Showing papers on "Acoustic source localization published in 1977"

Improved acoustic system for auditory research

Abstract: A closed acoustic system, based on the principles of lumped‐element and transmission‐line acoustics, has been developed for use in acute physiological experiments on small mammals. Through the appropriate utilization of a high‐quality push‐pull electrostatic earspeaker (Stax, SRX), a low‐impedance sound source having a relatively flat frequency response and a bandwidth of over 30 kHz is obtained. The output impedance of the source is increased by means of a lumped acoustic resistance in order to match the characteristic impedance of a uniform delivery line. The characteristic impedance of the delivery line is selected so that acoustic stimuli are propagated from the source to the eardrum without the introduction of substantial amplitude and phase distortion. Sound near the eardrum is coupled to a 12‐in. precision condenser microphone through a high‐impedance uniform probe line that is terminated in its characteristic impedance over the range of higher sound frequencies. When electrical equalization of +6 ...

Binaural sound reproducing system with acoustic reverberation unit

Abstract: A binaural sound reproducing system for transmitting sound radiated from an electro-acoustic transducer through a sound wave transmission path such as a pipe to the left and right ears of a listener includes an acoustic reverberation unit comprising a mechanical-acoustic element. The sound radiated from the electro-acoustic transducer is applied to the acoustic reverberation unit to produce indirect sound with acoustic reverberation. The indirect and direct sounds radiated from the electro-acoustic transducer are mixed and transmited through a sound wave transmission path such as the pipe to the left and right ears of the listener so that the sound image felt by the listener is localized externally of the head of the listener.

Fluid mechanical model of the Helmholtz resonator

Abstract: A semi-empirical fluid mechanical model of the acoustic behavior of Helmholtz resonators is presented which predicts impedance as a function of the amplitude and frequency of the incident sound pressure field and resonator geometry. The model assumes that the particle velocity approaches the orifice in a spherical manner. The incident and cavity sound fields are connected by solving the governing oscillating mass and momentum conservation equations. The model is in agreement with the Rayleigh slug-mass model at low values of incident sound pressure level. At high values, resistance is predicted to be independent of frequency, proportional to the square root of the amplitude of the incident sound pressure field, and virtually independent of resonator geometry. Reactance is predicted to depend in a very complicated way upon resonator geometry, incident sound pressure level, and frequency. Nondimensional parameters are defined that divide resonator impedance into three categories corresponding to low, moderately low, and intense incident sound pressure amplitudes. The two-microphone method was used to measure the impedance of a variety of resonators. The data were used to refine and verify the model.

Attenuation of sound waves in ducts

Abstract: Apparatus for attenuating a sound wave propagating in a given direction along a fluid-containing duct comprises two sound sources spaced along the duct in a given direction; a sound detector between the two sources at a null point at which sound emanating only from the two sources substantially cancels; and means for utilizing the output of the sound detector including a phase-shifter and a frequency-sensitive amplifier to control the operation of the sound sources so that they emit sound in relative antiphase and at equal amplitudes and at such phases relative to the phase of the detected sound that the resultant of the sound radiations emitted in the given direction substantially attenuates the sound wave propagating along the duct.

Finite-difference theory for sound propagation in a lined duct with uniform flow using the wave envelope concept

Abstract: Finite difference equations are derived for sound propagation in a two dimensional, straight, soft wall duct with a uniform flow by using the wave envelope concept. This concept reduces the required number of finite difference grid points by one to two orders of magnitude depending on the length of the duct and the frequency of the sound. The governing acoustic difference equations in complex notation are derived. An exit condition is developed that allows a duct of finite length to simulate the wave propagation in an infinitely long duct. Sample calculations presented for a plane wave incident upon the acoustic liner show the numerical theory to be in good agreement with closed form analytical theory. Complete pressure and velocity printouts are given to some sample problems and can be used to debug and check future computer programs.

