Showing papers on "Acoustic source localization published in 1984"

Acoustic direction identification system.

Abstract: A system insensitive to nonspeech sounds utilizes a pair or spatially separated microphones (101, 102) to obtain the direction of origin of speech signals from a common sound source. The speech signal from each microphone is transformed (330, 340, 350, 355, 360, 365, 370, 375) into a pulse representative signal having a rapid increase responsive to pitch peaks of energy from the sound source. The cross correlation of these pulses accurately reflects the phase relationship between the speech signals arriving at the microphones. The cross correlation is implemented (450, 460) as time interval histograms which are periodically read to identify the direction of the common sound source.

Attenuation of sound waves

Abstract: An active sound control system is described in which allowance is made in a relatively uncomplicated circuit for acoustic coupling between a sound generating system for generating a cancelling sound wave and a detector for sensing a sound wave to be cancelled Unwanted sound from a source is detected by a microphone and cancelled by sound from a speaker connected by way of an amplifier to the microphone The amplifier has a feedback processing system with a transfer function which takes account of acoustic feedback between the speaker and the microphone in deriving, with the amplifier, a signal to drive the speaker

Speed of sound and temperature in the ocean by Brillouin scattering.

Abstract: A method is described to measure the speed of sound and the temperature in the sea as functions of depth. Backscattered laser light is analyzed with an interferometric spectrometer. The speed of sound at very short acoustic wavelengths is obtained directly from the wavelength shift of the Brillouin scattered light, and the temperature is deduced from the speed of sound together with auxiliary information on depth and salinity. Experiments are described.

Velocity and Density of a Two-Dimensional Acoustic Medium from Point Source Surface Data,

Abstract: An inverse acoustic scattering theory and algorithm is presented for the reconstruction of a two‐dimensional inhomogeneous acoustic medium from surface measurements. The measurements of the surface pressure due to a harmonically oscillating surface point source at two arbitrary frequencies allows the separate reconstruction of the density and velocity of the subsurface. This is a first step towards solving the inverse problem of exploration geophyiscs.

Nearfield of a large acoustic transducer. Part III: General results

Abstract: The theory presented in two previous papers [Part I, J. Acoust. Soc. Am. 72, 1056–1061 (1982) and Part II, J. Acoust. Soc. Am. 74, 1013–1020 (1983)] is further developed and generalized to the case of no axisymmetry. Emphasis is given to a study of the parametric generated sound. Asymptotic formulas are presented, showing the development of the difference frequency sound from the source (transducer) into the farfield. New numerical results for the axisymmetric case are given for the linear and the parametric field of a source which is not radiating uniformly. New experimental results are reported and compared with the theory.

Unknown sound evaluating method and apparatus

Abstract: Method and apparatus for evaluating location of an unknown sound generated in a structure such as a pressure vessel. A plurality of sound detectors are mounted on the structure for detecting sounds generated in the structure. On the basis of sound information of the unknown sound source derived from the outputs of the detectors, the location where the unknown sound is produced is determined. To this end, reference sounds are first generated at a plurality of known reference sound source positions, wherein information of the reference sounds derived from the outputs of the detectors are stored in a storage unit. Equi-pattern-distance curves each of which is in an equal pattern distance between a supposed unknown sound source and each of the reference sound sources are calculated on the basis of the reference sound information. The equi-pattern-distance curves are further corrected in accordance with the reference sound information. Upon occurrence of an unknown sound, pattern distances between the desired reference sound source positions and the unknown sound source position are calculated through pattern recognition procedure from the sound information derived from the outputs of the detector and the reference sound information stored. On the basis of the calculated pattern distances and the equi-pattern-distance curves, the position of the unknown sound source is determined. On the basis of the position of the unknown sound source, kinetic energy thereof may be arithmetically determined.

Sound field of a parametric focusing source

Abstract: An analytical description of the sound field of a parametric focusing source was given in a previous paper by Lucas, Naze Tjo/tta, and Muir [J. Acoust. Soc. Am. 73, 1966–1971 (1983)]. Results of an experimental investigation were also presented and compared with the theory. The results of new numerical computations are shown in the present paper. They lead to a more accurate evaluation of the parametric field in planes perpendicular to the axis of symmetry and to a better agreement with the observations.

