Showing papers on "Acoustic source localization published in 1985"

Method and apparatus for measuring and correcting acoustic characteristic in sound field

Abstract: The acoustic transmission characteristics of a sound field, such as in the passenger compartment of a vehicle, are measured by placing microphones (1-3L,1-3R) at the positions of ears of a dummy mannequin (1-4) having a sound absorbing characteristics similar to that of a clothed adult human. The transmission characteristics are then corrected, such as with an automatic graphic equalizer (3-2), to provide optimized listening conditions inside the sound field for an actual listener. The use of the invention results in a listener's perception of completely natural sound.

The measurement of acoustic noise generated by moving artificial sediments

Abstract: Laboratory measurements relating to the acoustic detection of marine sediment transport are reported. A series of underwater measurements have been conducted on agitated artificial sediments, and the acoustic noise generated by interparticle collisions monitored. Measurements of the total acoustic pressure and spectral pressure levels were made on a wide range of particle diameters for different values of the mass of agitated material, the collision velocities, and the swept bandwidth of the spectrum analyzer. The objective was to relate the total pressure level to the mass of mobile material and ascertain if there was an acoustic spectral signature unique to particle size. This information could then be used to guide the interpretation of acoustic measurements of bedload transport taken in the marine environment and provide specifications for the development of an acoustic system to monitor remotely the material moving along the seabed.

Sound field correction system

Abstract: A sound field correcting system for correcting for multipath frequency-characteristic distortion in an acoustic reproducing system. In one embodiment, the level and delay of an original signal are adjusted and superposed on the original signal so as to obtain a signal which, when reproduced by a loudspeaker, yields a sound pattern at a listening point having a flat frequency characteristic. The delay adjustment is effected in accordance with a difference between the travel distances of direct and reflected sound waves to the listening point.

Current and current shear effects in the parabolic approximation for underwater sound channels

Abstract: The effect of currents on the acoustic pressure field in an underwater sound channel is investigated. Based on fundamental fluid equations, model equations are formulated for sound pressure while including nonuniform currents in the source–receiver plane. Application of parabolic‐type approximations yields a collection of parabolic equations. Each of these is valid in a different domain determined by the magnitudes of current speed, current shear, and depth variation of sound speed. Under certain conditions, it is possible to interpret current effects in terms of an effective sound speed. Using this effective sound speed in an existing numerical code, we examine sound speed in a shallow water isospeed channel with a simple shear flow and a lossy bottom. It is found that even small currents can induce very substantial variations in relative intensity. The degree of variation depends upon current speed, source and receiver geometry, and acoustic frequency. Particular emphasis is placed on intensity‐differen...

Spatial Distribution of the Speed of Sound in Biological Materials with the Scanning Laser Acoustic Microscope

Abstract: Abstmct-An important ultrasonic propagation property for tissue characterization is the speed of sound. The scanning laser acoustic microscope (SLAM) provides the capacity to determine the speed of sound in tissue specimens or portions of specimens on the submillimeter scale. This capability potentially can be utilized to develop indices that quantify the spatial gradient of the tissue’s speed of sound. An automated technique for determining the speed of sound using the SLAM has been developed. It is now possible to study quantitatively the degree of tissue heterogeneity from SLAM measurements of the speed of sound distribution. T

Method and means for measuring sound intensity

Abstract: Sound intensity is determined by simultaneously measuring instantaneous acoustic pressure and instantaneous particle velocity at a single point. A condenser microphone having a vibrating diaphragm generates an output voltage proportional to the instantaneous acoustic pressure. A laser Doppler vibrometer measures the velocity of the vibrating diaphragm and a Doppler frequency tracker converts the velocity measurement into another output voltage which is proportional to the instantaneous acoustic particle velocity. The sound intensity is then calculated from the known components.

Eikonal theory of strong acousto-optic interaction with curved wave fronts of sound

Abstract: The diffraction of light that is due to a converging sound field is interpreted and analyzed in terms of an eikonal ray theory. This theory, in combination with Feynman diagram techniques, indicates that the acousto-optic interaction is physically localized over a width of the sound field given roughly by the geometric mean of the sound’s wavelength and the sound field’s radius of curvature. Analytic results (for two diffracted orders) are in close agreement with 10-order numerical simulations, as long as sound amplitudes are not so strong as to violate assumptions made in the analytic model.

