Position Of Noise Source Research Articles

Data analysis results of the second sea trial of ambient noise imaging with acoustic lens in 2014: Two-dimensional target images affected by direction of field of view and spatial noise distribution

An aspherical lens with an aperture diameter of 1.0 m has been designed and fabricated to develop a prototype system for ambient noise imaging (ANI). A sea trial of silent target detection using the prototype ANI system was conducted under only natural ocean ambient noise at Uchiura Bay in November 2010. It was verified that targets are successfully detected under natural ocean ambient noise, mainly generated by snapping shrimps. Recently, we have built a second prototype ANI system using an acoustic lens with a two-dimensional (2D) receiver array with 127 elements corresponding to a field of view (FOV) spanning 15° horizontally by 9° vertically. In this study, we investigated the effects of the direction of the FOV and the spatial noise distribution on the 2D target image obtained by ANI. Here, the noise sources in front of the target are called “front light”, and those at the rear of the target are called “back light”. The second sea trial was conducted to image targets arranged in the FOV and measure the positions of noise sources at Uchiura Bay in November 10–14, 2014. For front light, the pixel values in the on-target directions were greater than those in other directions owing to the dominant target scatterings. Reversely, for back light, the pixel values in the on-target directions were lower than those in other directions owing to the dominant direct noises such as “silhouette”.

Identification of low-frequency noise sources in high-speed train via resolution improvement

The delay-and-sum beamforming method, which has been used in previous studies, is a useful technique to identify noise sources in a high-speed train. However, the method does not provide detailed noise source position in the low-frequency range. Thus, the lowfrequency noise sources of a high-speed train were not identified. Therefore, in this paper, a resolution improvement study was conducted to identify low-frequency noise sources in a high-speed train. The relation between an actual noise source and a beamforming output was first derived using the point spread function. The deconvolution approach of the relation was used to obtain an actual noise source, which was then transferred to an inverse problem. To solve the ill-conditioned inverse problem, an optimization problem was applied and the iteration method was conducted to solve the problem. The algorithm developed in this research was verified with a moving vehicle test. After the successful verification test, the method was applied on a high-speed train. The improved noise map obtained in this research provides the detailed noise sources of a high-speed train.

Identification of the Sectional Distribution of Sound Source in a Wide Duct

덕트 내 음원 면에서의 음압과 입자 속도분포를 상세히 알 수 있다면, 주된 소음원들의 위치와 강도를 분석하여 전파특성을 잘 이해할 수 있고, 이에 따라 저소음화 설계에 유용한 정보로 활용가능하다. 이를 위한 기존의 방법들은 대개 단면상 위치와 무관한 일정 변수로 나타내는 제한점이 있다. 본 논문에서는 음원의 단면 분포를 높은 공간분해능으로 관찰할 수 있는 방법에 대해 연구하였다. 모드 합성법을 기반으로 감쇠파의 영향과 근접장 측정을 포함하는 행렬식을 유도하였으며, 컴프레션 드라이버에 의해 일부 단면이 가진된 유동이 없는 덕트 시스템에서 검증하였다. 감쇠파모드 개수의 증가에 따라 음압 스펙트럼을 더욱 정확하게 근사화 할 수 있었으며, 26개의 감쇠파 모드를 포함한 수렴 결과로부터 관심 헬름홀쯔 수 영역에서 -25 dB 이하의 오차로 예측할 수 있었다. 수렴된 모드 진폭들을 이용하여 kR = 1에서 음원 면에서의 음원변수 분포를 관찰한 결과, 실제 음원이 설치된 국소 위치에서 높은 음압과 입자 속도 값을 분명히 나타내는 것을 보였다. 또한, 감쇠 모드의 역추산시에 정규화기법을 도입하여, 과결정된 반경방향 모드에 의해 발생된 무의미한 피크들을 효과적으로 제거할 수 있었다. If one identifies the detailed distribution of pressure and axial velocity at a source plane, the position and strength of major noise sources can be known, and the propagation characteristics in axial direction can be well understood to be used for the low noise design. Conventional techniques are usually limited in considering the constant source characteristics specified on the whole source surface; then, the source activity cannot be known in detail. In this work, a method to estimate the pressure and velocity field distribution on the source surface with high spatial resolution is studied. The matrix formulation including the evanescent modes is given, and the nearfield measurement method is proposed. Validation experiment is conducted on a wide duct system, at which a part of the source plane is excited by an acoustic driver in the absence of airflow. Increasing the number of evanescent modes, the prediction of pressure spectrum becomes further precise, and it has less than -25 dB error with 26 converged evanescent modes within the Helmholtz number range of interest. By using the converged modal amplitudes, the source parameter distribution is restored, and the position of the driver is clearly identified at kR = 1. By applying the regularization technique to the restored result, the unphysical minor peaks at the source plane can be effectively suppressed with the filtering of the over-estimated pure radial modes.