Oceanic sound speed profile inversion

Abstract: A modal (full-wave) method has been developed to predict ocean sound speed profiles from propagated acoustic field data. The method assumes a point source of sound in the ocean and uses as data the values of the transmitted acoustic field at an array. The formalism for depth-dependent sound speeds consists of the standard Hankel integral transform of the depth solution. In the travel length coordinate, the latter is written exactly, using the Green's function, in terms of an integral equation whose kernel includes the sound speed profile correction. A Born approximation to this equation is used. This is just the WKB solution, and permits the use of a nontrivial input (or guess) profile, here chosen as bilinear. The use of asymptotic methods enables us to write the data as an integral transform over the profile correction. The transform can be inverted. An example is presented for full-bandwidth inversion.

Experimental Investigation of Rocket Motor Flow-Turning Acoustic Losses.

Abstract: : Results are presented of an experimental investigation of the 'flow-turning' losses associated with the injection of steady lateral flow into a rectangular duct containing longitudinal acoustic waves. Test results show the flow-turning process absorbs sound. A one-dimensional model was derived that seriously underpredicted the measured acoustic energy losses. Two-dimensional effects in the form of redistribution of the sound pressure due to refraction by the injected mean flow velocity gradients were found to be important. Measurements showed the refraction process to increase the sound pressure at the walls thereby increasing the local wall absorption. Analysis of the data indicates that part of the flow-turning absorption process takes place at the finite admittance side walls and part within the field interior. Most of the sound absorption appears to take place within the fluid interior in support of Culick's ideas, but final interpretation of the data requires the development of a two-dimensional model of the flow-turning process. The identification of the refraction process in new and may have important applications to other rocket motor stability calculations. Key concepts include sound absorption, sound attenuation, sound flow interaction, sound flow energy exchange, flow-turning acoustic losses, and combustion instability.

The Echometer: An acoustic sound speed profiler

Abstract: Preliminary experimental results are presented which demonstrate the feasibility of an acoustic technique for remote sensing of ocean sound speed profiles. A three-dimensional acoustic interference pattern was produced in the water column by a ship-mounted active linear array. The scattered returns from the interference pattern were interrogated by a narrow-beam receiver displaced laterally from the source array. A dual-frequency technique employing signals differing by 1 percent in frequency produced calculable shifts in acoustic path lengths and hence, measurable travel time differences. The differences in path lengths and measured travel times (phase) were combined in an iterative process to calculate the sound speed at discrete depths, i.e., at the intersections of the constructive interference lines and the beam of the receiver.

Sound fields near building facades

Abstract: Measurement of sound transmission through the exterior facade of a building requires a determination of the incident sound power. Direct measurement of the sound field near the relevant surface seems preferable to the use of a `calibrated source' because of variability in outdoor propagation associated with ground reflections and atmospheric conditions. The interpretation of sound pressure level measurements in this environment is, however, complicated by the interference between incident sound waves and those reflected from building surfaces. This paper presents experimental results and a simple predictive model

Effect of directivity on the sound field produced by a source above a reflecting plane

Abstract: In this paper, the effect of source directivity on the sound field produced by a source near a reflecting plane by using a collinear array of point sources operating in phase, located above a reflecting plane, but in an otherwise reflection‐free environment is analytically and experimentally investigated. It was found that the presence of the reflecting plane and the source directivity can have a considerable effect on the sound pressure levels (SPL). When radiating a third‐octave band of noise centered at 500 Hz, for example, the variations in SPL with source orientation were as much as 12 dB. Furthermore, the maximum correction factor occurred when the mainlobe of the source directivity pattern pointed toward the reflecting plane rather than, as might be expected, toward the receiver. Finally, reasonably good agreement is found between the measured and corrected SPL, with the rms error being less than 2.6 for the 500‐Hz octave and third‐octave bands.

Measurement of acoustic background noise and simulated impact sound in BWR.

