Showing papers on "Acoustic source localization published in 1996"

On the reconstruction of the vibro‐acoustic field over the surface enclosing an interior space using the boundary element method

Abstract: The vibrational velocity, sound pressure, and acoustic power on the vibrating boundary comprising an enclosed space are reconstructed by the boundary element method based on the measured field pressures. The singular value decomposition is used to obtain the inverse solution in the least‐square sense and to express the acoustic modal expansion between the measurement and source fields. In general, such an inverse operation has been considered an ill‐posed problem having a divergence phenomenon involved with extremely small measurement errors. The ill‐conditioned nature of the acoustic inverse problem is caused by the singularity of the transfer matrix which produces nonradiating wave components. In order to minimize the singularity and to also reduce the number of measurement points, optimal measurement positions are determined by the effective independence method. Regularization methods are used to stabilize the reconstructed field by suppressing nonradiating components resulting in the singular transfer...

Shock waves in trombones

Abstract: Based on physical models of musical instruments and of the human voice, a new generation of sound synthesizers is born: virtual instruments. The models used for wind instruments are simple feedback loops in which a nonlinear sound source drives a linear filter representing the pipe of the instrument. While very rewarding musical sounds have been obtained with these models, it has become obvious that some essential phenomena escape such a description. In particular the brightness of the sound generated by trombones is expected to be due to the essential nonlinearity of the wave propagation in the pipe. At fortissimo levels this leads to shock wave formation observed in our experiments both from pressure measurements and flow visualization. A modest modification of the physical model could already take this phenomenon into account. The key idea is that the nonlinear effect is essential for the transfer of sound from the source toward the listener, but can be ignored in a model of the generation of the pipe ...

Source localization with broad-band matched-field processing in shallow water

Abstract: Acoustic source localization using matched-field processing is presented for multitone signals from the Shallow Water Evaluation cell Experiment 3 (SWellEX-3). The experiment was carried out in July 1994 west of Point Loma, CA, in 200 m of water of complex bathymetry. The multitone signal (ten tones between 50 and 200 Hz) was transmitted from an acoustic source towed at various depths over tracks which produced complex propagation paths to a vertical line array receiver. Broad-band and narrow-hand processing, localization, and tracking results are compared with each other and with independent estimates of source position. With narrow-band processing, mismatch between the data and the predicted signal replica of /spl sim/1 dB reduced the mainlobe to levels equal to or below the sidelobes. Incoherently averaging the processing output over the multiple tones reduced range/depth sidelobe levels, allowing accurate source localization and tracking.

Kaneohe acoustic thermometer further validated with rays over 3700 km and the demise of the idea of axially trapped energy

Abstract: The Kaneohe acoustic source transmitted 133‐Hz, 60‐ms resolution signals over 3709 km from Oahu at 183‐m depth to a Naval receiver at 1433‐m depth near northern California Ray theory successfully models the acoustic multipaths whose travel times are unambiguously tracked between 1983–89, despite the fact that the sound bounces one or more times from the Oahu slope before becoming trapped in the sound channel The eigenrays are inclined at about 15° at the axis of the sound channel The upper turning depths of the eigenrays are insensitive to realistic perturbations along the section This supports the finding that the changes in delay of ∼±02 s between 1983–89 are due to temperature and not due to changes in the multipaths Compared with transmission through a smoothed representation of the ocean’s acoustic waveguide, the mesoscale and submesoscale features vertically scatter axially trapped energy about 200 and 800 m, respectively The submesoscale structure may be associated with internal waves Scatt

Method for construction of transfer function table for virtual sound localization, memory with the transfer function table recorded therein, and acoustic signal editing scheme using the transfer function table

Abstract: In a method for constructing an acoustic transfer function table for virtual sound localization, acoustic transfer functions are measured at both ears for a large number of subjects for each sound source position and subjected to principal components analysis, and that one of the transfer functions which corresponds to a weighting vector closest to the centroid of weighting vectors obtained for each sound source position and each ear are determined as a representative.

Sound system that determines the position of an external sound source and points a directional microphone/speaker towards it

Abstract: An acoustical sound system that triangulates the position of an unknown external sound source by computer analysis The external sound intensity is measured in three fixed sound sensors The computer inputs the sound intensities and by the inverse square law of intensity vs distance calculates the coordinates of the external sound source In addition, once the source's position is known, the computer points a paraboloid microphone and speaker combined, towards the direction of the sound source This allows a more localized bidirectional link between the source and other electronic connection source

