated plates with the same curvature as the cut-off to preserve the original geometry of the casing. Tuning of the resonator was achieved by changing the length via a movable end plug. The noise measurements were made in an anechoically terminated outlet duct at nearly a free delivery operating condition of the blower. With appropriate tuning of the resonator, reductions in the blade passing frequency tones of up to 29 dB were observed with corresponding overall sound pressure levels reductions of up to 7 dB(A). Parameters which influenced the band width of the resonator response were the porosity and the size of the resonator mouth and the flow velocity near the cut-off region. Throughout the tests, the aerodynamic performance of the blower was unaffected by the addition of the resonator to the casing.

Spreadsheet tool for estimating noise reduction costs

International Nuclear Information System (INIS)

Frank, L.; Senden, V.; Leszczynski, Y.

2009-01-01

The Northeast Capital Industrial Association (NCIA) represents industry in Alberta's industrial heartland. The organization is in the process of developing a regional noise management plan (RNMP) for their member companies. The RNMP includes the development of a noise reduction cost spreadsheet tool to conduct reviews of practical noise control treatments available for individual plant equipment, inclusive of ranges of noise attenuation achievable, which produces a budgetary prediction of the installed cost of practical noise control treatments. This paper discussed the noise reduction cost spreadsheet tool, with particular reference to noise control best practices approaches and spreadsheet tool development such as prerequisite, assembling data required, approach, and unit pricing database. Use and optimization of the noise reduction cost spreadsheet tool was also discussed. It was concluded that the noise reduction cost spreadsheet tool is an easy interactive tool to estimate implementation costs related to different strategies and options of noise control mitigating measures and was very helpful in gaining insight for noise control planning purposes. 2 tabs.

Vibro-acoustics

CERN Document Server

Nilsson, Anders

2015-01-01

This three-volume book gives a thorough and comprehensive presentation of vibration and acoustic theories. Different from traditional textbooks which typically deal with some aspects of either acoustic or vibration problems, it is unique of this book to combine those two correlated subjects together. Moreover, it provides fundamental analysis and mathematical descriptions for several crucial phenomena of Vibro-Acoustics which are quite useful in noise reduction, including how structures are excited, energy flows from an excitation point to a sound radiating surface, and finally how a structure radiates noise to a surrounding fluid. Many measurement results included in the text make the reading interesting and informative. Problems/questions are listed at the end of each chapter and the solutions are provided. This will help the readers to understand the topics of Vibro-Acoustics more deeply. The book should be of interest to anyone interested in sound and vibration, vehicle acoustics, ship acoustics and inter...

Study on acoustical properties of sintered bronze porous material for transient exhaust noise of pneumatic system

Science.gov (United States)

Li, Jingxiang; Zhao, Shengdun; Ishihara, Kunihiko

2013-05-01

A novel approach is presented to study the acoustical properties of sintered bronze material, especially used to suppress the transient noise generated by the pneumatic exhaust of pneumatic friction clutch and brake (PFC/B) systems. The transient exhaust noise is impulsive and harmful due to the large sound pressure level (SPL) that has high-frequency. In this paper, the exhaust noise is related to the transient impulsive exhaust, which is described by a one-dimensional aerodynamic model combining with a pressure drop expression of the Ergun equation. A relation of flow parameters and sound source is set up. Additionally, the piston acoustic source approximation of sintered bronze silencer with cylindrical geometry is presented to predict SPL spectrum at a far-field observation point. A semi-phenomenological model is introduced to analyze the sound propagation and reduction in the sintered bronze materials assumed as an equivalent fluid with rigid frame. Experiment results under different initial cylinder pressures are shown to corroborate the validity of the proposed aerodynamic model. In addition, the calculated sound pressures according to the equivalent sound source are compared with the measured noise signals both in time-domain and frequency-domain. Influences of porosity of the sintered bronze material are also discussed.

Development of Adaptive Acoustic Impedance Control Technologies of Acoustic Duct Liner

Directory of Open Access Journals (Sweden)

Hiroshi Kobayashi

2011-01-01

Full Text Available This paper describes the development of adaptive acoustic impedance control (AAC technologies to achieve a larger fan noise reduction, by adaptively adjusting reactance and resistance of the acoustic liner impedance. For the actual proof of the AAC technology III performance, the advanced fan noise absorption control duct liner II was made on trial basis, with the simple control system and the plain device. And, then, the duct liner II was examined for the AAC technology I, II, and III models, using the high speed fan test facility. The test results made clear that the duct liner II of the AAC technology III model could achieve the fan noise reduction higher than O.A. SPL 10 dB (A at the maximum fan speed 6000 rpm, containing the reduction of fundamental BPF tone of 18 dB and 2nd BPF tone of 10 dB in response to the fan peed change from 3000 to 6000 rpm.

Acoustic noise improves motor learning in spontaneously hypertensive rats, a rat model of attention deficit hyperactivity disorder.

Science.gov (United States)

Söderlund, Göran B W; Eckernäs, Daniel; Holmblad, Olof; Bergquist, Filip

2015-03-01

The spontaneously hypertensive (SH) rat model of ADHD displays impaired motor learning. We used this characteristic to study if the recently described acoustic noise benefit in learning in children with ADHD is also observed in the SH rat model. SH rats and a Wistar control strain were trained in skilled reach and rotarod running under either ambient noise or in 75 dBA white noise. In other animals the effect of methylphenidate (MPH) on motor learning was assessed with the same paradigms. To determine if acoustic noise influenced spontaneous motor activity, the effect of acoustic noise was also determined in the open field activity paradigm. We confirm impaired motor learning in the SH rat compared to Wistar SCA controls. Acoustic noise restored motor learning in SH rats learning the Montoya reach test and the rotarod test, but had no influence on learning in Wistar rats. Noise had no effect on open field activity in SH rats, but increased corner time in Wistar. MPH completely restored rotarod learning and performance but did not improve skilled reach in the SH rat. It is suggested that the acoustic noise benefit previously reported in children with ADHD is shared by the SH rat model of ADHD, and the effect is in the same range as that of stimulant treatment. Acoustic noise may be useful as a non-pharmacological alternative to stimulant medication in the treatment of ADHD. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

Applied acoustics concepts, absorbers, and silencers for acoustical comfort and noise control alternative solutions, innovative tools, practical examples

CERN Document Server

Fuchs, Helmut V

2013-01-01

The author gives a comprehensive overview of materials and components for noise control and acoustical comfort. Sound absorbers must meet acoustical and architectural requirements, which fibrous or porous material alone can meet. Basics and applications are demonstrated, with representative examples for spatial acoustics, free-field test facilities and canal linings. Acoustic engineers and construction professionals will find some new basic concepts and tools for developments in order to improve acoustical comfort. Interference absorbers, active resonators and micro-perforated absorbers of different materials and designs complete the list of applications.

Pre-service Acoustic Emission Testing for Metal Pressure Vessel

International Nuclear Information System (INIS)

Lee, Jong O; Yoon, Woon Ha; Lee, Tae Hee; Lee, Jong Kyu

2003-01-01

The field application of acoustic emission(AE) testing for brand-new metal pressure vessel were performed. We will introduce the test procedure for acoustic emission test such as instrument check distance between sensors, sensor location, whole system calibration, pressurization sequence, noise reduction and evaluation. The data of acoustic emission test contain many noise signal, these noise can be reduced by time filtering which based on the description of observation during AE test

Objective approach for analysis of noise source characteristics and acoustic conditions in noisy computerized embroidery workrooms.

Science.gov (United States)

Aliabadi, Mohsen; Golmohammadi, Rostam; Mansoorizadeh, Muharram

2014-03-01

It is highly important to analyze the acoustic properties of workrooms in order to identify best noise control measures from the standpoint of noise exposure limits. Due to the fact that sound pressure is dependent upon environments, it cannot be a suitable parameter for determining the share of workroom acoustic characteristics in producing noise pollution. This paper aims to empirically analyze noise source characteristics and acoustic properties of noisy embroidery workrooms based on special parameters. In this regard, reverberation time as the special room acoustic parameter in 30 workrooms was measured based on ISO 3382-2. Sound power quantity of embroidery machines was also determined based on ISO 9614-3. Multiple linear regression was employed for predicting reverberation time based on acoustic features of the workrooms using MATLAB software. The results showed that the measured reverberation times in most of the workrooms were approximately within the ranges recommended by ISO 11690-1. Similarity between reverberation time values calculated by the Sabine formula and measured values was relatively poor (R (2) = 0.39). This can be due to the inaccurate estimation of the acoustic influence of furniture and formula preconditions. Therefore, this value cannot be considered representative of an actual acoustic room. However, the prediction performance of the regression method with root mean square error (RMSE) = 0.23 s and R (2) = 0.69 is relatively acceptable. Because the sound power of the embroidery machines was relatively high, these sources get the highest priority when it comes to applying noise controls. Finally, an objective approach for the determination of the share of workroom acoustic characteristics in producing noise could facilitate the identification of cost-effective noise controls.

Comparison of various decentralised structural and cavity feedback control strategies for transmitted noise reduction through a double panel structure

Science.gov (United States)

Ho, Jen-Hsuan; Berkhoff, Arthur

2014-03-01

This paper compares various decentralised control strategies, including structural and acoustic actuator-sensor configuration designs, to reduce noise transmission through a double panel structure. The comparison is based on identical control stability indexes. The double panel structure consists of two panels with air in between and offers the advantages of low sound transmission at high frequencies, low heat transmission, and low weight. The double panel structure is widely used, such as in the aerospace and automotive industries. Nevertheless, the resonance of the cavity and the poor sound transmission loss at low frequencies limit the double panel's noise control performance. Applying active structural acoustic control to the panels or active noise control to the cavity has been discussed in many papers. In this paper, the resonances of the panels and the cavity are considered simultaneously to further reduce the transmitted noise through an existing double panel structure. A structural-acoustic coupled model is developed to investigate and compare various structural control and cavity control methods. Numerical analysis and real-time control results show that structural control should be applied to both panels. Three types of cavity control sources are presented and compared. The results indicate that the largest noise reduction is obtained with cavity control by loudspeakers modified to operate as incident pressure sources.

Noise disturbance in open-plan study environments : a field study on noise sources, student tasks and room acoustic parameters

NARCIS (Netherlands)

Braat-Eggen, P.E.; van Heijst, A.W.M.; Hornikx, M.C.J.; Kohlrausch, A.G.

2017-01-01

The aim of this study is to gain more insight in the assessment of noise in open-plan study environments and to reveal correlations between noise disturbance experienced by students and the noise sources they perceive, the tasks they perform and the acoustic parameters of the open-plan study

Development of a 3D finite element acoustic model to predict the sound reduction index of stud based double-leaf walls

Science.gov (United States)

Arjunan, A.; Wang, C. J.; Yahiaoui, K.; Mynors, D. J.; Morgan, T.; Nguyen, V. B.; English, M.

2014-11-01

Building standards incorporating quantitative acoustical criteria to ensure adequate sound insulation are now being implemented. Engineers are making great efforts to design acoustically efficient double-wall structures. Accordingly, efficient simulation models to predict the acoustic insulation of double-leaf wall structures are needed. This paper presents the development of a numerical tool that can predict the frequency dependent sound reduction index R of stud based double-leaf walls at one-third-octave band frequency range. A fully vibro-acoustic 3D model consisting of two rooms partitioned using a double-leaf wall, considering the structure and acoustic fluid coupling incorporating the existing fluid and structural solvers are presented. The validity of the finite element (FE) model is assessed by comparison with experimental test results carried out in a certified laboratory. Accurate representation of the structural damping matrix to effectively predict the R values are studied. The possibilities of minimising the simulation time using a frequency dependent mesh model was also investigated. The FEA model presented in this work is capable of predicting the weighted sound reduction index Rw along with A-weighted pink noise C and A-weighted urban noise Ctr within an error of 1 dB. The model developed can also be used to analyse the acoustically induced frequency dependent geometrical behaviour of the double-leaf wall components to optimise them for best acoustic performance. The FE modelling procedure reported in this paper can be extended to other building components undergoing fluid-structure interaction (FSI) to evaluate their acoustic insulation.

Active noise control primer

CERN Document Server

Snyder, Scott D

2000-01-01

Active noise control - the reduction of noise by generating an acoustic signal that actively interferes with the noise - has become an active area of basic research and engineering applications. The aim of this book is to present all of the basic knowledge one needs for assessing how useful active noise control will be for a given problem and then to provide some guidance for designing, setting up, and tuning an active noise-control system. Written for students who have no prior knowledge of acoustics, signal processing, or noise control but who do have a reasonable grasp of basic physics and mathematics, the book is short and descriptive. It leaves for more advanced texts or research monographs all mathematical details and proofs concerning vibrations, signal processing and the like. The book can thus be used in independent study, in a classroom with laboratories, or in conjunction with a kit for experiment or demonstration. Topics covered include: basic acoustics; human perception and sound; sound intensity...

The influence of acoustical and non-acoustical factors on short-term annoyance due to aircraft noise in the field - The COSMA study.

Science.gov (United States)

Bartels, Susanne; Márki, Ferenc; Müller, Uwe

2015-12-15

Air traffic has increased for the past decades and is forecasted to continue to grow. Noise due to current airport operations can impair the physical and psychological well-being of airport residents. The field study investigated aircraft noise-induced short-term (i.e., within hourly intervals) annoyance in local residents near a busy airport. We aimed at examining the contribution of acoustical and non-acoustical factors to the annoyance rating. Across four days from getting up till going to bed, 55 residents near Cologne/Bonn Airport (M=46years, SD=14years, 34 female) rated their annoyance due to aircraft noise at hourly intervals. For each participant and each hour, 26 noise metrics from outdoor measurements and further 6 individualized metrics that took into account the sound attenuation due to each person's whereabouts in and around their homes were obtained. Non-acoustical variables were differentiated into situational factors (time of day, performed activity during past hour, day of the week) and personal factors (e.g., sensitivity to noise, attitudes, domestic noise insulation). Generalized Estimation Equations were applied for the development of a prediction model for annoyance. Acoustical factors explained only a small proportion (13.7%) of the variance in the annoyance ratings. The number of fly-overs predicted annoyance better than did equivalent and maximum sound pressure levels. The proportion of explained variance in annoyance rose considerably (to 27.6%) when individualized noise metrics as well as situational and personal variables were included in the prediction model. Consideration of noise metrics related to the number of fly-overs and individual adjustment of noise metrics can improve the prediction of short-term annoyance compared to models using equivalent outdoor levels only. Non-acoustical factors have remarkable impact not only on long-term annoyance as shown before but also on short-term annoyance judged in the home environment. Copyright

Results from an acoustic modelling study of seismic airgun survey noise in Queen Charlotte Basin

Energy Technology Data Exchange (ETDEWEB)

MacGillivray, A.O.; Chapman, N.R. [Victoria Univ., BC (Canada). School of Earth and Ocean Sciences

2005-12-07

An acoustic modelling study was conducted to examine seismic survey noise propagation in the Queen Charlotte Basin (QCB) and better understand the physical aspects of sound transmission. The study results are intended to help determine the potential physiological and behavioural effects of airgun noise on marine mammals and fish. The scope of the study included a numerical simulation of underwater sound transmission in QCB in areas where oil and gas exploration activities may be conducted; a forecast of received noise levels by combining acoustic transmission loss computations with acoustic source levels representative of seismic exploration activity and, the use of received forecasts to estimate zones of impact for marine mammals. The critical environmental parameters in the QCB are the bathymetry of the ocean, the sound speed profile in the water and the geoacoustic profile of the seabed. The RAM acoustic propagation model developed by the United States Naval Research Laboratory was used to compute acoustic transmission loss in the QCB. The source level and directionality of the seismic array was determined by a full-waveform array source signature model. This modelling study of noise propagation from seismic surveys revealed several key findings. Among them, it showed that received noise levels in the water are affected by the source location, array orientation and the shape of the sound speed profile with respect to water depth. It also showed that noise levels are lowest in shallow bathymetry. 30 refs., 5 tabs., 13 figs.

Neural underpinnings of background acoustic noise in normal aging and mild cognitive impairment.

Science.gov (United States)

Sinanaj, Indrit; Montandon, Marie-Louise; Rodriguez, Cristelle; Herrmann, François; Santini, Francesco; Haller, Sven; Giannakopoulos, Panteleimon

2015-12-03

Previous contributions in younger cohorts have revealed that reallocation of cerebral resources, a crucial mechanism for working memory (WM), may be disrupted by parallel demands of background acoustic noise suppression. To date, no study has explored the impact of such disruption on brain activation in elderly individuals with or without subtle cognitive deficits. We performed a functional Magnetic Resonance Imaging (fMRI) study in 23 cases (mean age=75.7 y.o., 16 men) with mild cognitive impairment (MCI) and 16 elderly healthy controls (HC, mean age=70.1 y.o., three men) using a 2-back WM task, under two distinct MRI background acoustic noise conditions (louder vs. lower noise echo-planar imaging). General linear models were used to assess brain activation as a function of group and noise. In both groups, lower background noise is associated with increased activation of the working memory network (WMN). A decrease of the normally observed deactivation of the default mode network (DMN) is found under louder noise in both groups. Unlike HC, MCI cases also show decreased deactivation of the DMN under both louder and lower background noise. Under louder noise, this decrease is observed in anterior parts of the DMN in HC, and in the posterior cingulate cortex in MCI cases. Our results suggest that background acoustic noise has a differential impact on WMN activation in normal aging as a function of the cognitive status. Only louder noise has a disruptive effect on the usually observed DMN deactivation during WM task performance in HC. In contrast, MCI cases show altered DMN reactivity even in the presence of lower noise. Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.

Broadband transmission noise reduction of smart panels featuring piezoelectric shunt circuits and sound-absorbing material.

Science.gov (United States)

Kim, Jaehwan; Lee, Joong-Kuen

2002-09-01

The possibility of a broadband noise reduction of piezoelectric smart panels is experimentally studied. A piezoelectric smart panel is basically a plate structure on which piezoelectric patches with electrical shunt circuits are mounted and sound-absorbing material is bonded on the surface of the structure. Sound-absorbing material can absorb the sound transmitted at the midfrequency region effectively while the use of piezoelectric shunt damping can reduce the transmission at resonance frequencies of the panel structure. To be able to reduce the sound transmission at low panel resonance frequencies, piezoelectric damping using the measured electrical impedance model is adopted. A resonant shunt circuit for piezoelectric shunt damping is composed of resistor and inductor in series, and they are determined by maximizing the dissipated energy through the circuit. The transmitted noise-reduction performance of smart panels is tested in an acoustic tunnel. The tunnel is a square cross-sectional tube and a loudspeaker is mounted at one side of the tube as a sound source. Panels are mounted in the middle of the tunnel and the transmitted sound pressure across panels is measured. When an absorbing material is bonded on a single plate, a remarkable transmitted noise reduction in the midfrequency region is observed except for the fundamental resonance frequency of the plate. By enabling the piezoelectric shunt damping, noise reduction is achieved at the resonance frequency as well. Piezoelectric smart panels incorporating passive absorbing material and piezoelectric shunt damping is a promising technology for noise reduction over a broadband of frequencies.

Odeon, a design tool for auditorium acoustics, noise control and loudspeaker systems

DEFF Research Database (Denmark)

Christensen, Claus Lynge

2001-01-01

The ODEON software was originally developed for prediction of auditorium acoustics. However current editions of the software are not limited to these fields, but also allow prediction in rooms such as churches and mosques, interior noise control, design of room acoustics and sound distribution...

Research on noise and vibration reduction at DB to improve the environmental friendliness of railway traffic

Science.gov (United States)

Schulte-Werning, B.; Beier, M.; Degen, K. G.; Stiebel, D.

2006-06-01

One of the most prominent keywords relating to the environmental friendliness of railway traffic is noise reduction. Thus, the research and development programme "Low Noise Railway" of Deutsche Bahn (DB) is under way to treat the noise of the vehicles and infrastructure. The noise reduction of the trains and the rail/wheel system are being tackled within several projects. The direct noise experienced by railway-lineside residents due to train movements on the track can be reduced by minimising the sound radiation directly at the source. This is the first-choice solution, as it proves to be the most effective countermeasure regarding a cost-benefit relation. The limit values for the noise emission as specified in the technical specification for interoperability are an essential criterion to be confirmed during the procurement process of railway vehicles. A recently developed acoustical quality management scheme establishes systematic noise management to complete the vehicle procurement process in the phases of concept, design, construction and manufacturing. In freight traffic quiet railway wheels for block brake operation will play an important role in the future to meet the goal of a low-noise railway system. A first attempt to realise successfully the low-noise potential of such optimised wheels was performed, even if with mixed results. To show ways of reducing the noise of the cooling ventilation in locomotives, DB is a partner in a development project led by Siemens. A notable 8 dB(A) noise reduction was measured. Concerning bridge noise, a project was started based on an effective and cost-efficient combination of experiments and simulations in order to develop specifications for the construction of generic low-noise bridges.

Landing Gear Door Liners for Airframe Noise Reduction

Science.gov (United States)

Jones, Michael G. (Inventor); Howerton, Brian M. (Inventor); Van De Ven, Thomas (Inventor)

2014-01-01

A landing gear door for retractable landing gear of aircraft includes an acoustic liner. The acoustic liner includes one or more internal cavities or chambers having one or more openings that inhibit the generation of sound at the surface and/or absorb sound generated during operation of the aircraft. The landing gear door may include a plurality of internal chambers having different geometries to thereby absorb broadband noise.

Background noise of acoustic emission signals in sodium piping loop

International Nuclear Information System (INIS)

Mori, Y.; Aoki, K.; Kuribayashi, K.; Kishi, T.; Sakakibara, Y.

1985-01-01

Background noise measurement in the frequency range of acoustic emission (AE) signals was made on the sodium piping loops of a 50 MW steam generator test facility in the Power Reactor and Nuclear Fuel Development Corporation (PNC). During the dynamic characteristics test of the steam generator over a wide range of operating conditions, the background noise generated on the pipe surface was measured using wideband AE sensor externally mounted with waveguide. Data were obtained for the effect of power loads of steam generator on both amplitude and frequency spectra of background noise signals. Source and nature of background noise were established

Analysis tools for the design of active structural acoustic control systems

NARCIS (Netherlands)

Oude nijhuis, M.H.H.

2003-01-01

Acoustic noise is an important problem in the modern society and provides much of the impetus for the development of noise reduction techniques. Passive methods, such as the use of sound absorbing materials, provide an adequate solution to many noise problems, but for noise reduction at low

Acoustical contribution calculation and analysis of compressor shell based on acoustic transfer vector method

Science.gov (United States)

Chen, Xiaol; Guo, Bei; Tuo, Jinliang; Zhou, Ruixin; Lu, Yang

2017-08-01

Nowadays, people are paying more and more attention to the noise reduction of household refrigerator compressor. This paper established a sound field bounded by compressor shell and ISO3744 standard field points. The Acoustic Transfer Vector (ATV) in the sound field radiated by a refrigerator compressor shell were calculated which fits the test result preferably. Then the compressor shell surface is divided into several parts. Based on Acoustic Transfer Vector approach, the sound pressure contribution to the field points and the sound power contribution to the sound field of each part were calculated. To obtain the noise radiation in the sound field, the sound pressure cloud charts were analyzed, and the contribution curves in different frequency of each part were acquired. Meanwhile, the sound power contribution of each part in different frequency was analyzed, to ensure those parts where contributes larger sound power. Through the analysis of acoustic contribution, those parts where radiate larger noise on the compressor shell were determined. This paper provides a credible and effective approach on the structure optimal design of refrigerator compressor shell, which is meaningful in the noise and vibration reduction.

Topography and biological noise determine acoustic detectability on coral reefs

KAUST Repository

Cagua, Edgar F.

2013-08-19

Acoustic telemetry is an increasingly common tool for studying the movement patterns, behavior and site fidelity of marine organisms, but to accurately interpret acoustic data, the variability, periodicity and range of detectability between acoustic tags and receivers must be understood. The relative and interactive effects of topography with biological and environmental noise have not been quantified on coral reefs. We conduct two long-term range tests (1- and 4-month duration) on two different reef types in the central Red Sea to determine the relative effect of distance, depth, topography, time of day, wind, lunar phase, sea surface temperature and thermocline on detection probability. Detectability, as expected, declines with increasing distance between tags and receivers, and we find average detection ranges of 530 and 120 m, using V16 and V13 tags, respectively, but the topography of the reef can significantly modify this relationship, reducing the range by ~70 %, even when tags and receivers are in line-of-sight. Analyses that assume a relationship between distance and detections must therefore be used with care. Nighttime detection range was consistently reduced in both locations, and detections varied by lunar phase in the 4-month test, suggesting a strong influence of biological noise (reducing detection probability up to 30 %), notably more influential than other environmental noises, including wind-driven noise, which is normally considered important in open-water environments. Analysis of detections should be corrected in consideration of the diel patterns we find, and range tests or sentinel tags should be used for more than 1 month to quantify potential changes due to lunar phase. Some studies assume that the most usual factor limiting detection range is weather-related noise; this cannot be extrapolated to coral reefs. © 2013 Springer-Verlag Berlin Heidelberg.

Listening to the Deep: Live monitoring of ocean noise and cetacean acoustic signals

OpenAIRE

André, Michel; Van der Schaar, Mike Connor Roger Malcolm; Zaugg, Serge Alain; Houégnigan, Ludwig; Sánchez, A.M.; Castell, Joan

2011-01-01

The development and broad use of passive acoustic monitoring techniques have the potential to help assessing the large-scale influence of artificial noise on marine organisms and ecosystems. Deep-sea observatories have the potential to play a key role in understanding these recent acoustic changes. LIDO(Listening to the Deep Ocean Environment) is an international project that is allowing the real-time longterm monitoring of marine ambient noise as well as marine mammal sounds at cabled and...

Active structural acoustic control of helicopter interior multifrequency noise using input-output-based hybrid control

Science.gov (United States)

Ma, Xunjun; Lu, Yang; Wang, Fengjiao

2017-09-01

This paper presents the recent advances in reduction of multifrequency noise inside helicopter cabin using an active structural acoustic control system, which is based on active gearbox struts technical approach. To attenuate the multifrequency gearbox vibrations and resulting noise, a new scheme of discrete model predictive sliding mode control has been proposed based on controlled auto-regressive moving average model. Its implementation only needs input/output data, hence a broader frequency range of controlled system is modelled and the burden on the state observer design is released. Furthermore, a new iteration form of the algorithm is designed, improving the developing efficiency and run speed. To verify the algorithm's effectiveness and self-adaptability, experiments of real-time active control are performed on a newly developed helicopter model system. The helicopter model can generate gear meshing vibration/noise similar to a real helicopter with specially designed gearbox and active struts. The algorithm's control abilities are sufficiently checked by single-input single-output and multiple-input multiple-output experiments via different feedback strategies progressively: (1) control gear meshing noise through attenuating vibrations at the key points on the transmission path, (2) directly control the gear meshing noise in the cabin using the actuators. Results confirm that the active control system is practical for cancelling multifrequency helicopter interior noise, which also weakens the frequency-modulation of the tones. For many cases, the attenuations of the measured noise exceed the level of 15 dB, with maximum reduction reaching 31 dB. Also, the control process is demonstrated to be smoother and faster.

Acoustic noise induces attention shifts and reduces foraging performance in three-spined sticklebacks (Gasterosteus aculeatus.

Directory of Open Access Journals (Sweden)

Julia Purser

2011-02-01

Full Text Available Acoustic noise is known to have a variety of detrimental effects on many animals, including humans, but surprisingly little is known about its impacts on foraging behaviour, despite the obvious potential consequences for survival and reproductive success. We therefore exposed captive three-spined sticklebacks (Gasterosteus aculeatus to brief and prolonged noise to investigate how foraging performance is affected by the addition of acoustic noise to an otherwise quiet environment. The addition of noise induced only mild fear-related behaviours--there was an increase in startle responses, but no change in the time spent freezing or hiding compared to a silent control--and thus had no significant impact on the total amount of food eaten. However, there was strong evidence that the addition of noise increased food-handling errors and reduced discrimination between food and non-food items, results that are consistent with a shift in attention. Consequently, noise resulted in decreased foraging efficiency, with more attacks needed to consume the same number of prey items. Our results suggest that acoustic noise has the potential to influence a whole host of everyday activities through effects on attention, and that even very brief noise exposure can cause functionally significant impacts, emphasising the threat posed by ever-increasing levels of anthropogenic noise in the environment.

Generation of broadband electrostatic noise by electron acoustic solitons

International Nuclear Information System (INIS)

Dubouloz, N.; Pottelette, R.; Malingre, M.; Treumann, R.A.

1991-01-01

Broadband electrostatic noise (BEN) bursts whose amplitude sometimes reaches about 100 mV m -1 have been observed by the Viking satellite in the dayside auroral zone. These emissions have been shown to be greatly influenced by nonlinear effects and to occur simultaneously with the observation of particle distributions favouring the destabilization of the electron acoustic mode. It is shown that electron acoustic solitons passing by the satellite would generate spectra that can explain the high-frequency part of BEN, above the electron plasma frequency

A numerical model for ocean ultra-low frequency noise: wave-generated acoustic-gravity and Rayleigh modes.

Science.gov (United States)

Ardhuin, Fabrice; Lavanant, Thibaut; Obrebski, Mathias; Marié, Louis; Royer, Jean-Yves; d'Eu, Jean-François; Howe, Bruce M; Lukas, Roger; Aucan, Jerome

2013-10-01

The generation of ultra-low frequency acoustic noise (0.1 to 1 Hz) by the nonlinear interaction of ocean surface gravity waves is well established. More controversial are the quantitative theories that attempt to predict the recorded noise levels and their variability. Here a single theoretical framework is used to predict the noise level associated with propagating pseudo-Rayleigh modes and evanescent acoustic-gravity modes. The latter are dominant only within 200 m from the sea surface, in shallow or deep water. At depths larger than 500 m, the comparison of a numerical noise model with hydrophone records from two open-ocean sites near Hawaii and the Kerguelen islands reveal: (a) Deep ocean acoustic noise at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, in which the presence of the ocean bottom amplifies the noise by 10 to 20 dB; (b) in agreement with previous results, the local maxima in the noise spectrum support the theoretical prediction for the vertical structure of acoustic modes; and (c) noise level and variability are well predicted for frequencies up to 0.4 Hz. Above 0.6 Hz, the model results are less accurate, probably due to the poor estimation of the directional properties of wind-waves with frequencies higher than 0.3 Hz.

Fan interaction noise reduction using a wake generator: experiments and computational aeroacoustics

Science.gov (United States)

Polacsek, C.; Desbois-Lavergne, F.

2003-08-01

A control grid (wake generator) aimed at reducing rotor-stator interaction modes in fan engines when mounted upstream of the rotor has been studied here. This device complements other active noise control systems currently proposed. The compressor model of the instrumented ONERA CERF-rig is used to simulate suitable conditions. The design of the grid is drafted out using semi-empirical models for wake and potential flow, and experimentally achieved. Cylindrical rods are able to generate a spinning mode of the same order and similar level as the interaction mode. Mounting the rods on a rotating ring allows for adjusting the phase of the control mode so that an 8 dB sound pressure level (SPL) reduction at the blade passing frequency is achieved when the two modes are out of phase. Experimental results are assessed by a numerical approach using computational fluid dynamics (CFD). A Reynolds averaged Navier-Stokes 2-D solver, developed at ONERA, is used to provide the unsteady force components on blades and vanes required for acoustics. The loading noise source term of the Ffowcs Williams and Hawkings equation is used to model the interaction noise between the sources, and an original coupling to a boundary element method (BEM) code is realized to take account of the inlet geometry effects on acoustic in-duct propagation. Calculations using the classical analytical the Green function of an infinite annular duct are also addressed. Simple formulations written in the frequency domain and expanded into modes are addressed and used to compute an in-duct interaction mode and to compare with the noise reduction obtained during the tests. A fairly good agreement between predicted and measured SPL is found when the inlet geometry effects are part of the solution (by coupling with the BEM). Furthermore, computed aerodynamic penalties due to the rods are found to be negligible. These results partly validate the computation chain and highlight the potential of the wake generator

Prediction of Landing Gear Noise Reduction and Comparison to Measurements

Science.gov (United States)

Lopes, Leonard V.

2010-01-01

Noise continues to be an ongoing problem for existing aircraft in flight and is projected to be a concern for next generation designs. During landing, when the engines are operating at reduced power, the noise from the airframe, of which landing gear noise is an important part, is equal to the engine noise. There are several methods of predicting landing gear noise, but none have been applied to predict the change in noise due to a change in landing gear design. The current effort uses the Landing Gear Model and Acoustic Prediction (LGMAP) code, developed at The Pennsylvania State University to predict the noise from landing gear. These predictions include the influence of noise reduction concepts on the landing gear noise. LGMAP is compared to wind tunnel experiments of a 6.3%-scale Boeing 777 main gear performed in the Quiet Flow Facility (QFF) at NASA Langley. The geometries tested in the QFF include the landing gear with and without a toboggan fairing and the door. It is shown that LGMAP is able to predict the noise directives and spectra from the model-scale test for the baseline configuration as accurately as current gear prediction methods. However, LGMAP is also able to predict the difference in noise caused by the toboggan fairing and by removing the landing gear door. LGMAP is also compared to far-field ground-based flush-mounted microphone measurements from the 2005 Quiet Technology Demonstrator 2 (QTD 2) flight test. These comparisons include a Boeing 777-300ER with and without a toboggan fairing that demonstrate that LGMAP can be applied to full-scale flyover measurements. LGMAP predictions of the noise generated by the nose gear on the main gear measurements are also shown.

The effect of human activity noise on the acoustic quality in open plan office

DEFF Research Database (Denmark)

Dehlbæk, Tania Stenholt; Jeong, Cheol-Ho; Brunskog, Jonas

2016-01-01

A disadvantage of open plan offices is the noise annoyance. Noise problems in open plan offices have been dealt with in several studies, and standards have been set up. Still, what has not been taken into account is the effect of human activity noise on acoustic conditions. In this study......, measurements of the general office noise levels and the room acoustic conditions according to ISO 3382-3 have been carried out in five open plan offices. Probability density functions of the sound pressure level have been obtained, and the human activity noise has been identified. Results showed a decrease...... in STI-values including the human activity noise compared to STI-values including only technical background noise as the standard recommends. Furthermore, at 500 Hz a regression analysis showed that the density of people in an room, absorption area, reverberation time as well as the ISO 3382-3 parameter...