Propeller sheet cavitation noise source modeling and inversion

Propeller sheet cavitation is the main contributor to high level of noise and vibration in the after body of a ship. Full measurement of the cavitation-induced hull pressure over the entire surface of the affected area is desired but not practical. Therefore, using a few measurements on the outer hull above the propeller in a cavitation tunnel, empirical or semi-empirical techniques based on physical model have been used to predict the hull-induced pressure (or hull-induced force). In this paper, with the analytic source model for sheet cavitation, a multi-parameter inversion scheme to find the positions of noise sources and their strengths is suggested. The inversion is posed as a nonlinear optimization problem, which is solved by the optimization algorithm based on the adaptive simplex simulated annealing algorithm. Then, the resulting hull pressure can be modeled with boundary element method from the inverted cavitation noise sources. The suggested approach is applied to the hull pressure data measured in a cavitation tunnel of the Samsung Heavy Industry. Two monopole sources are adequate to model the propeller sheet cavitation noise. The inverted source information is reasonable with the cavitation dynamics of the propeller and the modeled hull pressure shows good agreement with cavitation tunnel experimental data.

Sound field characteristics of underground railway stations – Effect of interior materials and noise source positions

In the case of most underground railway stations, no acoustical solutions are used to reduce train noise. Because the reflecting features of train noise in an underground station are not known, appropriate methods for controlling these features have yet to be established. The aim of this study was to clarify the sound field characteristics of underground stations by putting a sound source and receiver on the railway track and platform, respectively. The impulse responses for two vacant underground stations were measured to clarify the effects of the interior materials of the station (Comparison I), and the sound source was put in each station and tunnel to clarify the effect of the noise source positions (Comparison II). Results showed that the sound fields were similar between the stations whose lateral walls were covered with either metallic or fire-resistant wooden panels (Comparison I), and that the sound field for the sound sources near or in the tunnel presented a higher strength (G) by 5.1dB and longer reverberation time (EDT) by 0.7s compared to the sound source in the station (Comparison II). The sound sources in the tunnel presented strong and long reverberations at around 500Hz due to the convergence effect of the tunnel. Therefore, this study proposes a platform screen with doors to limit noise transmission into the platform.

Undirected head movements of listeners with asymmetrical hearing impairment during a speech-in-noise task

It has long been understood that the level of a sound at the ear is dependent on head orientation, but the way in which listeners move their heads during listening has remained largely unstudied. Given the task of understanding a speech signal in the presence of a simultaneous noise, listeners could potentially use head orientation to either maximize the level of the signal in their better ear, or to maximize the signal-to-noise ratio in their better ear. To establish what head orientation strategy listeners use in a speech comprehension task, we used an infrared motion-tracking system to measure the head movements of 36 listeners with large (>16 dB) differences in hearing threshold between their left and right ears. We engaged listeners in a difficult task of understanding sentences presented at the same time as a spatially separated background noise. We found that they tended to orient their heads so as to maximize the level of the target sentence in their better ear, irrespective of the position of the background noise. This is not ideal orientation behavior from the perspective of maximizing the signal-to-noise ratio (SNR) at the ear, but is a simple, easily implemented strategy that is often effective in an environment where the spatial position of multiple noise sources may be difficult or impossible to determine.

NAH기법을 이용한 공조용 컴프레서 소음저감 응용

The paper demonstrates how to deal with the Near-field Acoustic Holography method (NAH) for reducing noise source which is generated in air-conditioning compressor. Sound radiation was measured for both normal compressor and fault compressor. The acoustic noise holograms are predicted by measuring at discrete multiple points around the two compressors and are thereafter reconstructed on the surface of the compressors. 1344 measuring points are used by two microphones in which one is scanning microphone and the other is reference microphone. NAH is a good tool for the visualization of Sound so we can show the source of sound graphically. In this paper, the NAH method found the exact noise source position on the surface of the compressor and the noise-related sub part in the compressor. We found the NAH and is very useful as a noise reduction tool for home-appliance device.