Sound propagation in the rest atmosphere with linear sound velocity profile

Abstract: Sound propagation is considered in the rest atmosphere where the sound velocity varies linearly with height. With the results of the ray theory of refraction being introduced to the asymptotic solution of spherical wave propagating over a locally reacting ground surface, the approximated solution of the sound field is obtained. The results of calculation by this theory explains the measurements satisfactorily, as a result quantitative prediction of excess attenuation is available.

Quality factor and boundary-layer attenuation of lower order modes in acoustic cavities

Abstract: Some acoustic devices make use of closed cavities, filled with gas, the dimensions of which are of the same order of magnitude as the acoustic wavelength and the walls of which are perfectly rigid To know the acoustic response of such small cavities, driven by a mechanical or a thermodynamical source, one needs to take into account the damping processes In this case they are essentially due to viscous and thermal effects in the boundary layers and are described as a finite apparent acoustic impedance depending on the modes In this paper, the sound field is determined in a « rectangular » enclosure excited by a point source and is described by a modal theory The Q-factor is calculated and its properties are discussed and compared with experimental results The agreement is quite good

Relation between physical characteristics of orthostereophonic system and horizontal plane localization.

Abstract: Digital simulation of sound field in the horizontal plane was carried out using orthostereophonic system (OSS). In simulations, several combinations of head and torso simulator (HATS) and equalizing networks were applied for a specified subject. On the other hand, a new method of analyzing the directional hearing in the horizontal plane was proposed. With the results of localization tests, the proposed method has demonstrated that:(1) Sound image directions and its quality as a difference between original and simulated sound field was estimated; The value2.3deg in error mean square for estimating the sound image direction difference and the value 0.78 in correlation coefficient for estimating the sound image quality difference were obtained, respectively.(2) For the given errors of sound image quality and direction, the tolerance limits of OSS performance as the interaural difference margin were illustrated using the proposed method.

A method of detecting sound impulses

Abstract: In a method of associating sound impulses derived from a common sound source, e.g. a gun or mortar, the sound impulses are detected by a plurality of spaced apart detector clusters (not shown) each of which comprises a plurality of sound detectors. The method includes the step of analysing data calculated from signals derived from the detector clusters, which data is indicative of the time of arrival and the angle of arrival of the sound impulses at the detector clusters, to associate those signals and thereby associate the related sound impulses which arise from the common sound source. The progressive 'filtering' action involves first monitoring a primary channel for an arrival, then choosing a secondary channel from the knowledge of the approximate angle of arrival in Channel 1 and searching for angles of arrival compatible with the known extent of the area of observation, thereby choosing a predicted time window for searching in Channel 2. A third channel is then examined using time and angle windows, and so on.

Approximation of impulse response through computer simulation based on finite sound ray integration

Abstract: The calculating estimation of the initial impulse response at a receiving point within an auditorium through the computer simulation has developed as one of the effective measures to obtain design information for room acoustic designing. In simulating sound field in a room, it has generally been assumed to be a diffusive sound field. However, in analyzing the impulse response of a hall in terms of initial impulse response, which has a significant acoustic effect, the reflected sound from a wall surfaces reaches a receiving point discretely and not in a diffused state. Accordingly, such an assumption is not necessarily appropriate. This paper deals with the analysis of and experiments on the reflection response of finite rigid surfaces to acquire basic information for sound field simulation. In the analysis, the areal integrals on reflecting surfaces are found through the application of the sound ray tracing method, which has originally been developed on the basis of geometrical acoustics, for the approximation of impulse response incorporating the effect of the wave motion of sound. The appropriateness of the new finite sound ray integration simulation system is verified by proving the possibility of the approximation of a transfer function corresponding to the accuracy of simulation for the multiple reflection, through the comparative evaluation of the measured results and the results of simulation calculation regarding flat plate, diffusive plates and closed spaces.