Acoustic engineering and technology '90. Acoustic monitoring methods in maintenance and quality assurance and their effects on noise reduction. Schalltechnik '90. Akustische Ueberwachungsmethoden bei der Instandhaltung und Qualitaetssicherung und ihre Auswirkungen auf die Laermminderung

Energy Technology Data Exchange (ETDEWEB)

1990-01-01

Acoustic monitoring, testing and diagnosis in machines, production processes and products enhance the uptimes and profitability of machinery and plants. 18 papers discuss the current state of the art of acoustic monitoring systems including integrated factory planning as well as industrial health, and noise protection. (DG).

A modal-based reduction method for sound absorbing porous materials in poro-acoustic finite element models.

Science.gov (United States)

Rumpler, Romain; Deü, Jean-François; Göransson, Peter

2012-11-01

Structural-acoustic finite element models including three-dimensional (3D) modeling of porous media are generally computationally costly. While being the most commonly used predictive tool in the context of noise reduction applications, efficient solution strategies are required. In this work, an original modal reduction technique, involving real-valued modes computed from a classical eigenvalue solver is proposed to reduce the size of the problem associated with the porous media. In the form presented in this contribution, the method is suited for homogeneous porous layers. It is validated on a 1D poro-acoustic academic problem and tested for its performance on a 3D application, using a subdomain decomposition strategy. The performance of the proposed method is estimated in terms of degrees of freedom downsizing, computational time enhancement, as well as matrix sparsity of the reduced system.

An artificial neural network approach for aerodynamic performance retention in airframe noise reduction design of a 3D swept wing model

Directory of Open Access Journals (Sweden)

Tao Jun

2016-10-01

Full Text Available With the progress of high-bypass turbofan and the innovation of silencing nacelle in engine noise reduction, airframe noise has now become another important sound source besides the engine noise. Thus, reducing airframe noise makes a great contribution to the overall noise reduction of a civil aircraft. However, reducing airframe noise often leads to aerodynamic performance loss in the meantime. In this case, an approach based on artificial neural network is introduced. An established database serves as a basis and the training sample of a back propagation (BP artificial neural network, which uses confidence coefficient reasoning method for optimization later on. Then the most satisfactory configuration is selected for validating computations through the trained BP network. On the basis of the artificial neural network approach, an optimization process of slat cove filler (SCF for high lift devices (HLD on the Trap Wing is presented. Aerodynamic performance of both the baseline and optimized configurations is investigated through unsteady detached eddy simulations (DES, and a hybrid method, which combines unsteady DES method with acoustic analogy theory, is employed to validate the noise reduction effect. The numerical results indicate not merely a significant airframe noise reduction effect but also excellent aerodynamic performance retention simultaneously.

A conceptual framework for noise reduction

CERN Document Server

Benesty, Jacob

2015-01-01

Though noise reduction and speech enhancement problems have been studied for at least five decades, advances in our understanding and the development of reliable algorithms are more important than ever, as they support the design of tailored solutions for clearly defined applications. In this work, the authors propose a conceptual framework that can be applied to the many different aspects of noise reduction, offering a uniform approach to monaural and binaural noise reduction problems, in the time domain and in the frequency domain, and involving a single or multiple microphones. Moreover, the derivation of optimal filters is simplified, as are the performance measures used for their evaluation.

Supersonic impinging jet noise reduction using a hybrid control technique

Science.gov (United States)

Wiley, Alex; Kumar, Rajan

2015-07-01

Control of the highly resonant flowfield associated with supersonic impinging jet has been experimentally investigated. Measurements were made in the supersonic impinging jet facility at the Florida State University for a Mach 1.5 ideally expanded jet. Measurements included unsteady pressures on a surface plate near the nozzle exit, acoustics in the nearfield and beneath the impingement plane, and velocity field using particle image velocimetry. Both passive control using porous surface and active control with high momentum microjet injection are effective in reducing nearfield noise and flow unsteadiness over a range of geometrical parameters; however, the type of noise reduction achieved by the two techniques is different. The passive control reduces broadband noise whereas microjet injection attenuates high amplitude impinging tones. The hybrid control, a combination of two control methods, reduces both broadband and high amplitude impinging tones and surprisingly its effectiveness is more that the additive effect of the two control techniques. The flow field measurements show that with hybrid control the impinging jet is stabilized and the turbulence quantities such as streamwise turbulence intensity, transverse turbulence intensity and turbulent shear stress are significantly reduced.

Reduction of airfoil trailing edge noise by trailing edge blowing

International Nuclear Information System (INIS)

Gerhard, T; Carolus, T; Erbslöh, S

2014-01-01

The paper deals with airfoil trailing edge noise and its reduction by trailing edge blowing. A Somers S834 airfoil section which originally was designed for small wind turbines is investigated. To mimic realistic Reynolds numbers the boundary layer is tripped on pressure and suction side. The chordwise position of the blowing slot is varied. The acoustic sources, i.e. the unsteady flow quantities in the turbulent boundary layer in the vicinity of the trailing edge, are quantified for the airfoil without and with trailing edge blowing by means of a large eddy simulation and complementary measurements. Eventually the far field airfoil noise is measured by a two-microphone filtering and correlation and a 40 microphone array technique. Both, LES-prediction and measurements showed that a suitable blowing jet on the airfoil suction side is able to reduce significantly the turbulence intensity and the induced surface pressure fluctuations in the trailing edge region. As a consequence, trailing edge noise associated with a spectral hump around 500 Hz could be reduced by 3 dB. For that a jet velocity of 50% of the free field velocity was sufficient. The most favourable slot position was at 90% chord length

Novel Acoustic Feedback Cancellation Approaches In Hearing Aid Applications Using Probe Noise and Probe Noise Enhancement

DEFF Research Database (Denmark)

Guo, Meng; Jensen, Søren Holdt; Jensen, Jesper

2012-01-01

. In many cases, this bias problem causes the cancellation system to fail. The traditional probe noise approach, where a noise signal is added to the loudspeaker signal can, in theory, prevent the bias. However, in practice, the probe noise level must often be so high that the noise is clearly audible...... and annoying; this makes the traditional probe noise approach less useful in practical applications. In this work, we explain theoretically the decreased convergence rate when using low-level probe noise in the traditional approach, before we propose and study analytically two new probe noise approaches...... the proposed approaches much more attractive in practical applications. We demonstrate this through a simulation experiment with audio signals in a hearing aid acoustic feedback cancellation system, where the convergence rate is improved by as much as a factor of 10....

Student design projects in applied acoustics.

Science.gov (United States)

Bös, Joachim; Moritz, Karsten; Skowronek, Adam; Thyes, Christian; Tschesche, Johannes; Hanselka, Holger

2012-03-01

This paper describes a series of student projects which are intended to complement theoretical education in acoustics and engineering noise control with practical experience. The projects are also intended to enhance the students' ability to work in a team, to manage a project, and to present their results. The projects are carried out in close cooperation with industrial partners so that the students can get a taste of the professional life of noise control engineers. The organization of such a project, its execution, and some of the results from the most recent student project are presented as a demonstrative example. This latest project involved the creation of noise maps of a production hall, the acoustic analysis of a packaging machine, and the acoustic analysis of a spiral vibratory conveyor. Upon completion of the analysis, students then designed, applied, and verified some simple preliminary noise reduction measures to demonstrate the potential of these techniques. © 2012 Acoustical Society of America

Airport acoustics: Aircraft noise distribution and modelling of some ...

African Journals Online (AJOL)

Airport acoustics: Aircraft noise distribution and modelling of some aircraft parameters. MU Onuu, EO Obisung. Abstract. No Abstract. Nigerian Journal of Physics Vol. 17 (Supplement) 2005: pp. 177-186. Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT.

Active Structural Acoustic Control of Interior Noise on a Raytheon 1900D

Science.gov (United States)

Palumbo, Dan; Cabell, Ran; Sullivan, Brenda; Cline, John

2000-01-01

An active structural acoustic control system has been demonstrated on a Raytheon Aircraft Company 1900D turboprop airliner. Both single frequency and multi-frequency control of the blade passage frequency and its harmonics was accomplished. The control algorithm was a variant of the popular filtered-x LMS implemented in the principal component domain. The control system consisted of 21 inertial actuators and 32 microphones. The actuators were mounted to the aircraft's ring frames. The microphones were distributed uniformly throughout the interior at head height, both seated and standing. Actuator locations were selected using a combinatorial search optimization algorithm. The control system achieved a 14 dB noise reduction of the blade passage frequency during single frequency tests. Multi-frequency control of the first 1st, 2nd and 3rd harmonics resulted in 10.2 dB, 3.3 dB and 1.6 dB noise reductions respectively. These results fall short of the predictions which were produced by the optimization algorithm (13.5 dB, 8.6 dB and 6.3 dB). The optimization was based on actuator transfer functions taken on the ground and it is postulated that cabin pressurization at flight altitude was a factor in this discrepancy.

Definition of 1992 Technology Aircraft Noise Levels and the Methodology for Assessing Airplane Noise Impact of Component Noise Reduction Concepts

Science.gov (United States)

Kumasaka, Henry A.; Martinez, Michael M.; Weir, Donald S.

1996-01-01

This report describes the methodology for assessing the impact of component noise reduction on total airplane system noise. The methodology is intended to be applied to the results of individual study elements of the NASA-Advanced Subsonic Technology (AST) Noise Reduction Program, which will address the development of noise reduction concepts for specific components. Program progress will be assessed in terms of noise reduction achieved, relative to baseline levels representative of 1992 technology airplane/engine design and performance. In this report, the 1992 technology reference levels are defined for assessment models based on four airplane sizes - an average business jet and three commercial transports: a small twin, a medium sized twin, and a large quad. Study results indicate that component changes defined as program final goals for nacelle treatment and engine/airframe source noise reduction would achieve from 6-7 EPNdB reduction of total airplane noise at FAR 36 Stage 3 noise certification conditions for all of the airplane noise assessment models.

Research status on aero-acoustic noise from wind turbine blades

International Nuclear Information System (INIS)

Yang, B

2013-01-01

This paper describes the noise mechanisms and categories of modern large wind turbine and main noise sources. Then the latest progresses in wind turbine noise researches are described from three aspects: noise prediction model, detection of noise sources by microphone array technique and methods for noise reduction. Although the turbine is restricted to horizontal axis wind turbines, the noise prediction model and reduction methods also can be applied to other turbines when the noise mechanisms are similar. Microphone array technique can be applied to locate any kind of noise sources

Active Noise Control for Dishwasher noise

Science.gov (United States)

Lee, Nokhaeng; Park, Youngjin

2016-09-01

The dishwasher is a useful home appliance and continually used for automatically washing dishes. It's commonly placed in the kitchen with built-in style for practicality and better use of space. In this environment, people are easily exposed to dishwasher noise, so it is an important issue for the consumers, especially for the people living in open and narrow space. Recently, the sound power levels of the noise are about 40 - 50 dBA. It could be achieved by removal of noise sources and passive means of insulating acoustical path. For more reduction, such a quiet mode with the lower speed of cycle has been introduced, but this deteriorates the washing capacity. Under this background, we propose active noise control for dishwasher noise. It is observed that the noise is propagating mainly from the lower part of the front side. Control speakers are placed in the part for the collocation. Observation part of estimating sound field distribution and control part of generating the anti-noise are designed for active noise control. Simulation result shows proposed active noise control scheme could have a potential application for dishwasher noise reduction.

Passive acoustic measurement of bedload grain size distribution using self-generated noise

Directory of Open Access Journals (Sweden)

T. Petrut

2018-01-01

Full Text Available Monitoring sediment transport processes in rivers is of particular interest to engineers and scientists to assess the stability of rivers and hydraulic structures. Various methods for sediment transport process description were proposed using conventional or surrogate measurement techniques. This paper addresses the topic of the passive acoustic monitoring of bedload transport in rivers and especially the estimation of the bedload grain size distribution from self-generated noise. It discusses the feasibility of linking the acoustic signal spectrum shape to bedload grain sizes involved in elastic impacts with the river bed treated as a massive slab. Bedload grain size distribution is estimated by a regularized algebraic inversion scheme fed with the power spectrum density of river noise estimated from one hydrophone. The inversion methodology relies upon a physical model that predicts the acoustic field generated by the collision between rigid bodies. Here we proposed an analytic model of the acoustic energy spectrum generated by the impacts between a sphere and a slab. The proposed model computes the power spectral density of bedload noise using a linear system of analytic energy spectra weighted by the grain size distribution. The algebraic system of equations is then solved by least square optimization and solution regularization methods. The result of inversion leads directly to the estimation of the bedload grain size distribution. The inversion method was applied to real acoustic data from passive acoustics experiments realized on the Isère River, in France. The inversion of in situ measured spectra reveals good estimations of grain size distribution, fairly close to what was estimated by physical sampling instruments. These results illustrate the potential of the hydrophone technique to be used as a standalone method that could ensure high spatial and temporal resolution measurements for sediment transport in rivers.

Passive acoustic measurement of bedload grain size distribution using self-generated noise

Science.gov (United States)

Petrut, Teodor; Geay, Thomas; Gervaise, Cédric; Belleudy, Philippe; Zanker, Sebastien

2018-01-01

Monitoring sediment transport processes in rivers is of particular interest to engineers and scientists to assess the stability of rivers and hydraulic structures. Various methods for sediment transport process description were proposed using conventional or surrogate measurement techniques. This paper addresses the topic of the passive acoustic monitoring of bedload transport in rivers and especially the estimation of the bedload grain size distribution from self-generated noise. It discusses the feasibility of linking the acoustic signal spectrum shape to bedload grain sizes involved in elastic impacts with the river bed treated as a massive slab. Bedload grain size distribution is estimated by a regularized algebraic inversion scheme fed with the power spectrum density of river noise estimated from one hydrophone. The inversion methodology relies upon a physical model that predicts the acoustic field generated by the collision between rigid bodies. Here we proposed an analytic model of the acoustic energy spectrum generated by the impacts between a sphere and a slab. The proposed model computes the power spectral density of bedload noise using a linear system of analytic energy spectra weighted by the grain size distribution. The algebraic system of equations is then solved by least square optimization and solution regularization methods. The result of inversion leads directly to the estimation of the bedload grain size distribution. The inversion method was applied to real acoustic data from passive acoustics experiments realized on the Isère River, in France. The inversion of in situ measured spectra reveals good estimations of grain size distribution, fairly close to what was estimated by physical sampling instruments. These results illustrate the potential of the hydrophone technique to be used as a standalone method that could ensure high spatial and temporal resolution measurements for sediment transport in rivers.

Structural sensing of interior sound for active control of noise in structural-acoustic cavities.

Science.gov (United States)

Bagha, Ashok K; Modak, S V

2015-07-01

This paper proposes a method for structural sensing of acoustic potential energy for active control of noise in a structural-acoustic cavity. The sensing strategy aims at global control and works with a fewer number of sensors. It is based on the established concept of radiation modes and hence does not add too many states to the order of the system. Acoustic potential energy is sensed using a combination of a Kalman filter and a frequency weighting filter with the structural response measurements as the inputs. The use of Kalman filter also makes the system robust against measurement noise. The formulation of the strategy is presented using finite element models of the system including that of sensors and actuators so that it can be easily applied to practical systems. The sensing strategy is numerically evaluated in the framework of Linear Quadratic Gaussian based feedback control of interior noise in a rectangular box cavity with a flexible plate with single and multiple pairs of piezoelectric sensor-actuator patches when broadband disturbances act on the plate. The performance is compared with an "acoustic filter" that models the complete transfer function from the structure to the acoustic domain. The sensing performance is also compared with a direct estimation strategy.

Jet Noise Reduction by Microjets - A Parametric Study

Science.gov (United States)

Zaman, K. B. M. Q.

2010-01-01

The effect of injecting tiny secondary jets (microjets ) on the radiated noise from a subsonic primary jet is studied experimentally. The microjets are injected on to the primary jet near the nozzle exit with variable port geometry, working fluid and driving pressure. A clear noise reduction is observed that improves with increasing jet pressure. It is found that smaller diameter ports with higher driving pressure, but involving less thrust and mass fraction, can produce better noise reduction. A collection of data from the present as well as past experiments is examined in an attempt to correlate the noise reduction with the operating parameters. The results indicate that turbulent mixing noise reduction, as monitored by OASPL at a shallow angle, correlates with the ratio of jet to primary jet driving pressures normalized by the ratio of corresponding diameters (p d /pjD). With gaseous injection, the spectral amplitudes decrease at lower frequencies while an increase is noted at higher frequencies. It is apparent that this amplitude crossover is at least partly due to shock-associated noise from the underexpanded jets themselves. Such crossover is not seen with water injection since the flow in that case is incompressible and there is no shock-associated noise. Centerline velocity data show that larger noise reduction is accompanied by faster jet decay as well as significant reduction in turbulence intensities. While a physical understanding of the dependence of noise reduction on p d /pjD remains unclear, given this correlation, an analysis explains the observed dependence of the effect on various other parameters.

Direct Numerical Simulation of Acoustic Noise Generation from the Nozzle Wall of a Hypersonic Wind Tunnel

Science.gov (United States)

Huang, Junji; Duan, Lian; Choudhari, Meelan; Missouri Univ of Sci; Tech Team; NASA Langley Research Center Team

2017-11-01

Direct numerical simulations (DNS) are used to examine the acoustic noise generation from the turbulent boundary layer on the nozzle wall of a Mach 6 Ludwieg Tube. The emphasis is on characterizing the freestream acoustic pressure disturbances radiated from the nozzle-wall turbulent boundary layer and comparing it with acoustic noise generated from a single, flat wall in an unconfined setting at a similar freestream Mach number to assess the effects of noise reverberation. In particular, the numerical database is used to provide insights into the pressure disturbance spectrum and amplitude scaling with respect to the boundary-layer parameters as well as to understand the acoustic source mechanisms. Such information is important for characterizing the freestream disturbance environment in conventional (i.e., noisy) hypersonic wind tunnels. Air Force Office of Scientific Research Award No. FA9550-14-1-0170.

Prewhitening for Rank-Deficient Noise in Subspace Methods for Noise Reduction

DEFF Research Database (Denmark)

Hansen, Per Christian; Jensen, Søren Holdt

2005-01-01

A fundamental issue in connection with subspace methods for noise reduction is that the covariance matrix for the noise is required to have full rank, in order for the prewhitening step to be defined. However, there are important cases where this requirement is not fulfilled, e.g., when the noise...... has narrow-band characteristics, or in the case of tonal noise. We extend the concept of prewhitening to include the case when the noise covariance matrix is rank deficient, using a weighted pseudoinverse and the quotient SVD, and we show how to formulate a general rank-reduction algorithm that works...... also for rank deficient noise. We also demonstrate how to formulate this algorithm by means of a quotient ULV decomposition, which allows for faster computation and updating. Finally we apply our algorithm to a problem involving a speech signal contaminated by narrow-band noise....

Research on Aerodynamic Noise Reduction for High-Speed Trains

OpenAIRE

Zhang, Yadong; Zhang, Jiye; Li, Tian; Zhang, Liang; Zhang, Weihua

2016-01-01

A broadband noise source model based on Lighthill’s acoustic theory was used to perform numerical simulations of the aerodynamic noise sources for a high-speed train. The near-field unsteady flow around a high-speed train was analysed based on a delayed detached-eddy simulation (DDES) using the finite volume method with high-order difference schemes. The far-field aerodynamic noise from a high-speed train was predicted using a computational fluid dynamics (CFD)/Ffowcs Williams-Hawkings (FW-H)...

Noise reduction in the beam current monitor

International Nuclear Information System (INIS)

Arai, Shigeaki.

1982-02-01

A simple noise reduction system using a pulse transformer and a pair of L C low pass filters has been introduced to the beam current monitor of a current transformer type at the INS electron linac. With this system, the pick-up noise has been reduced to be 1% of the noise without noise reduction. Signal deformation caused by this system is relatively small and the beam current pulse down to 20 mA is successfully monitored in the actual accelerator operation. (author)

Acoustic noises of the BOR-60 reactor steam generators when simulating leaks with argon and steam

International Nuclear Information System (INIS)

Sokolov, V.M.; Golushko, V.V.; Afanas'ev, V.A.; Grebenkin, Yu.P.; Muralev, A.B.

1985-01-01

Background acoustic noises of stea generators in different operational regimes and noises of argon and steam small leads (about 0.1 g/s) are studied to determine the possibility of designing the acoustic system for leak detection in sodium-water steamgenerators. Investigations are carried out at the 30 MW micromodule steam generator being in operation at the BOR-60 reactor as well as at the 20 MW tank type steam generator. Immersed ransduceres made of lithium niobate 6 mm in-diameter and waveguide transducers made of a stainless steel in the form of rods 10 mm in-diameter and 500 mm long are used as acoustic monitors. It is shown that the leak noise is more wide-band than the background noise of the steam generator and both high and low frequencies appear in the spectrum. The use of monitors of different types results in similar conslusions inrelation to the character of background noises and leak signals (spectral density, signal to-noise ratio) in the ase of similar bandroidths of the transduceres. A conclusion is made that the change of operational regimes leads to changes of background noise level, which can be close to the reaction of

Interior noise analysis of a construction equipment cabin based on airborne and structure-borne noise predictions

Energy Technology Data Exchange (ETDEWEB)

Kim, Sung Hee; Hong, Suk Yoon [Seoul National University, Seoul (Korea, Republic of); Song, Jee Hun [Chonnam National University, Gwangju (Korea, Republic of); Joo, Won Ho [Hyundai Heavy Industries Co. Ltd, Ulsan (Korea, Republic of)

2012-04-15

Noise from construction equipment affects not only surrounding residents, but also the operators of the machines. Noise that affects drivers must be evaluated during the preliminary design stage. This paper suggests an interior noise analysis procedure for construction equipment cabins. The analysis procedure, which can be used in the preliminary design stage, was investigated for airborne and structure borne noise. The total interior noise of a cabin was predicted from the airborne noise analysis and structure-borne noise analysis. The analysis procedure consists of four steps: modeling, vibration analysis, acoustic analysis and total interior noise analysis. A mesh model of a cabin for numerical analysis was made at the modeling step. At the vibration analysis step, the mesh model was verified and modal analysis and frequency response analysis are performed. At the acoustic analysis step, the vibration results from the vibration analysis step were used as initial values for radiated noise analysis and noise reduction analysis. Finally, the total cabin interior noise was predicted using the acoustic results from the acoustic analysis step. Each step was applied to a cabin of a middle-sized excavator and verified by comparison with measured data. The cabin interior noise of a middle-sized wheel loader and a large-sized forklift were predicted using the analysis procedure of the four steps and were compared with measured data. The interior noise analysis procedure of construction equipment cabins is expected to be used during the preliminary design stage.

Interior noise analysis of a construction equipment cabin based on airborne and structure-borne noise predictions

International Nuclear Information System (INIS)

Kim, Sung Hee; Hong, Suk Yoon; Song, Jee Hun; Joo, Won Ho

2012-01-01

Noise from construction equipment affects not only surrounding residents, but also the operators of the machines. Noise that affects drivers must be evaluated during the preliminary design stage. This paper suggests an interior noise analysis procedure for construction equipment cabins. The analysis procedure, which can be used in the preliminary design stage, was investigated for airborne and structure borne noise. The total interior noise of a cabin was predicted from the airborne noise analysis and structure-borne noise analysis. The analysis procedure consists of four steps: modeling, vibration analysis, acoustic analysis and total interior noise analysis. A mesh model of a cabin for numerical analysis was made at the modeling step. At the vibration analysis step, the mesh model was verified and modal analysis and frequency response analysis are performed. At the acoustic analysis step, the vibration results from the vibration analysis step were used as initial values for radiated noise analysis and noise reduction analysis. Finally, the total cabin interior noise was predicted using the acoustic results from the acoustic analysis step. Each step was applied to a cabin of a middle-sized excavator and verified by comparison with measured data. The cabin interior noise of a middle-sized wheel loader and a large-sized forklift were predicted using the analysis procedure of the four steps and were compared with measured data. The interior noise analysis procedure of construction equipment cabins is expected to be used during the preliminary design stage

Noise in the passenger cars of high-speed trains.

Science.gov (United States)

Hong, Joo Young; Cha, Yongwon; Jeon, Jin Yong

2015-12-01

The aim of this study is to investigate the effects of both room acoustic conditions and spectral characteristics of noises on acoustic discomfort in a high-speed train's passenger car. Measurement of interior noises in a high-speed train was performed when the train was operating at speeds of 100 km/h and 300 km/h. Acoustic discomfort caused by interior noises was evaluated by paired comparison methods based on the variation of reverberation time (RT) in a passenger car and the spectral differences in interior noises. The effect of RT on acoustic discomfort was not significant, whereas acoustic discomfort significantly varied depending on spectral differences in noise. Acoustic discomfort increased with increment of the sound pressure level (SPL) ratio at high frequencies, and variation in high-frequency noise components were described using sharpness. Just noticeable differences of SPL with low- and high-frequency components were determined to be 3.7 and 2.9 dB, respectively. This indicates that subjects were more sensitive to differences in SPLs at the high-frequency range than differences at the low-frequency range. These results support that, for interior noises, reduction in SPLs at high frequencies would significantly contribute to improved acoustic quality in passenger cars of high-speed trains.

Structural Acoustic Characteristics of Aircraft and Active Control of Interior Noise

Science.gov (United States)

Fuller, C. R.

1998-01-01

The reduction of aircraft cabin sound levels to acceptable values still remains a topic of much research. The use of conventional passive approaches has been extensively studied and implemented. However performance limits of these techniques have been reached. In this project, new techniques for understanding the structural acoustic behavior of aircraft fuselages and the use of this knowledge in developing advanced new control approaches are investigated. A central feature of the project is the Aircraft Fuselage Test Facility at Va Tech which is based around a full scale Cessna Citation III fuselage. The work is divided into two main parts; the first part investigates the use of an inverse technique for identifying dominant fuselage vibrations. The second part studies the development and implementation of active and active-passive techniques for controlling aircraft interior noise.

High levels of sound pressure: acoustic reflex thresholds and auditory complaints of workers with noise exposure

Directory of Open Access Journals (Sweden)

Alexandre Scalli Mathias Duarte

2015-08-01

Full Text Available INTRODUCTION: The clinical evaluation of subjects with occupational noise exposure has been difficult due to the discrepancy between auditory complaints and auditory test results. This study aimed to evaluate the contralateral acoustic reflex thresholds of workers exposed to high levels of noise, and to compare these results to the subjects' auditory complaints.METHODS: This clinical retrospective study evaluated 364 workers between 1998 and 2005; their contralateral acoustic reflexes were compared to auditory complaints, age, and noise exposure time by chi-squared, Fisher's, and Spearman's tests.RESULTS: The workers' age ranged from 18 to 50 years (mean = 39.6, and noise exposure time from one to 38 years (mean = 17.3. We found that 15.1% (55 of the workers had bilateral hearing loss, 38.5% (140 had bilateral tinnitus, 52.8% (192 had abnormal sensitivity to loud sounds, and 47.2% (172 had speech recognition impairment. The variables hearing loss, speech recognition impairment, tinnitus, age group, and noise exposure time did not show relationship with acoustic reflex thresholds; however, all complaints demonstrated a statistically significant relationship with Metz recruitment at 3000 and 4000 Hz bilaterally.CONCLUSION: There was no significance relationship between auditory complaints and acoustic reflexes.

Objective and subjective evaluation of the acoustic comfort in classrooms.

Science.gov (United States)

Zannin, Paulo Henrique Trombetta; Marcon, Carolina Reich

2007-09-01

The acoustic comfort of classrooms in a Brazilian public school has been evaluated through interviews with 62 teachers and 464 pupils, measurements of background noise, reverberation time, and sound insulation. Acoustic measurements have revealed the poor acoustic quality of the classrooms. Results have shown that teachers and pupils consider the noise generated and the voice of the teacher in neighboring classrooms as the main sources of annoyance inside the classroom. Acoustic simulations resulted in the suggestion of placement of perforated plywood on the ceiling, for reduction in reverberation time and increase in the acoustic comfort of the classrooms.

Simulation of sound transmission through the porous material, determining the parameters of acoustic absorption and sound reduction

Directory of Open Access Journals (Sweden)

Zvolenský Peter

2018-01-01

Full Text Available Currently, the quality of structural design of a railway coach is evaluated by so called acoustic comfort, which is characterized by achieved levels of internal noise. Therefore, acoustic parameters of car body are being developed purposely. The paper presents the results of the computer simulation of noise transmission through the wagon walls and the use of noise tests from the train running. The acoustic properties of the original and new materials in the care body are compared.

A measure of acoustic noise generated from transcranial magnetic stimulation coils.

Science.gov (United States)

Dhamne, Sameer C; Kothare, Raveena S; Yu, Camilla; Hsieh, Tsung-Hsun; Anastasio, Elana M; Oberman, Lindsay; Pascual-Leone, Alvaro; Rotenberg, Alexander

2014-01-01

The intensity of sound emanating from the discharge of magnetic coils used in repetitive transcranial magnetic stimulation (rTMS) can potentially cause acoustic trauma. Per Occupational Safety and Health Administration (OSHA) standards for safety of noise exposure, hearing protection is recommended beyond restricted levels of noise and time limits. We measured the sound pressure levels (SPLs) from four rTMS coils with the goal of assessing if the acoustic artifact levels are of sufficient amplitude to warrant protection from acoustic trauma per OSHA standards. We studied the SPLs at two frequencies (5 and 10 Hz), three machine outputs (MO) (60, 80 and 100%), and two distances from the coil (5 and 10 cm). We found that the SPLs were louder at closer proximity from the coil and directly dependent on the MO. We also found that in all studied conditions, SPLs were lower than the OSHA permissible thresholds for short (8 h) exposure. Copyright © 2014 Elsevier Inc. All rights reserved.

Testing Time and Frequency Fiber-Optic Link Transfer by Hardware Emulation of Acoustic-Band Optical Noise

Directory of Open Access Journals (Sweden)

Lipiński Marcin

2016-06-01

Full Text Available The low-frequency optical-signal phase noise induced by mechanical vibration of the base occurs in field-deployed fibers. Typical telecommunication data transfer is insensitive to this type of noise but the phenomenon may influence links dedicated to precise Time and Frequency (T&F fiber-optic transfer that exploit the idea of stabilization of phase or propagation delay of the link. To measure effectiveness of suppression of acoustic noise in such a link, a dedicated measurement setup is necessary. The setup should enable to introduce a low-frequency phase corruption to the optical signal in a controllable way. In the paper, a concept of a setup in which the mechanically induced acoustic-band optical signal phase corruption is described and its own features and measured parameters are presented. Next, the experimental measurement results of the T&F transfer TFTS-2 system’s immunity as a function of the fibre-optic length vs. the acoustic-band noise are presented. Then, the dependency of the system immunity on the location of a noise source along the link is also pointed out.

Principal Components as a Data Reduction and Noise Reduction Technique

Science.gov (United States)

Imhoff, M. L.; Campbell, W. J.

1982-01-01

The potential of principal components as a pipeline data reduction technique for thematic mapper data was assessed and principal components analysis and its transformation as a noise reduction technique was examined. Two primary factors were considered: (1) how might data reduction and noise reduction using the principal components transformation affect the extraction of accurate spectral classifications; and (2) what are the real savings in terms of computer processing and storage costs of using reduced data over the full 7-band TM complement. An area in central Pennsylvania was chosen for a study area. The image data for the project were collected using the Earth Resources Laboratory's thematic mapper simulator (TMS) instrument.

Drone noise

Science.gov (United States)

Tinney, Charles; Sirohi, Jayant; University of Texas at Austin Team

2017-11-01

A basic understanding of the noise produced by single and multirotor drones operating at static thrust conditions is presented. This work acts as an extension to previous efforts conducted at The University of Texas at Austin (Tinney et al. 2017, AHS Forum 73). Propeller diameters ranging from 8 inch to 12 inch are examined for configurations comprising an isolated rotor, a quadcopter configuration and a hexacopter configuration, and with a constant drone pitch of 2.25. An azimuthal array of half-inch microphones, placed between 2 and 3 hub-center diameters from the drone center, are used to assess the acoustic near-field. Thrust levels, acquired using a six degree-of-freedom load cell, are then used to correlate acoustic noise levels to aerodynamic performance for each drone configuration. The findings reveal a nearly logarithmic increase in noise with increasing thrust. However, for the same thrust condition, considerable noise reduction is achieved by increasing the number of propeller blades thereby reducing the blade passage frequency and both the thickness and loading noise sources that accompany it.

Acoustic noise production of wind turbines in practice

International Nuclear Information System (INIS)

Van der Borg, N.J.C.M.; Vink, P.W.

1994-10-01

Within the framework of national and European projects ECN has conducted various acoustic noise measurements on wind turbines. The measurements can be divided into the following two categories: (1) measurements of the total noise emitted by the turbine ('standard measurements') and (2) measurement of the noise emitted by different blades on the same rotor ('research measurements'). The applied procedures for the 'standard measurements' are given in IEA and IEC documents on wind turbine noise measurements. The applied procedures for the 'research measurements' are given in this paper. General results obtained with both kind of measurements are presented. The 'research measurements' have been performed on a limited number of turbines: the UNIWEX turbine in Germany and a commercial turbine in The Netherlands. The turbines were equipped with differently shaped blade tips or trailing edges on the same rotor. The experiments showed no large differences in the sound production of the different blades on the same rotor. The detailed information on the commercial wind turbine in The Netherlands is confidential. 9 figs., 2 tabs., 3 refs

Helicopter Flight Procedures for Community Noise Reduction

Science.gov (United States)

Greenwood, Eric

2017-01-01

A computationally efficient, semiempirical noise model suitable for maneuvering flight noise prediction is used to evaluate the community noise impact of practical variations on several helicopter flight procedures typical of normal operations. Turns, "quick-stops," approaches, climbs, and combinations of these maneuvers are assessed. Relatively small variations in flight procedures are shown to cause significant changes to Sound Exposure Levels over a wide area. Guidelines are developed for helicopter pilots intended to provide effective strategies for reducing the negative effects of helicopter noise on the community. Finally, direct optimization of flight trajectories is conducted to identify low noise optimal flight procedures and quantify the magnitude of community noise reductions that can be obtained through tailored helicopter flight procedures. Physically realizable optimal turns and approaches are identified that achieve global noise reductions of as much as 10 dBA Sound Exposure Level.