Inversion Techniques and the Variability of Sound Propagation in Shallow Water

Abstract: HIS special issue deals with inversion methods for determining oceanographic and geoacoustic parameters in shallow water. This field has seen a burst of activity in recent years that has been motivated by interest in the Navy for developing methods for obtaining the environmental parameters that go into various propagation models from field measurements. The oil industry has been involved in the development of inverse methods for obtaining the structure of the earth and their work has focused on obtaining the properties of the ocean floor using ray arrival times from seismic reflectionh-efraction type experiment. Because of multipath propagation in shallow water it is difficult to identify and measure ray arrivals. Therefore, different approaches have been investigated for obtaining the geoacoustic properties of the bottom from field measurements made in the water column. Two experimental methodologies have been proposed. In the first case, the acoustic field (due to a narrow or broadband source) is measured on a vertical array of receivers with the source at known distance from the array. Then the inverse problem is to determine the unknown parameters, i.e., the geoacoustic properties of the medium, from the measured field. The other experimental configuration is where the acoustic field is measured on a horizontal array which may be a real or a synthetic array. Again the inverse problem is the determination of the environmental parameters from the measured field. A second type of inverse problem is the estimation of the source position from the field measured on either a vertical or horizontal array given the properties of the water column and bottom. In this special issue, we present different approaches for obtaining the geoacoustic parameters of the bottom. This issue also presents methods for estimating the source position. One of the important inverse problem is the determination of the statistical properties of the ocean bottom interface and volume inhomogeneities present in the sediment. In order to determine thcse parameters we need to have a good foward model that can predict the scattered field. The issue also contains a paper that deals with solving the forward problem, i.e., estimating the scattered field. Though this is strictly not in the realm of inverse problcm we have included it in this issue because in many cases the inverse problem is solved by repeated application of the forward problem. The inverse techniques that are discussed here fall under two broad categories. Matched-field processing and linear inverse methods. Matched-field processing was initially suggested for estimating the source position from data obtained on vertical array. The scheme involved searching through the entire parameter space. For each parameter set in the model space, the replica of the field on the vertical array is computed

Sound source localization in reverberant environments using an outlier elimination algorithm

Abstract: Differences in the arrival times of acoustic waves at multiple sensors permit computation of the source's location. The computation depends upon delay estimation between sensor pairs. In severe acoustic environments, the estimates are degraded by reverberation and interfering noise, and some estimates are poor, constituting outliers. This report describes a computational method for outlier elimination to improve the accuracy of source location.

Matched‐field source localization in a range‐dependent environment

Abstract: In this paper source localization results obtained by matched‐field (MF) processing of vertical line array (VLA) data from the PACIFIC ECHO III sea trial are presented The experimental site was located in a region of significant bathymetric variation An harmonic source was towed on a series of arcs, providing data for a sequence of different ranges and azimuths In spite of the significant bathymetric variation, good MF localization results were obtained for a large fraction of the trial time In the first part of this analysis it is assumed that the azimuth of the source is known Substantial improvements in MF localization were obtained by using an adiabatic normal mode model to calculate replica acoustic fields for the range‐dependent bathymetry The improvement over the results obtained with flat‐bottom waveguide replicas is demonstrated for data from the longer range arcs In the second part of the analysis, the concept of environmental signal processing, an enhancement to MF processing that is obt

Active noise-suppressive control method and apparatus

Abstract: A reproduced sound is sent from a speaker as a sound source unit provided in a sound field. An error signal is produced by a microphone on the basis of a difference in sound between the reproduced sound from the speaker and noise coming from the outside of the sound field into the sound field. A digital filter has a fixed transfer function approximated to a transfer function of the sound field, to which a signal for driving the speaker is supplied. Variation of the transfer function of the sound field is detected by the digital filter. A difference signal between the error signal and an output signal from the digital filter is calculated by an adder. The difference signal determined by the adder is inputted into an IMC filter. A signal for compensating the variation of the transfer function of the sound field and variation of the noise is produced by the IMC filter. A variable parameter of the IMC filter is set so that an absolute value of a product of a value of an approximated and set amount of variation, a distance from the sound source unit to the error-detecting unit, and the variable parameter of the IMC filter is less than 1. Thus, the noise coming into the inside of the sound field is canceled by using an output sound of the speaker.

On sound in an inverse sinusoidal nozzle with low Mach number mean flow

Abstract: The quasi‐one‐dimensional propagation of sound, in a throated convergent–divergent nozzle, with entry and exit baffle at finite distance, containing a low Mach number mean flow, is studied in four steps. The low Mach number nozzle wave equation, is obtained, both for the acoustic potential and velocity, using two methods, viz. (a) elimination between the equations of motion and (b) an acoustic variational principle. For the case of inverse sinusoidal ducts, exact solutions are obtained, in terms of elementary functions, for the acoustic potential and velocity, in horns and nozzles. The reduced acoustic velocity, i.e., correction to ray approximation, is reconsidered as an exact, closed series solution, of a modified Mathieu equation, with imaginary coefficients. The plots of amplitude and phase versus distance, for various low Mach numbers, and increasing wave numbers show a number of effects, which may be interpreted as follows: (i) acoustic energy is focused in the converging duct, leading to a peak half‐way between baffle and throat; (ii) a part of the sound field is reflected before the throat, leaving a weaker propagating acoustic field after. Thus although the duct is symmetric relative to the throat, the sound field is unsymmetric, due to the initial one‐directional propagation, this effect being most marked for half‐wavelength comparable to the length of the duct.