도달지연시간 기법을 이용한 수중 소음원의 위치추적

As considerable interests in noise emission from a ship have been increased, the need for localization of noise sources of the marine propeller generating cavitation and singing noise is looming large. In many practical cases, cavitation and singing noise occur on a particular position of the certain blade of the propeller. It is so important to know the position of noise source correctly in order to eliminate or suppress unwanted noise. In this study, we develop "noise source localization technology" using TDOA method. Experimental measurements carried out at the circulating water channel and towing tank show that noise source can be clearly identified and localized using TDOA method.

Acoustic measurement for 12% scaled model of NREL Phase VI wind turbine by using beamforming

Wind tunnel test for the 12% scaled model of NREL Phase VI wind turbine was conducted at Korea Aerospace Research Institute (KARI) low speed wind tunnel. Test condition for the scaled model was decided to match the blade tip mach number with real scale model test which was conducted at NASA Ames (80′ × 120′) Tunnel. Aerodynamic performance represented by torque of the blades was measured by using the torque sensor installed in rotating shaft and compared with real scale model test results. Acoustic noise for scaled model was also measured at closed type test section with acoustic array of 144 microphones. Time based beamforming method to identify the rotating noise source position was applied to analyze the test results. 1/3 octave band was used in post processing for various wind speeds. Test results shows that the main acoustic noise source position moves toward the blade tip as frequency increases and the noise level at low frequency below 2 kHz has much higher when the blade is in stall condition.

A Method of Calculation for Average Noise Level in a Room considering the Relative Position of Noise Source and Sound Absorbing Surface

A Method of Calculation for Average Noise Level in a Room considering the Relative Position of Noise Source and Sound Absorbing Surface

Active Shield Circuit for Digital Noise Suppression in Mixed-Signal Integrated Circuits

An active shield circuit which effectively reduces the substrate noise on the entire area inside the guard ring regardless of the noise source position is proposed. Simulation result shows that the proposed circuit can reduce the noise level to -85 dB while a conventional guard ring gives -52 dB.

Evaluation of an adaptive, directional-microphone hearing aid: Evaluación de un auxiliar auditivo de micrófono direccional adaptable

The effectiveness of adaptive directional processing for improvement of speech recognition in comparison to non-adaptive directional and omnidirectional processing was examined across four listening environments intended to simulate those found in the real world. The test environment was a single, moderately reverberant room with four loudspeaker configurations: three with fixed discrete noise source positions and one with a single panning noise source. Sentence materials from the Hearing in Noise Test (HINT) and Connected Speech Test (CST) were selected as test materials. Speech recognition across all listening conditions was evaluated for 20 listeners fitted binaurally with Phonak Claro behind-the-ear (BTE) style hearing aids. Results indicated improved speech recognition performance with adaptive and non-adaptive directional processing over that measured with the omnidirectional processing across all four listening conditions. While the magnitudes of directional benefit provided to subjects listening in adaptive and fixed directional modes were similar in some listening environments, a significant speech recognition advantage was measured for the adaptive mode in specific conditions. The advantage for adaptive over fixed directional processing was most prominent when a competing noise was presented from the listener's sides (both fixed and panning noise conditions), and was partially predictable from electroacoustically measured directional pattern data.SumarioLa efectividad del procesamiento direccional adaptable para mejorar el reconocimiento del lenguaje en comparación con el procesamiento omnidireccional o el direccional no adaptable, fue examinada en cuatro ambientes diferentes, tratando de simular aquellos encontrados en el mundo real. El ambiente de evaluación fue una habitación moderadamente reverberante con una configuratión de cuatro parlantes: tres con posiciones discretas y fijas de la fuente de ruido y uno con una fuente única de ruido variable. Se seleccionó material de oraciones de la Prueba de Auditión en Ruido (HINT) y de la Prueba de Lenguaje Conectado (CST) como material de evaluatión. El reconocimiento del lenguaje en todas las diferentes condiciones auditivas fue evaluado en 20 sujetos adaptados binauralmente con audifonos retroauriculares (BTE) del tipo Phonak Claro. Los resultados indicaron mejoria en el rendimiento de la función de reconocimiento del lenguaje con procesamiento direccional adaptable o no adaptable, comparado con el medido a través de procesamiento omnidireccional en los cuatro ambientes. En tanto la magnitud del beneficio direccional resultanle fue similar en algunos ambientes de audition para sujetos que escuchan en modo direccional adaptable y fijo, una ventaja significativa en el reconocimiento del lenguaje fue obtenida para el modo adaptable, en condiciones especificas. La ventaja del procesamiento direccional adaptable sobre el fijo fue más prominente cuando se presentaba un ruido de competencia a los lados del sujeto (tanto en condiciones de ruido fijo y variable), y fue parcialmente predecible con base en la información sobre el patrón direccional electroacústicamente medido.