Noise Exposure of Teachers in Nursery Schools-Evaluation of Measures for Noise Reduction When Dropping DUPLO Toy Bricks into Storage Cases by Sound Analyses.

Science.gov (United States)

Gebauer, Konstanze; Scharf, Thomas; Baumann, Uwe; Groneberg, David A; Bundschuh, Matthias

2016-07-04

Although noise is one of the leading work-related health risk factors for teachers, many nursery schools lack sufficient noise reduction measures. This intervention study evaluated the noise exposure of nursery school teachers when dropping DUPLO toy bricks into storage cases. Sound analyses of the impact included assessment of the maximum sound pressure level (LAFmax) as well as frequency analyses with 1/3 octave band filter. For the purpose of standardization, a customized gadget was developed. Recordings were performed in 11 cases of different materials and designs to assess the impact on sound level reduction. Thereby, the acoustic effects of three damping materials (foam rubber, carpet, and PU-foam) were investigated. The lowest LAFmax was measured in cases consisting of "metal grid" (90.71 dB) or of a woven willow "basket" (91.61 dB), whereas a case of "aluminium" (103.34 dB) generated the highest impact LAFmax. The frequency analyses determined especially low LAFmax in the frequency bands between 80 and 2500 Hz in cases designs "metal grid" and "basket". The insertion of PU-foam achieved the most significant attenuation of LAFmax (-13.88 dB) and, in the frequency analyses, the best sound damping. The dropping of DUPLO bricks in cases contributes to the high noise level in nursery schools, but measured LAFmax show no evidence for the danger of acute hearing loss. However, continuous exposure may lead to functional impairment of the hair cells and trigger stress reactions. We recommend noise reduction by utilizing cases of woven "basket" with an insert of PU-foam.

Prediction and reduction of aircraft noise in outdoor environments

Science.gov (United States)

Tong, Bao N.

absorption mechanism due to the source's motion. To help mitigate the noise that propagates to the ground, multi-layered acoustic treatments can be applied to provide good performance over a wide range of frequencies. An accurate representation of material properties for each of the constituent layers is needed in the design of such treatments. The parameter of interest is the specific acoustic impedance, which can be obtained via inversion of acoustic transfer function measurements. However, several different impedance values can correspond to the same sound field predictions. The boundary loss factor F (associated with spherical wave reflection) is the source of this ambiguity. A method for identifying the family of solutions and selecting the physically meaningful branch is proposed to resolve this non-uniqueness issue. Accurate deduction of the acoustic impedance depends on precise measurements of the acoustic transfer function. However, measurement uncertainties exists in both the magnitude and the phase of the acoustic transfer function. The ASA/ANSI S1.18 standard impedance deduction method uses phase information, which can be unreliable in many outdoor environments. An improved technique which only relies on magnitude information is developed in this dissertation. A selection of optimal geometries become necessary to reduce the sensitivity of the deduced impedance to small variations in the measured data. A graphical approach is provided which offers greater insight into the optimization problem. A downhill simplex algorithm has been implemented to automate the impedance deduction procedure. Physical constraints are applied to limit the search region and to eliminate rogue solutions. Several case studies consisting of both indoor and outdoor acoustical measurements are presented to validate the proposed technique. The current analysis is limited to locally reacting materials where the acoustic impedance does not depend on the incidence angle of the reflected wave.

An Application of the Acoustic Similarity Law to the Numerical Analysis of Centrifugal Fan Noise

Science.gov (United States)

Jeon, Wan-Ho; Lee, Duck-Joo; Rhee, Huinam

Centrifugal fans, which are frequently used in our daily lives and various industries, usually make severe noise problems. Generally, the centrifugal fan noise consists of tones at the blade passing frequency and its higher harmonics. These tonal sounds come from the interaction between the flow discharged from the impeller and the cutoff in the casing. Prediction of the noise from a centrifugal fan becomes more necessary to optimize the design to meet both the performance and noise criteria. However, only some limited studies on noise prediction method exist because there are difficulties in obtaining detailed information about the flow field and casing effect on noise radiation. This paper aims to investigate the noise generation mechanism of a centrifugal fan and to develop a prediction method for the unsteady flow and acoustic pressure fields. In order to do this, a numerical analysis method using acoustic similarity law is proposed, and it is verified that the method can predict the noise generation mechanism very well by comparing the predicted results with available experimental results.

Low-Frequency Acoustic Noise Mitigation Characteristics of Metamaterials-Inspired Vibro-Impact Structures

Science.gov (United States)

Rekhy, Anuj

Acoustic absorbers like foams, fiberglass or liners have been used commonly in structures for infrastructural, industrial, automotive and aerospace applications to mitigate noise. However, these conventional materials have limited effectiveness to mitigate low-frequency (LF) acoustic waves with frequency less than 400 Hz owing to the need for impractically large mass or volume. LF acoustic waves contribute significantly towards environmental noise pollution as well as unwanted structural responses. Therefore, there is a need to develop lightweight, compact, structurally-integrated solutions to mitigate LF noise in several applications. Inspired by metamaterials, which are man-made structural materials that derive their unique dynamic behavior not just from material constituents but more so from engineered configurations, tuned mass-loaded membranes as vibro-impact attachments on a baseline structure are investigated to determine their performance as a LF acoustic barrier. The hypothesis is that the LF incident waves are up-converted via impact to higher modes in the baseline structure which are far more evanescent and may then be effectively mitigated using conventional means. Such Metamaterials-Inspired Vibro-Impact Structures (MIVIS) could be tuned to match the dominant frequency content of LF acoustic sources in specific applications. Prototype MIVIS unit cells were designed and tested to study the energy transfer mechanism via impact-induced frequency up-conversion, and the consequent sound transmission loss. Structural acoustic simulations were done to predict responses using models based on normal incidence transmission loss tests. Experimental proof-of-concept was achieved and further correlations to simulations were utilized to optimize the energy up-conversion mechanism using parametric studies. Up to 36 dB of sound transmission loss increase is obtained at the anti-resonance frequency (326 Hz) within a tunable LF bandwidth of about 200 Hz while impact

Modification of computational auditory scene analysis (CASA) for noise-robust acoustic feature

Science.gov (United States)

Kwon, Minseok

While there have been many attempts to mitigate interferences of background noise, the performance of automatic speech recognition (ASR) still can be deteriorated by various factors with ease. However, normal hearing listeners can accurately perceive sounds of their interests, which is believed to be a result of Auditory Scene Analysis (ASA). As a first attempt, the simulation of the human auditory processing, called computational auditory scene analysis (CASA), was fulfilled through physiological and psychological investigations of ASA. CASA comprised of Zilany-Bruce auditory model, followed by tracking fundamental frequency for voice segmentation and detecting pairs of onset/offset at each characteristic frequency (CF) for unvoiced segmentation. The resulting Time-Frequency (T-F) representation of acoustic stimulation was converted into acoustic feature, gammachirp-tone frequency cepstral coefficients (GFCC). 11 keywords with various environmental conditions are used and the robustness of GFCC was evaluated by spectral distance (SD) and dynamic time warping distance (DTW). In "clean" and "noisy" conditions, the application of CASA generally improved noise robustness of the acoustic feature compared to a conventional method with or without noise suppression using MMSE estimator. The intial study, however, not only showed the noise-type dependency at low SNR, but also called the evaluation methods in question. Some modifications were made to capture better spectral continuity from an acoustic feature matrix, to obtain faster processing speed, and to describe the human auditory system more precisely. The proposed framework includes: 1) multi-scale integration to capture more accurate continuity in feature extraction, 2) contrast enhancement (CE) of each CF by competition with neighboring frequency bands, and 3) auditory model modifications. The model modifications contain the introduction of higher Q factor, middle ear filter more analogous to human auditory system

Occupational Noise Reduction in CNC Striping Process

Science.gov (United States)

Mahmad Khairai, Kamarulzaman; Shamime Salleh, Nurul; Razlan Yusoff, Ahmad

2018-03-01

Occupational noise hearing loss with high level exposure is common occupational hazards. In CNC striping process, employee that exposed to high noise level for a long time as 8-hour contributes to hearing loss, create physical and psychological stress that reduce productivity. In this paper, CNC stripping process with high level noises are measured and reduced to the permissible noise exposure. First condition is all machines shutting down and second condition when all CNC machine under operations. For both conditions, noise exposures were measured to evaluate the noise problems and sources. After improvement made, the noise exposures were measured to evaluate the effectiveness of reduction. The initial average noise level at the first condition is 95.797 dB (A). After the pneumatic system with leakage was solved, the noise reduced to 55.517 dB (A). The average noise level at the second condition is 109.340 dB (A). After six machines were gathered at one area and cover that area with plastic curtain, the noise reduced to 95.209 dB (A). In conclusion, the noise level exposure in CNC striping machine is high and exceed the permissible noise exposure can be reduced to acceptable levels. The reduction of noise level in CNC striping processes enhanced productivity in the industry.

An acoustic vector based approach to locate low frequency noise sources in 3D

NARCIS (Netherlands)

Bree, H.-E. de; Ostendorf, C.; Basten, T.

2009-01-01

Although low frequency noise is an issue of huge societal importance, traditional acoustic testing methods have limitations in finding the low frequency source. It is hard to determine the direction of the noise using traditional microphones. Three dimensional sound probes capturing the particle

Advanced Noise Control Fan: A 20-Year Retrospective

Science.gov (United States)

Sutliff, Dan

2016-01-01

The ANCF test bed is used for evaluating fan noise reduction concepts, developing noise measurement technologies, and providing a database for Aero-acoustic code development. Rig Capabilities: 4 foot 16 bladed rotor @ 2500 rpm, Auxiliary air delivery system (3 lbm/sec @ 6/12 psi), Variable configuration (rotor pitch angle, stator count/position, duct length), synthetic acoustic noise generation (tone/broadband). Measurement Capabilities: 112 channels dynamic data system, Unique rotating rake mode measuremen, Farfield (variable radius), Duct wall microphones, Stator vane microphones, Two component CTA w/ traversing, ESP for static pressures.

Acoustical topology optimization for Zwicker's loudness model - Application to noise barriers

DEFF Research Database (Denmark)

Kook, Junghwan; Koo, Kunmo; Hyun, Jaeyub

2012-01-01

acoustic properties may not represent adequate parameters for optimizing acoustic devices. In this paper, we first present a design method for acoustical topology optimization by considering human's subjective conception of sound. To consider human hearing characteristics. Zwicker's loudness is calculated...... according to DIN45631 (ISO 532B). The main objective of this work is to minimize the main specific loudness of a target critical band rate by optimizing the distribution of the reflecting material in a design domain. The Helmholtz equation is used to model acoustic wave propagation and, it is solved using...... the finite element method. The sensitivity of the main specific loudness is calculated using the adjoint variable method and the chain rule. To demonstrate the effectiveness of the proposed method, various examples of noise barriers are presented with different source and receiver locations. The results...

Aircraft interior noise prediction using a structural-acoustic analogy in NASTRAN modal synthesis

Science.gov (United States)

Grosveld, Ferdinand W.; Sullivan, Brenda M.; Marulo, Francesco

1988-01-01

The noise induced inside a cylindrical fuselage model by shaker excitation is investigated theoretically and experimentally. The NASTRAN modal-synthesis program is used in the theoretical analysis, and the predictions are compared with experimental measurements in extensive graphs. Good general agreement is obtained, but the need for further refinements to account for acoustic-cavity damping and structural-acoustic interaction is indicated.

Study on Noise Prediction Model and Control Schemes for Substation

Science.gov (United States)

Gao, Yang; Liu, Songtao

2014-01-01

With the government's emphasis on environmental issues of power transmission and transformation project, noise pollution has become a prominent problem now. The noise from the working transformer, reactor, and other electrical equipment in the substation will bring negative effect to the ambient environment. This paper focuses on using acoustic software for the simulation and calculation method to control substation noise. According to the characteristics of the substation noise and the techniques of noise reduction, a substation's acoustic field model was established with the SoundPLAN software to predict the scope of substation noise. On this basis, 4 reasonable noise control schemes were advanced to provide some helpful references for noise control during the new substation's design and construction process. And the feasibility and application effect of these control schemes can be verified by using the method of simulation modeling. The simulation results show that the substation always has the problem of excessive noise at boundary under the conventional measures. The excess noise can be efficiently reduced by taking the corresponding noise reduction methods. PMID:24672356

Noise Exposure of Teachers in Nursery Schools—Evaluation of Measures for Noise Reduction When Dropping DUPLO Toy Bricks into Storage Cases by Sound Analyses

Directory of Open Access Journals (Sweden)

Konstanze Gebauer

2016-07-01

Full Text Available Background: Although noise is one of the leading work-related health risk factors for teachers, many nursery schools lack sufficient noise reduction measures. Methods: This intervention study evaluated the noise exposure of nursery school teachers when dropping DUPLO toy bricks into storage cases. Sound analyses of the impact included assessment of the maximum sound pressure level (LAFmax as well as frequency analyses with 1/3 octave band filter. For the purpose of standardization, a customized gadget was developed. Recordings were performed in 11 cases of different materials and designs to assess the impact on sound level reduction. Thereby, the acoustic effects of three damping materials (foam rubber, carpet, and PU-foam were investigated. Results: The lowest LAFmax was measured in cases consisting of “metal grid” (90.71 dB or of a woven willow “basket” (91.61 dB, whereas a case of “aluminium” (103.34 dB generated the highest impact LAFmax. The frequency analyses determined especially low LAFmax in the frequency bands between 80 and 2500 Hz in cases designs “metal grid” and “basket”. The insertion of PU-foam achieved the most significant attenuation of LAFmax (−13.88 dB and, in the frequency analyses, the best sound damping. Conclusion: The dropping of DUPLO bricks in cases contributes to the high noise level in nursery schools, but measured LAFmax show no evidence for the danger of acute hearing loss. However, continuous exposure may lead to functional impairment of the hair cells and trigger stress reactions. We recommend noise reduction by utilizing cases of woven “basket” with an insert of PU-foam.

Embedded Acoustic Sensor Array for Engine Fan Noise Source Diagnostic Test: Feasibility of Noise Telemetry via Wireless Smart Sensors

Science.gov (United States)

Zaman, Afroz; Bauch, Matthew; Raible, Daniel

2011-01-01

Aircraft engines have evolved into a highly complex system to meet ever-increasing demands. The evolution of engine technologies has primarily been driven by fuel efficiency, reliability, as well as engine noise concerns. One of the sources of engine noise is pressure fluctuations that are induced on the stator vanes. These local pressure fluctuations, once produced, propagate and coalesce with the pressure waves originating elsewhere on the stator to form a spinning pressure pattern. Depending on the duct geometry, air flow, and frequency of fluctuations, these spinning pressure patterns are self-sustaining and result in noise which eventually radiate to the far-field from engine. To investigate the nature of vane pressure fluctuations and the resulting engine noise, unsteady pressure signatures from an array of embedded acoustic sensors are recorded as a part of vane noise source diagnostics. Output time signatures from these sensors are routed to a control and data processing station adding complexity to the system and cable loss to the measured signal. "Smart" wireless sensors have data processing capability at the sensor locations which further increases the potential of wireless sensors. Smart sensors can process measured data locally and transmit only the important information through wireless communication. The aim of this wireless noise telemetry task was to demonstrate a single acoustic sensor wireless link for unsteady pressure measurement, and thus, establish the feasibility of distributed smart sensors scheme for aircraft engine vane surface unsteady pressure data transmission and characterization.

Architectural acoustics

National Research Council Canada - National Science Library

Long, Marshall

2014-01-01

.... Beginning with a brief history, it reviews the fundamentals of acoustics, human perception and reaction to sound, acoustic noise measurements, noise metrics, and environmental noise characterization...

Listening to the Deep: live monitoring of ocean noise and cetacean acoustic signals.

Science.gov (United States)

André, M; van der Schaar, M; Zaugg, S; Houégnigan, L; Sánchez, A M; Castell, J V

2011-01-01

The development and broad use of passive acoustic monitoring techniques have the potential to help assessing the large-scale influence of artificial noise on marine organisms and ecosystems. Deep-sea observatories have the potential to play a key role in understanding these recent acoustic changes. LIDO (Listening to the Deep Ocean Environment) is an international project that is allowing the real-time long-term monitoring of marine ambient noise as well as marine mammal sounds at cabled and standalone observatories. Here, we present the overall development of the project and the use of passive acoustic monitoring (PAM) techniques to provide the scientific community with real-time data at large spatial and temporal scales. Special attention is given to the extraction and identification of high frequency cetacean echolocation signals given the relevance of detecting target species, e.g. beaked whales, in mitigation processes, e.g. during military exercises. Copyright © 2011. Published by Elsevier Ltd.

Evaluation of noise pollution in urban traffic hubs—Noise maps and measurements

International Nuclear Information System (INIS)

Fiedler, Paulo Eduardo Kirrian; Zannin, Paulo Henrique Trombetta

2015-01-01

A study was made of some of the main traffic hubs in a Latin American metropolis, in order to determine the presence or absence of noise by means of noise measurements and acoustic mapping. To characterize noise in the evaluated road stretches, 232 measurements were taken at different points. The Predictor software package was used for the noise mapping calculations. Noise sensitive areas, e.g., hospitals, were identified in the evaluated road stretches. Noise maps were calculated for two hospitals, showing the current levels of noise that reach their facades. Hypothetical scenarios were simulated by making changes in the composition of traffic and total number of vehicles, and an assessment was made of the potential influence of these modifications in reducing the noise levels reaching the facades of the buildings in question. The simulations indicated that a 50% reduction in total traffic flow, or a 50% reduction in heavy vehicle traffic flow, would reduce the noise levels by about 3 dB(A). - Highlights: • Evaluation of noise pollution in urban traffic hubs • Street systems • Environmental noise impacts • Noise mapping

Evaluation of noise pollution in urban traffic hubs—Noise maps and measurements

Energy Technology Data Exchange (ETDEWEB)

Fiedler, Paulo Eduardo Kirrian; Zannin, Paulo Henrique Trombetta, E-mail: paulo.zannin@pesquisador.cnpq.br

2015-02-15

A study was made of some of the main traffic hubs in a Latin American metropolis, in order to determine the presence or absence of noise by means of noise measurements and acoustic mapping. To characterize noise in the evaluated road stretches, 232 measurements were taken at different points. The Predictor software package was used for the noise mapping calculations. Noise sensitive areas, e.g., hospitals, were identified in the evaluated road stretches. Noise maps were calculated for two hospitals, showing the current levels of noise that reach their facades. Hypothetical scenarios were simulated by making changes in the composition of traffic and total number of vehicles, and an assessment was made of the potential influence of these modifications in reducing the noise levels reaching the facades of the buildings in question. The simulations indicated that a 50% reduction in total traffic flow, or a 50% reduction in heavy vehicle traffic flow, would reduce the noise levels by about 3 dB(A). - Highlights: • Evaluation of noise pollution in urban traffic hubs • Street systems • Environmental noise impacts • Noise mapping.

A hybrid SEA/modal technique for modeling structural-acoustic interior noise in rotorcraft.

Science.gov (United States)

Jayachandran, V; Bonilha, M W

2003-03-01

This paper describes a hybrid technique that combines Statistical Energy Analysis (SEA) predictions for structural vibration with acoustic modal summation techniques to predict interior noise levels in rotorcraft. The method was applied for predicting the sound field inside a mock-up of the interior panel system of the Sikorsky S-92 helicopter. The vibration amplitudes of the frame and panel systems were predicted using a detailed SEA model and these were used as inputs to the model of the interior acoustic space. The spatial distribution of the vibration field on individual panels, and their coupling to the acoustic space were modeled using stochastic techniques. Leakage and nonresonant transmission components were accounted for using space-averaged values obtained from a SEA model of the complete structural-acoustic system. Since the cabin geometry was quite simple, the modeling of the interior acoustic space was performed using a standard modal summation technique. Sound pressure levels predicted by this approach at specific microphone locations were compared with measured data. Agreement within 3 dB in one-third octave bands above 40 Hz was observed. A large discrepancy in the one-third octave band in which the first acoustic mode is resonant (31.5 Hz) was observed. Reasons for such a discrepancy are discussed in the paper. The developed technique provides a method for modeling helicopter cabin interior noise in the frequency mid-range where neither FEA nor SEA is individually effective or accurate.

Measurements and Predictions of the Noise from Three-Stream Jets

Science.gov (United States)

Henderson, Brenda S.; Leib, Stewart J.; Wernet, Mark P.

2015-01-01

An experimental and numerical investigation of the noise produced by high-subsonic and supersonic three-stream jets was conducted. The exhaust system consisted of externally-mixed-convergent nozzles and an external plug. Bypass- and tertiary-to-core area ratios between 1.0 and 2.5, and 0.4 and 1.0, respectively, were studied. Axisymmetric and offset tertiary nozzles were investigated for heated and unheated conditions. For axisymmetric configurations, the addition of the third stream was found to reduce peak- and high-frequency acoustic levels in the peak-jet-noise direction, with greater reductions at the lower bypass-to-core area ratios. For the offset configurations, an offset duct was found to decrease acoustic levels on the thick side of the tertiary nozzle relative to those produced by the simulated two-stream jet with up to 8 dB mid-frequency noise reduction at large angles to the jet inlet axis. Noise reduction in the peak-jet-noise direction was greater for supersonic core speeds than for subsonic core speeds. The addition of a tertiary nozzle insert used to divert the third-stream jet to one side of the nozzle system provided no noise reduction. Noise predictions are presented for selected cases using a method based on an acoustic analogy with mean flow interaction effects accounted for using a Green's function, computed in terms of its coupled azimuthal modes for the offset cases, and a source model previously used for round and rectangular jets. Comparisons of the prediction results with data show that the noise model predicts the observed increase in low-frequency noise with the introduction of a third, axisymmetric stream, but not the high-frequency reduction. For an offset third stream, the model predicts the observed trend of decreased sound levels on the thick side of the jet compared with the thin side, but the predicted azimuthal variations are much less than those seen in the data. Also, the shift of the spectral peak to lower frequencies with

Analytical prediction of the interior noise for cylindrical models of aircraft fuselages for prescribed exterior noise fields. Phase 2: Models for sidewall trim, stiffened structures and cabin acoustics with floor partition

Science.gov (United States)

Pope, L. D.; Wilby, E. G.

1982-01-01

An airplane interior noise prediction model is developed to determine the important parameters associated with sound transmission into the interiors of airplanes, and to identify apropriate noise control methods. Models for stiffened structures, and cabin acoustics with floor partition are developed. Validation studies are undertaken using three test articles: a ring stringer stiffened cylinder, an unstiffened cylinder with floor partition, and ring stringer stiffened cylinder with floor partition and sidewall trim. The noise reductions of the three test articles are computed using the heoretical models and compared to measured values. A statistical analysis of the comparison data indicates that there is no bias in the predictions although a substantial random error exists so that a discrepancy of more than five or six dB can be expected for about one out of three predictions.

Development of Lightweight, Compact, Structurally-Integrated Acoustic Liners for Broadband Low-Frequency Noise Mitigation

Science.gov (United States)

Chambers, Andrew T.

Airborne noise with a low dominant frequency content (scope of conventional acoustic noise mitigation techniques using liners, foams or claddings owing to mass and volume considerations. Its low evanescence contributes significantly to environmental noise pollution, and unwanted structural vibrations causing diminished efficiency, comfort, payload integrity and mission capabilities. An alternative approach using liner configurations with realistic mass and volume constraints having innovative 'folded' core geometries is investigated to ascertain its low-frequency noise absorption characteristics. In contrast to mass-driven approaches, the folded core approach relies on tailoring interactions between acoustic resonances to tune the liner's impedance to suit the dominant low-frequency content of the source. This allows to keep non-structural mass-addition to a minimum, while retaining an overall thickness comparable to conventional liners for these low-frequency liner designs. The relative acoustic performance of various candidate folded core designs is evaluated by means of a new composite metric termed the Low-Frequency Performance (LFP) factor, which is educed from the absorption coefficient spectrum obtained using Zwikker-Kosten Transmission Line (ZKTL) theory-based numerical studies. An LFP-based software tool is developed to determine optimal 3D cavity packing for a prescribed liner volume and target frequency range. ZKTL-based parametric studies on core dimensions and face sheet porosity are utilized for detailed design of test articles. Experimental verification of absorption coefficient spectra conducted using 3D printed test articles in a normal incidence acoustic impedance tube yield good correlation with simulations. More than 100 Hz of continuous bandwidth with an absorption coefficient greater than 0.6 is shown to be possible in the 300 to 400 Hz range with a 38.1-mm (1.5-inch) thick liner. Further, the influence of face sheet type, Mach number, and

Reduction of external noise of mobile energy facilities by using active noise control system in muffler

Science.gov (United States)

Polivaev, O. I.; Kuznetsov, A. N.; Larionov, A. N.; Beliansky, R. G.

2018-03-01

The paper describes a method for the reducing emission of low-frequency noise of modern automotive vehicles into the environment. The importance of reducing the external noise of modern mobile energy facilities made in Russia is substantiated. Standard methods for controlling external noise in technology are of low efficiency when low-frequency sound waves are reduced. In this case, it is in the low-frequency zone of the sound range that the main power of the noise emitted by the machinery lies. The most effective way to reduce such sound waves is to use active noise control systems. A design of a muffler using a similar system is presented. This muffler allowed one to reduce the emission of increased noise levels into the environment by 7-11 dB and to increase acoustic comfort at the operator's workplace by 3-5 dB.

The simulation calculation of acoustics energy transfer through the material structure

Directory of Open Access Journals (Sweden)

Zvolenský Peter

2016-01-01

Full Text Available The paper deals with the modification of the rail passenger coach floor design aimed at improvement of sound reduction index. Refurbishing was performed by using a new acoustic material with a filamentary microstructure. The materials proposed in research were compared by simulation calculation of acoustic energy transfer trough porous microstructure of filamentary material, and the effect of material porosity on sound reduction index and sound absorption coefficient were observed. This proposed filamentary material can be used in the railway bed structure, too. High degree of noise absorbing, resistance to climate conditions, low specific mass, enable to choose a system of low anti-noise barriers having similar properties as standard high anti-noise walls..

Wind Turbine Generator System Acoustic Noise Test Report for the ARE 442 Wind Turbine

Energy Technology Data Exchange (ETDEWEB)

Huskey, A.; van Dam, J.

2010-11-01

This test was conducted on the ARE 442 as part of the U.S. Department of Energy's (DOE's) Independent Testing project. This project was established to help reduce the barriers of wind energy expansion by providing independent testing results for small turbines. In total, five turbines are being tested at the National Wind Technology Center (NWTC) as a part of this project. Acoustic noise testing is one of up to five tests that may be performed on the turbines, including duration, safety and function, power performance, and power quality tests. The acoustic noise test was conducted to the IEC 61400-11 Edition 2.1.

Noise-robust cortical tracking of attended speech in real-world acoustic scenes

DEFF Research Database (Denmark)

Fuglsang, Søren; Dau, Torsten; Hjortkjær, Jens

2017-01-01

Selectively attending to one speaker in a multi-speaker scenario is thought to synchronize low-frequency cortical activity to the attended speech signal. In recent studies, reconstruction of speech from single-trial electroencephalogram (EEG) data has been used to decode which talker a listener...... is attending to in a two-talker situation. It is currently unclear how this generalizes to more complex sound environments. Behaviorally, speech perception is robust to the acoustic distortions that listeners typically encounter in everyday life, but it is unknown whether this is mirrored by a noise......-robust neural tracking of attended speech. Here we used advanced acoustic simulations to recreate real-world acoustic scenes in the laboratory. In virtual acoustic realities with varying amounts of reverberation and number of interfering talkers, listeners selectively attended to the speech stream...

Investigation of signal models and methods for evaluating structures of processing telecommunication information exchange systems under acoustic noise conditions

Science.gov (United States)

Kropotov, Y. A.; Belov, A. A.; Proskuryakov, A. Y.; Kolpakov, A. A.

2018-05-01

The paper considers models and methods for estimating signals during the transmission of information messages in telecommunication systems of audio exchange. One-dimensional probability distribution functions that can be used to isolate useful signals, and acoustic noise interference are presented. An approach to the estimation of the correlation and spectral functions of the parameters of acoustic signals is proposed, based on the parametric representation of acoustic signals and the components of the noise components. The paper suggests an approach to improving the efficiency of interference cancellation and highlighting the necessary information when processing signals from telecommunications systems. In this case, the suppression of acoustic noise is based on the methods of adaptive filtering and adaptive compensation. The work also describes the models of echo signals and the structure of subscriber devices in operational command telecommunications systems.

Acoustic Measurements of a Large Civil Transport Main Landing Gear Model

Science.gov (United States)

Ravetta, Patricio A.; Khorrami, Mehdi R.; Burdisso, Ricardo A.; Wisda, David M.

2016-01-01

Microphone phased array acoustic measurements of a 26 percent-scale, Boeing 777-200 main landing gear model with and without noise reduction fairings installed were obtained in the anechoic configuration of the Virginia Tech Stability Tunnel. Data were acquired at Mach numbers of 0.12, 0.15, and 0.17 with the latter speed used as the nominal test condition. The fully and partially dressed gear with the truck angle set at 13 degrees toe-up landing configuration were the two most extensively tested configurations, serving as the baselines for comparison purposes. Acoustic measurements were also acquired for the same two baseline configurations with the truck angle set at 0 degrees. In addition, a previously tested noise reducing, toboggan-shaped fairing was re-evaluated extensively to address some of the lingering questions regarding the extent of acoustic benefit achievable with this device. The integrated spectra generated from the acoustic source maps reconfirm, in general terms, the previously reported noise reduction performance of the toboggan fairing as installed on an isolated gear. With the recent improvements to the Virginia Tech tunnel acoustic quality and microphone array capabilities, the present measurements provide an additional, higher quality database to the acoustic information available for this gear model.

Application of system concept in vibration and noise reduction

Directory of Open Access Journals (Sweden)

SHENG Meiping

2017-08-01

Full Text Available Although certain vibration and noise control technologies are maturing, such as vibration absorption, vibration isolation, sound absorption and sound insulation, and new methods for specific frequency bands or special environments have been proposed unceasingly, there is still no guarantee that practical effective vibration and noise reduction can be obtained. An important constraint for vibration and noise reduction is the lack of a system concept, and the integrity and relevance of such practical systems as ship structure have not obtained enough attention. We have tried to use the system engineering theory in guiding vibration and noise reduction, and have already achieved certain effects. Based on the system concept, the noise control of a petroleum pipeline production workshop has been completed satisfactorily, and the abnormal noise source identification of an airplane has been accomplished successfully. We want to share our experience and suggestions to promote the popularization of the system engineering theory in vibration and noise control.

Wind Turbine Generator System Acoustic Noise Test Report for the Gaia Wind 11-kW Wind Turbine

Energy Technology Data Exchange (ETDEWEB)

Huskey, A.

2011-11-01

This report details the acoustic noise test conducted on the Gaia-Wind 11-kW wind turbine at the National Wind Technology Center. The test turbine is a two- bladed, downwind wind turbine with a rated power of 11 kW. The test turbine was tested in accordance with the International Electrotechnical Commission standard, IEC 61400-11 Ed 2.1 2006-11 Wind Turbine Generator Systems -- Part 11 Acoustic Noise Measurement Techniques.

Nonlinear acoustic propagation of launch vehicle and military jet aircraft noise

Science.gov (United States)

Gee, Kent L.

2010-10-01

The noise from launch vehicles and high-performance military jet aircraft has been shown to travel nonlinearly as a result of an amplitude-dependent speed of sound. Because acoustic pressure compressions travel faster than rarefactions, the waveform steepens and shocks form. This process results in a very different (and readily audible) noise signature and spectrum than predicted by linear models. On-going efforts to characterize the nonlinearity using statistical and spectral measures are described with examples from recent static tests of solid rocket boosters and the F-22 Raptor.

Reduction of interior sound fields in flexible cylinders by active vibration control

Science.gov (United States)

Jones, J. D.; Fuller, C. R.

1988-01-01

The mechanisms of interior sound reduction through active control of a thin flexible shell's vibrational response are presently evaluated in view of an analytical model. The noise source is a single exterior acoustic monopole. The active control model is evaluated for harmonic excitation; the results obtained indicate spatially-averaged noise reductions in excess of 20 dB over the source plane, for acoustic resonant conditions inside the cavity.

Experimental investigation of wavy leading edges on rod-aerofoil interaction noise

Science.gov (United States)

Chen, Weijie; Qiao, Weiyang; Tong, Fan; Wang, Liangfeng; Wang, Xunnian

2018-05-01

Experimental studies are performed to investigate the effect of wavy leading edges on rod-aerofoil interaction noise in an open-jet anechoic wind tunnel. NACA 0012 aerofoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) are embedded in the wake of a circular rod. The WLEs are in the form of sinusoidal profiles of amplitude, A, and wavelength, W. Parametric studies of the amplitude and wavelength characteristics are conducted to understand the effect of WLEs on noise reduction. It is observed that the sound power reduction level is sensitive to both the amplitude and wavelength of the WLEs. The WLE with the largest amplitude and smallest wavelength can achieve the most considerable noise reduction effect of up to 4 dB. The influences of rod diameter, d, and free-stream velocity, U0, on the noise reduction effect of the WLEs are also investigated. In addition, a parametric study of the influence of separating rod-aerofoil distance on the acoustic radiation of the SLE case and on the sound power reduction level of the WLE cases is performed. It is found that a critical spacing exists where the acoustic radiation and noise reduction can be divided into two different "modes".

The electrical properties of a planar coil electromagnetic acoustic transducer and their implications for noise performance

International Nuclear Information System (INIS)

Seher, Matthias; Challis, Richard

2016-01-01

This paper is concerned with the electrical properties of an electromagnetic acoustic transducer (EMAT) formed of a flat spiral coil coupled to steel sheet components and operating over a narrow band of frequencies around 50 kHz, well below significant resonances. The electromagnetic skin effect is a significant contributor to the terminal impedance of the EMAT and hence to signal sensitivity, Johnson noise generation and the achievable signal-to-noise ratios (SNR). A transformer model is developed to simulate these effects and to assist in the optimization of the SNR. In this analysis Johnson noise in the system is compared to the unknown emf generated in the eddy current path by an incident acoustic wave to yield a fundamental SNR. The attainable SNR of the whole system is normalized to this in the form of a noise figure. (paper)

Localized, Non-Harmonic Active Flap Motions for Low Frequency In-Plane Rotor Noise Reduction

Science.gov (United States)

Sim, Ben W.; Potsdam, Mark; Kitaplioglu, Cahit; LeMasurier, Philip; Lorber, Peter; Andrews, Joseph

2012-01-01

A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels.

