Showing papers on "Acoustic source localization published in 1992"

Partial discharge. XIII. Acoustic partial discharge detection-fundamental considerations

Abstract: An overview of the basic acoustics theory required to understand the finer points of acoustic partial discharge (PD) detection systems is given. PD and acoustic test methods are discussed, and acoustic wave motion, impedance, and intensity are described. Wave propagation and signal absorption, and the velocity of sound are discussed. Acoustic characteristics of media gases, liquids, and solid materials are described. >

Method for generating three-dimensional sound

Abstract: A method for producing three dimensional sound associated with an object that is moving from a first position to a second position with respect to the listener. The method includes the effects of doppler shifting, head shadowing, distance on frequency components of the sound as well as the volume of the sound, and the natural sensitivity of the human ear in the 7-8 kHz range. The method provides a sequence of digital sound samples which when converted into analog waveforms and for production of audio signals will provide an audio signal which will provide sound queues to the listener for the location of the sound in three dimensional space.

Active control of far‐field sound radiated by a rectangular panel—A general analysis

Abstract: In this paper a general analysis is presented for the active control of the far‐field harmonic sound radiated by a rectangular panel that is built into an infinite baffle. In this analysis, the panel vibration may be generated by either airborne sound (incident sound field) or by structure borne vibrations. The far‐field radiated sound is controlled either by acoustical sources or vibration sources. Minimization of both the local sound pressure and the total power output is considered. Analytical results for the particular case involving minimization of the sound pressure at a single point are compared with experimental data. The physical mechanisms involved for different control sources (vibration or acoustic) are demonstrated analytically. For the case of vibration control sources, the panel modal velocity components are adjusted to produce far‐field sound control. This can be done either by decreasing their amplitudes, and/or by changing the temporal phases of the panel modes. However, for acoustic control sources, the far‐field sound is minimized by alteration of the radiation impedance seen by the vibrating panel and the control sources.

Method of detecting localization of acoustic image and acoustic image localizing system

Abstract: A method of detecting localization of an acoustic image, in which an acoustic impulse is emitted from a sound source to a dummy of a human head, an acoustic sensor is provided to a portion of the dummy's ears, and the response waveform is received by the acoustic sensor. This enables the detection of what effects are derived from interruption, reflection, and the like of a tone due to the human head. The received response waveform is analyzed and parameters for an acoustic image localization system are obtained. The acoustic image localization system comprising a delay circuit, a filter and an amplification controller sets the parameters into the delay circuit, the filter and the amplification controller, so that the detected localization of an acoustic image is reproduced.

Sound field offset device

Abstract: A sound field offset device having two channels, each of which includes a frequency selection filter for dividing a stereophonic input signal into two frequency bands by a given frequency falling within an audio frequency, at least one digital filter for performing sound field offsetting within a lower frequency band, and at least one loudspeaker assembly for a higher frequency band having a sharp directivity pattern and capable of defining an area to which acoustic power is emitted. This device allows a sound field to be offset in a cost effective and simple manner, by improving the frequency characteristic of a sound field space and by clarifying the sense of locality of acoustic images.

Boundary integral equation method for source localization with a continuous wave sonar

Abstract: In this paper, matched‐field processing is combined with the boundary integral equation method (BIEM) of scattering theory to study a sound source localization problem in a perturbed shallow ocean It is assumed that there is a known inclusion embedded in a shallow water waveguide Continuous waves (cw), produced by a sound source, are scattered by the inclusion and then received by a hydrophone array Because the symmetry of the waveguide has been destroyed by the existence of the inclusion, a proper procedure is required to avoid the mismatching A numerical scheme is presented that makes use of the separation of the source and the detection array, and greatly reduces the computation A numerical simulation using this method is presented

Acoustic particle acceleration sensor and array of such sensors

Abstract: An element responsive to acoustic particle acceleration for sensing acoustic signals in a region of low acoustic pressure is disclosed. The element may be isolated from acoustic noise when positioned adjacent an acoustic noise generating high acoustic impedance structure by a baffle which provides isolation from radiated and evanescent acoustic signals and structure vibration.

Sound produced by an aerodynamic source adjacent to a partly coated, finite elastic plate

Abstract: An analysis is made of the scattering of bending waves at the edge of an unbafiled, thin elastic plate in the presence of arbitrary fluid loading. Detailed predictions are made of the sound scattered from free and clamped edges, and empirical formulae given for the radiation loss factor over a range of frequencies and fluid loadings. Application is made to the generation of sound by an aerodynamic dipole source adjacent to a finite plate, a finite length of which has been treated with damping material. The dipole models the production of sound by blade-vortex interactions occurring when turbulence or discrete vortices are ingested by a ducted rotor, in which the plate assumes the role of a neighbouring duct wall. In typical underwater applications, when the influence of fluid loading is important, sound produced by the source at frequencies below the coincidence frequency of the bending waves can propagate directly to the far field, essentially as if the plate were absent. However, flexural plate-motions are also generated by the source. These contribute to the radiation by scattering at the edges and, in the absence of dissipation in the plate, the intensity of the edge-scattered sound can dominate the direct radiation from the source. When the edges can vibrate freely, it is shown that a relatively modest amount of damping is sufficient to reduce the edge generated sound to levels below those of the direct radiation. The efficiency with which bending wave energy is converted into sound is much larger for clamped edges, and larger values of coating loss factor and length are necessary to achieve significant reductions in the structural component of the radiated sound.