Abstract: In order to develop a method for detecting and locating metallic loose parts in BWRs, sound properties were studied. Five acoustic sensors were attached to the BWR pressure vessel and simulated impacts were given to the vessel by hitting it with a hammer. Background noise during the actual plant operation and the impact sound were measured and analyzed.The following results were obtained:(1) Signals with S/N of five or more for impacts with an energy of 0.2 J at full power plant operation were obtained by accelerometers located within 6m from the impact positions.(2) Arrival time and amplitude of the impact signals showed a good reproducibility for the same impact position. On the other hand, there was a poor relationship between time or amplitude information and acoustic path length. This fact suggested that there is little chance for impact sound location into reality by analytical methods such as triangulation. It will be one of the solution for the acculate location to make use of data for reference impacts.

Method and apparatus for locating a sound source

Abstract: Method and apparatus for evaluating location (P) of an ! unknown sound generated in a structure (1) such as a pressure vessel. A plurality of sound detectors (S) are mounted on the structure for detecting sounds generated in the structure. On the basis of sound information of the unknown sound source derived from the outputs of the detectors, the location where the unknown sound is produced is determined. To this end, reference sounds (A, B, C, I) are first generated at a plurality of known reference sound source positions, wherein information of the reference sounds derived from the outputs of the detectors are stored in a storage unit (140). Equi-pattern-distance curves each of which is in an equal pattern distance between a supposed unknown sound source and each of the reference sound sources are calculated on the basis of the reference sound information. The equi-pattern-distance curves are further corrected in accordance with the reference sound information. Upon occurrence of an unknown sound, pattern distances between the desired reference sound source positions and the unknown sound source position are calculated through pattern recognition procedure from the sound information derived from the outputs of the detector and the reference sound information stored. On the basis of the calculated pattern distances and the equi-pattern-distance curves, the position of the unknown sound source is determined. On the basis of the position of the unknown sound source, kinetic energy thereof may be arithmetically determined.

Measurement of hydroacoustic particle motion by hot-film anemometry

Abstract: : The parameter most often measured in acoustic fields is the pressure. Other scalar field variables, like the density or temperature, may be directly computed from the pressure fluctuations at one point. To determine the particle velocity vector, one needs to know the pressure in the neighborhood of a given point in order to derive the acceleration by numerically computing the gradient field of the pressure. One may measure the velocity field more directly by recording the effect of accelerators attached to a neutrally buoyant sphere that follows the particle motion more or less closely. Its sensitivity to velocity, therefore, will be inversely proportional to the frequency. Hot-film (or hot-wire) anemometry is based on the phenomenon that the heat transfer from an electrically heated film or wire is a function of the fluid motion past the sensor. It is extensively used in study of turbulence, where it is assumed that there is an exponential relation between heat flux and particle velocity, indicated as King's law. The importance of free convection implies a different mode of operation of the anemometer in horizontal or in vertical acoustic particle motion. In the first case the received frequency is twice that of the acoustic field, and the voltage is proportional to the square of the particle displacement. In the second case the frequency is equal to that of the field, and the voltage is linear in the particle displacement. The sensitivity and directional response may be increased by an imposed bias flow. This report describes the measurement of the anemometer output in horizontal and vertical particle motion for water and ethylene glycol.

Intensity Vectors of Sound Scattering by a Spherical Shell.

Abstract: : Acoustic intensity vector plots can illustrate vividly the power flow in an acoustic fluid. It is the main purpose of this memorandum to examine, by means of acoustic intensity vector plots, the distortion of the incident sound field due to the presence of a spherical shell whose target strength spectrum contains well-defined resonant peaks. Mathematical formulae are given from which target strength spectra and acoustic intensity vectors are calculated. The excitation is a time-harmonic plane wave. Intensity vector plots show the considerable distortion of the incident sound field that may be present when an elastic scatterer is excited at a resonant frequency.

A canonical ocean bottom sound velocity profile

Abstract: A new canonical sound velocity profile is presented in which the velocity cubed varies linearly with depth and is characterized by two parameters. The ray acoustic equations have exact analytic solutions for this profile, and the expressions for horizontal range, travel time, and intensity are derived. It is shown that the canonical profile can be derived approximately from Hamilton’s profile for bottom sediments obtained from sonobuoy data. The agreement between the two is shown to be excellent for both the velocity and the velocity gradient even for sediment thicknesses of 1 km.