CALCULATION OF ACOUSTIC EFFICIENCY OF PORTABLE ACOUSTIC SCREEN

Directory of Open Access Journals (Sweden)

Aleksandr Skvortsov

2016-03-01

Full Text Available The research of influence of life environment adverse factors on physical development and health of population is an actual problem of ecology. The aspects of the most actual problems of the modern world, namely environmental industrial noise pollution are considered in the article. Industrial facilities everywhere have noisy equipment. Noise is a significant factors of negative influenceon people and environment. Combined effects of noise and of other physical pollutions on people may cause amplification of their negative impact. If the noise pollution level from the object in a residential area exceeds the permissible levels (MPL, noise protection measures can be initiated. Today, the most common design decisions for noise protection are sound absorbing construction, noise screens and barriers, acousting housings, soundproff cabins. Many of them are popular, others are less known. The article deals with one of the most wide spread means of noise protection – a portable acoustic screen. The aim of the research is to determine the efficiency of portable acoustic screens. It is shown that the installation of such structures can reduce the average value of the sound level. The authors analyzed acoustic screens as device to reduce noise pollution. The authors offer a potable acoustic screen differing from the used easyness, mobility, minimum price and good sound protective properties. Effectiveness, a sound absorption coefficient and sound conductivity coefficient of a portable acoustic screen are evaluated. The descriptions of the algorithm calculations and the combination of technical solutions have practical originality. The results of the research demonstrate the advantages of the proposed solutions for reducing noise levels in the agro-industrial complex.

Acoustic Investigation of Jet Mixing Noise in Dual Stream Nozzles

Science.gov (United States)

Khavaran, Abbas; Dahl, Milo D.

2012-01-01

In an earlier study, a prediction model for jet noise in dual stream jets was proposed that is founded on velocity scaling laws in single stream jets and similarity features of the mean velocity and turbulent kinetic energy in dual stream flows. The model forms a composite spectrum from four component single-stream jets each believed to represent noise-generation from a distinct region in the actual flow. While the methodology worked effectively at conditions considered earlier, recent examination of acoustic data at some unconventional conditions indicate that further improvements are necessary in order to expand the range of applicability of the model. The present work demonstrates how these predictions compare with experimental data gathered by NASA and industry for the purpose of examining the aerodynamic and acoustic performance of such nozzles for a wide range of core and fan stream conditions. Of particular interest are jets with inverted velocity and temperature profiles and the appearance of a second spectral peak at small aft angles to the jet under such conditions. It is shown that a four-component spectrum succeeds in modeling the second peak when the aft angle refraction effects are properly incorporated into the model. A tradeoff of noise emission takes place between two turbulent regions identified as transition and fully mixed regions as the fan stream velocity exceeds that of the core stream. The effect of nozzle discharge coefficients will also be discussed.

Theoretical vibro-acoustic modeling of acoustic noise transmission through aircraft windows

Science.gov (United States)

Aloufi, Badr; Behdinan, Kamran; Zu, Jean

2016-06-01

In this paper, a fully vibro-acoustic model for sound transmission across a multi-pane aircraft window is developed. The proposed model is efficiently applied for a set of window models to perform extensive theoretical parametric studies. The studied window configurations generally simulate the passenger window designs of modern aircraft classes which have an exterior multi-Plexiglas pane, an interior single acrylic glass pane and a dimmable glass ("smart" glass), all separated by thin air cavities. The sound transmission loss (STL) characteristics of three different models, triple-, quadruple- and quintuple-paned windows identical in size and surface density, are analyzed for improving the acoustic insulation performances. Typical results describing the influence of several system parameters, such as the thicknesses, number and spacing of the window panes, on the transmission loss are then investigated. In addition, a comparison study is carried out to evaluate the acoustic reduction capability of each window model. The STL results show that the higher frequencies sound transmission loss performance can be improved by increasing the number of window panels, however, the low frequency performance is decreased, particularly at the mass-spring resonances.

Predicting word-recognition performance in noise by young listeners with normal hearing using acoustic, phonetic, and lexical variables.

Science.gov (United States)

McArdle, Rachel; Wilson, Richard H

2008-06-01

To analyze the 50% correct recognition data that were from the Wilson et al (this issue) study and that were obtained from 24 listeners with normal hearing; also to examine whether acoustic, phonetic, or lexical variables can predict recognition performance for monosyllabic words presented in speech-spectrum noise. The specific variables are as follows: (a) acoustic variables (i.e., effective root-mean-square sound pressure level, duration), (b) phonetic variables (i.e., consonant features such as manner, place, and voicing for initial and final phonemes; vowel phonemes), and (c) lexical variables (i.e., word frequency, word familiarity, neighborhood density, neighborhood frequency). The descriptive, correlational study will examine the influence of acoustic, phonetic, and lexical variables on speech recognition in noise performance. Regression analysis demonstrated that 45% of the variance in the 50% point was accounted for by acoustic and phonetic variables whereas only 3% of the variance was accounted for by lexical variables. These findings suggest that monosyllabic word-recognition-in-noise is more dependent on bottom-up processing than on top-down processing. The results suggest that when speech-in-noise testing is used in a pre- and post-hearing-aid-fitting format, the use of monosyllabic words may be sensitive to changes in audibility resulting from amplification.

Complete de-Dopplerization and acoustic holography for external noise of a high-speed train.

Science.gov (United States)

Yang, Diange; Wen, Junjie; Miao, Feng; Wang, Ziteng; Gu, Xiaoan; Lian, Xiaomin

2016-09-01

Identification and measurement of moving sound sources are the bases for vehicle noise control. Acoustic holography has been applied in successfully identifying the moving sound source since the 1990s. However, due to the high demand for the accuracy of holographic data, currently the maximum velocity achieved by acoustic holography is just above 100 km/h. The objective of this study was to establish a method based on the complete Morse acoustic model to restore the measured signal in high-speed situations, and to propose a far-field acoustic holography method applicable for high-speed moving sound sources. Simulated comparisons of the proposed far-field acoustic holography with complete Morse model, the acoustic holography with simplified Morse model and traditional delay-and-sum beamforming were conducted. Experiments with a high-speed train running at the speed of 278 km/h validated the proposed far-field acoustic holography. This study extended the applications of acoustic holography to high-speed situations and established the basis for quantitative measurements of far-field acoustic holography.

Analysis of Individual Preferences for Tuning Noise-Reduction Algorithms

NARCIS (Netherlands)

Houben, Rolph; Dijkstra, Tjeerd M. H.; Dreschler, Wouter A.

2012-01-01

There is little research on user preference for different settings of noise reduction, especially for individual users. We therefore measured individual preferences for pairs of audio streams differing in the trade-off between noise reduction and speech distortion. A logistic probability model was

Long-term measurements of acoustic background noise in very deep sea

International Nuclear Information System (INIS)

Riccobene, G.

2009-01-01

The NEMO (NEutrino Mediterranean Observatory) Collaboration installed, 25 km E offshore the port of Catania (Sicily) at 2000 m depth, an underwater laboratory to perform long-term tests of prototypes and new technologies for an underwater high energy neutrino km 3 -scale detector in the Mediterranean Sea. In this framework the Collaboration deployed and successfully operated for about two years, starting from January 2005, an experimental apparatus for on-line monitoring of deep-sea noise. The station was equipped with four hydrophones and it is operational in the range 30 Hz-43 kHz. This interval of frequencies matches the range suitable for the proposed acoustic detection technique of high energy neutrinos. Hydrophone signals were digitized underwater at 96 kHz sampling frequency and 24 bits resolution. The stored data library, consisting of more than 2000 h of recordings, is a unique tool to model underwater acoustic noise at large depth, to characterize its variations as a function of environmental parameters, biological sources and human activities (ship traffic, etc.), and to determine the presence of cetaceans in the area.

Detection of Anomalous Noise Events on Low-Capacity Acoustic Nodes for Dynamic Road Traffic Noise Mapping within an Hybrid WASN

Directory of Open Access Journals (Sweden)

Rosa Ma Alsina-Pagès

2018-04-01

Full Text Available One of the main aspects affecting the quality of life of people living in urban and suburban areas is the continuous exposure to high road traffic noise (RTN levels. Nowadays, thanks to Wireless Acoustic Sensor Networks (WASN noise in Smart Cities has started to be automatically mapped. To obtain a reliable picture of the RTN, those anomalous noise events (ANE unrelated to road traffic (sirens, horns, people, etc. should be removed from the noise map computation by means of an Anomalous Noise Event Detector (ANED. In Hybrid WASNs, with master-slave architecture, ANED should be implemented in both high-capacity (Hi-Cap and low-capacity (Lo-Cap sensors, following the same principle to obtain consistent results. This work presents an ANED version to run in real-time on μ Controller-based Lo-Cap sensors of a hybrid WASN, discriminating RTN from ANE through their Mel-based spectral energy differences. The experiments, considering 9 h and 8 min of real-life acoustic data from both urban and suburban environments, show the feasibility of the proposal both in terms of computational load and in classification accuracy. Specifically, the ANED Lo-Cap requires around 1 6 of the computational load of the ANED Hi-Cap, while classification accuracies are slightly lower (around 10%. However, preliminary analyses show that these results could be improved in around 4% in the future by means of considering optimal frequency selection.

Detection of Anomalous Noise Events on Low-Capacity Acoustic Nodes for Dynamic Road Traffic Noise Mapping within an Hybrid WASN.

Science.gov (United States)

Alsina-Pagès, Rosa Ma; Alías, Francesc; Socoró, Joan Claudi; Orga, Ferran

2018-04-20

One of the main aspects affecting the quality of life of people living in urban and suburban areas is the continuous exposure to high road traffic noise (RTN) levels. Nowadays, thanks to Wireless Acoustic Sensor Networks (WASN) noise in Smart Cities has started to be automatically mapped. To obtain a reliable picture of the RTN, those anomalous noise events (ANE) unrelated to road traffic (sirens, horns, people, etc.) should be removed from the noise map computation by means of an Anomalous Noise Event Detector (ANED). In Hybrid WASNs, with master-slave architecture, ANED should be implemented in both high-capacity (Hi-Cap) and low-capacity (Lo-Cap) sensors, following the same principle to obtain consistent results. This work presents an ANED version to run in real-time on μ Controller-based Lo-Cap sensors of a hybrid WASN, discriminating RTN from ANE through their Mel-based spectral energy differences. The experiments, considering 9 h and 8 min of real-life acoustic data from both urban and suburban environments, show the feasibility of the proposal both in terms of computational load and in classification accuracy. Specifically, the ANED Lo-Cap requires around 1 6 of the computational load of the ANED Hi-Cap, while classification accuracies are slightly lower (around 10%). However, preliminary analyses show that these results could be improved in around 4% in the future by means of considering optimal frequency selection.

Aeroacoustic characteristics and noise reduction of a centrifugal fan for a vacuum cleaner

Energy Technology Data Exchange (ETDEWEB)

Jeon, Wan Ho; Rew, Ho Seon; Kim, Chang Joon [LG Electronics, Seoul (Korea, Republic of)

2004-02-01

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 30000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall Sound Power Level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental Blade Passing Frequency (BPF) is reduced by about 6 dB(A) and the 2{sup nd} BPF is reduced about 20 dB(A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced.

Aeroacoustic characteristics and noise reduction of a centrifugal fan for a vacuum cleaner

International Nuclear Information System (INIS)

Jeon, Wan Ho; Rew, Ho Seon; Kim, Chang Joon

2004-01-01

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 30000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall Sound Power Level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental Blade Passing Frequency (BPF) is reduced by about 6 dB(A) and the 2 nd BPF is reduced about 20 dB(A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced

Advanced digital signal processing and noise reduction

CERN Document Server

Vaseghi, Saeed V

2008-01-01

Digital signal processing plays a central role in the development of modern communication and information processing systems. The theory and application of signal processing is concerned with the identification, modelling and utilisation of patterns and structures in a signal process. The observation signals are often distorted, incomplete and noisy and therefore noise reduction, the removal of channel distortion, and replacement of lost samples are important parts of a signal processing system. The fourth edition of Advanced Digital Signal Processing and Noise Reduction updates an

Noise and Fuel Burn Reduction Potential of an Innovative Subsonic Transport Configuration

Science.gov (United States)

Guo, Yueping; Nickol, Craig L.; Thomas, Russell H.

2014-01-01

A study is presented for the noise and fuel burn reduction potential of an innovative double deck concept aircraft with two three-shaft direct-drive turbofan engines. The engines are mounted from the fuselage so that the engine inlet is over the main wing. It is shown that such an aircraft can achieve a cumulative Effective Perceived Noise Level (EPNL) about 28 dB below the current aircraft noise regulations of Stage 4. The combination of high bypass ratio engines and advanced wing design with laminar flow control technologies provide fuel burn reduction and low noise levels simultaneously. For example, the fuselage mounted engine position provides more than 4 EPNLdB of noise reduction by shielding the inlet radiated noise. To identify the potential effect of noise reduction technologies on this concept, parametric studies are presented to reveal the system level benefits of various emerging noise reduction concepts, for both engine and airframe noise reduction. These concepts are discussed both individually to show their respective incremental noise reduction potential and collectively to assess their aggregate effects on the total noise. Through these concepts approximately about 8 dB of additional noise reduction is possible, bringing the cumulative noise level of this aircraft to 36 EPNLdB below Stage 4, if the entire suite of noise reduction technologies would mature to practical application. In a final step, an estimate is made for this same aircraft concept but with higher bypass ratio, geared, turbofan engines. With this geared turbofan propulsion system, the noise is estimated to reach as low as 40-42 dB below Stage 4 with a fuel burn reduction of 43-47% below the 2005 best-in-class aircraft baseline. While just short of the NASA N+2 goals of 42 dB and 50% fuel burn reduction, for a 2025 in service timeframe, this assessment shows that this innovative concept warrants refined study. Furthermore, this design appears to be a viable potential future passenger

Noise, buildings and people

Energy Technology Data Exchange (ETDEWEB)

Croome, D J

1977-01-01

This book covers the physics of acoustics necessary to understand the analytical aspects of acoustical design and noise control in buildings. The major part is devoted to the problems of noise and man, and other chapters cover features of noise control in and around buildings. In an introduction, building environmental engineering is dealth with in general terms of architecture, creativity, systms design, etc. Aspects of the acoustical environment, noise sources in buildings, control of airborne and structure-borne noise and acoustical design techniques are covered in Part II. Items include: comfort, physiological response to noise and vibrations, noise criteria, human performance, speech communication, landscaped offices, sound generation by air-conditioning and heating equipment, building structure and noise attenuation, acoustical design. Part III gives some fundamentals of acoustics; mechanical vibration, wave motion, propagation of sound, structure-borne sound, behavior of sound in rooms, transmission of sound through structure. References include lists of British standards and booklets on health and safety at work.

Magneto acoustic emission and magnetic barkhausen noise

International Nuclear Information System (INIS)

Neyra Astudillo, M R; Nunez, N; Lopez Pumarega, M I; Ruzzante, J

2012-01-01

Results obtained in the characterization of a sample of A508 Class II steel, are showed. This material is usually used for pressure vessels construction. Two techniques not very spread in our country, but developed at our Research Group were used: Magnetic Barkhausen Noise (MBN) and Magneto Acoustic Emission (MAE). Both techniques only can be used with ferromagnetic materials. A sinusoidal low frequency magnetic field (10 Hz) was applied on the material under test, producing a sudden movement of the magnetic domain walls. This movement produces an induced EMF. In this case it is amplified and filtered in the wide band between 20 kHz and 300 kHz. The electrical signal generated at the sensing coil is called Magnetic Barkhausen Noise (MBN). The MBN was known since 1919 when it was observed for the first time. The movement of the magnetic domain walls generates at the same time elastic waves which propagate inside the material. Fixing a piezoelectric transducer on the sample surface, it is possible to detect these waves. This phenomenon is known as Magneto Acoustic Emission (MAE) and its frequency band is 20 kHz up to 1 MHz. As it is widely known, the domain structure and their walls movement are deeply influenced by the metal defects and microstructure (stress, grain size, precipitates, etc.). Then studying the domain wall movement it is possible to induce the material state. At the present study, we can infer that the material analyzed with these two techniques, has an anisotropy showed at the polar graphs, but does not totally showed at the metallographic study. Subsequent studies employing the Baumann imprint technique showed that manganese sulphides present an orientation similar to that founded with MNB and MAE. This work is completed with MEB and EDAX (author)

Wind Noise Reduction in a Non-Porous Subsurface Windscreen

Science.gov (United States)

Zuckerwar, Allan J.; Shams, Qamar A.; Knight, H. Keith

2012-01-01

Measurements of wind noise reduction were conducted on a box-shaped, subsurface windscreen made of closed cell polyurethane foam. The windscreen was installed in the ground with the lid flush with the ground surface. The wind was generated by means of a fan, situated on the ground, and the wind speed was measured at the center of the windscreen lid with an ultrasonic anemometer. The wind speed was controlled by moving the fan to selected distances from the windscreen. The wind noise was measured on a PCB Piezotronics 3†electret microphone. Wind noise spectra were measured with the microphone exposed directly to the wind (atop the windscreen lid) and with the microphone installed inside the windscreen. The difference between the two spectra comprises the wind noise reduction. At wind speeds of 3, 5, and 7 m/s, the wind noise reduction is typically 15 dB over the frequency range of 0.1-20 Hz.

Experimental Study of Wake / Flap Interaction Noise and the Reduction of Flap Side Edge Noise

Science.gov (United States)

Hutcheson, Florence V.; Stead, Daniel J.; Plassman, Gerald E.

2016-01-01

The effects of the interaction of a wake with a half-span flap on radiated noise are examined. The incident wake is generated by bars of various widths and lengths or by a simplified landing gear model. Single microphone and phased array measurements are used to isolate the effects of the wake interaction on the noise radiating from the flap side edge and flap cove regions. The effects on noise of the wake generator's geometry and relative placement with respect to the flap are assessed. Placement of the wake generators upstream of the flap side edge is shown to lead to the reduction of flap side edge noise by introducing a velocity deficit and likely altering the instabilities in the flap side edge vortex system. Significant reduction in flap side edge noise is achieved with a bar positioned directly upstream of the flap side edge. The noise reduction benefit is seen to improve with increased bar width, length and proximity to the flap edge. Positioning of the landing gear model upstream of the flap side edge also leads to decreased flap side edge noise. In addition, flap cove noise levels are significantly lower than when the landing gear is positioned upstream of the flap mid-span. The impact of the local flow velocity on the noise radiating directly from the landing gear is discussed. The effects of the landing gear side-braces on flap side edge, flap cove and landing gear noise are shown.

TU-F-CAMPUS-I-04: Head-Only Asymmetric Gradient System Evaluation: ACR Image Quality and Acoustic Noise

Energy Technology Data Exchange (ETDEWEB)

Weavers, P; Shu, Y; Tao, S; Bernstein, M [Mayo Clinic, Rochester, Minnesota (United States); Lee, S; Piel, J; Foo, T [GE Global Research, Niskayuna, NY (United States); Mathieu, J-B [GE Healthcare, Florence, SC (Italy)

2015-06-15

Purpose: A high-performance head-only magnetic resonance imaging gradient system with an acquisition volume of 26 cm employing an asymmetric design for the transverse coils has been developed. It is able to reach a magnitude of 85 mT/m at a slew rate of 700 T/m/s, but operated at 80 mT/m and 500 T/m/s for this test. A challenge resulting from this asymmetric design is that the gradient nonlinearly exhibits both odd- and even-ordered terms, and as the full imaging field of view is often used, the nonlinearity is pronounced. The purpose of this work is to show the system can produce clinically useful images after an on-site gradient nonlinearity calibration and correction, and show that acoustic noise levels fall within non-significant risk (NSR) limits for standard clinical pulse sequences. Methods: The head-only gradient system was inserted into a standard 3T wide-bore scanner without acoustic damping. The ACR phantom was scanned in an 8-channel receive-only head coil and the standard American College of Radiology (ACR) MRI quality control (QC) test was performed. Acoustic noise levels were measured for several standard pulse sequences. Results: Images acquired with the head-only gradient system passed all ACR MR image quality tests; Both even and odd-order gradient distortion correction terms were required for the asymmetric gradients to pass. Acoustic noise measurements were within FDA NSR guidelines of 99 dBA (with assumed 20 dBA hearing protection) A-weighted and 140 dB for peak for all but one sequence. Note the gradient system was installed without any shroud or acoustic batting. We expect final system integration to greatly reduce noise experienced by the patient. Conclusion: A high-performance head-only asymmetric gradient system operating at 80 mT/m and 500 T/m/s conforms to FDA acoustic noise limits in all but one case, and passes all the ACR MR image quality control tests. This work was supported in part by the NIH grant 5R01EB010065.

TU-F-CAMPUS-I-04: Head-Only Asymmetric Gradient System Evaluation: ACR Image Quality and Acoustic Noise

International Nuclear Information System (INIS)

Weavers, P; Shu, Y; Tao, S; Bernstein, M; Lee, S; Piel, J; Foo, T; Mathieu, J-B

2015-01-01

Purpose: A high-performance head-only magnetic resonance imaging gradient system with an acquisition volume of 26 cm employing an asymmetric design for the transverse coils has been developed. It is able to reach a magnitude of 85 mT/m at a slew rate of 700 T/m/s, but operated at 80 mT/m and 500 T/m/s for this test. A challenge resulting from this asymmetric design is that the gradient nonlinearly exhibits both odd- and even-ordered terms, and as the full imaging field of view is often used, the nonlinearity is pronounced. The purpose of this work is to show the system can produce clinically useful images after an on-site gradient nonlinearity calibration and correction, and show that acoustic noise levels fall within non-significant risk (NSR) limits for standard clinical pulse sequences. Methods: The head-only gradient system was inserted into a standard 3T wide-bore scanner without acoustic damping. The ACR phantom was scanned in an 8-channel receive-only head coil and the standard American College of Radiology (ACR) MRI quality control (QC) test was performed. Acoustic noise levels were measured for several standard pulse sequences. Results: Images acquired with the head-only gradient system passed all ACR MR image quality tests; Both even and odd-order gradient distortion correction terms were required for the asymmetric gradients to pass. Acoustic noise measurements were within FDA NSR guidelines of 99 dBA (with assumed 20 dBA hearing protection) A-weighted and 140 dB for peak for all but one sequence. Note the gradient system was installed without any shroud or acoustic batting. We expect final system integration to greatly reduce noise experienced by the patient. Conclusion: A high-performance head-only asymmetric gradient system operating at 80 mT/m and 500 T/m/s conforms to FDA acoustic noise limits in all but one case, and passes all the ACR MR image quality control tests. This work was supported in part by the NIH grant 5R01EB010065

Reduction of sound transmission across plenum windows by incorporating an array of rigid cylinders

Science.gov (United States)

Tang, S. K.

2018-02-01

The potential improvement of plenum window noise reduction by installing rigid circular cylinder arrays into the window cavity is investigated numerically using the finite-element method in this study. A two-dimensional approach is adopted. The sound transmission characteristics and propagation within the plenum window are also examined in detail. Results show that the installation of the cylinders in general gives rise to broadband improvement of noise reduction across a plenum window regardless of the direction of sound incidence. Such acoustical performance becomes better when more cylinder columns are installed, but it is suggested that the number of cylinder rows should not exceed two. Results also show that the cylinder positions relative to the nodal/anti-nodal planes of the acoustic modes are crucial in the noise reduction enhancement mechanisms. Noise reduction can further be enhanced by staggering the cylinder rows, such that each cylinder row supports the development of a different acoustic mode. For the simple cylinder arrangements considered in this study, the traffic noise reduction enhancement observed in this study can be as high as 4-5 dB, which is already comparable to or higher than the maximum achieved by installing sound absorption into a plenum window.

Wind Turbine Acoustic Investigation: Infrasound and Low-Frequency Noise--A Case Study

Science.gov (United States)

Ambrose, Stephen E.; Rand, Robert W.; Krogh, Carmen M. E.

2012-01-01

Wind turbines produce sound that is capable of disturbing local residents and is reported to cause annoyance, sleep disturbance, and other health-related impacts. An acoustical study was conducted to investigate the presence of infrasonic and low-frequency noise emissions from wind turbines located in Falmouth, Massachusetts, USA. During the…

Jet noise reduction via dispersed phase injection

Science.gov (United States)

Greska, Brent; Krothapalli, Anjaneyulu; Arakeri, Vijay

2001-11-01

A recently developed hot jet aeroacoustics facility at FMRL,FAMU-FSU College of Engineering has been used to study the far field noise characteristics of hot supersonic jets as influenced by the injection of a dispersed phase with low mass loading.The measured SPL from a fully expanded Mach 1.36 hot jet shows a peak value of about 139 dB at 40 deg from the jet axis.By injecting atomized water,the SPL are reduced in the angular region of about 30 deg to 50 deg with the maximum reduction being about 2 dB at 40 deg.However,with the use of non atomized aqueous polymer solution as a dispersed phase the noise levels are reduced over all angular positions by at least 1 dB with the maximum reduction being about 3 dB at 40 deg.The injection of a dispersed phase readily kills the screech; the initial results show promise and optimization studies are underway to find methods of further noise reduction.

Noise Reduction of Measurement Data using Linear Digital Filters

Directory of Open Access Journals (Sweden)

Hitzmann B.

2007-12-01

Full Text Available In this paper Butterworth, Chebyshev (Type I and II and Elliptic digital filters are designed for signal noise reduction. On-line data measurements of substrate concentration from E. coli fed-batch cultivation process are used. Application of the designed filters leads to a successful noise reduction of on-line glucose measurements. The digital filters presented here are simple, easy to implement and effective - the used filters allow for a smart compromise between signal information and noise corruption.

Magnetic field induced random pulse trains of magnetic and acoustic noises in martensitic single-crystal Ni2MnGa

Science.gov (United States)

Daróczi, Lajos; Piros, Eszter; Tóth, László Z.; Beke, Dezső L.

2017-07-01

Jerky magnetic and acoustic noises were evoked in a single variant martensitic Ni2MnGa single crystal (produced by uniaxial compression) by application of an external magnetic field along the hard magnetization direction. It is shown that after reaching the detwinning threshold, spontaneous reorientation of martensite variants (twins) leads not only to acoustic emission but magnetic two-directional noises as well. At small magnetic fields, below the above threshold, unidirectional magnetic emission is also observed and attributed to a Barkhausen-type noise due to magnetic domain wall motions during magnetization along the hard direction. After the above first run, in cycles of decreasing and increasing magnetic field, at low-field values, weak, unidirectional Barkhausen noise is detected and attributed to the discontinuous motion of domain walls during magnetization along the easy magnetization direction. The magnetic noise is also measured by constraining the sample in the same initial variant state along the hard direction and, after the unidirectional noise (as obtained also in the first run), a two-directional noise package is developed and it is attributed to domain rotations. From the statistical analysis of the above noises, the critical exponents, characterizing the power-law behavior, are calculated and compared with each other and with the literature data. Time correlations within the magnetic as well as acoustic signals lead to a common scaled power function (with β =-1.25 exponent) for both types of signals.

Boundary layer noise subtraction in hydrodynamic tunnel using robust principal component analysis.

Science.gov (United States)

Amailland, Sylvain; Thomas, Jean-Hugh; Pézerat, Charles; Boucheron, Romuald

2018-04-01

The acoustic study of propellers in a hydrodynamic tunnel is of paramount importance during the design process, but can involve significant difficulties due to the boundary layer noise (BLN). Indeed, advanced denoising methods are needed to recover the acoustic signal in case of poor signal-to-noise ratio. The technique proposed in this paper is based on the decomposition of the wall-pressure cross-spectral matrix (CSM) by taking advantage of both the low-rank property of the acoustic CSM and the sparse property of the BLN CSM. Thus, the algorithm belongs to the class of robust principal component analysis (RPCA), which derives from the widely used principal component analysis. If the BLN is spatially decorrelated, the proposed RPCA algorithm can blindly recover the acoustical signals even for negative signal-to-noise ratio. Unfortunately, in a realistic case, acoustic signals recorded in a hydrodynamic tunnel show that the noise may be partially correlated. A prewhitening strategy is then considered in order to take into account the spatially coherent background noise. Numerical simulations and experimental results show an improvement in terms of BLN reduction in the large hydrodynamic tunnel. The effectiveness of the denoising method is also investigated in the context of acoustic source localization.

Digitally controlled active noise reduction with integrated speech communication

NARCIS (Netherlands)

Steeneken, H.J.M.; Verhave, J.A.

2004-01-01

Active noise reduction is a successful addition to passive ear-defenders for improvement of the sound attenuation at low frequencies. Design and assessment methods are discussed, focused on subjective and objective attenuation measurements, stability, and high noise level applications. Active noise

Hearing loss associated with repeated MRI acquisition procedure-related acoustic noise exposure: an occupational cohort study.

Science.gov (United States)

Bongers, Suzan; Slottje, Pauline; Kromhout, Hans

2017-11-01

To study the effects of repeated exposure to MRI-related acoustic noise during image acquisition procedures (scans) on hearing. A retrospective occupational cohort study was performed among workers of an MRI manufacturing facility (n=474). Longitudinal audiometry data from the facility's medical surveillance scheme collected from 1973 to 2010 were analysed by studying the association of cumulative exposure to MRI-related acoustic noise from voluntary (multiple) MRI scans and the hearing threshold of the volunteer. Repeated acoustic noise exposure during volunteer MRI scans was found to be associated with a small exposure-dependent increased rate change of hearing threshold level (dB/year), but the association was only found related to the number of voluntary MRI scans and not to modelled cumulative noise exposure (dB*hour) based on MRI-system type. The increased rate change of hearing threshold level was found to be statistically significant for the frequencies 500, 1000, 2000, 3000 and 4000 Hz in the right ear. From our longitudinal cohort study, it appeared that exposure to noise from voluntarily MRI scans may have resulted in a slight amount of hearing loss. Mandatory use of hearing protection might have prevented more severe hearing loss. Lack of consistency in findings between the left and right ears and between the two exposure measures prohibits definitive conclusions. Further research that addresses the study's methodological limitations is warranted to corroborate our findings. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

Simulation on a car interior aerodynamic noise control based on statistical energy analysis

Science.gov (United States)

Chen, Xin; Wang, Dengfeng; Ma, Zhengdong

2012-09-01

How to simulate interior aerodynamic noise accurately is an important question of a car interior noise reduction. The unsteady aerodynamic pressure on body surfaces is proved to be the key effect factor of car interior aerodynamic noise control in high frequency on high speed. In this paper, a detail statistical energy analysis (SEA) model is built. And the vibra-acoustic power inputs are loaded on the model for the valid result of car interior noise analysis. The model is the solid foundation for further optimization on car interior noise control. After the most sensitive subsystems for the power contribution to car interior noise are pointed by SEA comprehensive analysis, the sound pressure level of car interior aerodynamic noise can be reduced by improving their sound and damping characteristics. The further vehicle testing results show that it is available to improve the interior acoustic performance by using detailed SEA model, which comprised by more than 80 subsystems, with the unsteady aerodynamic pressure calculation on body surfaces and the materials improvement of sound/damping properties. It is able to acquire more than 2 dB reduction on the central frequency in the spectrum over 800 Hz. The proposed optimization method can be looked as a reference of car interior aerodynamic noise control by the detail SEA model integrated unsteady computational fluid dynamics (CFD) and sensitivity analysis of acoustic contribution.

Wind Noise Reduction using Non-negative Sparse Coding

DEFF Research Database (Denmark)

Schmidt, Mikkel N.; Larsen, Jan; Hsiao, Fu-Tien

2007-01-01

We introduce a new speaker independent method for reducing wind noise in single-channel recordings of noisy speech. The method is based on non-negative sparse coding and relies on a wind noise dictionary which is estimated from an isolated noise recording. We estimate the parameters of the model ...... and discuss their sensitivity. We then compare the algorithm with the classical spectral subtraction method and the Qualcomm-ICSI-OGI noise reduction method. We optimize the sound quality in terms of signal-to-noise ratio and provide results on a noisy speech recognition task....

An Exceptional Purity of Sound: Noise Reduction Technology and the Inevitable Noise of Sound Recording

NARCIS (Netherlands)

Kromhout, M.

2014-01-01

The phenomenon of noise has resisted many attempts at framing it within a singular conceptual framework. Critically questioning the tendency to do so, this article asserts the complexities of different noise-phenomena by analysing a specific technology: technological noise reduction systems. Whereas

Interior acoustic cloak

OpenAIRE

Wael Akl; A. Baz

2014-01-01

Acoustic cloaks have traditionally been intended to externally surround critical objects to render these objects acoustically invisible. However, in this paper, the emphasis is placed on investigating the application of the acoustic cloaks to the interior walls of acoustic cavities in an attempt to minimize the noise levels inside these cavities. In this manner, the acoustic cloaks can serve as a viable and efficient alternative to the conventional passive noise attenuation treatments which a...

DART Core/Combustor-Noise Initial Test Results

Science.gov (United States)

Boyle, Devin K.; Henderson, Brenda S.; Hultgren, Lennart S.

2017-01-01

Contributions from the combustor to the overall propulsion noise of civilian transport aircraft are starting to become important due to turbofan design trends and advances in mitigation of other noise sources. Future propulsion systems for ultra-efficient commercial air vehicles are projected to be of increasingly higher bypass ratio from larger fans combined with much smaller cores, with ultra-clean burning fuel-flexible combustors. Unless effective noise-reduction strategies are developed, combustor noise is likely to become a prominent contributor to overall airport community noise in the future. The new NASA DGEN Aero0propulsion Research Turbofan (DART) is a cost-efficient testbed for the study of core-noise physics and mitigation. This presentation gives a brief description of the recently completed DART core combustor-noise baseline test in the NASA GRC Aero-Acoustic Propulsion Laboratory (AAPL). Acoustic data was simultaneously acquired using the AAPL overhead microphone array in the engine aft quadrant far field, a single midfield microphone, and two semi-infinite-tube unsteady pressure sensors at the core-nozzle exit. An initial assessment shows that the data is of high quality and compares well with results from a quick 2014 feasibility test. Combustor noise components of measured total-noise signatures were educed using a two-signal source-separation method an dare found to occur in the expected frequency range. The research described herein is aligned with the NASA Ultra-Efficient Commercial Transport strategic thrust and is supported by the NASA Advanced Air Vehicle Program, Advanced Air Transport Technology Project, under the Aircraft Noise Reduction Subproject.