Acoustic vector sensor array processing

Abstract: An approach is proposed for localization of acoustic sources using an array of sensors for which the measurement of each sensor is a vector consisting of the acoustic pressure and acoustic particle velocity. A compact expression is derived for the Cramer-Rao bound (CRB) on the estimation errors of the source direction-of-arrival (DOA) parameters in the multi-source multi-vector sensor model. An explicit expression is found for the mean-square angular error bound for source localization with a single vector sensor. Two simple algorithms for estimating the source DOA with this sensor are presented along with their statistical performance analysis. >

Sound source signal estimating device

Abstract: PURPOSE:To securely separate a signal from a noise and extract it CONSTITUTION:Signals from sound sources 0-M-1 are detected by microphones 0-M-1 of a signal detection part 21 A sound source which generates a noise is considered to correspond to one of the sound sources 0-M-1, not to mention a sound signal which generates an original speech signal to be extracted A transfer function estimation part 23 estimates a transfer function H' between the respective sound sources and respective microphones by using the output of the signal detection part 21 A sound source estimation error minimization part 24 finds an update value dX1 of a sound source estimation signal X minimizing an error of the sound source estimation signal X obtained when a transfer function is H' An update part 26 calculates a final sound source estimation signal X from a restriction dX2 and an update value dX1 regarding the sound sources which are given by a restriction part 25

Multipole sources for cancellation of radiated sound fields.

Abstract: It is of interest to be able to cancel the sound field generated by a noise source everywhere exterior to the source. The nature of the secondary source or sources required to achieve that cancellation is a subject of current interest. It has recently been suggested that the sound radiation from coherent, finite‐size radiators may be represented as a superposition of monopole fields [G. H. Koopman et al., J. Acoust. Soc. Am. 86, 2433–2438 (1989)]. It has also been observed that a monopole source may be represented by an infinite‐order multipole source placed elsewhere [A. J. Kempton, J. Sound Vib. 48, 475–483 (1976)]. In principle it is thus possible to create a single multipole source that could represent, and thus cancel, the sound field generated by an arbitrary coherent radiator. In this paper, the initial results of a study to determine the feasibility of such an approach are presented. In particular, the realizable far‐field attenuation will be considered as a function of frequency, secondary source...

Distance control of sound images by a two-dimensional loudspeaker array

Abstract: A new method of sound-image distance-control using a loudspeaker array is discussed. It is shown that a stable sound image can be localized in front of the loudspeaker array. An audio signal is fed to the loudspeakers of the array with appropriate time delays so that the sound waves from the loudspeakers focus at one point between the listener and the loudspeakers. The sound pressure is very great near the focal point, and spherical equal-phase contours are synthesized from this focal point. The results of subjec tive evaluation of sound image distance using an experimental loudspeaker array show that a stable sound image is actually perceived near the focal point. Moreover, the direction of the sound image is little affected by motion of the listener's heads. This indicates that the focal point is perceived exactly like a real sound source. With this method, a sound image can be localized at the distance of the corresponding video image in 3D TV.

The hydroacoustics of a raindrop impact

Abstract: Raindrops produce sound underwater by two known mechanisms: a relatively low energy impact sound and a much stronger bubble sound when a bubble in trapped during the drop splash. Although the bubble sound dominates when it occurs, in other circumstances the impact sound is important. The impact sound has been studied in the laboratory using single drops falling at terminal velocity and with numerical simulation. In both instances, it is convenient to monitor the pressure field in the immediate vicinity of the drop impact. This ‘‘near‐field’’ pressure contains acoustic and nonacoustic components. The acoustic components include an impulsive acoustic water hammer and internal resonances of the water drop itself. The nonacoustic component of the pressure field is part of the hydrodynamic establishment of the splash flow and should not be interpreted as acoustic energy. The two components have been separated in order to identify the far‐field acoustic propagation.

Acoustic resonances in a liquid with vapor bubbles: Effect of liquid-vapor transition on sound velocity and attenuation.