Acoustic imaging systems

Abstract: An ultrasonic inspection system for inspecting a test object and producing substantially artifact-free images, which system includes (1) a sound source for emitting ultrasonic energy toward a test object, (2) a liquid crystal detector for detecting emitted ultrasonic energy and displaying an image, and (3) a coupling medium for sonically coupling the sound source, the test object and the detector. The ultrasonic energy is emitted at each of a plurality of frequencies within a predetermined range. It has been determined that the ultrasonic energy insonifing the object can be caused to scan the object and be angularly varied with respect thereto. Moreover, the rate of frequency scanning is substantially less that the detector image decay so as to produce a substantially flicker-free image. The angular variation is performed by rocking the sound source through a small angle, such as 2° to 6° relative to the liquid crystal detector. Desirably the pivot axis about which the sound source is rocked falls within the body of the sound source or locus of points through which the sound source is moved. This rocking action minimizes disturbance of the coupling medium.

Sound propagation over impedance discontinuities with the parabolic approximation

Abstract: Long‐range, low‐frequency sound propagation over varying terrain conditions is an important problem with both civilian and military applications This work considers the modeling of cw acoustic signals as they propagate over variable‐impedance topography The NASA implicit finite‐difference (NIFD) implementation of the parabolic approximation sound propagation model that incorporates variable‐impedance ground surfaces was used The accuracy of this numerical model is demonstrated with a pair of test problems An application of the results is used to predict excess attenuation of pure‐tone signals whose propagation path includes portions of a flat lake surface

An auditory illusion predicted from a weighted cross-correlation model of binaural interaction.

Abstract: In humans, the lateral movement of an acoustic source produces dynamic changes in the relative sound-pressure level and time of arrival of the acoustic wave at the 2 ears. The dynamic nature of these cues is assumed to play an important role in the perception of lateral motion. A phenomenon of auditory motion is reported whose lateral direction and relative velocity may be specified while interaural differences are kept constant. The stimulus producing this percept is a narrowband wave-form whose instantaneous bandwidth is a cosine function of time. This phenomenon is predicted from a model of cross-correlation that estimates the running position of an image from a weighted combination of 2 variables: (a) magnitude of interaural delay, with smaller delays receiving more weight, and (b) consistency of interaural information across frequency.

Robust source localization in an acoustic waveguide

Abstract: Matched‐field source localization methods attempt to estimate the range and depth of a source in an acoustic waveguide. These methods give good results when the waveguide parameters are known precisely; however, matched‐field methods have been shown to be very sensitive to model mismatch resulting from errors in the assumed environmental parameters. Described in this paper is an approach which minimizes model mismatch, caused by uncertainty in the sound velocity profile, by jointly estimating the environmental parameters and source location. An efficient way to initialize the maximum‐likelihood search by projecting the received data onto subspaces corresponding to regions in parameter space is proposed. Monte Carlo simulation results in a shallow‐water environment are reported.

Distance-measuring method, and method and apparatus for positioning

Abstract: PROBLEM TO BE SOLVED: To obtain a distance-measuring method in which electromagnetic waves and sound waves are transmitted simultaneously in a field or a mountain having a height difference or in a place of bad visibility, in which the electromagnetic waves are triggered in a receiving point and in which the horizontal distance between a transmitting point and the receiving point is found in accordance with the straight-line distance, between the transmitting point and the receiving point, found on the basis of the arrival-time difference between the electromagnetic waves and the sound waves. SOLUTION: A sound source S1 and a sound source S2 are installed on a reference point C at the upper stage and the lower stage, and a straight-line distance x1 and a straight-line distance x2 are found respectively on the basis of the arrival-time difference up to an object D, to be measured, between sound waves and electromagnetic waves which are transmitted toward the object D, to be measured, from the respective sound sources. Then, the horizontal distance (y) between the reference point C and the object D to be measured and the height difference h2 of the sound source S2 with reference to a horizontal straight line passing the object D to be measured are found by the theorem of right-angled triangle three squares on the basis of the two measured straight-line distances and on the basis of the distance h1 between the sound sources at the upper stage and the lower stage.

Pulsed waves: Reflections and the speed of sound

Abstract: A simple, direct, and inexpensive determination of the speed of sound in air, suitable for an undergraduate laboratory exercise, is presented. The same apparatus is used to demonstrate acoustic pulse reflections from closed and open ended tubes of circular cross section.