Subharmonics and noise excitation in transmission of acoustic wave through unconsolidated granular medium

International Nuclear Information System (INIS)

Tournat, V.; Gusev, V.E.; Castagnede, B.

2004-01-01

First laboratory-scale experimental observation of both subharmonics excitation and significant increase in noise level caused by propagation of the acoustic wave in unconsolidated granular material is reported. The bifurcation phenomenon, taking place above a critical level of acoustic excitation (and opening the subharmonics route to chaos) is attributed to the interaction of acoustic wave with distributed system of highly nonlinear inter-grain contacts. The estimates demonstrated that these are weak contacts (loaded at least two orders of magnitude weaker than in average) that might be responsible for the observed nonlinear effects. The additional intermittent contacts created by the acoustic wave (which are open in the absence of acoustic loading) can also contribute. In the clapping (tapping) regime, each of these contacts individually is similar to an impact oscillator, for which the scenario of period doubling cascade and the transition to chaotic behavior has been predicted theoretically and observed experimentally earlier. The experiments confirm that the nonlinear interactions of acoustic waves in granular assemblages are highly sensitive to the fraction of weakly loaded (and unloaded) contacts, information on which is difficult to access by any other experimental methods

Virtual sensors for active noise control in acoustic-structural coupled enclosures using structural sensing: robust virtual sensor design.

Science.gov (United States)

Halim, Dunant; Cheng, Li; Su, Zhongqing

2011-03-01

The work was aimed to develop a robust virtual sensing design methodology for sensing and active control applications of vibro-acoustic systems. The proposed virtual sensor was designed to estimate a broadband acoustic interior sound pressure using structural sensors, with robustness against certain dynamic uncertainties occurring in an acoustic-structural coupled enclosure. A convex combination of Kalman sub-filters was used during the design, accommodating different sets of perturbed dynamic model of the vibro-acoustic enclosure. A minimax optimization problem was set up to determine an optimal convex combination of Kalman sub-filters, ensuring an optimal worst-case virtual sensing performance. The virtual sensing and active noise control performance was numerically investigated on a rectangular panel-cavity system. It was demonstrated that the proposed virtual sensor could accurately estimate the interior sound pressure, particularly the one dominated by cavity-controlled modes, by using a structural sensor. With such a virtual sensing technique, effective active noise control performance was also obtained even for the worst-case dynamics. © 2011 Acoustical Society of America

A Two-Microphone Noise Reduction System for Cochlear Implant Users with Nearby Microphones—Part I: Signal Processing Algorithm Design and Development

Directory of Open Access Journals (Sweden)

Marco Pelizzone

2008-06-01

Full Text Available Users of cochlear implant systems, that is, of auditory aids which stimulate the auditory nerve at the cochlea electrically, often complain about poor speech understanding in noisy environments. Despite the proven advantages of multimicrophone directional noise reduction systems for conventional hearing aids, only one major manufacturer has so far implemented such a system in a product, presumably because of the added power consumption and size. We present a physically small (intermicrophone distance 7 mm and computationally inexpensive adaptive noise reduction system suitable for behind-the-ear cochlear implant speech processors. Supporting algorithms, which allow the adjustment of the opening angle and the maximum noise suppression, are proposed and evaluated. A portable real-time device for test in real acoustic environments is presented.

Reduction of Background Noise in the NASA Ames 40- by 80-Foot Wind Tunnel

Science.gov (United States)

Jaeger, Stephen M.; Allen, Christopher S.; Soderman, Paul T.; Olson, Larry E. (Technical Monitor)

1995-01-01

Background noise in both open-jet and closed wind tunnels adversely affects the signal-to-noise ratio of acoustic measurements. To measure the noise of increasingly quieter aircraft models, the background noise will have to be reduced by physical means or through signal processing. In a closed wind tunnel, such as the NASA Ames 40- by 80- Foot Wind Tunnel, the principle background noise sources can be classified as: (1) fan drive noise; (2) microphone self-noise; (3) aerodynamically induced noise from test-dependent hardware such as model struts and junctions; and (4) noise from the test section walls and vane set. This paper describes the steps taken to minimize the influence of each of these background noise sources in the 40 x 80.

Market Analysis of Soundproof and Noise Reduction Plate

Directory of Open Access Journals (Sweden)

Chang Heyu

2017-01-01

Full Text Available Since the reform and opening up, China has a booming economy development, transportation industry as an important part of the economic processes has made a considerable progress, and continue to promote the rapid economic development. At the end of 2012, China's highway mileage has reached 4.238 million km and highway mileage ranks first in the world. Transportation in promoting rapid economic development, but also brings the traffic noise which has a tremendous influence on residents’ daily life, and this influence has gradually deepening and widening, in this situation the production of noise reduction panel gradually emerged. In this paper, a noise barriers manufacturer’ business model in Beijing Daxing District and analyze existing data will be analyzed, it will give much guidance and reference for a new noise reduction factory. The study has shown that plant will target all levels of government departments in charge of roads and the property of management department of residence as our customer groups, increasing technological innovation and improving product quality to establish a more extensive business relationships, and gradually formed noise barriers market competitiveness.

Preliminary study of acoustic emission (ae) noise signal identification for crude oil storage tank

International Nuclear Information System (INIS)

Nurul Ain Ahmad Latif; Shukri Mohd

2008-08-01

This preliminary work was carried out to simulate the Acoustic Emission (AE) signal contributed by pitting corrosion, and noise signal from environment during crude oil storage tanks monitoring. The purpose of this study is to prove that acoustic emission (AE) could be used to detect the formation of pitting corrosion in the crude oil storage tank and differentiated it from other sources of noise signal. In this study, the pitting corrosion was simulated by inducing low voltage and low amperage current onto the crude oil storage tank material (ASTM 516 G 70). Water drop, air blow and surface rubbing were applied onto the specimen surface. To simulate the noise signal produce by rain fall, wind blow and other sources of noise during AE crude oil storage tanks monitoring. AE sensor was attached onto the other surface of specimen to acquire all of these AE signals which then has send to AE DiSP 24 data acquisition system for signal conditioning. AE win software has been used to analyse this entire signal. It is found that, simulated pitting corrosion could be detected by AE system and differentiated from other sources of noise by using amplitude analysis. From the amplitude analysis is shown that 20-30 dB is the range amplitude for the blow test, 50-60 dB for surface rubbing test and over than 60 dB for water drop test. (Author)

Acoustic isolation vessel for measurement of the background noise in microphones

Science.gov (United States)

Ngo, Kim C. T.; Zuckerwar, Allan J.

1993-01-01

An acoustic isolation vessel has been developed to measure the background noise in microphones. The test microphone is installed in an inner vessel, which is suspended within an outer vessel, and the intervening air space is evacuated to a high vacuum. An analytical expression for the transmission coefficient is derived, based on a five-media model, and compared to experiment. At an isolation vacuum of 5 x 10 exp -6 Torr the experimental transmission coefficient was found to be lower than -155 dB at frequencies ranging from 40 to 1200 Hz. Measurements of the A-weighted noise levels of commercial condenser microphones of four different sizes show good agreement with published values.

Effect of a Background Noise on the Acoustic Leak Detection Methodology for a SFR Steam Generator

International Nuclear Information System (INIS)

Kim, Tae-Joon; Jeong, Ji-Young; Kim, Jong-Man

2007-01-01

The protection of a water/steam leak into a sodium in the SFR SG at an early phase of a leak origin depends on a fast response and sensitivity of a leak detection system not to a response against the several kinds of noises. The subject in this study is to introduce a detection performance by using our developed acoustic leak detection methodology discriminated by a backpropagation neural network according to a preprocessing of the 1/6 Octave band analysis or 1/12 Octave band analysis and the x n method defined by us. It was used for the acoustic signals generated from the simulation works which are the noises of an artificial background such as a scratching, a hammering on a steel structure and so on. In a previous study, we showed that the performance of a LabVIEW tool embedded with the developed acoustic leak detection methodology detected the SWR leak signals

Applications of adaptive filters in active noise control

Science.gov (United States)

Darlington, Paul

The active reduction of acoustic noise is achieved by the addition of a cancelling acoustic signal to the unwanted sound. Successful definition of the cancelling signal amounts to a system identification problem. Recent advances in adaptive signal processing have allowed this problem to be tackled using adaptive filters, which offer significant advantages over conventional solutions. The extension of adaptive noise cancelling techniques, which were developed in the electrical signal conditioning context, to the control of acoustic systems is studied. An analysis is presented of the behavior of the Widrow-Hoff LMS adaptive noise canceller with a linear filter in its control loop. The active control of plane waves propagating axially in a hardwalled duct is used as a motivating model problem. The model problem also motivates the study of the effects of feedback around an LMS adaptive filter. An alternative stochastic gradient algorithm for controlling adaptive filters in the presence of feedback is presented.

Effect of train type on annoyance and acoustic features of the rolling noise.

Science.gov (United States)

Kasess, Christian H; Noll, Anton; Majdak, Piotr; Waubke, Holger

2013-08-01

This study investigated the annoyance associated with the rolling noise of different railway stock. Passbys of nine train types (passenger and freight trains) equipped with different braking systems were recorded. Acoustic features showed a clear distinction of the braking system with the A-weighted energy equivalent sound level (LAeq) showing a difference in the range of 10 dB between cast-iron braked trains and trains with disk or K-block brakes. Further, annoyance was evaluated in a psychoacoustic experiment where listeners rated the relative annoyance of the rolling noise for the different train types. Stimuli with and without the original LAeq differences were tested. For the original LAeq differences, the braking system significantly affected the annoyance with cast-iron brakes being most annoying, most likely as a consequence of the increased wheel roughness causing an increased LAeq. Contribution of the acoustic features to the annoyance was investigated revealing that the LAeq explained up to 94% of the variance. For the stimuli without differences in the LAeq, cast-iron braked train types were significantly less annoying and the spectral features explained up to 60% of the variance in the annoyance. The effect of these spectral features on the annoyance of the rolling noise is discussed.

METHODS OF NOISE LEVEL REDUCTION OF DRIVE IN LATHES

Directory of Open Access Journals (Sweden)

Janusz ROGULA

2014-06-01

Full Text Available The aim of this work is method presentation to noise level reduction of fixed headstock of the lathe. It is connected with the causes finding of non-uniform work of lathe headstock, description of recent design and its analysis. Problem of the excessive noise level concern to near 35% of the lathes have been produced. In spite of lack of noise reduction possibility there were no system solution of problem. Design optimisation weren’t done after application the electric motor with inverter. New solution of electric motor control let to reduce number of gear wheels in lathe drive system. For this drive solution there weren’t made the analysis of drive particular parts influence on the noise generation.

Aerodynamic noise prediction of a Horizontal Axis Wind Turbine using Improved Delayed Detached Eddy Simulation and acoustic analogy

International Nuclear Information System (INIS)

Ghasemian, Masoud; Nejat, Amir

2015-01-01

Highlights: • The noise predictions are performed by Ffowcs Williams and Hawkings method. • There is a direct relation between the radiated noise and the wind speed. • The tonal peaks in the sound spectra match with the blade passing frequency. • The quadrupole noises have negligible effect on the low frequency noises. - Abstract: This paper presents the results of the aerodynamic and aero-acoustic prediction of the flow field around the National Renewable Energy Laboratory Phase VI wind turbine. The Improved Delayed Detached Eddy Simulation turbulence model is applied to obtain the instantaneous turbulent flow field. The noise prediction is carried out using the Ffowcs Williams and Hawkings acoustic analogy. Simulations are performed for three different inflow conditions, U = 7, 10, 15 m/s. The capability of the Improved Delayed Detached Eddy Simulation turbulence model in massive separation is verified with available experimental data for pressure coefficient. The broadband noises of the turbulent boundary layers and the tonal noises due to the blade passing frequency are predicted via flow field noise simulation. The contribution of the thickness, loading and quadrupole noises are investigated, separately. The results indicated that there is a direct relation between the strength of the radiated noise and the wind speed. Furthermore, the effect of the receiver location on the Overall Sound Pressure Level is investigated

Observation of the fundamental Nyquist noise limit in an ultra-high Q-factor cryogenic bulk acoustic wave cavity

Energy Technology Data Exchange (ETDEWEB)

Goryachev, Maxim, E-mail: maxim.goryachev@uwa.edu.au; Ivanov, Eugene N.; Tobar, Michael E. [ARC Centre of Excellence for Engineered Quantum Systems, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Kann, Frank van [School of Physics, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Galliou, Serge [Department of Time and Frequency, FEMTO-ST Institute, ENSMM, 26 Chemin de l' Épitaphe, 25000 Besançon (France)

2014-10-13

Thermal Nyquist noise fluctuations of high-Q bulk acoustic wave cavities have been observed at cryogenic temperatures with a DC superconducting quantum interference device amplifier. High Q modes with bandwidths of few tens of milliHz produce thermal fluctuations with a signal-to-noise ratio of up to 23 dB. The estimated effective temperature from the Nyquist noise is in good agreement with the physical temperature of the device, confirming the validity of the equivalent circuit model and the non-existence of any excess resonator self-noise. The measurements also confirm that the quality factor remains extremely high (Q > 10{sup 8} at low order overtones) for very weak (thermal) system motion at low temperatures, when compared to values measured with relatively strong external excitation. This result represents an enabling step towards operating such a high-Q acoustic device at the standard quantum limit.

Application of an Aligned and Unaligned Signal Processing Technique to Investigate Tones and Broadband Noise in Fan and Contra-Rotating Open Rotor Acoustic Spectra

Science.gov (United States)

Miles, Jeffrey Hilton; Hultgren, Lennart S.

2015-01-01

The study of noise from a two-shaft contra-rotating open rotor (CROR) is challenging since the shafts are not phase locked in most cases. Consequently, phase averaging of the acoustic data keyed to a single shaft rotation speed is not meaningful. An unaligned spectrum procedure that was developed to estimate a signal coherence threshold and reveal concealed spectral lines in turbofan engine combustion noise is applied to fan and CROR acoustic data in this paper (also available as NASA/TM-2015-218865). The NASA Advanced Air Vehicles Program, Advanced Air Transport Technology Project, Aircraft Noise Reduction Subproject supported the current work. The fan and open rotor data were obtained under previous efforts supported by the NASA Quiet Aircraft Technology (QAT) Project and the NASA Environmentally Responsible Aviation (ERA) Project of the Integrated Systems Research Program in collaboration with GE Aviation, respectively. The overarching goal of the Advanced Air Transport (AATT) Project is to explore and develop technologies and concepts to revolutionize the energy efficiency and environmental compatibility of fixed wing transport aircrafts. These technological solutions are critical in reducing the impact of aviation on the environment even as this industry and the corresponding global transportation system continue to grow.

Jet Noise Shielding Provided by a Hybrid Wing Body Aircraft

Science.gov (United States)

Doty, Michael J.; Brooks, Thomas F.; Burley, Casey L.; Bahr, Christopher J.; Pope, Dennis S.

2014-01-01

One approach toward achieving NASA's aggressive N+2 noise goal of 42 EPNdB cumulative margin below Stage 4 is through the use of novel vehicle configurations like the Hybrid Wing Body (HWB). Jet noise measurements from an HWB acoustic test in NASA Langley's 14- by 22-Foot Subsonic Tunnel are described. Two dual-stream, heated Compact Jet Engine Simulator (CJES) units are mounted underneath the inverted HWB model on a traversable support to permit measurement of varying levels of shielding provided by the fuselage. Both an axisymmetric and low noise chevron nozzle set are investigated in the context of shielding. The unshielded chevron nozzle set shows 1 to 2 dB of source noise reduction (relative to the unshielded axisymmetric nozzle set) with some penalties at higher frequencies. Shielding of the axisymmetric nozzles shows up to 6.5 dB of reduction at high frequency. The combination of shielding and low noise chevrons shows benefits beyond the expected additive benefits of the two, up to 10 dB, due to the effective migration of the jet source peak noise location upstream for increased shielding effectiveness. Jet noise source maps from phased array results processed with the Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) algorithm reinforce these observations.

Acoustic topological insulator and robust one-way sound transport

Science.gov (United States)

He, Cheng; Ni, Xu; Ge, Hao; Sun, Xiao-Chen; Chen, Yan-Bin; Lu, Ming-Hui; Liu, Xiao-Ping; Chen, Yan-Feng

2016-12-01

Topological design of materials enables topological symmetries and facilitates unique backscattering-immune wave transport. In airborne acoustics, however, the intrinsic longitudinal nature of sound polarization makes the use of the conventional spin-orbital interaction mechanism impossible for achieving band inversion. The topological gauge flux is then typically introduced with a moving background in theoretical models. Its practical implementation is a serious challenge, though, due to inherent dynamic instabilities and noise. Here we realize the inversion of acoustic energy bands at a double Dirac cone and provide an experimental demonstration of an acoustic topological insulator. By manipulating the hopping interaction of neighbouring ’atoms’ in this new topological material, we successfully demonstrate the acoustic quantum spin Hall effect, characterized by robust pseudospin-dependent one-way edge sound transport. Our results are promising for the exploration of new routes for experimentally studying topological phenomena and related applications, for example, sound-noise reduction.

SU-C-207B-02: Maximal Noise Reduction Filter with Anatomical Structures Preservation

Energy Technology Data Exchange (ETDEWEB)

Maitree, R; Guzman, G; Chundury, A; Roach, M; Yang, D [Washington University School of Medicine, St Louis, MO (United States)

2016-06-15

Purpose: All medical images contain noise, which can result in an undesirable appearance and can reduce the visibility of anatomical details. There are varieties of techniques utilized to reduce noise such as increasing the image acquisition time and using post-processing noise reduction algorithms. However, these techniques are increasing the imaging time and cost or reducing tissue contrast and effective spatial resolution which are useful diagnosis information. The three main focuses in this study are: 1) to develop a novel approach that can adaptively and maximally reduce noise while preserving valuable details of anatomical structures, 2) to evaluate the effectiveness of available noise reduction algorithms in comparison to the proposed algorithm, and 3) to demonstrate that the proposed noise reduction approach can be used clinically. Methods: To achieve a maximal noise reduction without destroying the anatomical details, the proposed approach automatically estimated the local image noise strength levels and detected the anatomical structures, i.e. tissue boundaries. Such information was used to adaptively adjust strength of the noise reduction filter. The proposed algorithm was tested on 34 repeating swine head datasets and 54 patients MRI and CT images. The performance was quantitatively evaluated by image quality metrics and manually validated for clinical usages by two radiation oncologists and one radiologist. Results: Qualitative measurements on repeated swine head images demonstrated that the proposed algorithm efficiently removed noise while preserving the structures and tissues boundaries. In comparisons, the proposed algorithm obtained competitive noise reduction performance and outperformed other filters in preserving anatomical structures. Assessments from the manual validation indicate that the proposed noise reduction algorithm is quite adequate for some clinical usages. Conclusion: According to both clinical evaluation (human expert ranking) and

SU-C-207B-02: Maximal Noise Reduction Filter with Anatomical Structures Preservation

International Nuclear Information System (INIS)

Maitree, R; Guzman, G; Chundury, A; Roach, M; Yang, D

2016-01-01

Purpose: All medical images contain noise, which can result in an undesirable appearance and can reduce the visibility of anatomical details. There are varieties of techniques utilized to reduce noise such as increasing the image acquisition time and using post-processing noise reduction algorithms. However, these techniques are increasing the imaging time and cost or reducing tissue contrast and effective spatial resolution which are useful diagnosis information. The three main focuses in this study are: 1) to develop a novel approach that can adaptively and maximally reduce noise while preserving valuable details of anatomical structures, 2) to evaluate the effectiveness of available noise reduction algorithms in comparison to the proposed algorithm, and 3) to demonstrate that the proposed noise reduction approach can be used clinically. Methods: To achieve a maximal noise reduction without destroying the anatomical details, the proposed approach automatically estimated the local image noise strength levels and detected the anatomical structures, i.e. tissue boundaries. Such information was used to adaptively adjust strength of the noise reduction filter. The proposed algorithm was tested on 34 repeating swine head datasets and 54 patients MRI and CT images. The performance was quantitatively evaluated by image quality metrics and manually validated for clinical usages by two radiation oncologists and one radiologist. Results: Qualitative measurements on repeated swine head images demonstrated that the proposed algorithm efficiently removed noise while preserving the structures and tissues boundaries. In comparisons, the proposed algorithm obtained competitive noise reduction performance and outperformed other filters in preserving anatomical structures. Assessments from the manual validation indicate that the proposed noise reduction algorithm is quite adequate for some clinical usages. Conclusion: According to both clinical evaluation (human expert ranking) and

Aircraft Engine Noise Research and Testing at the NASA Glenn Research Center

Science.gov (United States)

Elliott, Dave

2015-01-01

The presentation will begin with a brief introduction to the NASA Glenn Research Center as well as an overview of how aircraft engine noise research fits within the organization. Some of the NASA programs and projects with noise content will be covered along with the associated goals of aircraft noise reduction. Topics covered within the noise research being presented will include noise prediction versus experimental results, along with engine fan, jet, and core noise. Details of the acoustic research conducted at NASA Glenn will include the test facilities available, recent test hardware, and data acquisition and analysis methods. Lastly some of the actual noise reduction methods investigated along with their results will be shown.

Psycho-acoustic evaluation of the indoor noise in cabins of a naval vessel using a back-propagation neural network algorithm

Directory of Open Access Journals (Sweden)

Hyung-Suk Han

2012-12-01

Full Text Available The indoor noise of a ship is usually determined using the A-weighted sound pressure level. However, in order to better understand this phenomenon, evaluation parameters that more accurately reflect the human sense of hearing are required. To find the level of the satisfaction index of the noise inside a naval vessel such as “Loudness” and “Annoyance”, psycho-acoustic evaluation of various sound recordings from the naval vessel was performed in a laboratory. The objective of this paper is to develop a single index of “Loudness” and “Annoyance” for noise inside a naval vessel according to a psycho-acoustic evaluation by using psychological responses such as Noise Rating (NR, Noise Criterion (NC, Room Criterion (RC, Preferred Speech Interference Level (PSIL and loudness level. Additionally, in order to determine a single index of satisfaction for noise such as “Loudness” and “Annoyance”, with respect to a human's sense of hearing, a back-propagation neural network is applied.

Noise Reduction Effect of Multiple-Sampling-Based Signal-Readout Circuits for Ultra-Low Noise CMOS Image Sensors

Directory of Open Access Journals (Sweden)

Shoji Kawahito

2016-11-01

Full Text Available This paper discusses the noise reduction effect of multiple-sampling-based signal readout circuits for implementing ultra-low-noise image sensors. The correlated multiple sampling (CMS technique has recently become an important technology for high-gain column readout circuits in low-noise CMOS image sensors (CISs. This paper reveals how the column CMS circuits, together with a pixel having a high-conversion-gain charge detector and low-noise transistor, realizes deep sub-electron read noise levels based on the analysis of noise components in the signal readout chain from a pixel to the column analog-to-digital converter (ADC. The noise measurement results of experimental CISs are compared with the noise analysis and the effect of noise reduction to the sampling number is discussed at the deep sub-electron level. Images taken with three CMS gains of two, 16, and 128 show distinct advantage of image contrast for the gain of 128 (noise(median: 0.29 e−rms when compared with the CMS gain of two (2.4 e−rms, or 16 (1.1 e−rms.

An intervention for noise control of blast furnace in steel industry.

Science.gov (United States)

Golmohammadi, Rostam; Giahi, Omid; Aliabadi, Mohsen; Darvishi, Ebrahim

2014-01-01

Noise pollution is currently a major health risk factor for workers in industries. The aim of this study was to investigate noise pollution and implement a control intervention plan for blast furnace in a steel industry. The measurement of sound pressure level (SPL) along with frequency analysis was done with the sound-level-meter Cell-450. Personal noise exposure was performed using dosimeter TES-1345 calibrated with CEL-282. Before planning noise controls, acoustic insulation properties of the furnace control unit and workers' rest room were assessed. Control room and workers' rest room were redesigned in order to improve acoustical condition. The SPL before intervention around the Blast Furnace was 90.3 dB (L) and its dominant frequency was 4000 Hz. Besides, noise transmission loss of the control and rest rooms were 10.3 dB and 4.2 dB, respectively. After intervention, noise reduction rates in the control and rest rooms were 27.4 dB and 27.7 dB, respectively. The workers' noise dose before and after the intervention was 240% and less than 100%, respectively. Improvement the workroom acoustic conditions through noise insulation can be considered effective method for preventing workers exposure to harmful noise.

On the numerical investigation of sound transmission through double-walled structures with membrane-type acoustic metamaterials.

Science.gov (United States)

Marinova, Polina; Lippert, Stephan; von Estorff, Otto

2017-10-01

Acoustic metamaterials appear to be of great help in the design of reliable and effective noise reduction measures in the low frequency range. The current contribution is concerned with the modeling of a low-frequency noise shield, based on a double wall arrangement, which includes membrane-type acoustic metamaterials (MAMs), considered as the most promising approach when it comes especially to the tonal noise at frequencies below 300 Hz. MAMs consist of small-sized membranes loaded with a mass. Due to their robustness and relatively simple production, MAMs have been proven to decrease the sound transmission in frequency ranges, for which poro-elastic materials have a rather negligible effect. A simulation model of a double wall panel, whose acoustic cavity is furnished with layers of metamaterials, has been developed and the sound transmission loss (STL) through the structure was calculated, using the finite element method. In order to validate the modelling approach, the STL estimation from the finite element analysis was compared to experimental measurements. The achieved results indicate a noise-decreasing possibility in tunable narrow bands as well as a broadband noise reduction for frequencies less than 300 Hz without significantly adding to the panel mass.

Experimental Research into Noise Emission of A Gear Micropump with Plastic Rotor

Science.gov (United States)

Rodionov, L. V.; Rekadze, P. D.

2018-01-01

The previous researches show that it’s possible to replace several parts of gear pump to plastic ones. This substitution leads to cost and noise reduction of the pump. Therefore, the series of acoustic experiments on a test bench were carry-out. Sound pressure levels were recorded with microphone, located in a pipe made of a vacuum rubber. Conducted experiment shows that acoustic characteristics of the micropump depend on the different material of driven rotor. Experimental result indicates that the proposed measures for replacing metal rotor to plastic one reduce micropump noise on the studied modes. The maximum achieved acoustic efficiency on equivalent level is 11 dB.

Reduced In-Plane, Low Frequency Helicopter Noise of an Active Flap Rotor

Science.gov (United States)

Sim, Ben W.; Janakiram, Ram D.; Barbely, Natasha L.; Solis, Eduardo

2009-01-01

Results from a recent joint DARPA/Boeing/NASA/Army wind tunnel test demonstrated the ability to reduce in-plane, low frequency noise of the full-scale Boeing-SMART rotor using active flaps. Test data reported in this paper illustrated that acoustic energy in the first six blade-passing harmonics could be reduced by up to 6 decibels at a moderate airspeed, level flight condition corresponding to advance ratio of 0.30. Reduced noise levels were attributed to selective active flap schedules that modified in-plane blade airloads on the advancing side of the rotor, in a manner, which generated counteracting acoustic pulses that partially offset the negative pressure peaks associated with in-plane, steady thickness noise. These favorable reduced-noise operating states are a strong function of the active flap actuation amplitude, frequency and phase. The associated noise reductions resulted in reduced aural detection distance by up to 18%, but incurred significant vibratory load penalties due to increased hub shear forces. Small reductions in rotor lift-to-drag ratios, of no more than 3%, were also measured

Noise-based tube current reduction method with iterative reconstruction for reduction of radiation exposure in coronary CT angiography

International Nuclear Information System (INIS)

Shen, Junlin; Du, Xiangying; Guo, Daode; Cao, Lizhen; Gao, Yan; Bai, Mei; Li, Pengyu; Liu, Jiabin; Li, Kuncheng

2013-01-01

Purpose: To investigate the potential of noise-based tube current reduction method with iterative reconstruction to reduce radiation exposure while achieving consistent image quality in coronary CT angiography (CCTA). Materials and methods: 294 patients underwent CCTA on a 64-detector row CT equipped with iterative reconstruction. 102 patients with fixed tube current were assigned to Group 1, which was used to establish noise-based tube current modulation formulas, where tube current was modulated by the noise of test bolus image. 192 patients with noise-based tube current were randomly assigned to Group 2 and Group 3. Filtered back projection was applied for Group 2 and iterative reconstruction for Group 3. Qualitative image quality was assessed with a 5 point score. Image noise, signal intensity, volume CT dose index, and dose-length product were measured. Results: The noise-based tube current modulation formulas were established through regression analysis using image noise measurements in Group 1. Image noise was precisely maintained at the target value of 35.00 HU with small interquartile ranges for Group 2 (34.17–35.08 HU) and Group 3 (34.34–35.03 HU), while it was from 28.41 to 36.49 HU for Group 1. All images in the three groups were acceptable for diagnosis. A relative 14% and 41% reduction in effective dose for Group 2 and Group 3 were observed compared with Group 1. Conclusion: Adequate image quality could be maintained at a desired and consistent noise level with overall 14% dose reduction using noise-based tube current reduction method. The use of iterative reconstruction further achieved approximately 40% reduction in effective dose

Adaptive noise reduction circuit for a sound reproduction system

Science.gov (United States)

Engebretson, A. Maynard (Inventor); O'Connell, Michael P. (Inventor)

1995-01-01

A noise reduction circuit for a hearing aid having an adaptive filter for producing a signal which estimates the noise components present in an input signal. The circuit includes a second filter for receiving the noise-estimating signal and modifying it as a function of a user's preference or as a function of an expected noise environment. The circuit also includes a gain control for adjusting the magnitude of the modified noise-estimating signal, thereby allowing for the adjustment of the magnitude of the circuit response. The circuit also includes a signal combiner for combining the input signal with the adjusted noise-estimating signal to produce a noise reduced output signal.

Passive Techniques for Fan Noise Reduction in New Turbofan Engines: Review

Directory of Open Access Journals (Sweden)

M.Gorj-Bandpy

2013-03-01

Full Text Available Among the various environmental concerns, the aircraft noise item has been constantly growing in importance over the past years. Measures for its reduction at the source as well its mitigation around airports must take into account aspects of medicine and technical design as well as legal and land use planning aspects. Fan noise is one of the principal noise sources in turbofan aero-engines. In this paper a review of the main technologies employed for the reduction of fan noise turbofan engines is presented.

Noise reduction by wavelet thresholding

National Research Council Canada - National Science Library

Jansen, Maarten

2001-01-01

.... I rather present new material and own insights in the que stions involved with wavelet based noise reduction . On the other hand , the presented material does cover a whole range of methodologies, and in that sense, the book may serve as an introduction into the domain of wavelet smoothing. Throughout the text, three main properties show up ever again: spar...

Active Control of Fan Noise: Feasibility Study. Volume 3; Active Fan Noise Cancellation in the NASA Lewis Active Noise Control Fan Facility

Science.gov (United States)

Pla, Frederic G.; Hu, Ziqiang; Sutliff, Daniel L.

1996-01-01

This report describes the Active Noise Cancellation (ANC) System designed by General Electric and tested in the NASA Lewis Research Center's (LERC) 48 inch Active Noise Control Fan (ANCF). The goal of this study is to assess the feasibility of using wall mounted secondary acoustic sources and sensors within the duct of a high bypass turbofan aircraft engine for global active noise cancellation of fan tones. The GE ANC system is based on a modal control approach. A known acoustic mode propagating in the fan duct is canceled using an array of flush-mounted compact sound sources. The canceling modal signal is generated by a modal controller. Inputs to the controller are signals from a shaft encoder and from a microphone array which senses the residual acoustic mode in the duct. The key results are that the (6,0) was completely eliminated at the 920 Hz design frequency and substantially reduced elsewhere. The total tone power was reduced 6.8 dB (out of a possible 9.8 dB). Farfield reductions of 15 dB (SPL) were obtained. The (4,0) and (4,1) modes were reduced simultaneously yielding a 15 dB PWL decrease. The results indicate that global attenuation of PWL at the target frequency was obtained in the aft quadrant using an ANC actuator and sensor system totally contained within the duct. The quality of the results depended on precise mode generation. High spillover into spurious modes generated by the ANC actuator array caused less than optimum levels of PWL reduction. The variation in spillover is believed to be due to calibration procedure, but must be confirmed in subsequent tests.

Noise reduction in a Mach 5 wind tunnel with a rectangular rod-wall sound shield

Science.gov (United States)

Creel, T. R., Jr.; Keyes, J. W.; Beckwith, I. E.

1980-01-01

A rod wall sound shield was tested over a range of Reynolds numbers of 0.5 x 10 to the 7th power to 8.0 x 10 to the 7th power per meter. The model consisted of a rectangular array of longitudinal rods with boundary-layer suction through gaps between the rods. Suitable measurement techniques were used to determine properties of the flow and acoustic disturbance in the shield and transition in the rod boundary layers. Measurements indicated that for a Reynolds number of 1.5 x 10 to the 9th power the noise in the shielded region was significantly reduced, but only when the flow is mostly laminar on the rods. Actual nozzle input noise measured on the nozzle centerline before reflection at the shield walls was attenuated only slightly even when the rod boundary layer were laminar. At a lower Reynolds number, nozzle input noise at noise levels in the shield were still too high for application to a quiet tunnel. At Reynolds numbers above 2.0 x 10 the the 7th power per meter, measured noise levels were generally higher than nozzle input levels, probably due to transition in the rod boundary layers. The small attenuation of nozzle input noise at intermediate Reynolds numbers for laminar rod layers at the acoustic origins is apparently due to high frequencies of noise.

Virtual sensors for active noise control in acoustic-structural coupled enclosures using structural sensing: part II--Optimization of structural sensor placement.