Abstract: We present an experimental study of a diphasic medium that consists of diethyl ether containing vapor bubbles. We show that the liquid-vapor transfers affect the sound velocity and attenuation so that the usual liquid-gas effective-medium theory is in error at low frequency. At high sound amplitude the shape of the resonance curve shows nonlinear erects, and acoustic bistability is observed

Acoustic daylight: Imaging the ocean with ambient noise.

Abstract: For many years the principal means of probing the ocean using sound has been through the use of either ‘‘active’’ or ‘‘passive’’ techniques. With an active system, an object is illuminated by a pulse of sound and its presence inferred from the echo it produces, whereas the passive approach involves simply listening for the sound that the object itself emits. Here a new method of employing sound in the ocean is reported, which is neither passive nor active. It relies on the naturally occurring, incoherent ambient noise field in the ocean as the sole source of acoustic illumination. By analogy with daylight in the atmosphere, ambient noise scattered from an object in the ocean can be focused onto an image plane, and from this acoustic image, with appropriate signal processing, a visual image can be produced on a television‐type monitor of the object space in the ocean. To test this concept, several simple experiments have been conducted in the ocean off Scripps pier, with a single parabolic reflector acting as an acoustic lens, which confirm that objects illuminated only by ambient noise can indeed be ‘‘seen’’ over a frequency band between 5 and 50 kHz. [Work supported by ONR.]

A three‐dimensional sound intensity probe.

Abstract: A commonly used sound intensity probe is one‐dimensional, that is, only the sound intensity in the direction of the probe axis is measured. This makes the sound intensity measurement very time consuming if two‐ or three‐dimensional intensities are needed. Very rarely a two‐ or three‐dimensional intensity probe is used for practical applications. A conventional three‐dimensional intensity probe consists of six (three pair) microphones, making the probe itself very clumsy. Due to its non‐negligible size, the sound field is disturbed and an accurate measurement becomes difficult. A three‐dimensional intensity probe was developed that solves this problem. Four 1/4‐in. microphones are located at each apex of a regular tetrahedron. Each of them are attached at the tops of four parallel tubes with a 4 mm diameter. When viewed from the front, the four microphones are located at the three apexes and the center of a triangle. The pressure at the center of the tetrahedron is given by the average of the four pressure outputs. The intensities from the center to the four apexes are obtained by use of the average pressure and individual pressure output. These four components are distributed to three (x,y,z) components. Results of numerical calculations that show the accuracy of the algorithm will be given.

Active noise controller

Abstract: PURPOSE: To obtain the active noise controller which performs effective active noise control even when a sound receiver detecting the sound generated by a sound source is brought close to the sound source. CONSTITUTION: A mesh type straightening member 10 is arranged between the sound source (fan) 6 arranged in the flow passage in a duct 5 and the sound receiver (sensing microphone) 1 and then the sound generated by the sound source 6, i.e., a flow of fluid (air) propagating the sound is straightened into a nearly uniform flow to obtain coherence, so the active noise control can effectively be performed by bringing the sound receiver 1 close to the sound source 6. COPYRIGHT: (C)1993,JPO&Japio

Array processing with acoustic measurements at a single point in the ocean.

Abstract: In order to obtain information on the spatial dependence of the underwater acoustic pressure field, the traditional approach has been to deploy a spatially distributed set of hydrophones. However, by use of a Taylor series expansion, the spatial dependence of the sound field can also be obtained from measurements at a single point in space. The purpose of this presentation is to discuss the adaptation of high‐resolution array processing algorithms to such single‐point measurements. Simulation results will be presented to illustrate the application of Capon’s minimum variance method, the linear prediction method, and the multiple signal classification scheme to measurements in a Taylor series expansion to first order and in an expansion to second order of the pressure field. In addition, a comparison will be made of the high‐resolution methods to standard processing (equivalent to the Bartlett method) using actual ocean acoustic data from geophones and hydrophones. Extensions of these techniques to data co...

Acoustic impedance measurements of transverse and longitudinal sound in superfluid3He

Abstract: We report on simultaneous acoustic impedance measurements of transverse and longitudinal sound at 61 MHz and pressures of 15.6, 10.5, and 8.0 bar.

Exploiting sound absorption for target motion analysis

Abstract: Normally, sound level as a function of time originating from a target moving with constant (and, compared to the speed of sound, small) velocity, only permits the determination of angular velocity. However, sound absorption becoming important in the ultrasonic region can be exploited to estimate both target velocity and range. The theoretical estimation accuracy is investigated employing model assumptions of increasing complexity, including the exploitation of possibly available measurements of target bearing angle. The proposed procedures are applied to both simulated and real data.