Digital sound velocity calculator

Abstract: A digital apparatus for determining the velocity of sound at a selected position in a liquid media is provided with a means for representing the conductivity, temperature and depth of the position in the form of digital numbers, and provides a digital calculating means receiving each of the digital numbers for calculating the velocity of sound as a function of conductivity, temperature, and depth. The sound velocity may be calculated at a succession of positions to provide sound velocity versus depth profile of the liquid media.

Simultaneous measurement of sound velocity and sound attenuation in liquids by a correlation method

Abstract: The correlation between the input and output signals of an ultrasonic ransmitter–receiver system with two quartz transducers was used for the simultaneous measurement of sound speed and sound absorption in liquids With a correlator built from a semiconductor heterodyne detector (active mixer) followed by a low‐pass filter, the space‐dependent cross‐correlation function of the signals, which depicts the sound field in the liquid, was recorded on a x‐t recorder by continuous variation of the transmitter–receiver distance First tests with the apparatus yielded a reproducibility of the sound velocity of ±01%, that of the sound attenuation was within ±3%

An experimental investigation of acoustic radiation from a source inside a large turbulent free jet

Abstract: An experiment has been conducted in NASA Langley's free-jet anechoic facility to assess the effect of a free-jet shear layer on sound radiation from an acoustic source placed inside the jet. The nozzle diameter was 1.22 m and operated at an exit velocity of 35 m/s. Two different types of sources were used; one was a compact source with a nearly uniform radiation pattern, the other was a noncompact source with highly directional radiation pattern. The acoustic source was driven by pure tone and 1/3-octave band white noise. Acoustic measurements were made both inside the jet flow in the potential core region and outside the jet in the acoustic farfield. The effects of mean flow convection and mean shear refraction on sound radiation were determined. The experimental results compared favorably with analytical predictions. The effect of free-jet turbulence on sound scattering was found to be insignificant.

Analog sound velocity calculator

Abstract: An analog apparatus for determining the velocity of sound at a selected position in a liquid media is provided with a means for representing the conductivity, temperature, and depth of the position in the form of analog voltages, and is further provided with an analog calculating means receiving each of the voltages for calculating the velocity of sound as a function of conductivity, temperature, and depth. The sound velocity may be calculated at a succession of positions to provide a sound velocity versus depth profile of the liquid media.

Aerodynamic sound in a relaxing medium

Abstract: A theory of aerodynamic sound propagation, when inhomogeneities characterized by a relaxation process are present in both the source and propagation region, is formulated. The details of the relaxation process need not be specified at the outset, although the relaxation process is characterized by a relaxation time and by an equilibrium and a frozen sound speed in a propagation region which is otherwise in equilibrium. Propagation is described in terms of a D'Alembertian characterized by the frozen sound speed relaxing toward one characterized by the equilibrium sound speed, while the source is interpreted in terms of a frozen Lighthill stress tensor relaxing toward the equilibrium stress tensor. An appropriate Green's function for the three-dimensional relaxing wave propagation operator is used to construct an exact integral for the aerodynamic sound. The sound generated far from the source is then estimated in terms of the aerodynamic sound source.

The Inverse Fast Field Program (IFFP): An Application to the Determination of the Acoustic Parameters of the Ocean Bottom

Abstract: : The problem of estimating the acoustic field produced by a point source located in an environment which is arbitrarily stratified with depth only has received considerable attention. Various models exist which provide reasonable results provided sufficient information about the environment and source characteristic is available. This paper is concerned with solving for the inverse of this problem, i.e., information about the environment, in particular the impedance at the ocean-bottom interface is sought from a knowledge of the received acoustic field and the source which produced it. The theoretical formulation of the scheme is presented and its numerical implementation is discussed and illustrated for three examples of successive orders of environmental complexity.

Sonic attenuation system

Abstract: A beam of sound, of sufficient amplitude for inducing a finite amplitude effect in water, is directed into a field of sound for interaction therewith to produce intermodulation products. Energy is removed from the sound field in the formation of the intermodulation products resulting in an attenuation of sound in the sound field.