Science.gov (United States)

Halim, Dunant; Cheng, Li; Su, Zhongqing

2011-04-01

The work proposed an optimization approach for structural sensor placement to improve the performance of vibro-acoustic virtual sensor for active noise control applications. The vibro-acoustic virtual sensor was designed to estimate the interior sound pressure of an acoustic-structural coupled enclosure using structural sensors. A spectral-spatial performance metric was proposed, which was used to quantify the averaged structural sensor output energy of a vibro-acoustic system excited by a spatially varying point source. It was shown that (i) the overall virtual sensing error energy was contributed additively by the modal virtual sensing error and the measurement noise energy; (ii) each of the modal virtual sensing error system was contributed by both the modal observability levels for the structural sensing and the target acoustic virtual sensing; and further (iii) the strength of each modal observability level was influenced by the modal coupling and resonance frequencies of the associated uncoupled structural/cavity modes. An optimal design of structural sensor placement was proposed to achieve sufficiently high modal observability levels for certain important panel- and cavity-controlled modes. Numerical analysis on a panel-cavity system demonstrated the importance of structural sensor placement on virtual sensing and active noise control performance, particularly for cavity-controlled modes.

Development of a Multifidelity Approach to Acoustic Liner Impedance Eduction

Science.gov (United States)

Nark, Douglas M.; Jones, Michael G.

2017-01-01

The use of acoustic liners has proven to be extremely effective in reducing aircraft engine fan noise transmission/radiation. However, the introduction of advanced fan designs and shorter engine nacelles has highlighted a need for novel acoustic liner designs that provide increased fan noise reduction over a broader frequency range. To achieve aggressive noise reduction goals, advanced broadband liner designs, such as zone liners and variable impedance liners, will likely depart from conventional uniform impedance configurations. Therefore, educing the impedance of these axial- and/or spanwise-variable impedance liners will require models that account for three-dimensional effects, thereby increasing computational expense. Thus, it would seem advantageous to investigate the use of multifidelity modeling approaches to impedance eduction for these advanced designs. This paper describes an extension of the use of the CDUCT-LaRC code to acoustic liner impedance eduction. The proposed approach is applied to a hardwall insert and conventional liner using simulated data. Educed values compare well with those educed using two extensively tested and validated approaches. The results are very promising and provide justification to further pursue the complementary use of CDUCT-LaRC with the currently used finite element codes to increase the efficiency of the eduction process for configurations involving three-dimensional effects.

Noise reduction in optically controlled quantum memory

Science.gov (United States)

Ma, Lijun; Slattery, Oliver; Tang, Xiao

2018-05-01

Quantum memory is an essential tool for quantum communications systems and quantum computers. An important category of quantum memory, called optically controlled quantum memory, uses a strong classical beam to control the storage and re-emission of a single-photon signal through an atomic ensemble. In this type of memory, the residual light from the strong classical control beam can cause severe noise and degrade the system performance significantly. Efficiently suppressing this noise is a requirement for the successful implementation of optically controlled quantum memories. In this paper, we briefly introduce the latest and most common approaches to quantum memory and review the various noise-reduction techniques used in implementing them.

Perceptual effects of noise reduction by time-frequency masking of noisy speech.

Science.gov (United States)

Brons, Inge; Houben, Rolph; Dreschler, Wouter A

2012-10-01

Time-frequency masking is a method for noise reduction that is based on the time-frequency representation of a speech in noise signal. Depending on the estimated signal-to-noise ratio (SNR), each time-frequency unit is either attenuated or not. A special type of a time-frequency mask is the ideal binary mask (IBM), which has access to the real SNR (ideal). The IBM either retains or removes each time-frequency unit (binary mask). The IBM provides large improvements in speech intelligibility and is a valuable tool for investigating how different factors influence intelligibility. This study extends the standard outcome measure (speech intelligibility) with additional perceptual measures relevant for noise reduction: listening effort, noise annoyance, speech naturalness, and overall preference. Four types of time-frequency masking were evaluated: the original IBM, a tempered version of the IBM (called ITM) which applies limited and non-binary attenuation, and non-ideal masking (also tempered) with two different types of noise-estimation algorithms. The results from ideal masking imply that there is a trade-off between intelligibility and sound quality, which depends on the attenuation strength. Additionally, the results for non-ideal masking suggest that subjective measures can show effects of noise reduction even if noise reduction does not lead to differences in intelligibility.

SELECTED PROBLEMS OF PROTECTION AGAINST ROAD TRAFFIC NOISE

Directory of Open Access Journals (Sweden)

Władysław Gardziejczyk

2015-11-01

Full Text Available The paper presents factors for assessment of road traffic noise level and possible actions towards the minimization of excessive noise in the roadway neighborhood. Changes of equivalent sound level values were analyzed in relation to traffic intensity, categorization and vehicles speed. In relation to measures reducing noise level in roadway’s surroundings particular attention was given to anti-noise protections and tyre/noise reduction. Acoustic effectiveness of specific solutions was showed based on chosen examples. It was proved that when admissible noise level is slightly exceeded the need for noise barrier use may be replaced by a proper design and maintenance of road pavement or by enforcement of speed limit.

40 CFR 211.207 - Computation of the noise -reduction rating (NRR).

Science.gov (United States)

2010-07-01

... 40 Protection of Environment 24 2010-07-01 2010-07-01 false Computation of the noise -reduction... of the noise -reduction rating (NRR). Calculate the NRR for hearing protective devices by... “A”-weighting relative response corrections applied to any sound levels at the indicated octave band...

Active Control of Fan Noise-Feasibility Study. Volume 2: Canceling Noise Source-Design of an Acoustic Plate Radiator Using Piezoceramic Actuators

Science.gov (United States)

Pla, F. G.; Rajiyah, H.

1995-01-01

The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling sources for active control of aircraft engine fan noise is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy acoustic plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of acoustic plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable acoustic source for active control of aircraft engine fan noise.

Passive noise control by enhancing aeroacoustic interference due to structural discontinuities in close proximity

Science.gov (United States)

Leung, R. C. K.; So, R. M. C.; Tang, S. K.; Wang, X. Q.

2011-07-01

In-duct devices are commonly installed in flow ducts for various flow management purposes. The structural construction of these devices indispensably creates disruption to smooth flow through duct passages so they exist as structural discontinuities in duct flow. The presence of these discontinuities provides additional possibility of noise generation. In real practice, in-duct devices do not exist alone in any duct system. Even though each in-duct device would generate its own noise, it might be possible that these devices could be properly arranged so as to strengthen the interference between individual noise; thus giving rise to an overall reduction of noise radiation in the in-duct far field. This concept of passive noise control is investigated by considering different configurations of two structural discontinuities of simple form (i.e., a cavity) in tandem in an unconfined flow and in opposing setting within a flow duct. It is known that noise generated by a cavity in unconfined domain (unconfined cavity) is strongly dependent on flow-resonant behavior within the cavity so the interference it produces is merely aeroacoustic. The objective of the present study is to verify the concept of passive noise reduction through enhancement of aeroacoustic interference due to two cavities by considering laminar flow only. A two-dimensional approach is adopted for the direct aeroacoustic calculations using a direct numerical simulation (DNS) technique. The position and geometries of the cavities and the Mach number are varied; the resultant aeroacoustic behavior and acoustic power are calculated. The numerical results are compared with a single cavity case to highlight the effect of introducing additional cavities to the aeroacoustic problem. Resonant flow oscillations occur when two unconfined cavities are very close and the associated acoustic field is very intense with no noise reduction possible. However, for duct aeroacoustics, it is found that a 7.9 db reduction

Research on Noise Reduction of Reed Valves of a Hermetic Refrigerator Compressor

Science.gov (United States)

He, Zhilong; Chen, Qian; Li, Dantong; Wang, Ju; Xia, Pu; Wang, Tao

2017-08-01

The noise level of the refrigerator compressor has received more and more attention in recent years. As the key component of a compressor, reed valve is its main noise source. In this paper, a new noise reduction technology of coating on reed valve surface is proposed and verified by experiments. Firstly, the reed valves were coated, and their surface characteristics were checked. Then, the refrigerator compressor p-V diagram test was carried out to investigate the influence of doped diamond-like carbon (DLC) coating on power consumption. Finally, the noise test rig for the refrigerator compressor was set up. Based on the standard test method, noise spectrum was measured in a semi-anechoic room under standard working condition. Research results showed that the compressor noise was significantly reduced by 1.8dB (A) after coating. Moreover, the effect of aerodynamic noise reduction at suction side is better than that at discharge side. However, the influence of the film thickness on noise reduction value is little. The COP was reduced by 0.6% as compared to the compressor with uncoated reed valves.

Increase of Investment Appeal of Projects for Noise Control Measures in Urban Environment

Science.gov (United States)

Kolmakov, A. V.; Ignatyeva, V. O.

2017-11-01

The authors analyzed the contemporary noise pollution level in the large cities of the Russian Federation. The article identifies the factors causing the reduction of acoustically comfortable urban territories. It states the task for the increase of investment appeal of the projects aimed at noise control measures adoption.

Noise abatement in air-water heat pump systems. Basic considerations, guidelines for practice; Laermreduktion bei Luft/Wasser-Waermepumpenanlagen. Grundlagen und Massnahmen

Energy Technology Data Exchange (ETDEWEB)

Graf, H.R.

2002-07-01

With increasing numbers of installations of air/water heat pumps the issue of noise emissions is becoming more of a concern. In reaction to this situation, the company Sulzer Innotec has developed these guidelines by order of the Swiss Federal Office of Energy. Typically, more than 90% of the noise emitted outdoors is produced by the fan. Due to the strong tonal components, the noise emitted is substantially more annoying than a reference broadband noise of the same intensity. For further noise reduction mainly the fan noise must be addressed. Despite the dominance of fan noise, other noise sources must not be neglected. The most promising countermeasures are: Reduction of fan noise by (i) low blade tip speed (prerequisite is a pressure drop in the air channels including the evaporator as low as possible), (ii) improvement of flow geometry in the vicinity of the fan, (iii) insulation of air ducts with acoustic foam (thickness 50 mm or more), (iv) elbows in the air duct line for sound dissipation. Reduction of compressor noise by (i) a highly effective acoustic enclosure, (ii) vibration insulation of structure-borne noise by elastic mounts, (iii) decoupling of refrigerant pipes. (author)

Joint models for noise annoyance and willingness to pay for road noise reduction

DEFF Research Database (Denmark)

Fosgerau, Mogens; Bue Bjørner, Thomas

2006-01-01

Recent contingent valuation (CV) studies of the willingness to pay (WTP) for road noise reduction have used stated annoyance as an independent variable. We argue that this may be inappropriate due to potential endogeneity bias. Instead, an alternative model is proposed that treats both WTP...... and annoyance as endogenous variables in a simultaneous equation model as a combination of a linear regression with an ordered probit with correlated error terms and possibly common parameters. Thus, information on stated annoyance is utilised to estimate WTP with increased efficiency. Application of the model...... to a dataset from Copenhagen indicates a potential for improving the precision of the estimate of WTP for noise reduction with CV data....

Control source development for reduction of noise transmitted through a double panel structure

OpenAIRE

Ho, J.

2014-01-01

A double panel structure, which consists of two panels with air in between, is widely adopted in many applications such as aerospace, automotive industries, and buildings due to its low sound transmission at high frequencies, low heat transmission, and low weight. Nevertheless, the resonance of the cavity and the poor sound transmission loss at low frequencies limit the double panel’s noise control performance. Applying active structural acoustic control to the panels or active noise control ...

Study of the characteristics of water into sodium leak acoustic noise in LMR steam generator

International Nuclear Information System (INIS)

Kim, Tae Joon; Jeong, Kyung Chai; Jeong, Ji Young; Hur, Seop; Nam, Ho Yun

2005-01-01

A successful time for detecting a water/steam leak into sodium in the LMR SG (steam generator) at an early phase of a leak origin depends on the fast response and sensitivity of a leak detection system. It is considered, that the acoustic system is intended for a fast detecting of a water/steam into sodium leak of an intermediate flow rate, 1∼10 g/s. This intention of an acoustic system is stipulated by a key impossibility of a fast detecting of an intermediate leak by the present nominal systems on measuring the hydrogen in the sodium and in the cover gas concentration generated at a leak. During the self-wastage of a water/steam into sodium leak in a particular instant, it is usual in 30∼40 minutes from the moment of a leak origin, there is a modification of a leak flow out regime from bubble regime to the steam jet outflow. This evolution occurs as a jump function of the self-wastage of a leak and is escorted by an increase of a leak noise power and qualitative change of a leak noise spectrum. Subject of this study is by means of two experiments, one is an acoustic leak noise analysis of the water into sodium leak results in no damage to the LMR SG tube bundle, and another is for prediction of the frequency band under a high outflow leak condition. We experimented with the Argon gas injection considered with the phenomena of secondary leaks in real

Noise Reduction in the Time Domain using Joint Diagonalization

DEFF Research Database (Denmark)

Nørholm, Sidsel Marie; Benesty, Jacob; Jensen, Jesper Rindom

2014-01-01

, an estimate of the desired signal is found by subtraction of the noise estimate from the observed signal. The filter can be designed to obtain a desired trade-off between noise reduction and signal distortion, depending on the number of eigenvectors included in the filter design. This is explored through...... simulations using a speech signal corrupted by car noise, and the results confirm that the output signal-to-noise ratio and speech distortion index both increase when more eigenvectors are included in the filter design....

Damping layout optimization for ship's cabin noise reduction based on statistical energy analysis

Directory of Open Access Journals (Sweden)

WU Weiguo

2017-08-01

Full Text Available An optimization analysis study concerning the damping control of ship's cabin noise was carried out in order to improve the effect and reduce the weight of damping. Based on the Statistical Energy Analysis (SEA method, a theoretical deduction and numerical analysis of the first-order sensitivity analysis of the A-weighted sound pressure level concerning the damping loss factor of the subsystem were carried out. On this basis, a mathematical optimization model was proposed and an optimization program developed. Next, the secondary development of VA One software was implemented through the use of MATLAB, while the cabin noise damping control layout optimization system was established. Finally, the optimization model of the ship was constructed and numerical experiments of damping control optimization conducted. The damping installation region was divided into five parts with different damping thicknesses. The total weight of damping was set as an objective function and the A-weighted sound pressure level of the target cabin was set as a constraint condition. The best damping thickness was obtained through the optimization program, and the total damping weight was reduced by 60.4%. The results show that the damping noise reduction effect of unit weight is significantly improved through the optimization method. This research successfully solves the installation position and thickness selection problems in the acoustic design of damping control, providing a reliable analysis method and guidance for the design.

Intensity of noise in the classroom and analysis of acoustic emissions in schoolchildren

Directory of Open Access Journals (Sweden)

Almeida Filho, Nelson de

2012-01-01

Full Text Available Introduction: Noise-induced hearing loss is a sensorineural hearing loss, usually bilateral, irreversible and progressive with time of exposure. As the noise made by children in school may be considered detrimental, the study looks of their occurrence in Taubaté's schools. Objective: To determine if students are exposed to noise intensity affecting the cochlea, define the profile of these schoolchildren, demonstrating the occurrence of changes in cochlear activity following exposure to noise in a day of class. Method: Study's way prospective transversal cross sectional cut with 28 elementary school students in the first half of 2009. Questionnaires for assessing preexisting cochlear damage . Evaluation of cochlear function by analysis of acoustic emissions evoked distortion product, made before the students come into class and immediately after the end of these. Measurement of noise inside the classrooms and recreation areas during the interval. Results: 57.1% accused some hearing loss in the examinations before class. By day's end, 04 girls and 03 boys had worsened in relation of the first examination. The noise reached levels higher than recommended at the three class rooms. The largest number of students with worsening, belong to the class room with higher noise level. The noise during the intervals is also excessive. Conclusions: The noise in this school is above the limit. 42.85% of students who had experienced worsening had school performance inadequate. 25% had worse after noise exposure in a school day.

Modeling of the acoustic boiling noise of sodium during an assembly blockage in sodium-cooled reactors

International Nuclear Information System (INIS)

Vanderhaegen, M.

2013-01-01

In the framework of the fourth generation of nuclear reactors safety requirements, the acoustic boiling detection is studied to detect subassembly blockages. Boiling, that might occur during subassembly blockages and that can lead to clad failure, generates hydrodynamic noise that can be related to the two-phase flow. A bubble dynamics study shows that the sound source during subassembly boiling is condensation. This particular phenomenon generates most noise as a high subcooling is present in the subassembly and because of the high thermal diffusivity of sodium. This result leads to an estimate of the form of the acoustic spectrum that will be filtered and amplified during propagation inside the liquid. And even though it is unlikely that bubbles will be present inside the subassembly, due to the very gradual temperature profile at the wall and due to the geometry that leads to a strong confinement of the vapor, the historical bubble dynamics approach gives some insight in previous measurements. Additionally, some hypotheses can be disproved. These theoretical ideas are validated with a small water experiment, yet it also shows that a simple experience in sodium doesn't lead to a better knowledge of the acoustic source. A theoretical analysis also revealed that a realistic experiment with a simulant fluid, such as water or mercury, isn't representative. A similar conclusion is obtained when studying cavitation as a simulant acoustic source. As such, the acoustic detection of boiling, in comparison with other detection systems, isn't sufficiently developed yet to be applied as a reactor protective system. (author) [fr

THE USE OF NOISE MAPS AND PLANNING TOOLS IN THE MANAGEMENT OF AN ACOUSTIC CLIMATE IN AN URBAN AREA

Directory of Open Access Journals (Sweden)

Tomasz Zubala

2016-09-01

Full Text Available Nowadays, noise is considered as one of the most significant factors polluting the environment. It is classified in the first place among the indicators of the comfort of home, leisure and work. Therefore, more and more attention is paid to the need to study the sources and effects of noise on the environment and to develop effective methods of protection against nuisance and harmful sounds. Analysis of environmental factors is an especially important part of the process of spatial planning. The article covers characteristics of spatial and temporal differentiation of acoustic phenomena occurring within selected district of Lublin – the largest Polish city east of the Vistula River. Field measurements and analytical operations, which enable mapping noise, and consequently measuring the exposure of residents to the impact of abnormal sound levels, were made. There was also an attempt to evaluate the spatial development and its relationship with prevailing acoustic conditions. The collected results allowed developing recommendations for planning the city centre area acting as a standard. The need to design buffer zones to reduce the sound level near roads or locating residential areas away from sources of noise was underlined. The study should prove helpful in forecasting changes in the acoustic conditions and spatial planning and deciding on protection measures in urban areas.

Effect of scanner acoustic background noise on strict resting-state fMRI

Directory of Open Access Journals (Sweden)

C. Rondinoni

2013-04-01

Full Text Available Functional MRI (fMRI resting-state experiments are aimed at identifying brain networks that support basal brain function. Although most investigators consider a ‘resting-state' fMRI experiment with no specific external stimulation, subjects are unavoidably under heavy acoustic noise produced by the equipment. In the present study, we evaluated the influence of auditory input on the resting-state networks (RSNs. Twenty-two healthy subjects were scanned using two similar echo-planar imaging sequences in the same 3T MRI scanner: a default pulse sequence and a reduced “silent” pulse sequence. Experimental sessions consisted of two consecutive 7-min runs with noise conditions (default or silent counterbalanced across subjects. A self-organizing group independent component analysis was applied to fMRI data in order to recognize the RSNs. The insula, left middle frontal gyrus and right precentral and left inferior parietal lobules showed significant differences in the voxel-wise comparison between RSNs depending on noise condition. In the presence of low-level noise, these areas Granger-cause oscillations in RSNs with cognitive implications (dorsal attention and entorhinal, while during high noise acquisition, these connectivities are reduced or inverted. Applying low noise MR acquisitions in research may allow the detection of subtle differences of the RSNs, with implications in experimental planning for resting-state studies, data analysis, and ergonomic factors.

Effect of scanner acoustic background noise on strict resting-state fMRI.

Science.gov (United States)

Rondinoni, C; Amaro, E; Cendes, F; dos Santos, A C; Salmon, C E G

2013-04-01

Functional MRI (fMRI) resting-state experiments are aimed at identifying brain networks that support basal brain function. Although most investigators consider a 'resting-state' fMRI experiment with no specific external stimulation, subjects are unavoidably under heavy acoustic noise produced by the equipment. In the present study, we evaluated the influence of auditory input on the resting-state networks (RSNs). Twenty-two healthy subjects were scanned using two similar echo-planar imaging sequences in the same 3T MRI scanner: a default pulse sequence and a reduced "silent" pulse sequence. Experimental sessions consisted of two consecutive 7-min runs with noise conditions (default or silent) counterbalanced across subjects. A self-organizing group independent component analysis was applied to fMRI data in order to recognize the RSNs. The insula, left middle frontal gyrus and right precentral and left inferior parietal lobules showed significant differences in the voxel-wise comparison between RSNs depending on noise condition. In the presence of low-level noise, these areas Granger-cause oscillations in RSNs with cognitive implications (dorsal attention and entorhinal), while during high noise acquisition, these connectivities are reduced or inverted. Applying low noise MR acquisitions in research may allow the detection of subtle differences of the RSNs, with implications in experimental planning for resting-state studies, data analysis, and ergonomic factors.

Room acoustic analysis of blower unit and noise control plan in the typical steel industry

Directory of Open Access Journals (Sweden)

2013-02-01

Full Text Available Introduction: In the steel industry,air blowers used to supply compressed air are considered as sources of annoying noise. This study aims to acoustics analysis of theairblower workroomand sound source characteristics in order to present noise controlmeasuresinthe steel industry. .Material and Method: Measurement of noiselevel and its frequency analysis was performed usingsound levelmetermodelof CASELLA-Cell.450. Distribution of noise level in the investigated workroom in form of noise map was provided using Surfer software. In addition, acoustic analysis of workroom and control room was performed in view point of soundabsorption andinsulation. Redesignofdoor and window of controlroom and installation of soundabsorbing materialson theceiling of the workroom were proposed and the efficiency of these interventionswasestimated. .Result: The totalsound pressurelevelin the blower workroom was 95.4 dB(L and the dominant frequency was 2000Hz. Sound pressure level inside the room control was 80.1dB(A. The average absorption coefficient and reverberation time in the blower workroom was estimated equal to 0.082 Sab.m2 and 3.9 seconds respectively. These value in control room was 0.04 Sab.m2 and 3/4 seconds respectively. In control room, sound transmission loss between the two parts of the wall dividing was 13.7 dB(A. The average of noise dose in blower operators was 230%. With the installation of sound absorber on ceiling of workroom, average of absorption coefficient can increase to 0.33 Sab.m2 and sound transmission loss of the new designed door and window was estimated equal to 20dB. . Conclusion: The main cause of noise leakage in the control room was insufficient insulation properties of door and windows. By replacing the door and window and installation of sound absorbing on ceiling of workroom, the noise dose can reduce to 49.6%. New Improved door and window of control room can reduce noise dose to 69.65% solely.

Dynamical reduction models with general gaussian noises

International Nuclear Information System (INIS)

Bassi, Angelo; Ghirardi, GianCarlo

2002-02-01

We consider the effect of replacing in stochastic differential equations leading to the dynamical collapse of the statevector, white noise stochastic processes with non white ones. We prove that such a modification can be consistently performed without altering the most interesting features of the previous models. One of the reasons to discuss this matter derives from the desire of being allowed to deal with physical stochastic fields, such as the gravitational one, which cannot give rise to white noises. From our point of view the most relevant motivation for the approach we propose here derives from the fact that in relativistic models the occurrence of white noises is the main responsible for the appearance of untractable divergences. Therefore, one can hope that resorting to non white noises one can overcome such a difficulty. We investigate stochastic equations with non white noises, we discuss their reduction properties and their physical implications. Our analysis has a precise interest not only for the above mentioned subject but also for the general study of dissipative systems and decoherence. (author)

Dynamical reduction models with general Gaussian noises

International Nuclear Information System (INIS)

Bassi, Angelo; Ghirardi, GianCarlo

2002-01-01

We consider the effect of replacing in stochastic differential equations leading to the dynamical collapse of the state vector, white-noise stochastic processes with nonwhite ones. We prove that such a modification can be consistently performed without altering the most interesting features of the previous models. One of the reasons to discuss this matter derives from the desire of being allowed to deal with physical stochastic fields, such as the gravitational one, which cannot give rise to white noises. From our point of view, the most relevant motivation for the approach we propose here derives from the fact that in relativistic models intractable divergences appear as a consequence of the white nature of the noises. Therefore, one can hope that resorting to nonwhite noises, one can overcome such a difficulty. We investigate stochastic equations with nonwhite noises, we discuss their reduction properties and their physical implications. Our analysis has a precise interest not only for the above-mentioned subject but also for the general study of dissipative systems and decoherence

Noise Reduction Design of the Volute for a Centrifugal Compressor

Science.gov (United States)

Song, Zhen; Wen, Huabing; Hong, Liangxing; Jin, Yudong

2017-08-01

In order to effectively control the aerodynamic noise of a compressor, this paper takes into consideration a marine exhaust turbocharger compressor as a research object. According to the different design concept of volute section, tongue and exit cone, six different volute models were established. The finite volume method is used to calculate the flow field, whiles the finite element method is used for the acoustic calculation. Comparison and analysis of different structure designs from three aspects: noise level, isentropic efficiency and Static pressure recovery coefficient. The results showed that under the concept of volute section model 1 yielded the best result, under the concept of tongue analysis model 3 yielded the best result and finally under exit cone analysis model 6 yielded the best results.

Data Quality Assurance for Supersonic Jet Noise Measurements

Science.gov (United States)

Brown, Clifford A.; Henderson, Brenda S.; Bridges, James E.

2010-01-01

The noise created by a supersonic aircraft is a primary concern in the design of future high-speed planes. The jet noise reduction technologies required on these aircraft will be developed using scale-models mounted to experimental jet rigs designed to simulate the exhaust gases from a full-scale jet engine. The jet noise data collected in these experiments must accurately predict the noise levels produced by the full-scale hardware in order to be a useful development tool. A methodology has been adopted at the NASA Glenn Research Center s Aero-Acoustic Propulsion Laboratory to insure the quality of the supersonic jet noise data acquired from the facility s High Flow Jet Exit Rig so that it can be used to develop future nozzle technologies that reduce supersonic jet noise. The methodology relies on mitigating extraneous noise sources, examining the impact of measurement location on the acoustic results, and investigating the facility independence of the measurements. The methodology is documented here as a basis for validating future improvements and its limitations are noted so that they do not affect the data analysis. Maintaining a high quality jet noise laboratory is an ongoing process. By carefully examining the data produced and continually following this methodology, data quality can be maintained and improved over time.

Study of noise reduction characteristics of double-wall panels

Science.gov (United States)

Navaneethan, R.; Quayle, B.; Stevenson, S.; Graham, M.

1983-05-01

The noise reduction characteristics of general aviation type, flat, double-wall structures were investigated. The experimental study was carried out on 20-by-20 inch panels with an exposed area of 18 by 18 inches. A frequency range from 20 to 5000 Hz was covered. The experimental results, in general, follow the expected trends. At low frequencies the double-wall structures are no better than the single-wall structures. However, for depths normally used in the general aviation industry, the double-wall panels are very attractive. The graphite-spoxy skin panels have higher noise reduction at very low frequencies ( 100 Hz) than the Kevlar skin panels. But the aluminum panels have higher noise reduction in the high frequency region, due to their greater mass. Use of fiberglass insulation is not effective in the low frequency region, and at times it is even negative. But the insulation is effective in the high-frequency region. The theoretical model for predicting the transmission loss of these multilayered panels is also discussed.

Noise reduction in Arterial Spin Labeling based Functional Connectivity using nuisance variables

Directory of Open Access Journals (Sweden)

Kay Jann

2016-08-01

Full Text Available Arterial Spin Labeling (ASL perfusion image series have recently been utilized for functional connectivity (FC analysis in healthy volunteers and children with autism spectrum disorders (ASD. Noise reduction by using nuisance variables has been shown to be necessary to minimize potential confounding effects of head motion and physiological signals on BOLD based FC analysis. The purpose of the present study is to systematically evaluate the effectiveness of different noise reduction strategies using nuisance variables to improve perfusion based FC analysis in two cohorts of healthy adults using state of the art 3D background-suppressed (BS GRASE pseudo-continuous ASL (pCASL and dual-echo 2D-EPI pCASL sequences. Five different noise reduction strategies (NRS were performed in healthy volunteers to compare their performance. We then compared seed-based FC analysis using 3D BS GRASE pCASL in a cohort of 12 children with ASD (3f/9m, age 12.8±1.3y and 13 typically developing (TD children (1f/12m; age 13.9±3years in conjunction with noise reduction strategies. Regression of different combinations of nuisance variables affected FC analysis from a seed in the posterior cingulate cortex (PCC to other areas of the default mode network (DMN in both BOLD and pCASL data sets. Consistent with existing literature on BOLD-FC, we observed improved spatial specificity after physiological noise reduction and improved long-range connectivity using head movement related regressors. Furthermore, 3D BS GRASE pCASL shows much higher temporal SNR compared to dual-echo 2D-EPI pCASL and similar effects of noise reduction as those observed for BOLD. Seed-based FC analysis using 3D BS GRASE pCASL children with ASD and TD children showed that noise reduction including physiological and motion related signals as nuisance variables is crucial for identifying altered long-range connectivity from PCC to frontal brain areas associated with ASD. This is the first study that

Adaptive mean filtering for noise reduction in CT polymer gel dosimetry

International Nuclear Information System (INIS)

Hilts, Michelle; Jirasek, Andrew

2008-01-01

X-ray computed tomography (CT) as a method of extracting 3D dose information from irradiated polymer gel dosimeters is showing potential as a practical means to implement gel dosimetry in a radiation therapy clinic. However, the response of CT contrast to dose is weak and noise reduction is critical in order to achieve adequate dose resolutions with this method. Phantom design and CT imaging technique have both been shown to decrease image noise. In addition, image postprocessing using noise reduction filtering techniques have been proposed. This work evaluates in detail the use of the adaptive mean filter for reducing noise in CT gel dosimetry. Filter performance is systematically tested using both synthetic patterns mimicking a range of clinical dose distribution features as well as actual clinical dose distributions. Both low and high signal-to-noise ratio (SNR) situations are examined. For all cases, the effects of filter kernel size and the number of iterations are investigated. Results indicate that adaptive mean filtering is a highly effective tool for noise reduction CT gel dosimetry. The optimum filtering strategy depends on characteristics of the dose distributions and image noise level. For low noise images (SNR ∼20), the filtered results are excellent and use of adaptive mean filtering is recommended as a standard processing tool. For high noise images (SNR ∼5) adaptive mean filtering can also produce excellent results, but filtering must be approached with more caution as spatial and dose distortions of the original dose distribution can occur

The underwater acoustic environment at SGaan Kinghlas-Bowie Seamount Marine Protected Area: Characterizing vessel traffic and associated noise using satellite AIS and acoustic datasets.

Science.gov (United States)

Allen, Ainsley S; Yurk, Harald; Vagle, Svein; Pilkington, James; Canessa, Rosaline

2018-03-01

Vessel traffic is one of the most wide-spread anthropogenic contributors to ocean noise worldwide and has the potential to alter ecosystems upon which cetaceans and other acoustically sensitive marine organisms rely. Canada's SGaan Kinghlas-Bowie Seamount Marine Protected Area (SK-B MPA) is one such area whose productive ecosystem could benefit from greater monitoring of human induced threats in order to inform management. Despite earning official designation as a Marine Protected Area under the Oceans Act in 2008, little remains known about vessel traffic in the region and the associated potential impacts on vulnerable marine species. Therefore, to increase our understanding of vessel traffic and accompanying noise at SK-B MPA, satellite AIS and acoustic data were investigated. The results of this study suggest that variations in ambient sound levels in the region are driven by near and distant shipping events, thus having implications for future management of the MPA. Copyright © 2018 Elsevier Ltd. All rights reserved.

Hearing loss associated with repeated MRI acquisition procedure-related acoustic noise exposure: an occupational cohort study

NARCIS (Netherlands)

Bongers, Suzan; Slottje, Pauline; Kromhout, Hans

2017-01-01

OBJECTIVE: To study the effects of repeated exposure to MRI-related acoustic noise during image acquisition procedures (scans) on hearing. METHODS: A retrospective occupational cohort study was performed among workers of an MRI manufacturing facility (n=474). Longitudinal audiometry data from the

Use of co-combustion bottom ash to design an acoustic absorbing material for highway noise barriers

International Nuclear Information System (INIS)

Arenas, Celia; Leiva, Carlos; Vilches, Luis F.; Cifuentes, Héctor

2013-01-01

Highlights: • The particle size of bottom ash influenced the acoustic behavior of the barrier. • The best sound absorption coefficients were measured for larger particle sizes. • The maximum noise absorption is displaced to lower frequencies for higher thickness. • A noise barrier was designed with better properties than commercial products. • Recycling products from bottom ash no present leaching and radioactivity problems. - Abstract: The present study aims to determine and evaluate the applicability of a new product consisting of coal bottom ash mixed with Portland cement in the application of highway noise barriers. In order to effectively recycle the bottom ash, the influence of the grain particle size of bottom ash, the thickness of the panel and the combination of different layers with various particle sizes have been studied, as well as some environmental properties including leachability (EN-12457-4, NEN-7345) and radioactivity tests. Based on the obtained results, the acoustic properties of the final composite material were similar or even better than those found in porous concrete used for the same application. According to this study, the material produced presented no environmental risk

Use of co-combustion bottom ash to design an acoustic absorbing material for highway noise barriers

Energy Technology Data Exchange (ETDEWEB)

Arenas, Celia; Leiva, Carlos; Vilches, Luis F. [University of Seville, School of Industrial Engineering, Department of Chemical and Environmental Engineering, Camino de los Descubrimientos s/n, E-41092 Seville (Spain); Cifuentes, Héctor, E-mail: bulte@us.es [University of Seville, School of Industrial Engineering, Continuum Mechanics and Structural Analysis Department, Camino de los Descubrimientos s/n, E-41092 Seville (Spain)

2013-11-15

Highlights: • The particle size of bottom ash influenced the acoustic behavior of the barrier. • The best sound absorption coefficients were measured for larger particle sizes. • The maximum noise absorption is displaced to lower frequencies for higher thickness. • A noise barrier was designed with better properties than commercial products. • Recycling products from bottom ash no present leaching and radioactivity problems. - Abstract: The present study aims to determine and evaluate the applicability of a new product consisting of coal bottom ash mixed with Portland cement in the application of highway noise barriers. In order to effectively recycle the bottom ash, the influence of the grain particle size of bottom ash, the thickness of the panel and the combination of different layers with various particle sizes have been studied, as well as some environmental properties including leachability (EN-12457-4, NEN-7345) and radioactivity tests. Based on the obtained results, the acoustic properties of the final composite material were similar or even better than those found in porous concrete used for the same application. According to this study, the material produced presented no environmental risk.