A small pressurized vessel for measuring the acoustic properties of materials

Abstract: A laboratory system is described that measures the acoustic properties of materials in the frequency range from 10–100 kHz, at pressures to 150 psi (1000 kPa), and from 0°–40° C. By using transducer arrays and broadband pulses together with digital data acquisition and analysis techniques it is possible to contain this (essentially) free‐field system in a vessel with a volume of only 0.42 m3. The system provides measurements of complex reflection and transmission coefficients as a continuous function of frequency. From the data one can obtain the following material parameters: sound speed, frequency‐dependent sound attenuation coefficient, complex acoustic impedance, echo reduction, and insertion loss. Results are presented for a variety of samples to illustrate the capability of this system.

High accuracy noncontact laser‐optical method for measuring surface acoustic wave velocity and attenuation

Abstract: A high accuracy noncontact laser‐optical method for measuring surface acoustic wave (SAW) velocity and attenuation is described. The accuracy depends on the power of the two lasers, used for generation and probe of SAW and on bandwidth of the intensity modulation. The method is applicable to all acoustic materials including the nonpiezoelectrical ones.

Sound measuring system

Abstract: A sound measuring system for determining the coordinates of a sound source and comprising a central station and a number of measuring points, is described in which - each measuring point (1) contains three sound transducers (11), means for digitising the signals output by the sound transducers and means for transmitting the digital signals to the central station (2), - the differences of the sound transit times to the individual sound transducers of each measuring point are determined, from these a bearing angle (a) is determined for each measuring point and from the bearing angles and the coordinates of the sound transducers the coordinates of the sound source are determined, - the entire calculation of the coordinates of the sound source (3) is carried out in the central station (2). Furthermore, a method for determining the differences of the sound transit times to two sound transducers by means of the cross correlation function of the signals output by the sound transducers is specified which determines the differences in transit time by calculating the centroid of the square of the amounts of the cross correlation function.

The approximation of pressure waveforms of impact sound radiation from clamped circular plates of various thicknesses

Abstract: The purpose of this paper is to investigate the mechanism of impact noise generation, in order to reduce noise at its source. A fundamental model, the case of a ball striking a clamped circular plate, was studied. In the experiments, the effects of plate thickness and observation distance on sound pressure were observed. In the theoretical analysis, the rotary inertia of the plate, shear deformation, and the air reaction of the radiated sound were considered. The impact force history was assumed to be a triangular pulse, since it was determined by three parameters: the maximum impact force, the impact duration, and the rise time. The time when the maximum sound pressure occurred, the influence of the rise time on the sound pressure level, and the vibrational modes which contributed to the sound were obtained using this approximation.

Sound intensity in diffuse sound fields

Abstract: The net sound intensity field in a room containing a random noise source is the vector sum of the direct field and the reverberant intensity field If the room is diffuse, the net reverberant intensity will be zero and only the direct field will constitute a net intensity flow The net sound intensity field in the vicinity of a source placed in a diffuse room will therefore be identical to that in a free field, decreasing by 6 dB per doubling of the radial distance from a simple source In any other environment the reverberant field will also yield a flow and the resulting distortion of the free‐field radiation pattern will reflect a lack of directional diffusion A simple descriptive model of the intensity field in various types of acoustic environment is presented

Measurement of sound transmission loss by sound intensity

Abstract: The sound intensity technique is being implemented to measure sound transmission loss at the Centre for Building Studies acoustics test facility. The use of the intensity technique for this purpose is being investigated in three main areas; validation with respect to standard techniques; determination of appropriate measuring procedure; exploiting the analytical capabilities of the technique. This paper presents some preliminary findings with respect to these areas

A photographical sound visualization method by using light emitting diodes.

