Showing papers on "Acoustic source localization published in 1988"

Sound field control device

Abstract: In the sound field control device, main signals and a surround signal are generated on the basis of input left and right 2 channel signals, and 4 channel main sound field signals and 4 channel surround sound field signals which are respectively aggregations of reflected sound signals of various directions in the respective sound fields are generated on the basis of reflected sound parameters of sound fields established with respect to the main signals and the surround signal, and the 4 channel main sound field signals and the 4 channel surround sound field signals of each corresponding channel are combined together and provided as 4 channel sound field signals to be sounded Reflected sounds are created on the basis of reflected sound parameters of a certain established sound field regardless of sound field components contained in a source signal and output as a sound field signal By sounding the sound field signals by sound field control loudspeakers arranged about a listener, an effect that gives to the listener the impression that he is surrounded by the sound can be produced

Two‐sensor methods for the measurement of sound intensity and acoustic properties in ducts

Abstract: A unified theoretical approach to the development of two‐sensor methods is presented. It is shown that various methods developed in the last 10 years for sound intensity measurement and for the measurement of acoustic properties in ducts may be systematically derived from a general decomposition theory. In the decomposition theory, the incident and reflected wave auto and cross spectra are obtained from a set of decomposition equations using the measurement of the total acoustic pressure at two arbitrary points in a one‐dimensional steady, random sound field. The application of the wave spectra to the measurement of sound intensity and acoustic properties follows directly. It is further shown that the decomposition theory predicts a set of characteristic wavenumbers at which two‐sensor methods fail to yield meaningful data. Experimental data are presented showing the application of the decomposition theory to acoustic property determination, sound intensity measurement, and the estimation of sound pressure and particle velocity in a duct.

The photoacoustic effect generated by a spherical droplet in a fluid

Abstract: In general, the absorption of amplitude‐modulated radiation by a body results in heating and a subsequent thermal expansion that gives rise to the emission of sound waves. Here, the properties of sound waves emitted by uniformly heated spherical droplets are found as a frequency domain solution to a boundary‐value problem for the acoustic pressure. The expression for the pressure is Fourier transformed to give the time domain pressure response to a delta function light pulse. Owing to the different sound speeds and densities in the sphere and its surrounding medium, the effects of reflection, dispersion, and phase cancellation can be seen in the acoustic signal.

Visualizing method for three dimensional standing wave sound field

Abstract: A visualizing method for three dimensional standing wave sound field comprises the steps of mixing into a liquid medium a large number of fine particles of the same density as said liquid medium and exposing the liquid medium containing the fine aparticles to a three dimensional standing wave sound field produced by ultrasonic waves thus causing the fine particles to move to positions where the amplitude of the sound pressure is minimum, the sound pressure distribution of the three dimensional standing wave sound field being visualized by the distribution of the fine particles.

Scattering of sound by sound from two Gaussian beams

Abstract: The scattering of sound by sound from Gaussian beams that interact at small angles is investigated theoretically with a quasilinear solution of the Khokhlov‐Zabolotskaya nonlinear parabolic wave equation. The analytical solution, which is valid throughout the entire paraxial field, is a generalization of the result obtained for parametric receiving arrays by Hamilton, Naze Tjotta, and Tjotta [J. Acoust. Soc. Am. 82, 311–318 (1987)]. Significant levels of scattered difference frequency sound are shown to exist outside the nonlinear interaction region. An asymptotic formula reveals that difference frequency sound is scattered in the approximate direction of k1‐k2, where ki is the wave vector associated with the direction and frequency of the ith primary beam. Computed propagation curves and beam patterns demonstrate the dependence of the scattered radiation on source separation, frequency ratio, interaction angle, and focusing. Results are also presented for the scattered sum frequency sound. Comparisons ar...

Information Processing Concerning Moving Sound Sources in the Auditory Centers and its Utilization by Brain Integrative and Motor Structures

Abstract: It is noteworthy that although extensive literature has been devoted to psychoacoustic, behavioral (on animals) and electrophysiologic studies of sound source localization in the horizontal plane, until quite recently basic attention has been focused on the investigation of the localization of unmoved sound sources (Altman, 1972).