Effect of urban noise to the acoustical performance of the secondary school’s learning spaces - A case study in Batu Pahat.

Science.gov (United States)

Tong, Y. G.; Abu Bakar, H.; Mohd. Sari, K. A.; Ewon, U.; Labeni, M. N.; Fauzan, N. F. A.

2017-11-01

Classrooms and laboratories are important spaces that use for teaching and learning process in the school. Therefore, good acoustical performances of these spaces are essential to ensure the speech or message from the teacher can be delivered to the students effectively and clearly. The aims of this study is to determine the acoustical performance of the teaching and learning spaces in public school that situated near to the traffic roads. The acoustical performance of the classrooms and laboratories at Sekolah Menengah Kebangsaan Convent Batu Pahat was evaluated in this study. The reverberation time and ambient noise of these learning spaces which are the main parameters for classroom design criteria were evaluated. Field measurements were carried out inside six classrooms and four laboratories unoccupied furnished according to the international standards. The acoustical performances of the tested learning spaces were poor where the noise criteria and reverberation times inside the measured classrooms and laboratories were higher than recommended values.

Improved Separation of Tone and Broadband Noise Components from Open Rotor Acoustic Data

Directory of Open Access Journals (Sweden)

Dave Sree

2016-09-01

Full Text Available The term “open rotor” refers to unducted counter-rotating dual rotors or propellers used for propulsion. The noise generated by an open rotor is very complicated and requires special techniques for its analysis. The determination of its tone and broadband components is vital for properly assessing the noise control parameters and also for validating open rotor noise prediction codes. The data analysis technique developed by Sree for processing raw acoustic data of open rotors has been modified to yield much better results of tone and broadband separation particularly for the case when the two rotor speeds are approximately the same. The modified algorithm is found to eliminate most or all of the “spikes” previously observed in the broadband spectra computed from the original algorithm. A full description of the modified algorithm and examples of improved results from its application are presented in this paper.

Calling at the highway: The spatiotemporal constraint of road noise on Pacific chorus frog communication.

Science.gov (United States)

Nelson, Danielle V; Klinck, Holger; Carbaugh-Rutland, Alexander; Mathis, Codey L; Morzillo, Anita T; Garcia, Tiffany S

2017-01-01

. Additionally, this model can be applied to other vocal taxonomic groups provided the necessary acoustic parameters are determined, including the frequency parameters and perception thresholds. Reduction in acoustic habitat by anthropogenic noise may emerge as a compounding environmental stressor for an already sensitive taxonomic group.

Discrimination of acoustic communication signals by grasshoppers (Chorthippus biguttulus): temporal resolution, temporal integration, and the impact of intrinsic noise.

Science.gov (United States)

Ronacher, Bernhard; Wohlgemuth, Sandra; Vogel, Astrid; Krahe, Rüdiger

2008-08-01

A characteristic feature of hearing systems is their ability to resolve both fast and subtle amplitude modulations of acoustic signals. This applies also to grasshoppers, which for mate identification rely mainly on the characteristic temporal patterns of their communication signals. Usually the signals arriving at a receiver are contaminated by various kinds of noise. In addition to extrinsic noise, intrinsic noise caused by stochastic processes within the nervous system contributes to making signal recognition a difficult task. The authors asked to what degree intrinsic noise affects temporal resolution and, particularly, the discrimination of similar acoustic signals. This study aims at exploring the neuronal basis for sexual selection, which depends on exploiting subtle differences between basically similar signals. Applying a metric, by which the similarities of spike trains can be assessed, the authors investigated how well the communication signals of different individuals of the same species could be discriminated and correctly classified based on the responses of auditory neurons. This spike train metric yields clues to the optimal temporal resolution with which spike trains should be evaluated. (c) 2008 APA, all rights reserved

Reducing the ingress of urban noise through natural ventilation openings.

Science.gov (United States)

Oldham, D J; de Salis, M H; Sharples, S

2004-01-01

For buildings in busy urban areas affected by high levels of road traffic noise the potential to use natural ventilation can be limited by excessive noise entering through ventilation openings. This paper is concerned with techniques to reduce noise ingress into naturally ventilated buildings while minimizing airflow path resistance. A combined experimental and theoretical approach to the interaction of airflow and sound transmission through ventilators for natural ventilation applications is described. A key element of the investigation has been the development of testing facilities capable of measuring the airflow and sound transmission losses for a range of ventilation noise control strategies. It is demonstrated that a combination of sound reduction mechanisms -- one covering low frequency sound and another covering high frequency sound -- is required to attenuate effectively noise from typical urban sources. A method is proposed for quantifying the acoustic performance of different strategies to enable comparisons and informed decisions to be made leading to the possibility of a design methodology for optimizing the ventilation and acoustic performance of different strategies. The need for employing techniques for combating low frequency sound in tandem with techniques for reducing high frequency sound in reducing the ingress of noise from urban sources such as road traffic to acceptable levels is demonstrated. A technique is proposed for enabling the acoustic and airflow performance of apertures for natural ventilation systems to be designed simultaneously.

Acoustic control study of turbofan nozzles with triangular chevrons

Directory of Open Access Journals (Sweden)

Grigore CICAN

2014-03-01

Full Text Available This paper has a small part dealing with the notion of chevron and the process that helps reducing the noise pollution. Based on the gas dynamics and the geometrical parameters of the turbofan jet engine a model of CFD data processing is created. In this process the influence of chevrons on acoustic wave intensity produced by the jet is observed by analyzing this process. A series of tests have been made on 10 si 20 lobed chevrons. The combination between them and the 7 resulting cases have been studied, namely the triangular chevrons in order to settle the influence of the geometrical parameters on the flow and on the jet acoustics. Finally the contribution of the chevrons in noise pollution reduction has been highlighted.

Bias in mean velocities and noise in variances and covariances measured using a multistatic acoustic profiler: the Nortek Vectrino Profiler

Science.gov (United States)

Thomas, R. E.; Schindfessel, L.; McLelland, S. J.; Creëlle, S.; De Mulder, T.

2017-07-01

This paper compiles the technical characteristics and operating principles of the Nortek Vectrino Profiler and reviews previously reported user experiences. A series of experiments are then presented that investigate instrument behaviour and performance, with a particular focus on variations within the profile. First, controlled tests investigate the sensitivity of acoustic amplitude (and Signal-to-Noise Ratio, SNR) and pulse-to-pulse correlation coefficient, R 2, to seeding concentration and cell geometry. Second, a novel methodology that systematically shifts profiling cells through a single absolute vertical position investigates the sensitivity of mean velocities, SNR and noise to: (a) emitted sound intensity and the presence (or absence) of acoustic seeding; and (b) varying flow rates under ideal acoustic seeding conditions. A new solution is derived to quantify the noise affecting the two perpendicular tristatic systems of the Vectrino Profiler and its contribution to components of the Reynolds stress tensor. Results suggest that for the Vectrino Profiler: 1. optimum acoustic seeding concentrations are ~3000 to 6000 mg L-1 2. mean velocity magnitudes are biased by variable amounts in proximal cells but are consistently underestimated in distal cells; 3. noise varies parabolically with a minimum around the ‘sweet spot’, 50 mm below the transceiver; 4. the receiver beams only intersect at the sweet spot and diverge nearer to and further from the transceiver. This divergence significantly reduces the size of the sampled area away from the sweet spot, reducing data quality; 5. the most reliable velocity data will normally be collected in the region between approximately 43 and 61 mm below the transceiver.

Bias in mean velocities and noise in variances and covariances measured using a multistatic acoustic profiler: the Nortek Vectrino Profiler

International Nuclear Information System (INIS)

Thomas, R E; Schindfessel, L; Creëlle, S; De Mulder, T; McLelland, S J

2017-01-01

This paper compiles the technical characteristics and operating principles of the Nortek Vectrino Profiler and reviews previously reported user experiences. A series of experiments are then presented that investigate instrument behaviour and performance, with a particular focus on variations within the profile. First, controlled tests investigate the sensitivity of acoustic amplitude (and Signal-to-Noise Ratio, SNR) and pulse-to-pulse correlation coefficient, R 2 , to seeding concentration and cell geometry. Second, a novel methodology that systematically shifts profiling cells through a single absolute vertical position investigates the sensitivity of mean velocities, SNR and noise to: (a) emitted sound intensity and the presence (or absence) of acoustic seeding; and (b) varying flow rates under ideal acoustic seeding conditions. A new solution is derived to quantify the noise affecting the two perpendicular tristatic systems of the Vectrino Profiler and its contribution to components of the Reynolds stress tensor. Results suggest that for the Vectrino Profiler: 1. optimum acoustic seeding concentrations are ∼3000 to 6000 mg L −1 ; 2. mean velocity magnitudes are biased by variable amounts in proximal cells but are consistently underestimated in distal cells; 3. noise varies parabolically with a minimum around the ‘sweet spot’, 50 mm below the transceiver; 4. the receiver beams only intersect at the sweet spot and diverge nearer to and further from the transceiver. This divergence significantly reduces the size of the sampled area away from the sweet spot, reducing data quality; 5. the most reliable velocity data will normally be collected in the region between approximately 43 and 61 mm below the transceiver. (paper)

Aero-acoustic Computations of Wind Turbines

DEFF Research Database (Denmark)

Shen, Wen Zhong; Michelsen, Jess; Sørensen, Jens Nørkær

2002-01-01

A numerical algorithm for acoustic noise generation is extended to 3D flows. The approach involves two parts comprising a viscous incompressible flow part and an inviscid acoustic part. In order to simulate noise generated from a wind turbine, the incompressible and acoustic equations are written...

The effect of multimicrophone noise reduction systems on sound source localization by users of binaural hearing aids.

Science.gov (United States)

Van den Bogaert, Tim; Doclo, Simon; Wouters, Jan; Moonen, Marc

2008-07-01

This paper evaluates the influence of three multimicrophone noise reduction algorithms on the ability to localize sound sources. Two recently developed noise reduction techniques for binaural hearing aids were evaluated, namely, the binaural multichannel Wiener filter (MWF) and the binaural multichannel Wiener filter with partial noise estimate (MWF-N), together with a dual-monaural adaptive directional microphone (ADM), which is a widely used noise reduction approach in commercial hearing aids. The influence of the different algorithms on perceived sound source localization and their noise reduction performance was evaluated. It is shown that noise reduction algorithms can have a large influence on localization and that (a) the ADM only preserves localization in the forward direction over azimuths where limited or no noise reduction is obtained; (b) the MWF preserves localization of the target speech component but may distort localization of the noise component. The latter is dependent on signal-to-noise ratio and masking effects; (c) the MWF-N enables correct localization of both the speech and the noise components; (d) the statistical Wiener filter approach introduces a better combination of sound source localization and noise reduction performance than the ADM approach.

Detection threshold for sound distortion resulting from noise reduction in normal-hearing and hearing-impaired listeners.

Science.gov (United States)

Brons, Inge; Dreschler, Wouter A; Houben, Rolph

2014-09-01

Hearing-aid noise reduction should reduce background noise, but not disturb the target speech. This objective is difficult because noise reduction suffers from a trade-off between the amount of noise removed and signal distortion. It is unknown if this important trade-off differs between normal-hearing (NH) and hearing-impaired (HI) listeners. This study separated the negative effect of noise reduction (distortion) from the positive effect (reduction of noise) to allow the measurement of the detection threshold for noise-reduction (NR) distortion. Twelve NH subjects and 12 subjects with mild to moderate sensorineural hearing loss participated in this study. The detection thresholds for distortion were determined using an adaptive procedure with a three-interval, two-alternative forced-choice paradigm. Different levels of distortion were obtained by changing the maximum amount of noise reduction. Participants were also asked to indicate their preferred NR strength. The detection threshold for overall distortion was higher for HI subjects than for NH subjects, suggesting that stronger noise reduction can be applied for HI listeners without affecting the perceived sound quality. However, the preferred NR strength of HI listeners was closer to their individual detection threshold for distortion than in NH listeners. This implies that HI listeners tolerate fewer audible distortions than NH listeners.

Continuous and recurrent testing of acoustic emission sensors

International Nuclear Information System (INIS)

Sause, Markus G.R.; Schmitt, Stefan; Potstada, Philipp

2017-01-01

In many fields of application of acoustic emission, the testing can lead to a lasting change in the sensor characteristics. This can be caused by mechanical damage, thermal stress or use under aggressive environmental conditions. Irrespective of visually testable damages of the sensors, a shift in the spectral sensitivity, a reduction in the absolute sensitivity or a reduction in the signal-to-noise ratio can occur. During the test, this requires a possibility to periodically check the sensors, including the coupling aids used. For recurring testing, recommendations are given in Directive SE 02 ''Verification of acoustic emission sensors and their coupling in the laboratory''. This paper discusses possibilities for continuous monitoring of the sensors during the test and presents an application example for the partly automated recurring testing of acoustic emission sensors using Directive SE 02. For this purpose, a test stand for the supply of the sensors to be tested was constructed and the signal recording and data reduction implemented in freely available software programs. The operating principle is demonstrated using selected case studies. [de

Bit-rate reduction strategies for noise suppression with a remote wireless microphone

NARCIS (Netherlands)

Cvijanovic, N.; Sadiq, O.; Srinivasan, S.

2012-01-01

In single channel non-stationary noise reduction it is paramount that a good noise reference is available in a timely manner to maintaina high quality speech signal. Using a remote wireless microphone placed close to a noise source, a good estimate of the noise power spectral density (PSD) can be

Bit rate reduction strategies for noise suppression using a remote wireless microphone

NARCIS (Netherlands)

Cvijanovic, N.; Sadiq, O.; Srinivasan, S.

2012-01-01

In single-channel non-stationary noise reduction it is paramount that a good noise reference is available in a timely manner to maintain a high quality speech signal. Using a remote wireless microphone placed close to a noise source, a good estimate of the noise power spectral density (PSD) can be

Noise reduction methods for nucleic acid and macromolecule sequencing

Science.gov (United States)

Schuller, Ivan K.; Di Ventra, Massimiliano; Balatsky, Alexander

2018-05-08

Methods, systems, and devices are disclosed for processing macromolecule sequencing data with substantial noise reduction. In one aspect, a method for reducing noise in a sequential measurement of a macromolecule comprising serial subunits includes cross-correlating multiple measured signals of a physical property of subunits of interest of the macromolecule, the multiple measured signals including the time data associated with the measurement of the signal, to remove or at least reduce signal noise that is not in the same frequency and in phase with the systematic signal contribution of the measured signals.

Long Term Memory for Noise: Evidence of Robust Encoding of Very Short Temporal Acoustic Patterns.

Science.gov (United States)

Viswanathan, Jayalakshmi; Rémy, Florence; Bacon-Macé, Nadège; Thorpe, Simon J

2016-01-01

Recent research has demonstrated that humans are able to implicitly encode and retain repeating patterns in meaningless auditory noise. Our study aimed at testing the robustness of long-term implicit recognition memory for these learned patterns. Participants performed a cyclic/non-cyclic discrimination task, during which they were presented with either 1-s cyclic noises (CNs) (the two halves of the noise were identical) or 1-s plain random noises (Ns). Among CNs and Ns presented once, target CNs were implicitly presented multiple times within a block, and implicit recognition of these target CNs was tested 4 weeks later using a similar cyclic/non-cyclic discrimination task. Furthermore, robustness of implicit recognition memory was tested by presenting participants with looped (shifting the origin) and scrambled (chopping sounds into 10- and 20-ms bits before shuffling) versions of the target CNs. We found that participants had robust implicit recognition memory for learned noise patterns after 4 weeks, right from the first presentation. Additionally, this memory was remarkably resistant to acoustic transformations, such as looping and scrambling of the sounds. Finally, implicit recognition of sounds was dependent on participant's discrimination performance during learning. Our findings suggest that meaningless temporal features as short as 10 ms can be implicitly stored in long-term auditory memory. Moreover, successful encoding and storage of such fine features may vary between participants, possibly depending on individual attention and auditory discrimination abilities. Significance Statement Meaningless auditory patterns could be implicitly encoded and stored in long-term memory.Acoustic transformations of learned meaningless patterns could be implicitly recognized after 4 weeks.Implicit long-term memories can be formed for meaningless auditory features as short as 10 ms.Successful encoding and long-term implicit recognition of meaningless patterns may

MEASUREMENTS OF ABSORPTION, EMISSIVITY REDUCTION, AND LOCAL SUPPRESSION OF SOLAR ACOUSTIC WAVES IN SUNSPOTS

International Nuclear Information System (INIS)

Chou, D.-Y.; Liang, Z.-C.; Yang, M.-H.; Zhao Hui; Sun, M.-T.

2009-01-01

The power of solar acoustic waves in magnetic regions is lower relative to the quiet Sun. Absorption, emissivity reduction, and local suppression of acoustic waves contribute to the observed power reduction in magnetic regions. We propose a model for the energy budget of acoustic waves propagating through a sunspot in terms of the coefficients of absorption, emissivity reduction, and local suppression of the sunspot. Using the property that the waves emitted along the wave path between two points have no correlation with the signal at the starting point, we can separate the effects of these three mechanisms. Applying this method to helioseismic data filtered with direction and phase-velocity filters, we measure the fraction of the contribution of each mechanism to the power deficit in the umbra of the leading sunspot of NOAA 9057. The contribution from absorption is 23.3 ± 1.3%, emissivity reduction 8.2 ± 1.4%, and local suppression 68.5 ± 1.5%, for a wave packet corresponding to a phase velocity of 6.98 x 10 -5 rad s -1 .

Interior acoustic cloak

Directory of Open Access Journals (Sweden)

Wael Akl

2014-12-01

Full Text Available Acoustic cloaks have traditionally been intended to externally surround critical objects to render these objects acoustically invisible. However, in this paper, the emphasis is placed on investigating the application of the acoustic cloaks to the interior walls of acoustic cavities in an attempt to minimize the noise levels inside these cavities. In this manner, the acoustic cloaks can serve as a viable and efficient alternative to the conventional passive noise attenuation treatments which are invariably heavy and bulky. The transformation acoustics relationships that govern the operation of this class of interior acoustic cloaks are presented. Physical insights are given to relate these relationships to the reasons behind the effectiveness of the proposed interior acoustic cloaks. Finite element models are presented to demonstrate the characteristics of interior acoustic cloaks used in treating the interior walls of circular and square cavities both in the time and frequency domains. The obtained results emphasize the effectiveness of the proposed interior cloaks in eliminating the reflections of the acoustic waves from the walls of the treated cavities and thereby rendering these cavities acoustically quiet. It is important to note here that the proposed interior acoustic cloaks can find applications in acoustic cavities such as aircraft cabins and auditoriums as well as many other critical applications.

Application of an active device for helicopter noise reduction in JAXA

International Nuclear Information System (INIS)

Saito, Shigeru; Kobiki, Noboru; Tanabe, Yasutada

2010-01-01

Important issues in noise problems for current helicopters are described. An active tab (AT) was developed as a new active device for noise/vibration reduction under research cooperation between Japan Aerospace Exploration Agency (JAXA) and Kawada Industries, Inc. The wind tunnel test was conducted in order to investigate the effectiveness of the AT on the aeroacoustic characteristics of a helicopter. From the wind tunnel test, the capability of reducing blade vortex interaction (BVI) noise by an AT was verified. A new control law using instantaneous pressure change on a blade during BVI phenomena was introduced and applied to the wind tunnel testing. This new control law shows reasonable controllability for helicopter noise reduction. Furthermore, in order to analyze noise characteristics, the advanced computational fluid dynamics (CFD) code named JAXA o v3d was developed in JAXA and extended to include CFD-CSD (computational structure dynamics) coupling by using the beam theory for blade deformation. (invited paper)

Analysis of Beamformer Directed Single-Channel Noise Reduction System for Hearing Aid Applications

DEFF Research Database (Denmark)

Jensen, Jesper; Pedersen, Michael Syskind

2015-01-01

We study multi-microphone noise reduction systems consisting of a beamformer and a single-channel (SC) noise reduction stage. In particular, we present and analyse a maximum likelihood (ML) method for jointly estimating the target and noise power spectral densities (psd's) entering the SC filter....... We show that the estimators are minimum variance and unbiased, and provide closed-form expressions for their mean-square error (MSE). Furthermore, we show that the MSE of the noise psd estimator is particularly simple: it is independent of target signal characteristics, frequency, and microphone...

[The role of acoustic impedance test in the diagnosis for occupational noise induced deafness].

Science.gov (United States)

Chen, H; Xue, L J; Yang, A C; Liang, X Y; Chen, Z Q; Zheng, Q L

2018-01-20

Objective: To investigate the characteristics of acoustic impedance test and its diagnostic role for occupational noise induced deafness, in order to provide an objective basis for the differential diagnosis of occupational noise induced deafness. Methods: A retrospective study was conducted to investigate the cases on the diagnosis of occupational noise-induced deafness in Guangdong province hospital for occupational disease prevention and treatment from January 2016 to January 2017. A total of 198 cases (396 ears) were divided into occupation disease group and non occupation disease group based on the diagnostic criteria of occupational noise deafness in 2014 edition, acoustic conductivity test results of two groups were compared including tympanograms types, external auditory canal volume, tympanic pressure, static compliance and slope. Results: In the occupational disease group, 204 ears were found to have 187 ears (91.67%) of type A, which were significantly higher than those in the non occupational disease group 143/192 (74.48%) , the difference was statistically significant (χ(2)=21.038, P occupation disease group in other type were 16/204 (7.84%) , 3/204 (1.47%) , were lower than Ad or As type of occupation disease group (15.63%) , other type (9.38%) , the differences were statistically significant[ (χ(2)=5.834, P Occupation disease group canal volume average (1.68±0.39) ml higher than that of non occupation disease group (1.57 ± 0.47) ml, the difference was statistically significant ( t =2.756, P occupation disease group mean static compliance (1.06±0.82) ml higher than that of non occupation disease group (0.89±0.64) ml. The difference was statistically singificant ( t =2.59, P occupational noise induced deafness, More than 90% of the confirmed cases showed an A-form tympanograms, it is one of the objective examination methods which can be used in the differential diagnosis of pseudo deafness.

Sounds and Noises. A Position Paper on Noise Pollution.

Science.gov (United States)

Chapman, Thomas L.

This position paper focuses on noise pollution and the problems and solutions associated with this form of pollution. The paper is divided into the following five sections: Noise and the Ear, Noise Measurement, III Effects of Noise, Acoustics and Action, and Programs and Activities. The first section identifies noise and sound, the beginnings of…

Noise Reduction Techniques

Science.gov (United States)

Hallas, Tony

There are two distinct kinds of noise - structural and color. Each requires a specific method of attack to minimize. The great challenge is to reduce the noise without reducing the faint and delicate detail in the image. My most-used and favorite noise suppression is found in Photoshop CS 5 Camera Raw. If I cannot get the desired results with the first choice, I will use Noise Ninja, which has certain advantages in some situations that we will cover.

Acoustic noise diagnostics of leaks. Report of the E O Paton Electric Welding Institute, Kiev, 1997

International Nuclear Information System (INIS)

Volkov, L.P.; Zverev, A.F.; Kozeletskii, V.F.; Leonov, A.N.

1999-01-01

Special attention has been paid in recent years to safe service of nuclear energy plant (NEP): various safety programmes are being developed and applied, measures are taken in reactors of the WWER-RBMK type, the Gospromatomnadzor is introducing a package of new standard requirements and documents, etc. Formation of leaks in equipment and pipelines, actual leakage and the discharge of the heat carrier outside the limits of contour I of the NEP leads to undesirable and sometimes serious consequences. In most cases, elimination of these consequences is associated with the need to use a large amount of material, personnel, shutdown of nuclear equipment, disruption of the ecological situation, and partial or complete loss of electric or thermal power. The 'leak prior to fracture' concept, accepted several years ago in the EEC countries and the USA has been used as a strong impetus for the rapid development of diagnostic means of inspection of pipelines and equipment, including acoustic equipment. The development of means of acoustic leak detection as a variety of noise diagnostics is still important because the utilisation of the possibilities of the methods of noise diagnostics makes it possible to solve a complex problem: recording the actual leakage event, determination of its position and the degree of risk. The majority of modern leak inspection methods, having a low sensitivity threshold, require development of special testing conditions, the use of indicator or test substances and, most importantly, they should not be remote controlled. For example, the mass spectrometric, halide, luminescent, bubble and capillary methods have a sensitivity threshold of 6.7·10 -11 -6.7·10 -4 m 3 Pa/s, but require the presence of an operator in the inspection area. The use of these methods for determining leakage in pipelines and equipment of nuclear power plant is out of the question and it is not possible to develop a system for remote control of NEP equipment using these

Computational reduction techniques for numerical vibro-acoustic analysis of hearing aids

DEFF Research Database (Denmark)

Creixell Mediante, Ester

. In this thesis, several challenges encountered in the process of modelling and optimizing hearing aids are addressed. Firstly, a strategy for modelling the contacts between plastic parts for harmonic analysis is developed. Irregularities in the contact surfaces, inherent to the manufacturing process of the parts....... Secondly, the applicability of Model Order Reduction (MOR) techniques to lower the computational complexity of hearing aid vibro-acoustic models is studied. For fine frequency response calculation and optimization, which require solving the numerical model repeatedly, a computational challenge...... is encountered due to the large number of Degrees of Freedom (DOFs) needed to represent the complexity of the hearing aid system accurately. In this context, several MOR techniques are discussed, and an adaptive reduction method for vibro-acoustic optimization problems is developed as a main contribution. Lastly...

Light aircraft sound transmission studies - Noise reduction model

Science.gov (United States)

Atwal, Mahabir S.; Heitman, Karen E.; Crocker, Malcolm J.

1987-01-01

Experimental tests conducted on the fuselage of a single-engine Piper Cherokee light aircraft suggest that the cabin interior noise can be reduced by increasing the transmission loss of the dominant sound transmission paths and/or by increasing the cabin interior sound absorption. The validity of using a simple room equation model to predict the cabin interior sound-pressure level for different fuselage and exterior sound field conditions is also presented. The room equation model is based on the sound power flow balance for the cabin space and utilizes the measured transmitted sound intensity data. The room equation model predictions were considered good enough to be used for preliminary acoustical design studies.

Education in acoustics in Argentina

Science.gov (United States)

Miyara, Federico

2002-11-01

Over the last decades, education in acoustics (EA) in Argentina has experienced ups and downs due to economic and political issues interfering with long term projects. Unlike other countries, like Chile, where EA has reached maturity in spite of the acoustical industry having shown little development, Argentina has several well-established manufacturers of acoustic materials and equipment but no specific career with a major in acoustics. At the university level, acoustics is taught as a complementary--often elective--course for careers such as architecture, communication engineering, or music. In spite of this there are several research centers with programs covering environmental and community noise, effects of noise on man, acoustic signal processing, musical acoustics and acoustic emission, and several national and international meetings are held each year in which results are communicated and discussed. Several books on a variety of topics such as sound system, architectural acoustics, and noise control have been published as well. Another chapter in EA is technical and vocational education, ranging between secondary and postsecondary levels, with technical training on sound system operation or design. Over the last years there have been several attempts to implement master degrees in acoustics or audio engineering, with little or no success.

Building Acoustics

Science.gov (United States)

Cowan, James

This chapter summarizes and explains key concepts of building acoustics. These issues include the behavior of sound waves in rooms, the most commonly used rating systems for sound and sound control in buildings, the most common noise sources found in buildings, practical noise control methods for these sources, and the specific topic of office acoustics. Common noise issues for multi-dwelling units can be derived from most of the sections of this chapter. Books can be and have been written on each of these topics, so the purpose of this chapter is to summarize this information and provide appropriate resources for further exploration of each topic.

Noise annoys: effects of noise on breeding great tits depend on personality but not on noise characteristics

NARCIS (Netherlands)

Naguib, M.; Van Oers, K.; Braakhuis, A.; Griffioen, M.; De Goede, P.; Waas, J.R.

2013-01-01

Anthropogenic noise can have serious implications for animals, especially when they communicate acoustically. Yet, the impacts of noise may depend not only on noise characteristics but also on an individual's coping style or personality. We tested whether noise is more disturbing if it masks

Internal Acoustics of the ISS and Other Spacecraft

Science.gov (United States)

Allen, Christopher S.

2017-01-01

It is important to control the acoustic environment inside spacecraft and space habitats to protect for astronaut communications, alarm audibility, and habitability, and to reduce astronauts' risk for sleep disturbance, and hear-ing loss. But this is not an easy task, given the various design trade-offs, and it has been difficult, historically, to achieve. Over time it has been found that successful control of spacecraft acoustic levels is achieved by levying firm requirements at the system-level, using a systems engineering approach for design and development, and then validating these requirements with acoustic testing. In the systems engineering method, the system-level requirements must be flowed down to sub-systems and component noise sources, using acoustic analysis and acoustic modelling to develop allocated requirements for the sub-systems and components. Noise controls must also be developed, tested, and implemented so the sub-systems and components can achieve their allocated limits. It is also important to have management support for acoustics efforts to maintain their priority against the various trade-offs, including mass, volume, power, cost, and schedule. In this extended abstract and companion presentation, the requirements, approach, and results for controlling acoustic levels in most US spacecraft since Apollo will be briefly discussed. The approach for controlling acoustic levels in the future US space vehicle, Orion Multipurpose Crew Vehicle (MPCV), will also be briefly discussed. These discussions will be limited to the control of continuous noise inside the space vehicles. Other types of noise, such as launch, landing, and abort noise, intermittent noise, Extra-Vehicular Activity (EVA) noise, emergency operations/off-nominal noise, noise exposure, and impulse noise are important, but will not be discussed because of time limitations.

Spatial-temporal noise reduction method optimized for real-time implementation

Science.gov (United States)

Romanenko, I. V.; Edirisinghe, E. A.; Larkin, D.

2013-02-01

Image de-noising in the spatial-temporal domain has been a problem studied in-depth in the field of digital image processing. However complexity of algorithms often leads to high hardware resource usage, or computational complexity and memory bandwidth issues, making their practical use impossible. In our research we attempt to solve these issues with an optimized implementation of a practical spatial-temporal de-noising algorithm. Spatial-temporal filtering was performed in Bayer RAW data space, which allowed us to benefit from predictable sensor noise characteristics and reduce memory bandwidth requirements. The proposed algorithm efficiently removes different kinds of noise in a wide range of signal to noise ratios. In our algorithm the local motion compensation is performed in Bayer RAW data space, while preserving the resolution and effectively improving the signal to noise ratios of moving objects. The main challenge for the use of spatial-temporal noise reduction algorithms in video applications is the compromise between the quality of the motion prediction and the complexity of the algorithm and required memory bandwidth. In photo and video applications it is very important that moving objects should stay sharp, while the noise is efficiently removed in both the static background and moving objects. Another important use case is the case when background is also non-static as well as the foreground where objects are also moving. Taking into account the achievable improvement in PSNR (on the level of the best known noise reduction techniques, like VBM3D) and low algorithmic complexity, enabling its practical use in commercial video applications, the results of our research can be very valuable.

Objective Measures of Listening Effort: Effects of Background Noise and Noise Reduction

Science.gov (United States)

Sarampalis, Anastasios; Kalluri, Sridhar; Edwards, Brent; Hafter, Ervin

2009-01-01

Purpose: This work is aimed at addressing a seeming contradiction related to the use of noise-reduction (NR) algorithms in hearing aids. The problem is that although some listeners claim a subjective improvement from NR, it has not been shown to improve speech intelligibility, often even making it worse. Method: To address this, the hypothesis…

Detection threshold for sound distortion resulting from noise reduction in normal-hearing and hearing-impaired listeners

NARCIS (Netherlands)

Brons, Inge; Dreschler, Wouter A.; Houben, Rolph

2014-01-01

Hearing-aid noise reduction should reduce background noise, but not disturb the target speech. This objective is difficult because noise reduction suffers from a trade-off between the amount of noise removed and signal distortion. It is unknown if this important trade-off differs between

Tipping point analysis of ocean acoustic noise

Science.gov (United States)

Livina, Valerie N.; Brouwer, Albert; Harris, Peter; Wang, Lian; Sotirakopoulos, Kostas; Robinson, Stephen

2018-02-01

We apply tipping point analysis to a large record of ocean acoustic data to identify the main components of the acoustic dynamical system and study possible bifurcations and transitions of the system. The analysis is based on a statistical physics framework with stochastic modelling, where we represent the observed data as a composition of deterministic and stochastic components estimated from the data using time-series techniques. We analyse long-term and seasonal trends, system states and acoustic fluctuations to reconstruct a one-dimensional stochastic equation to approximate the acoustic dynamical system. We apply potential analysis to acoustic fluctuations and detect several changes in the system states in the past 14 years. These are most likely caused by climatic phenomena. We analyse trends in sound pressure level within different frequency bands and hypothesize a possible anthropogenic impact on the acoustic environment. The tipping point analysis framework provides insight into the structure of the acoustic data and helps identify its dynamic phenomena, correctly reproducing the probability distribution and scaling properties (power-law correlations) of the time series.

Tipping point analysis of ocean acoustic noise

Directory of Open Access Journals (Sweden)

V. N. Livina

2018-02-01

Full Text Available We apply tipping point analysis to a large record of ocean acoustic data to identify the main components of the acoustic dynamical system and study possible bifurcations and transitions of the system. The analysis is based on a statistical physics framework with stochastic modelling, where we represent the observed data as a composition of deterministic and stochastic components estimated from the data using time-series techniques. We analyse long-term and seasonal trends, system states and acoustic fluctuations to reconstruct a one-dimensional stochastic equation to approximate the acoustic dynamical system. We apply potential analysis to acoustic fluctuations and detect several changes in the system states in the past 14 years. These are most likely caused by climatic phenomena. We analyse trends in sound pressure level within different frequency bands and hypothesize a possible anthropogenic impact on the acoustic environment. The tipping point analysis framework provides insight into the structure of the acoustic data and helps identify its dynamic phenomena, correctly reproducing the probability distribution and scaling properties (power-law correlations of the time series.

System Noise Prediction of the DGEN 380 Turbofan Engine

Science.gov (United States)

Berton, Jeffrey J.