Quasi 3-D Quantitative Computerized Tomography for Reconstructing Sound Velocity Slices of a Weakly Scattering Object

Abstract: To obtain a quantitative sound velocity image using the technique of ultrasonic diffraction tomography, 3-D treatment is necessary. However, the amounts of data acquired and hardware resources used increase markedly when the conventional 3-D technique is applied. Furthermore, it is difficult to observe the waves over the full-aperture region around the 3-D object. In this paper, a quasi 3-D technique was proposed to reconstruct sound velocity slices of the object by transmitting and receiving acoustic waves over the cylindrical aperture around a single rotational axis. From the result of a simulation using the calculated scattered data from the spherical object, quantitative precision of the 3-D reconstructed sound velocity image was verified to satisfy the requirements for clinical applications.

Acoustic Characterization of Soil

Abstract: : Detection and classification of buried cultural artifacts in ground soil are principal goals for the production, detection and processing of acoustic signals Time domain, frequency domain, and combined time-frequency domain approaches to transmit and process acoustic signals all depend critically on the acoustic transduction device to transmit high-amplitude acoustic pressure waves and to receive low-amplitude acoustic pressure waves over a large band of frequencies

Hydrophone for determining direction of underwater sound

Abstract: The invention is directed to an improved acoustic sensor system for detering the direction of underwater sound signals relative to a user is disclosed. The sensor system includes first and second sensing means for sensing incoming acoustic energy and for providing first and second acoustic energy signals in response thereto; separation means for separating the first and second sensing means a distance S=E(C W /C A ) where E is substantially equal to the separation distance between the users ears, C W is the speed of sound in water, and C A is the speed of sound in air; detector means, operatively connected with the first and second sensing means, for providing first and second output signals in response to the first and second acoustic energy signals; and audio means, operatively connected with the detector means, for providing an audio output to the user in response to the first and second output signals.

空力音の発生機構に関する実験解析 : 第2報, 表面圧力変動と空力音の相互相関について

Abstract: The mechanism of aerodynamic sound generation from a circular cylinder is investigated experimentally using coherence functions between surface pressure fluctuation and radiated sound at Reynolds numbers from 104 to 1.4×105. The correlation between the surface pressure fluctuation and the radiated sound at the fundamental frequency is good, indicating the strong contribution of ordered structures to aerodynamic sound generation. The characteristic length of ordered structure Lc is estimated using the integral scale of the spanwise coherence function of surface pressure fluctuations. The sound pressure is calculated using a modified Curle's equation, with the characteristic length and measured surface pressure fluctuations. The predicted spectra of radiated sound are in good agreement with those actually measured up to five times the fundamental frequency. This result shows that LC is useful for estimating the character of radiated sound from a circular cylinder.

Some Applications of the Sound Intensity Technique to Noise Control in the Workplace.

Abstract: Over a decade has elapsed since commercial sound intensity measurement systems became available. A literature search has shown that the sound intensity technique has found increasing applications in recent years. In this article, the principle and errors of the sound intensity technique are briefly described. Four case studies are given to illustrate how the sound intensity technique can be applied to determine sound power under both laboratory and field conditions, to identify noise source and to measure sound transmission loss o f composite partitions “in situ.” It has been shown that, provided the limitations of the sound intensity technique are understood, results obtained by the sound intensity technique enable effective noise control to be implemented in the workplace.

Influence of acoustic environment on the vertical directionality of ambient noise in coastal water

Abstract: The vertical directionality of acoustic ambient noise has been a subject of much interest in the past. It is a well defined physical quantity that can be measured experimentally with a vertical array. It possesses certain deterministic features that can be modeled theoretically with environmental acoustic and source data. Ambient noise in coastal shallow waters, including its vertical directionality, is not very well known and also difficult to model/predict. This is because the acoustic environment varies with time and is location dependent. Thus arises the question "How does the vertical directionality of the ambient noise depend on the acoustic environments (found in typical coastal waters)?". The authors note that due to the shallow water depth, sound (noise) propagation can be significantly influenced by the bottom. How much bottom interaction will depend on the sound speed profile in the water column: whether it is downward refractive or not. Bottom attenuation will in turn determine how far the sound will propagate in the water column. Using a modal representation, the authors obtain a closed form expression which can be used to interpret and predict the noise vertical directionality as a function of the environmental acoustic parameters. As the deterministic features of the noise vertical directionality is controlled by the sound propagation in the channel, it could be used as an acoustic indicator of the acoustic environment in the area.

The research of cross array's acoustic direction-finding technique

Abstract: This paper presents the method for high precision bearing estimation under the condition that the volume of the array is strictly limited. It gives the principle of this method, the realizing method of beamforming, theory demonstration and simulation results.