Effects of the speed of moving noise sources on the sound visualization by means of moving frame acoustic holography

The moving frame acoustic holography (MFAH) method [H.-S. Kwon and Y.-H. Kim, J. Acoust. Soc. Am. 103, 1734–1742 (1998)] enables the visualization of noise generated by moving noise sources, e.g., moving vehicles, by using a line array of microphones affixed to the ground. However, the sound field of a moving noise source has a moving effect, which produces the wavefront distribution different from what would be generated by the source if it were not moving. The moving effect causes errors on the reconstructed hologram by means of MFAH. This paper studies this effect with regard to the speed of noise sources. A formula, which can show the effect, was derived. This enables the analysis of the effect not only on the hologram plane but also on a prediction plane. It was shown that the phase error is more undesirable than that of magnitude. The phase error, which is proportional to the speed of a noise source, shifts the position of noise sources and distorts radiation pattern. A theoretical investigation explicitly showed that the error is negligible for low Mach number (M<0.1). Furthermore, the phase error can be reduced by introducing a correction factor. Several numerical examples illustrate the feasibility of the proposed correction method for low Mach number.

Photoinduced noise amplification in semiconductor structures

To explain the noise amplification found experimentally in semiconductor structures under optical illumination, a physical model of this phenomenon has been considered for which the spectral power density of the surface potential fluctuations in the Schottky diodes and MIS structures has been calculated. Procedures for measuring low-level noise in a semiconductor structure have been proposed with its integral illumination and scanning of the surface of the structure with an optical beam to detect the positions of noise sources.

The impact of placement of noise sources on directional hearing aid benefit

The impact of the number and position of noise sources on measured directional hearing aid benefit was investigated. Directional benefit was quantified as the difference between hearing-in-noise test (HINT) signal-to-noise ratios for omnidirectional and directional hearing aid conditions. Noise environments included a single noise source placed at 180-degree azimuth, and three different five source arrays. All noise sources were uncorrelated and simulated noise only in the rear hemisphere, or noise surrounding the listener. Binaurally fit subjects listened through three different commercial hearing aids with significantly different polar directivity patterns. Testing was completed in two different reverberant environments with average reverberation times of 642 and 1456 ms. The relative level of hearing aid benefit differed significantly depending on the specific noise array used. Results revealed that the pattern of directional benefit across the noise environments could generally be predicted from differences in the hearing aids average polar directivity patterns. The directional benefit across hearing aid types revealed a similar pattern in both reverberant environments, though less benefit was generally obtained in the more reverberant environment in agreement with previous investigations of directional hearing aids. These results suggest that some previous investigations of directional benefit may need reevaluation.

騒音源の位置と語音了解度の関係について

騒音源の位置と語音了解度の関係について

Measurements of vehicle noise source height for noise barrier design

The height of a noise barrier required to give a certain insertion loss is strongly dependent on the elevation of the noise source above the ground. Currently, noise barrier design methods assume equivalent point source heights for different types of vehicles, but these have never been substantiated by measurements. This study used a microphone array, with parametric processing, to evaluate the equivalent noise source height of 100 different vehicles. The results give the noise source position as a function of frequency between 200 Hz and 2.5 kHz. The relative importance of engine, stack and tire noise on the source height is apparent. It was found that the equivalent source on heavy trucks is at 1.2 m, medium trucks 0.7 m, and small vehicles 0.6 m, above the ground. [Work sponsored by Florida Department of Transportation.]

Multiple reflection noise production on transmission systems with periodic or quasi-periodic impedance disturbances-A time-domain approach

The problem of multiple reflection noise production on a transmission line with periodic or quasi-periodic impedance disturbances has been studied. This work involved a time domain approach (including a Monte Carlo simulation), reported here, and also a frequency domain approach which has been reported separately. Particular attention was given to the case where pulsewidths \tau were of the same order of magnitude as the quantity (l)/ \upsilon where (l) is the average distance between disturbances and \upsilon is the propagation velocity of the signals in the transmission medium. The actual system studied was an array telemetry system used in oceanographic situations. However, the results reported here are general and can be applied directly to any digital transmission system having a periodic or quasi-periodic disturbance structure. In this paper, the time domain model is developed and the results of a Monte Carlo simulation employing this model are presented. Various system noise sensitivity studies are reported, including studies of the effects of noise source position, pulse rise time, and capacitive loading.