2015-01-01

The DGEN 380 is a small, separate-flow, geared turbofan. Its manufacturer, Price Induction, is promoting it for a small twinjet application in the emerging personal light jet market. Smaller, and producing less thrust than other entries in the industry, Price Induction is seeking to apply the engine to a 4- to 5-place twinjet designed to compete in an area currently dominated by propeller-driven airplanes. NASA is considering purchasing a DGEN 380 turbofan to test new propulsion noise reduction technologies in a relevant engine environment. To explore this possibility, NASA and Price Induction have signed a Space Act Agreement and have agreed to cooperate on engine acoustic testing. Static acoustic measurements of the engine were made by NASA researchers during July, 2014 at the Glenn Research Center. In the event that a DGEN turbofan becomes a NASA noise technology research testbed, it is in the interest of NASA to develop procedures to evaluate engine system noise metrics. This report documents the procedures used to project the DGEN static noise measurements to flight conditions and the prediction of system noise of a notional airplane powered by twin DGEN engines.

Research of noise emission sources in railway transport and effective ways of their reduction

Directory of Open Access Journals (Sweden)

Zvolenský Peter

2017-01-01

Full Text Available In the EU conditions attention is systematically paid to noise reduction on the railways. Because TSI rules systematically tighten limits for noise emissions from railway vehicles, noise research must be addressed by all Member States, as the main technical solutions for railway vehicles and construction technological aspects of railway operations can result in lower noise exposure of affected areas or objects. The paper focuses on theoretical investigation of sources and paths of sound propagation, possibilities of noise reduction both on vehicles and by infrastructure and experimental measurements of the situation in transport practice. Methodology for reducing railway noise around tracks has been presented, too.

Optimization of the poro-serrated trailing edges for airfoil broadband noise reduction.

Science.gov (United States)

Chong, Tze Pei; Dubois, Elisa

2016-08-01

This paper reports an aeroacoustic investigation of a NACA0012 airfoil with a number of poro-serrated trailing edge devices that contain porous materials of various air flow resistances at the gaps between adjacent members of the serrated-sawtooth trailing edge. The main objective of this work is to determine whether multiple-mechanisms on the broadband noise reduction can co-exist on a poro-serrated trailing edge. When the sawtooth gaps are filled with porous material of low-flow resistivity, the vortex shedding tone at low-frequency could not be completely suppressed at high-velocity, but a reasonably good broadband noise reduction can be achieved at high-frequency. When the sawtooth gaps are filled with porous material of very high-flow resistivity, no vortex shedding tone is present, but the serration effect on the broadband noise reduction becomes less effective. An optimal choice of the flow resistivity for a poro-serrated configuration has been identified, where it can surpass the conventional serrated trailing edge of the same geometry by achieving a further 1.5 dB reduction in the broadband noise while completely suppressing the vortex shedding tone. A weakened turbulent boundary layer noise scattering at the poro-serrated trailing edge is reflected by the lower-turbulence intensity at the near wake centreline across the whole spanwise wavelength of the sawtooth.

Acoustic Noise Alters Selective Attention Processes as Indicated by Direct Current (DC) Brain Potential Changes

OpenAIRE

Trimmel, Karin; Schätzer, Julia; Trimmel, Michael

2014-01-01

Acoustic environmental noise, even of low to moderate intensity, is known to adversely affect information processing in animals and humans via attention mechanisms. In particular, facilitation and inhibition of information processing are basic functions of selective attention. Such mechanisms can be investigated by analyzing brain potentials under conditions of externally directed attention (intake of environmental information) versus internally directed attention (rejection of environmental ...

Gene regulation and noise reduction by coupling of stochastic processes

Science.gov (United States)

Ramos, Alexandre F.; Hornos, José Eduardo M.; Reinitz, John

2015-02-01

Here we characterize the low-noise regime of a stochastic model for a negative self-regulating binary gene. The model has two stochastic variables, the protein number and the state of the gene. Each state of the gene behaves as a protein source governed by a Poisson process. The coupling between the two gene states depends on protein number. This fact has a very important implication: There exist protein production regimes characterized by sub-Poissonian noise because of negative covariance between the two stochastic variables of the model. Hence the protein numbers obey a probability distribution that has a peak that is sharper than those of the two coupled Poisson processes that are combined to produce it. Biochemically, the noise reduction in protein number occurs when the switching of the genetic state is more rapid than protein synthesis or degradation. We consider the chemical reaction rates necessary for Poisson and sub-Poisson processes in prokaryotes and eucaryotes. Our results suggest that the coupling of multiple stochastic processes in a negative covariance regime might be a widespread mechanism for noise reduction.

Gene regulation and noise reduction by coupling of stochastic processes.

Science.gov (United States)

Ramos, Alexandre F; Hornos, José Eduardo M; Reinitz, John

2015-02-01

Here we characterize the low-noise regime of a stochastic model for a negative self-regulating binary gene. The model has two stochastic variables, the protein number and the state of the gene. Each state of the gene behaves as a protein source governed by a Poisson process. The coupling between the two gene states depends on protein number. This fact has a very important implication: There exist protein production regimes characterized by sub-Poissonian noise because of negative covariance between the two stochastic variables of the model. Hence the protein numbers obey a probability distribution that has a peak that is sharper than those of the two coupled Poisson processes that are combined to produce it. Biochemically, the noise reduction in protein number occurs when the switching of the genetic state is more rapid than protein synthesis or degradation. We consider the chemical reaction rates necessary for Poisson and sub-Poisson processes in prokaryotes and eucaryotes. Our results suggest that the coupling of multiple stochastic processes in a negative covariance regime might be a widespread mechanism for noise reduction.

Objective measures of listening effort: effects of background noise and noise reduction.

Science.gov (United States)

Sarampalis, Anastasios; Kalluri, Sridhar; Edwards, Brent; Hafter, Ervin

2009-10-01

This work is aimed at addressing a seeming contradiction related to the use of noise-reduction (NR) algorithms in hearing aids. The problem is that although some listeners claim a subjective improvement from NR, it has not been shown to improve speech intelligibility, often even making it worse. To address this, the hypothesis tested here is that the positive effects of NR might be to reduce cognitive effort directed toward speech reception, making it available for other tasks. Normal-hearing individuals participated in 2 dual-task experiments, in which 1 task was to report sentences or words in noise set to various signal-to-noise ratios. Secondary tasks involved either holding words in short-term memory or responding in a complex visual reaction-time task. At low values of signal-to-noise ratio, although NR had no positive effect on speech reception thresholds, it led to better performance on the word-memory task and quicker responses in visual reaction times. Results from both dual tasks support the hypothesis that NR reduces listening effort and frees up cognitive resources for other tasks. Future hearing aid research should incorporate objective measurements of cognitive benefits.

On the study of wavy leading-edge vanes to achieve low fan interaction noise

Science.gov (United States)

Tong, Fan; Qiao, Weiyang; Xu, Kunbo; Wang, Liangfeng; Chen, Weijie; Wang, Xunnian

2018-04-01

The application of wavy leading-edge vanes to reduce a single-stage axial fan noise is numerically studied. The aerodynamic and acoustic performance of the fan is numerically investigated using a hybrid unsteady Reynolds averaged Navier-Stokes (URANS)/acoustic analogy method (Goldstein equations). First, the hybrid URANS/Goldstein method is developed and successfully validated against experiment results. Next, numerical simulations are performed to investigate the noise reduction effects of the wavy leading-edge vanes. The aerodynamic and acoustic performance is assessed for a fan with vanes equipped with two different wavy leading-edge profiles and compared with the performance of conventional straight leading-edge vanes. Results indicate that a fan with wavy leading-edge vanes produces lower interaction noise than the baseline fan without a significant loss in aerodynamic performance. In fact, it is demonstrated that wavy leading-edge vanes have the potential to lead to both aerodynamic and acoustic improvements. The two different wavy leading-edge profiles are shown to successfully reduce the fan tone sound power level by 1.2 dB and 4.3 dB, respectively. Fan efficiency is also improved by about 1% with one of the tested wavy leading-edge profiles. Large eddy simulation (LES) is also performed for a simplified fan stage model to assess the effects of wavy leading-edge vanes on the broadband fan noise. Results indicate that the overall sound power level of a fan can be reduced by about 4 dB with the larger wavy leading-edge profile. Finally, the noise reduction mechanisms are investigated and analysed. It is found that the wavy leading-edge profiles can induce significant streamwise vorticity around the leading-edge protuberances and reduce pressure fluctuations (especially at locations of wavy leading-edge hills) and unsteady forces on the stator vanes. The underlying mechanism of the reduced pressure fluctuations is also discussed by examining the magnitude

Numerical analysis of the impact of permeability on trailing-edge noise

Science.gov (United States)

Koh, Seong Ryong; Meinke, Matthias; Schröder, Wolfgang

2018-05-01

The impact of porous surfaces on the near-wall turbulent structures and the generated trailing-edge noise is analyzed for several trailing-edge shapes of finite thickness using a high resolution large-eddy simulation (LES)/computational aeroacoustics (CAA) method. The porous surface of the trailing edge is defined by the porosity and the viscous permeability determined by the solution of a turbulent flat plate boundary layer at a Reynolds number 1280 based on the displacement thickness in the inflow cross section. The volume-averaged approach for the homogeneous porous medium shows that the porous impedance scales linearly with the porosity and exponentially with the mean structure size of a porous medium. The drag induced by the porous surface changes the friction velocity and the permeability Reynolds number ReK which determines the porous impedance Rs scaled by ReK-2/3. The trailing-edge noise is analyzed for three solid and three porous trailing edges. The effect of a finite span is investigated by the spanwise correlation model based on the measured coherence distribution. The acoustic prediction shows a good agreement with measurements of the broadband spectrum and the strong tone generated by a finite trailing-edge thickness. The pressure gradient inside the porous media is redistributed by the Darcy drag defined by the viscous permeability and the porosity. The mean pressure increases in the upstream direction inside the porous medium such that the flow acceleration involved in the acoustic generation is reduced inside the porous medium. The noise reduction by a porous medium reaches 11 dB for the trailing-edge shape which possesses a sharp corner for the solid surface. The porous surface applied to a semi-circular trailing edge achieves a 4 dB noise reduction. The directivity pattern for individual components of the acoustic spectrum shows that the massive noise reduction is determined at the tone. Enhanced wave diffraction by the thick flat plate changes

Reduction of Poisson noise in measured time-resolved data for time-domain diffuse optical tomography.

Science.gov (United States)

Okawa, S; Endo, Y; Hoshi, Y; Yamada, Y

2012-01-01

A method to reduce noise for time-domain diffuse optical tomography (DOT) is proposed. Poisson noise which contaminates time-resolved photon counting data is reduced by use of maximum a posteriori estimation. The noise-free data are modeled as a Markov random process, and the measured time-resolved data are assumed as Poisson distributed random variables. The posterior probability of the occurrence of the noise-free data is formulated. By maximizing the probability, the noise-free data are estimated, and the Poisson noise is reduced as a result. The performances of the Poisson noise reduction are demonstrated in some experiments of the image reconstruction of time-domain DOT. In simulations, the proposed method reduces the relative error between the noise-free and noisy data to about one thirtieth, and the reconstructed DOT image was smoothed by the proposed noise reduction. The variance of the reconstructed absorption coefficients decreased by 22% in a phantom experiment. The quality of DOT, which can be applied to breast cancer screening etc., is improved by the proposed noise reduction.

Soundscape elaboration from anthrophonic adaptation of community noise

Science.gov (United States)

Teddy Badai Samodra, FX

2018-03-01

Under the situation of an urban environment, noise has been a critical issue in affecting the indoor environment. A reliable approach is required for evaluation of the community noise as one factor of anthrophonic in the urban environment. This research investigates the level of noise exposure from different community noise sources and elaborates the advantage of the noise disadvantages for soundscape innovation. Integrated building element design as a protector for noise control and speech intelligibility compliance using field experiment and MATLAB programming and modeling are also carried out. Meanwhile, for simulation analysis and building acoustic optimization, Sound Reduction-Speech Intelligibility and Reverberation Time are the main parameters for identifying tropical building model as case study object. The results show that the noise control should consider its integration with the other critical issue, thermal control, in an urban environment. The 1.1 second of reverberation time for speech activities and noise reduction more than 28.66 dBA for critical frequency (20 Hz), the speech intelligibility index could be reached more than fair assessment, 0.45. Furthermore, the environmental psychology adaptation result “Close The Opening” as the best method in high noise condition and personal adjustment as the easiest and the most adaptable way.

Channel noise enhances signal detectability in a model of acoustic neuron through the stochastic resonance paradigm.

Science.gov (United States)

Liberti, M; Paffi, A; Maggio, F; De Angelis, A; Apollonio, F; d'Inzeo, G

2009-01-01

A number of experimental investigations have evidenced the extraordinary sensitivity of neuronal cells to weak input stimulations, including electromagnetic (EM) fields. Moreover, it has been shown that biological noise, due to random channels gating, acts as a tuning factor in neuronal processing, according to the stochastic resonant (SR) paradigm. In this work the attention is focused on noise arising from the stochastic gating of ionic channels in a model of Ranvier node of acoustic fibers. The small number of channels gives rise to a high noise level, which is able to cause a spike train generation even in the absence of stimulations. A SR behavior has been observed in the model for the detection of sinusoidal signals at frequencies typical of the speech.

The normalized interaural correlation : accounting for NoSp thresholds obtained with Gaussian and 'low-noise' masking noise

NARCIS (Netherlands)

Bernstein, L.R.; Par, van de S.L.J.D.E.; Trahiotis, C.T.

1999-01-01

Recently, [J. Acoust. Soc. Am. 103, 2578–2589 (1998)] and [J. Acoust. Soc. Am. 103, 2573–2577 (1998)] independently reported that greater masking of interaurally phase-reversed (Sp) tones was produced by diotic low-noise noise than by diotic Gaussian noise. Based on quantitative analyses, Eddins and

Effect of fMRI acoustic noise on non-auditory working memory task: comparison between continuous and pulsed sound emitting EPI.

Science.gov (United States)

Haller, Sven; Bartsch, Andreas J; Radue, Ernst W; Klarhöfer, Markus; Seifritz, Erich; Scheffler, Klaus

2005-11-01

Conventional blood oxygenation level-dependent (BOLD) based functional magnetic resonance imaging (fMRI) is accompanied by substantial acoustic gradient noise. This noise can influence the performance as well as neuronal activations. Conventional fMRI typically has a pulsed noise component, which is a particularly efficient auditory stimulus. We investigated whether the elimination of this pulsed noise component in a recent modification of continuous-sound fMRI modifies neuronal activations in a cognitively demanding non-auditory working memory task. Sixteen normal subjects performed a letter variant n-back task. Brain activity and psychomotor performance was examined during fMRI with continuous-sound fMRI and conventional fMRI. We found greater BOLD responses in bilateral medial frontal gyrus, left middle frontal gyrus, left middle temporal gyrus, left hippocampus, right superior frontal gyrus, right precuneus and right cingulate gyrus with continuous-sound compared to conventional fMRI. Conversely, BOLD responses were greater in bilateral cingulate gyrus, left middle and superior frontal gyrus and right lingual gyrus with conventional compared to continuous-sound fMRI. There were no differences in psychomotor performance between both scanning protocols. Although behavioral performance was not affected, acoustic gradient noise interferes with neuronal activations in non-auditory cognitive tasks and represents a putative systematic confound.

Experimental and Numerical analysis of Metallic Bellow for Acoustic Performance

Science.gov (United States)

Panchwadkar, Amit A.; Awasare, Pradeep J., Dr.; Ingle, Ravidra B., Dr.

2017-08-01

Noise will concern about the work environment of industry. Machinery environment has overall noise which interrupts communication between the workers. This problem of miscommunication and health hazard will make sense to go for noise attenuation. Modification in machine setup may affect the performance of it. Instead of that, Helmholtz resonator principle will be a better option for noise reduction along the transmission path. Resonator has design variables which gives resonating frequency will help us to confirm the frequency range. This paper deals with metallic bellow which behaves like inertial mass under incident sound wave. Sound wave energy is affected by hard boundary condition of resonator and bellow. Metallic bellow is used in combination with resonator to find out Transmission loss (TL). Microphone attachment with FFT analyzer will give the frequency range for numerical analysis. Numerical analysis of bellow and resonator is carried out to summarize the acoustic behavior of bellow. Bellow can be numerically analyzed to check noise attenuation for centrifugal blower. An impedance tube measurement technique is performed to validate the numerical results for assembly. Dimensional and shape modification can be done to get the acoustic performance of bellow.

Acoustic energy propagation around railways

Science.gov (United States)

Cizkova, Petra

2017-09-01

The article deals with the issues of acoustic energy propagation around railways. The research subject was noise emission spreading into the surroundings during the passage of trains over a directly travelled steel bridge construction. Noise emissions were measured using direct measurements in the field. The measurements were performed in two measurement profiles. The noise exposures A LAE measured near the steel bridge construction were compared against the noise exposures A LAE captured on an open track. From the difference of these data, the noise level of the steel bridge structure was determined. Part of the research was to evaluate the effect of the reconstruction of the railway track superstructure on the acoustic situation in the given section of the railway track. The article describes the methodology of measurements, including the processing and evaluation of measured data. The article points out the noise levels of the steel bridge construction and assesses changes in the acoustic situation after the reconstruction.

The reduction of noise from hydraulic equipments; La reduction du bruit provenant des equipements hydrauliques

Energy Technology Data Exchange (ETDEWEB)

Gential, R.

1996-09-01

Noise pollution from hydraulic equipments (bath filling, toilets taps, waste waters flow, vibrations, knocks in water pipes, dilatation clattering in heating pipes, hissing of heater taps etc..) are one of the principal causes of nuisance inside residential buildings. Solutions exist and consist in the replacement of old cocks and fittings, the use of soundproof clamps for pipes and noise absorbing supports for baths etc.. This paper summarizes the available modern equipments with a low-noise warranty (cocks and fittings, noise dampers, anti-backflow valves, pressure reducers) and the practical solutions for the modification of existing installations (increase of pipe diameters, reduction of pipe lengths, use of flexible fittings, hydraulic counterbalancing of water flows in heaters etc..). (J.S.)

Understanding jet noise.

Science.gov (United States)

Karabasov, S A

2010-08-13

Jets are one of the most fascinating topics in fluid mechanics. For aeronautics, turbulent jet-noise modelling is particularly challenging, not only because of the poor understanding of high Reynolds number turbulence, but also because of the extremely low acoustic efficiency of high-speed jets. Turbulent jet-noise models starting from the classical Lighthill acoustic analogy to state-of-the art models were considered. No attempt was made to present any complete overview of jet-noise theories. Instead, the aim was to emphasize the importance of sound generation and mean-flow propagation effects, as well as their interference, for the understanding and prediction of jet noise.

Multichannel active control of random noise in a small reverberant room

DEFF Research Database (Denmark)

Laugesen, Søren; Elliott, Stephen J.

1993-01-01

An algorithm for multichannel adaptive IIR (infinite impulse response) filtering is presented and applied to the active control of broadband random noise in a small reverberant room. Assuming complete knowledge of the primary noise, the theoretically optimal reductions of acoustic energy are init...... with the primary noise field generated by a panel excited by a loudspeaker in an adjoining room. These results show that far better performances are provided by IIR and FIR filters when the primary source has a lightly damped dynamic behavior which the active controller must model...

Detection and localization of leak of pipelines of RBMK reactor. Methods of processing of acoustic noise

International Nuclear Information System (INIS)

Tcherkaschov, Y.M.; Strelkov, B.P.; Chimanski, S.B.; Lebedev, V.I.; Belyanin, L.A.

1997-01-01

For realization of leak detection of input pipelines and output pipelines of RBMK reactor the method, based on detection and control of acoustic leak signals, was designed. In this report the review of methods of processing and analysis of acoustic noise is submitted. These methods were included in the software of the leak detection system and are used for the decision of the following problems: leak detection by method of sound pressure level in conditions of powerful background noise and strong attenuation of a signal; detection of a small leak in early stage by high-sensitivity correlation method; determination of a point of a sound source in conditions of strong reflection of a signal by a correlation method and sound pressure method; evaluation of leak size by the analysis of a sound level and point of a sound source. The work of considered techniques is illustrated on an example of test results of a fragment of the leak detection system. This test was executed on a Leningrad NPP, operated at power levels of 460, 700, 890 and 1000 MWe. 16 figs

Sound quality measures for speech in noise through a commercial hearing aid implementing digital noise reduction.

Science.gov (United States)

Ricketts, Todd A; Hornsby, Benjamin W Y

2005-05-01

This brief report discusses the affect of digital noise reduction (DNR) processing on aided speech recognition and sound quality measures in 14 adults fitted with a commercial hearing aid. Measures of speech recognition and sound quality were obtained in two different speech-in-noise conditions (71 dBA speech, +6 dB SNR and 75 dBA speech, +1 dB SNR). The results revealed that the presence or absence of DNR processing did not impact speech recognition in noise (either positively or negatively). Paired comparisons of sound quality for the same speech in noise signals, however, revealed a strong preference for DNR processing. These data suggest that at least one implementation of DNR processing is capable of providing improved sound quality, for speech in noise, in the absence of improved speech recognition.

Improved multi-microphone noise reduction preserving binaural cues

NARCIS (Netherlands)

Koutrouvelis, A.; Hendriks, R.C.; Jensen, J; Heusdens, R.; Dong, Min; Zheng, Thomas Fang

2016-01-01

We propose a new multi-microphone noise reduction technique for binaural cue preservation of the desired source and the interferers. This method is based on the linearly constrained minimum variance (LCMV) framework, where the constraints are used for the binaural cue preservation of the desired

Noise pollution of air compressor and its noise reduction procedures by using an enclosure

Directory of Open Access Journals (Sweden)

Farhad Forouharmajd

2012-01-01

Conclusions: An overall noise reduction by 25 dB with the use of mineral wool as an extra liner on the inside of the enclosure, suggests that the effectiveness of the enclosure can be increased by using such absorber materials.

Research on the application of active sound barriers for the transformer noise abatement

Directory of Open Access Journals (Sweden)

Hu Sheng

2016-01-01

Full Text Available Sound barriers are a type of measure most commonly used in the noise abatement of transformers. In the noise abatement project of substations, the design of sound barriers is restrained by the portal frames which are used to hold up outgoing lines from the main transformers, which impacts the noise reduction effect. If active sound barriers are utilized in these places, the noise diffraction of sound barriers can be effectively reduced. At a 110kV Substation, an experiment using a 15-channel active sound barrier has been carried out. The result of the experiment shows that the mean noise reduction value (MNRV of the noise measuring points at the substation boundary are 1.5 dB (A. The effect of the active noise control system is impacted by the layout of the active noise control system, the acoustic environment on site and the spectral characteristic of the target area.

R&D for an innovative acoustic positioning system for the KM3NeT neutrino telescope

Science.gov (United States)

Ameli, F.; Ardid, M.; Bertin, V.; Bonori, M.; Bou-Cabo, M.; Calì, C.; D'Amico, A.; Giovanetti, G.; Imbesi, M.; Keller, P.; Larosa, G.; Llorens, C. D.; Masullo, R.; Randazzo, N.; Riccobene, G.; Speziale, F.; Viola, S.; KM3NeT Consortium

2011-01-01

An innovative Acoustic Positioning System for the km3-scale neutrino telescope has been designed and is under realization within the KM3NeT Consortium. Compared to the Acoustic Positioning Systems used for the km3 demonstrators, ANTARES and NEMO Phase 1, this new system is based on the “all data to shore” concept and it will permit the enhancement of detector positioning performances, reduction of costs and its use as real-time monitor of environmental acoustic noise.

Comparisons of spectral characteristics of wind noise between omnidirectional and directional microphones.

Science.gov (United States)

Chung, King

2012-06-01

Wind noise reduction is a topic of ongoing research and development for hearing aids and cochlear implants. The purposes of this study were to examine spectral characteristics of wind noise generated by directional (DIR) and omnidirectional (OMNI) microphones on different styles of hearing aids and to derive wind noise reduction strategies. Three digital hearing aids (BTE, ITE, and ITC) were fitted to Knowles Electronic Manikin for Acoustic Research. They were programmed to have linear amplification and matching frequency responses between the DIR and OMNI modes. Flow noise recordings were made from 0° to 360° azimuths at flow velocities of 4.5, 9.0, and 13.5 m/s in a quiet wind tunnel. Noise levels were analyzed in one-third octave bands from 100 to 8000 Hz. Comparison of wind noise revealed that DIR generally produced higher noise levels than OMNI for all hearing aids, but it could result in lower levels than OMNI at some frequencies and head angles. Wind noise reduction algorithms can be designed to detect noise levels of DIR and OMNI outputs in each frequency channel, remove the constraint to switch to OMNI in low-frequency channel(s) only, and adopt the microphone mode with lower noise levels to take advantage of the microphone differences.

Acoustic noise alters selective attention processes as indicated by direct current (DC) brain potential changes.

Science.gov (United States)

Trimmel, Karin; Schätzer, Julia; Trimmel, Michael

2014-09-26

Acoustic environmental noise, even of low to moderate intensity, is known to adversely affect information processing in animals and humans via attention mechanisms. In particular, facilitation and inhibition of information processing are basic functions of selective attention. Such mechanisms can be investigated by analyzing brain potentials under conditions of externally directed attention (intake of environmental information) versus internally directed attention (rejection of environmental stimuli and focusing on memory/planning processes). This study investigated brain direct current (DC) potential shifts-which are discussed to represent different states of cortical activation-of tasks that require intake and rejection of environmental information under noise. It was hypothesized that without background noise rejection tasks would show more positive DC potential changes compared to intake tasks and that under noise both kinds of tasks would show positive DC shifts as an expression of cortical inhibition caused by noise. DC potential shifts during intake and rejection tasks were analyzed at 16 standard locations in 45 persons during irrelevant speech or white noise vs. control condition. Without noise, rejection tasks were associated with more positive DC potential changes compared to intake tasks. During background noise, however, this difference disappeared and both kinds of tasks led to positive DC shifts. Results suggest-besides some limitations-that noise modulates selective attention mechanisms by switching to an environmental information processing and noise rejection mode, which could represent a suggested "attention shift". Implications for fMRI studies as well as for public health in learning and performance environments including susceptible persons are discussed.

Acoustic Noise Alters Selective Attention Processes as Indicated by Direct Current (DC Brain Potential Changes

Directory of Open Access Journals (Sweden)

Karin Trimmel

2014-09-01

Full Text Available Acoustic environmental noise, even of low to moderate intensity, is known to adversely affect information processing in animals and humans via attention mechanisms. In particular, facilitation and inhibition of information processing are basic functions of selective attention. Such mechanisms can be investigated by analyzing brain potentials under conditions of externally directed attention (intake of environmental information versus internally directed attention (rejection of environmental stimuli and focusing on memory/planning processes. This study investigated brain direct current (DC potential shifts—which are discussed to represent different states of cortical activation—of tasks that require intake and rejection of environmental information under noise. It was hypothesized that without background noise rejection tasks would show more positive DC potential changes compared to intake tasks and that under noise both kinds of tasks would show positive DC shifts as an expression of cortical inhibition caused by noise. DC potential shifts during intake and rejection tasks were analyzed at 16 standard locations in 45 persons during irrelevant speech or white noise vs. control condition. Without noise, rejection tasks were associated with more positive DC potential changes compared to intake tasks. During background noise, however, this difference disappeared and both kinds of tasks led to positive DC shifts. Results suggest—besides some limitations—that noise modulates selective attention mechanisms by switching to an environmental information processing and noise rejection mode, which could represent a suggested “attention shift”. Implications for fMRI studies as well as for public health in learning and performance environments including susceptible persons are discussed.

Sodium boiling detection in LMFBRs by acoustic-neutronic cross correlation

International Nuclear Information System (INIS)

Wright, S.A.

1977-01-01

The acoustic and neutronic noise signals caused by boiling are the signals primarily considered likely to detect sodium boiling in an LMFBR. Unfortunately, these signals may have serious signal-to-noise problems due to strong background noise sources. Neutronic-acoustic cross correlation techniques are expected to provide a means of improving the signal-to-noise ratio. This technique can improve the signal-to-noise ratio because the neutronic and acoustic signals due to boiling are highly correlated near the bubble repetition frequency, while the background noise sources are expected to be uncorrelated (or at most weakly correlated). An experiment was designed to show that the neutronic and acoustic noise signals are indeed highly correlated. The experiment consisted of simulating the void and pressure effects of local sodium boiling in the core of a zero-power reactor (ARK). The analysis showed that the neutronic and acoustic noise signals caused by boiling are almost perfectly correlated in a wide frequency band about the bubble repetition frequency. The results of the experiments were generalized to full-scale reactors to compare the inherent effectiveness of the methods which use the neutronic or acoustic signals alone with a hybrid method, which cross correlates the neutronic and acoustic signals. It was concluded that over a zone of the reactor where the void coefficient is sufficiently large (approximately 85 percent the core volume), the cross correlation method can provide a more rapid detection system for a given signal-to-noise ratio. However, where the void coefficient is small, one must probably rely on the acoustic method alone

Sound and noise in urban parks

OpenAIRE

António P. O. Carvalho; Ricardo A. F. Cleto

2012-01-01

The main goal of this work is to study the soundscape of city gardens and urban parks using a sample of ten sites in Oporto, Portugal to analyze their soundscape through the acoustic characterization of the park's exterior and interior noise levels (LAeq, LA10, LA50 and LA90) and by a socio-acoustic survey to the visitors to check their perception of acoustic quality. The measurements showed gardens/parks with interior noise levels from 47 to 61 dB(A) (with exterior noise levels up to 67 dB(A...

Acoustic event location and background noise characterization on a free flying infrasound sensor network in the stratosphere

Science.gov (United States)

Bowman, Daniel C.; Albert, Sarah A.

2018-06-01

A variety of Earth surface and atmospheric sources generate low-frequency sound waves that can travel great distances. Despite a rich history of ground-based sensor studies, very few experiments have investigated the prospects of free floating microphone arrays at high altitudes. However, recent initiatives have shown that such networks have very low background noise and may sample an acoustic wave field that is fundamentally different than that at Earth's surface. The experiments have been limited to at most two stations at altitude, making acoustic event detection and localization difficult. We describe the deployment of four drifting microphone stations at altitudes between 21 and 24 km above sea level. The stations detected one of two regional ground-based chemical explosions as well as the ocean microbarom while travelling almost 500 km across the American Southwest. The explosion signal consisted of multiple arrivals; signal amplitudes did not correlate with sensor elevation or source range. The waveforms and propagation patterns suggest interactions with gravity waves at 35-45 km altitude. A sparse network method that employed curved wave front corrections was able to determine the backazimuth from the free flying network to the acoustic source. Episodic signals similar to those seen on previous flights in the same region were noted, but their source remains unclear. Background noise levels were commensurate with those on infrasound stations in the International Monitoring System below 2 s.

Loudness and acoustic parameters of popular children's toys.

Science.gov (United States)

Ghavami, Yaser; Bhatt, Jay; Maducdoc, Marlon; Yau, Amy; Mahboubi, Hossein; Ziai, Kasra; Lin, Harrison W; Djalilian, Hamid R

2015-12-01

This project was conducted to evaluate the loudness and acoustic parameters of toys designed for children. In addition, we investigated whether occluding the toys' speaker with tape would result in a significant loudness reduction; thereby potentially reducing the risk of noise induced hearing loss. Twenty-six toys were selected after an initial screening at two national retailers. Noise amplitudes at 0.25, 0.5, 1, 2, 4, and 8kHz were measured using a digital sound level meter at a distance of 0 and 30cm. The toys' speakers were then occluded using adhesive tape and the same acoustic parameters were re-measured. Mean maximum noise amplitude of the toys at 0cm and 30cm was 104dBA (range, 97-125dBA) and 76dBA (range, 67-86dBA), respectively. Mean maximum noise amplitude after occlusion at 0cm and 30cm distances was 88dBA (range, 73-110dBA) and 66dBA (range, 55-82dBA), respectively, with a p-value toys at a distant of 30cm between the speaker and the child's ear will likely not pose a risk of noise-induced hearing loss. However, since most toys are used at closer distances, use of adhesive tape is recommended as an effective modification to decrease the risk of hearing loss. Published by Elsevier Ireland Ltd.

The Low-Noise Potential of Distributed Propulsion on a Catamaran Aircraft

Science.gov (United States)

Posey, Joe W.; Tinetti, A. F.; Dunn, M. H.

2006-01-01

The noise shielding potential of an inboard-wing catamaran aircraft when coupled with distributed propulsion is examined. Here, only low-frequency jet noise from mid-wing-mounted engines is considered. Because low frequencies are the most difficult to shield, these calculations put a lower bound on the potential shielding benefit. In this proof-of-concept study, simple physical models are used to describe the 3-D scattering of jet noise by conceptualized catamaran aircraft. The Fast Scattering Code is used to predict noise levels on and about the aircraft. Shielding results are presented for several catamaran type geometries and simple noise source configurations representative of distributed propulsion radiation. Computational analyses are presented that demonstrate the shielding benefits of distributed propulsion and of increasing the width of the inboard wing. Also, sample calculations using the FSC are presented that demonstrate additional noise reduction on the aircraft fuselage by the use of acoustic liners on the inboard wing trailing edge. A full conceptual aircraft design would have to be analyzed over a complete mission to more accurately quantify community noise levels and aircraft performance, but the present shielding calculations show that a large acoustic benefit could be achieved by combining distributed propulsion and liner technology with a twin-fuselage planform.

Analysis of room acoustics in Danish Hospitals

DEFF Research Database (Denmark)

Hoffmann, Ida Ørduk; Zapata Rodriguez, Valentina; Jeong, Cheol-Ho

2018-01-01

time (EDT) and T20, and the sound pressure level metrics, namely the equivalent level and peak level. In addition, the staff at the hospitals is asked about their personal perception of the acoustic and noise conditions and the correlation between their subjective disturbances......This project aims to compare room acoustic parameters and noise levels in various Danish hospitals: Odense, Gentofte, Bispebjerg, Hillerød and Aarhus Hospitals. Room acoustic conditions are measured in audiometric rooms at Odense, Gentofte, Bispebjerg and Aarhus hospitals. The noise levels...

Railway noise reduction by the application of CHFC material on the rail

Directory of Open Access Journals (Sweden)

Brigita ALTENBAHER

2015-06-01

Full Text Available Traffic is the most widespread source of environmental noise. Railway noise has become increasingly common in urban areas in the past few decades. Therefore environmental requirements for railway operations regarding noise are becoming very strict and will become even tighter in future. In the present paper we present actual track-based field test performed on Slovenian Railways. The significant noise reduction (up to 30dBA was achieved by the application of CHFC material on the rail using CL-E1 top anti noise system.