Showing papers on "Acoustic source localization published in 1976"

Sonic measuring system

Abstract: A distance measuring system which utilizes sound waves. The first unit can be separate or combined radio transmitter and sound sensor which is held at one of the two points between which the distance is to be measured. This sound sensor unit also has a radio receiver in it. At the other point there is a second unit. This second unit combines both a radio receiver and sound source. In addition there is distance indicating circuitry in the first unit which counts pulses corresponding to distance, and then visually displays the total number of pulses as a measured distance between points based upon the known speed of sound in air at a specific temperature. Initially, the radio transmitter emits a fixed frequency carrier wave which simultaneously triggers the sending by the sound source of a low frequency sound wave and the starting of a counter in the sound sensor. Since the radio wave is traveling at the speed of light its travel speed can be considered infinite when compared to the much slower traveling sound wave. When the slower sound wave is received by the sound sensor unit it is detected, amplified, filtered, changed to a dc electrical signal, differentiated, and acts as a stop pulse for the counter. The accumulated number of pulses, corresponding to the distance between sound source and sensor, is then displayed.

Sound field expanding device

Abstract: In a sound field expanding device, left and right channel sound signals of a two channel stereo are respectively divided into several frequency bands, adjusted on levels and phases, mixed again, and then supplied to loudspeakers, so as to reproduce a natural and clear sound field expanded at most into an angle of 180° around a listener. A pair of the expanding devices are used for four channel stereo to form a surrounding sound field. Sound signals derived from the expanding device can be recorded on sound discs or tapes so as to reproduce easily the expanded sound field.

Remote Wind Sensing by Acoustic Radar

Abstract: Acoustic radar offers a promising new technique for remotely measuring vector wind velocity. Engineered antenna systems have been constructed that effectively reject noise interference, and the corresponding detection logic has been developed that identifies the wind velocity from the processed signal. Recent tests employed an acoustic radar to measure the wind velocity in close proximity to conventional anemometer and vane instrumentation. Comparison between the measurements from the two sensors shows a high degree of correlation; the observed differences are also discussed.

Imaging of Acoustic Radiation Sources with Acoustical Holography

Abstract: If machines or apparatuses radiate partially coherent sound waves, locating their sources can be performed by the reconstruction of an acoustical hologram produced by the waves themselves. Since the practical spectrum of the sound fluctuates, a time average of the hologram signals can be taken, and a lock-in amplifier is used for the purpose. Using rotating gears as a test object, an experiment based on this principle has been successfully carried out to obtain the distribution of radiation sources at a frequency of 9·9 kHz.

Acoustic characteristics of a car cavity and estimation of interior sound field produced by vibrating panel

Abstract: The acoustic characteristics are determined by using a half size model. The acoustic resonances of the model compare favorably with those of an actual car. It is shown that by treating the body structure as an assemblage of a number of point sources, and determining the sound pressure transfer functions for various points on the body structure, the sound pressure level inside the car cavity can be determined with good accuracy. Using this technique, the source areas in a car body, which are major contributors to the total noise produced, can be identified.

Differential sound level meter

Abstract: This invention is a device for measuring small differences between relatively high sound pressure levels at two different microphone sites. It provides electrical insertion voltages, "pilot" voltages, as a means for continuously monitoring the gains of two acoustical channels. The difference between two pilot voltages is utilized to force the gain of one channel to track the other channel.

General treatment of source motion on the total acoustic field with application to an isospeed channel

Abstract: A treatment of the effects of arbitrary motion of a cw source and depth‐dependent sound speed on the total acoustic field at a fixed receiving point is considered for an ocean with horizontal boundaries. Application of our general method is made to a constant sound‐speed channel in which the range‐to‐depth ratio is large, when the source follows a short straight‐line path with constant velocity. Total‐field phase is investigated as a function of receiver time for various source trajectories and phase rate is examined in terms of an arbitrary, but fixed, acoustic frequency. It is shown that source motion may be accounted for by assuming the sound source to be stationary, and by replacing its frequency by approximate Doppler frequency. For long source trajectories, cumulative phase can be approximated as a hyperbolic function of time. The outputs of two uniform colinear arrays, together with power spectra there, are employed to illustrate one method for determing source speed, location, bearing, and frequen...

Sound image localizer

Abstract: PURPOSE:To obtain the localization of the sound image similar to the one when the sound source corresponding to input signals actually exists in the specific position, with the sound field reproduced by a plurality of spe akers disposed in space, using the signals without having localization information as input signals.