Phase and amplitude fluctuations in a refractive shadow

Abstract: For a point source in an upwardly refracting atmosphere, an acoustic shadow region exists beyond the limiting sound ray that grazes the ground. A receiver located within the shadow will have no direct ray path for sound propagation and sound energy arrives at the receiver through other mechanisms. Experiments using an array of microphones at a range of about 1 km and source tones of about 1 kHz indicate that the character of the phase and amplitude fluctuations of the received signal within an acoustic shadow region can vary dramatically. Relationships between the characteristics of the fluctuations and physical propagation mechanisms are explored. In particular, the possibility is investigated that the mechanisms of scattering, diffraction, and ‘‘line‐of‐sight’’ propagation, each intermittently, dominate the received sound field. Application to adaptive beamforming in the atmosphere is discussed.

Experimental verification of the theory for sound propagation in a wedge with a shear supporting bottom

Abstract: Laboratory experiments have been carried out to investigate underwater sound propagation over a sloping bottom that can support shear The sound field was measured in both the across slope and down slope direction for many different frequencies and bottom slopes The experimental results have been compared with the source image theory for sound propagation in a penetrable wedge [G B Deane, J Acoust Soc Am 91, 2390 (A) (1992)] and have shown very good agreement for both down slope and across slope propagation In particular the effect of shear waves on across slope propagation has been demonstrated both theoretically and experimentally Further the effect of a sediment layer has been successfully incorporated into the source image theory for comparison with the experimental measurements at low frequencies One of the problems with laboratory scale measurements of underwater sound propagation is the determination of the bottom parameters with sufficient accuracy for acoustic calculations In this case the model of the sea floor consisted of a sediment layer (modeled experimentally by epoxy) over a hard basement made of concrete requiring 11 variables to describe the geo‐acoustic features of the bottom These were obtained by inverting measurements of the acoustic field in water of constant depth over the same model The results are therefore geo‐acoustically calibrated [Work supported by ONR]

Scattering of hydrodynamic pressure pulses by coating inhomogeneities

Abstract: Sound generation by a deterministic, hydrodynamic pressure pulse in a fluid flowing over a compliant coating with an embedded void inhomogeneity is investigated. The inhomogeneity is represented by an acoustic monopole and its strength is found for several models of the pressure pulse. The far‐field acoustic pressure is calculated for all models and is compared with the sound generated by a statistically stationary turbulent boundary layer. It is found that for certain parameters of the coating, the intensity of scattered sound generated by a deterministic pulse may exceed by 10–40 dB the intensity of sound estimated for the statistical turbulent boundary layer forcing.

Source localization in a waveguide with unknown large inclusions

Abstract: In this paper, we combine the matched-field method with the boundary integral equation method from inverse scattering theory to study a sound source localization problem in a shallow ocean with an unknown large inclusion. We assume that there is an unknown inclusion embedded in a shallow water waveguide. To localize a continuous wave (CW) source, we send in a number of 'mode waves', which scatter off the unidentified inclusion and are received by a hydrophone array. Combining the information of these scattered waves and the signal from the point source, we present an algorithm to estimate the location of the CW source. A numerical simulation using this method is presented.

Sound scattering by a moving sphere

Abstract: The sound field in the vicinity of a small radius sphere moving through an ideal fluid with a constant velocity much smaller than the sound velocity is investigated theoritically

Sound power determination using the sound intensity scanning technique

Abstract: Sound intensity is the primary quantity required to compute the sound power of sources, which is given by the surface integral of the product of the normal component of the sound intensity and the associated elemental area over any surface fully enclosing the source. In the scanning method, the probe is moved continuously along one or more prescribed paths on the surface. The surface average value of the normal component of sound intensity is obtained in a few scans, instead of independent measurements at several points. This method is relatively quick and easy to perform and gives good results for measurements requiring engineering grades of accuracies. The author examines the range and effect of some of the major parameters associated with the scanning technique, for providing guidance to the user and to the standardization of the procedure

Measurement of Sound Velocity in Liquid Using Frequency Sweeping-Interdigital Transducer

Abstract: A system for measuring the sound velocity in a liquid is described, which uses an interdigital transducer (IDT) for a leaky surface acoustic wave. The IDT on a piezoelectric substrate effectively operates as a radiator and a detector of the bulk wave at a liquid-solid interface. The measurement is accomplished by a frequency sweeping method under the condition of the fixed sound path length. The output curve is obtained as a function of the frequency at the IDT in the form of the interference between the input and the output signal reflected from the reflector. The measurement resolution of the present system is within 0.1%.

Method for determining the acoustic intensity of focussing electroacoustic transducers and apparatus for carrying out this method

Abstract: The aim is for the acoustic power emitted by the shock wave transducer (2) and the sound pressure determined hereby to be controlled or regulated in the focus (3) in order to be able to ensure optimum and efficient application of the shock waves and high-power sound pulses. For this purpose, the sound waves (6) emitted by the transducer (2) are deflected at least partially in the direction towards the transducer (2), the electric voltage induced at the transducer (2) by the reflected sound waves serving as a measure of the emitted acoustic power.