Abstract: This paper describes the sound visualization method, some results visualized actually and the comparison of the graphic expression method of the sound pressure level distribution by X-Y plotter with the photographical one. This sound visualization method is based on an idea that the beams from three colored light emitting diodes are recorded photographically on a film, which go on and off in sequence every time the sound pressure level changes by 5 dB. The actual measurement of the distribution of sound pressure level can be performed with the sound visualizing device built as a trial according to the idea. The summary of the result is ; The directivity of a sound source and the properties of the sound field, such as the distribution of sound pressure level or sound diffraction can be grasped quantitatively and clearly by the sound visualization method. Furthermore, the photographic result of the sound pressure level distribution can be obtained in more detail and a shorter time as compared with the graphic one.

The use of acoustic pressure measurements to determine the particle motions associated with the low order acoustic modes in enclosures

Abstract: This paper describes a procedure for experimentally deriving, in terms of the particle motions, the shapes of the low order acoustic modes in enclosures. The procedure is based on finding differentiable functions which approximate the shape functions of the low order acoustic modes when the modes are defined in terms of the acoustic pressure. The differentiable approximating functions are formed from polynomials which are fitted by a least‐squares procedure to experimentally determined values which define the shapes of the low order acoustic modes in terms of the acoustic pressure. The experimentally determined values are found by a conventional technique in which the transfer functions, which relate the acoustic pressures at an array of points in the enclosure to the volume velocity of a fixed point source, are measured. The gradient of the function which approximates the shape of a particular mode in terms of the acoustic pressure is evaluated to give the mode shape in terms of the particle motion. The procedure was tested by using it to experimentally determine, in terms of the particle motions, the shapes of the low order acoustic modes in a small rectangular enclosure. Details of the experimental technique used and some of the results obtained are given.

Studies on Impact Sound : Second Report, Mechanism of Sound Generation

Abstract: In view of troublesome nature of impact sound, a series of studies have been undertaken in order to find out a way to reduce this effect. This second report concerns the mechanism of impact sound generation when a ball collides against a plate. Simply, a ball attached with a force transducer was collided with a freely suspended square steel plate. The pulse-like contact force occurring between the ball and the plate, vibration of the plate, and impact sounds at positions near and far from the plate surface were measured simultaneously. These signals were stored in a wave memory instrument and analyzed by FFT analyzer. Frequency characteristics at four steps concerning the impact sound generation were obtained. These frequency characteristics were not affected by the size of the ball, the ball material or the impact velocity. From the results of analysis, the mechanism of generation of impact sound has been clarified.

Sound source survey instrument

Abstract: PURPOSE: To create the sound pressure distribution information of a sound with a desired frequency from a sound source object generating a complex sound by a simple structure by performing the function of a filter for a number of provided amplifiers by a single amplification degree control signal generator provided with a function generator. CONSTITUTION: The position and the sound pressure distribution of a specified sound source in a sound source object generating a complex sound are sampled by a microphone array 8 directly opposed to the sound source object. On the other hand, by operating a function generator 181 in an amplification degree control signal generator 180 to generate sine wave electric signals from the function generator 180 and adjusting the phases of the sine wave signals, these signals are inputted to the control terminals of amplifiers 18a as the amplification degree control signals. The signals received by microphones 8a are amplified by the bias due to the amplification degree control signals and, on the basis of the amplified signals, a given sound pressure distribution information is obtained to be displayed by a display 19 as a sound image. COPYRIGHT: (C)1987,JPO&Japio

Process and device for determining the length of a sound path

Abstract: The subject of the invention is a process for determining the length of a sound path, in which the travel time of a sound signal (S2) along the sound path is measured. The invention is distinguished by the change in the travel time of the sound signal (S2) caused by a change in the length of the sound path being measured by evaluating the phase shift of the received signal in comparison with the transmitted signal.

Generation of Underwater Sound by a Moving High-Power Laser Source.