Interaction of sound waves. Part III: Two real beams

Abstract: This article is a theoretical study of the nonlinear interaction between two sound beams in a lossless fluid, intersecting each other at arbitrary angles. The governing equation for the sum and difference frequency components is solved in the quasilinear approximation for prescribed conditions on the sources of the two beams. A solution that is uniformly valid in space is obtained in the form of a Fourier integral. Asymptotic evaluations at large distance from the sources lead to simple formulas that relate the amplitude and phase of the generated sound to the on‐source conditions. Diffraction effects are fully accounted for, and shown to be important even at large distances. Relevance to earlier literature on the scattering of sound by sound is discussed.

Enhancement of the sound power of a component of a complex noise source by sound from other nearby components

Abstract: In determining the sound power of the components of a complex noise source, such as an engine or a piece of machinery, the interaction between the sound fields of the components has usually been considered to be unimportant. Existing experimental evidence for heavy‐duty diesel engines shows, however, that there is an enhancement of the sound power of individual components by sound from the rest of the engine. This enhancement effect is analyzed here in a theoretical study using a simple spherical model whose surface undergoes random vibrations similar to those of engines and machinery. Computations were also performed with a sphere pulsating like a monopole or oscillating like a dipole. The study shows that, for wavelengths greater than the radius of the sphere, the enhancement is due to an augmentation of the acoustical pressure on the surface of the component by correlated sound diffracted from regions of the surface immediately adjacent to the component. Essentially, in this low‐frequency range, correlated sound from adjacent surfaces increases the radiation efficiency of the component. For sources as large as heavy‐duty diesel engines, the enhancement is relatively small, roughly 20% to 60% over the audible frequency range, as indicated both by the theoretical model and the experimental data. The model predicts, however, that the magnitude of the enhancement increases significantly as the size of the source, or the maximum frequency of interest, decreases. Thus the enhancement should be greater for passenger car engines and greater still for smaller sources. The model also indicates that introducing correlation or phase changes between adjacent parts of the surface of a structure can provide a means of noise reduction, although this may be difficult to achieve in practice.

Sound power emission in reverberation chambers

Abstract: Sound power emission of a simple source in a reverberation chamber is derived from the normal mode theory and compared to that in free space. Both pure‐tone and noise sources are considered. The acoustic impedance of the sound source itself is deemed important in its power emission and incorporated into the analysis. The acoustic impedance presented to the source by the sound field produced in the chamber varies significantly from point to point, and this leads to the large variability of the power output of the source in the room. But the average obtained over the whole room approximates well the sound power produced in free space, provided that the source impedance is large compared to the field impedance and that the frequency is high enough so that the normal modes overlap. A statistical formula is derived for the power emission as a function of the space coordinates in the room. It is found that the power emission is a maximum on the boundary, and undulates about the free‐field value when the source ...

Boundary element analysis of the sound field around a finite barrier.

Abstract: The sound field around a finite barrier is analyzed by two- and three-dimensional boundary element methods. These results are compared with the results measured for an experimental model by a sound visualization method using three color-light-emitting diodes. In the case of two-dimensional analysis, considering the difference between the distance attenuation of the cylindrical wave caused by a line source and that of the spherical one caused by a point source, the sound pressure levels calculated are corrected to express those for the three-dimensional field approximately. For the sound field on the source side of the barrier, both of the sound pressure distributions calculated by two- and three-dimensional analyses agree fairly well with the measured ones. In the case of the opposite side to the source, the two-dimensional results are in good agreement with measured ones for lower frequencies but become inaccurate for higher frequencies. The three-dimensional results show good distribution patterns of sound pressure levels.

Slide Trombone Method for Measuring Sound Velocity and Attenuation in Liquid at Very High Frequencies with Sufficient Accuracy

Abstract: A new method which is suitable for measuring the sound velocity of liquid above 100 MHz is proposed and an apparatus was constructed based on the proposed principle. By examining the temperature dependence of water at 200 MHz it is proved that the apparatus provides correct values of sound velocity with fine resolution.

On ray trajectories and pathtimes for acoustic propagation in a medium with velocity gradients

Abstract: The author presents expressions for paths and pathtimes of rays in volume cells of the medium for which the sound velocity can be characterized in terms of a point velocity and a constant velocity gradient. Such parametrization permits the use of relatively large cells in the segmentation of the medium, so that the dimensional complexity of the tomographic formulation and inversion is reduced significantly. With a small number of segmentwise ramping vertical velocities, including velocity reversals, the profile parametrization allows the computational determination of arrival point targeted eigenrays from a given source point to a specified arrival point. >