Sound radiation from an accelerating sphere

Abstract: The sound radiated by an accelerating sphere has been studied. A careful critique of the existing literature has led to a more complete theoretical analysis of the problem. The acoustic field of an accelerating sphere has also been calculated for different fluid media. The radiated sound pressure from an impulsively accelerated sphere has been compared with a finite acceleration case to emphasize the effect of rate of change of velocity on the pressure waveform. The acoustic energy calculations have been made in both the time and frequency domains in order to further demonstrate that the energy lost in the acceleration is dissipated as sound.

Acoustic flow velocity measuring device - uses difference measurement between velocity of sound with and against current

Abstract: The flow velocity is measured by measuring the difference between velocity of sound with and against the current. Both measurements are made over the same test distance by the same measurement circuit. Sound velocity is measured by the sing-around method, and the difference frequency is counted by a reversible counter; or the sound velocity is calculated by an electronic calculator from the time one or a certain number of sound pulses take to travel over the test distance; or several test sections are operated in multiplex by a measurement circuit. In all cases a single test length and measuring circuit is used thereby keeping costs down.

The prediction and measurement of sound radiated by structures

Abstract: Theories regarding the radiation of sound are reviewed and the implementation in strategies for explaining or measuring the sound produced by practical strucutres are discussed. Particular attention is given to those aspects that relate to the determination of the relative amounts of sound generated by various parts of a machine or structure, which can be very useful information for noise reduction efforts.

Acoustic power of a moving point source in a moving medium

Abstract: The acoustic power output of a moving point-mass source in an acoustic medium which is in uniform motion and infinite in extent is examined. The acoustic medium is considered to be a homogeneous fluid having both zero viscosity and zero thermal conductivity. Two expressions for the acoustic power output are obtained based on a different definition cited in the literature for the average energy-flux vector in an acoustic medium in uniform motion. The acoustic power output of the source is found by integrating the component of acoustic intensity vector in the radial direction over the surface of an infinitely long cylinder which is within the medium and encloses the line of motion of the source. One of the power expressions is found to give unreasonable results even though the flow is uniform.

The normal-mode sound field in shallow water having a positive sound velocity gradient and a random fluctuation surface

Abstract: In this paper, the effect of a random fluctuation surface on the sound field of a harmonic point source in positive sound velocity gradient shallow water is consideved. Approximate expressions for the pole equations and amplitude functions are obtained. It is found that the results of reference [1] are the limiting case of the results of this paper.

Sound attenuation in acoustically lined curved ducts in the absence of fluid flow

Abstract: A study has been made of the sound attenuation in a lined curved duct with rectangular cross section. In this study, the derivation of eigenvalue equation was based on the continuity of the normal component of the particle displacement and the matching of the acoustic pressure on the acoustic lining surface. The sound attenuation was calculated using the acoustic energy expression for the waves propagating in a curve duct. For a given duct geometry and known acoustic lining impedances, a computer program was developed to solve for the eigenvalues and to obtain the sound attenuation of the propagating waves in the lined curved duct. It was found that the fundamental mode was least attenuated. The total sound attenuation was calculated assuming that the amplitudes for all propagating waves were equal at a given frequency. Effects of aspect ratio, bent angle, and the acoustic impedance on the sound attenuation were investigated in the present work. [Work sponsored in part by Naval Sea Systems Command Code 037.]

Sound radiation from randomly vibrating beams of finite circular cross section

Abstract: The radiation of sound from vibrating cylindrical beams is analyzed based on the frequency of the beam vibrations and the physical characteristics of the beam and its surroundings. A statistical analysis of random beam vibrations allows this result to be independent of the boundary conditions at the ends of the beam. The acoustic power radiated by the beam can be determined from a knowledge of the frequency band vibration data without a knowledge of the individual modal vibration amplitudes. A practical example of the usefulness of this technique is provided by the application of the theoretical calculations to the prediction of the octave band acoustic power output of the picking sticks of an automatic textile loom. Calculations are made of the expected octave band sound pressure levels based on measured acceleration data. These theoretical levels are subsequently compared with actual sound pressure level measurements of loom noise.

Parametric acoustic arrays: A state of the art review

Abstract: Following a brief introduction to the concept of parametric acoustic interactions, the basic properties of parametric transmitting and receiving arrays are considered in the light of conceptual advances resulting from experimental and theoretical investigations that have taken place since 1963.