Abstract: : The generation of underwater sound by high-power laser pulse is analyzed both theoretically and experimentally The mechanism of sound generation is the thermal expansion of the water caused by heat imparted by the laser The basic physical properties of such a laser-induced thermoacoustic source are investigated with a time domain approach which is valid in the nearfield of the source Results are then extended to the case of a thermoacoustic source moving at subsonic, transonic, or supersonic velocities on the surface of the water Special attention is paid to the case of a source moving at a velocity close to the speed of the sound in the water, because, at such a velocity, high pressure transients can be generated, making the thermoacoustic mechanism of sound generation more attractive for practical applications Experimental results were obtained with a laser system providing up to 5 joules of energy over a pulse duration of approximately 1 ms, during which the intensity was modulated at a single frequency between 5 and 80 kHz The laser emitted either in the infrared region of the spectrum or in the visible region of the spectrum Most of the experimental results presented in this study were obtained with the infrared Neodymium:Glass laser Four kinds of results were obtained: pressure waveforms, directivity patterns, sound level dependence on source velocity, and spreading curves In general, the experimental results are in good agreement with the theoretical predictions

Use of the complex intensity vector for sound radiation and sound field studies

Abstract: The traditional intensity technique to determine the sound power radiated by sources or propagating through a sound field uses the real part of the complex intensity only. More information on the sound field and sound radiation can be obtained if both real and imaginary components of the intensity vector are considered. This paper presents the results of studies of the fundamental relationships between sound pressure, particle velocity, complex intensity, and both potential and kinetic energy. As shown before, the real part of the intensity vector is rotational (curl Ir ≠ 0, div Ir ≠ 0), while the imaginary (reactive) component of the complex intensity vector is irrotational (curl Ii = 0, div Ii ≠ 0). The conditions of the vortex formation were studied as a function of the source distribution. The relation between the extremes of the intensity curl and the energy in the sound field have been formulated. The applications of the sound intensity field structure on the sound radiation from complex radiators i...

Method and apparatus for detecting acoustic homogeneity of object

Abstract: A pulsating sound wave beam is transmitted into an object using an array-type ultrasonic wave transducer which consists of a plurality of elements; the reflected sound waves are received using said transducer while electronically focusing the reflected sound waves depending upon an estimated speed of sound in the object, and the beam width of sound waves is measured repeatedly near a particular reflector while successively changing the estimated speed of sound. The estimated speed of sound of when the beam width is minimal is the mean speed of sound of the object in practice, and the beam width at that moment serves as an indication of acoustical homogeneity of the object.

Methods of controlling sound image distance by varying the cross‐correlation coefficient between two‐channel acoustic signals

Abstract: A number of problems is involved in controlling sound image distance and such control has been realized only over a very limited range. This paper presents three methods of sound image distance control based on the knowledge that “if we vary the correlation coefficient continuously from 1 to -1, the sound image will move from a remote point to approach close to the observer's head.” Using one of these methods (the 90° phase shift method) in psychological tests, it has been found that the sound image broadening can be held almost constant while the sound image distance is varied. However, because the orientation of the sound image shifts within a horizontal plane with that system, it is necessary to employ an orientation-correcting sound attenuator. As a means of automatically achieving this correction, we propose the α° phase-shift system and it is shown that the approach of the sound is practically linear when α° is 70°. In addition, as a simpler circuit configuration, we propose the delay circuit system, which is shown to be effective for sound image distance control.

Passive source localization with intersecting spherical surfaces from time delay estimates

Abstract: The problem of passive localization of an acoustic source is a classic area of research in underwater acoustics. While the three‐dimensional problem presents difficulties, most past investigations have been able to make suitable approximations to reduce the localization to one in a plane involving two dimensions. However, acoustic source localization in anechoic tanks, pressure vessels, or other similar enclosures often requires a truly three‐dimensional formulation. This paper presents the equations describing source localization in three dimensions, given time delays between four receiving channels. Numerical difficulties associated with their solution are discussed, particularly those involved in the nonlinear solution of sets of intersecting hyperboloids. An alternate formulation is presented which makes use of intersecting spheres rather than hyperboloids. This reduces the numerical complexity markedly since finding intersections of closed surfaces such as spheres is inherently more stable than for open surfaces like hyperboloids. Several possible algorithms for implementing this approach are presented, and the practical limitations of each for use with nonideal data are contrasted. Results indicate that the proposed method of intersecting spheres is numerically simpler and provides a more accurate solution for passive source localization than the method of intersecting hyperboloids. [Work partially supported by NAVSEA PMS 409 and by NAVSEA 63X5.]