Showing papers on "Acoustic source localization published in 1998"

Role of spectral detail in sound-source localization

Abstract: Sounds heard over headphones are typically perceived inside the head (internalized), unlike real sound sources which are perceived outside the head (externalized). If the acoustical waveforms from a real sound source are reproduced precisely using headphones, auditory images are appropriately externalized and localized. The filtering (relative boosting, attenuation and delaying of component frequencies) of a sound by the head and outer ear provides information about the location of a sound source by means of the differences in the frequency spectra between the ears as well as the overall spectral shape. This location-dependent filtering is explicitly described by the head-related transfer function (HRTF) from sound source to ear canal. Here we present sounds to subjects through open-canal tube-phones and investigate how accurately the HRTFs must be reproduced to achieve true three-dimensional perception of auditory signals in anechoic space. Listeners attempted to discriminate between 'real' sounds presented from a loudspeaker and 'virtual' sounds presented over tube-phones. Our results show that the HRTFs can be smoothed significantly in frequency without affecting the perceived location of a sound. Listeners cannot distinguish real from virtual sources until the HRTF has lost most of its detailed variation in frequency, at which time the perceived elevation of the image is the reported cue.

Spatial aspects of reproduced sound in small rooms

Abstract: This paper reports on the influence of individual reflections on the auditory spatial aspects of reproduced sound. The sound field produced by a single loudspeaker positioned in a normal listening room has been simulated using an electroacoustical synthesis of the direct sound, 17 individual reflections and the reverberant field. The threshold of detection was measured using the method of adjustment for five reflections using three subjects for noise and speech. The thresholds have been measured for two simulated situations (1) a loudspeaker with a frequency independent directivity characteristics and frequency independent absorption coefficients of the room surfaces and (2) a loudspeaker with directivity similar to a standard two-way system and absorption coefficients according to measurements of real materials. The results have shown that subjects can reliably distinguish between timbre and spatial aspect of the sound field, that the spectral energy above 2 kHz of the individual reflection determines the importance of the reflection for the spatial aspects, and that only the first order floor reflection will contribute to the spatial aspects.

Moving frame technique for planar acoustic holography

Abstract: Acoustic holography is one of the best methods to visualize sound fields. The quality of the visualized sound is primarily determined by the size of the hologram, its microphone spacing, and the number of microphones. This paper describes a way to virtually increase the hologram size and the spatial resolution of the holograph. For a stationary sound field, the method continuously sweeps the sound field by a line array of microphones. For moving sound sources, radiating sound is measured by using a line array of microphones fixed in space. In both cases, the measured signals have Doppler effects. The theoretical formulation has been systematically addressed by employing a moving coordinate which has relative motion between the measurement coordinate and the hologram coordinate. Simulations and experiments support the proposed theory. The drawback is that the method is only applicable to discrete frequencies.

Experiments with a new acoustic particle velocity sensor in an impedance tube

Abstract: The development of a new acoustic sensor makes it possible to measure acoustic particle velocity instead of sound pressure. The new sensor, called the Microflown, can be used in the frequency range of 0 to approximately 20 kHz. As one of the first applications, the new sensors are applied in an impedance tube to determine the impedance of an aluminium sample at the end of the tube. The sample has an orifice which accounts for the sound absorption. Comparing the results with theory and measurements with microphones leads to an excellent agreement. The characteristics of the Microflowns, like the simplicity and the small dimensions, make it a very attractive alternative to the microphones. Furthermore, the sensitivity to the direction of the acoustic waves and the matching of the phase and sensitivity of two sensors can be used in other research fields in acoustics as well.

Method and apparatus for ultrasonic doppler velocimetry using speed of sound and reflection mode pulsed wideband doppler

Abstract: According to the present invention, a method and apparatus rely upon tomographic measurement of the speed of sound and fluid velocity in a pipe. The invention provides a more accurate profile of velocity within flow fields where the speed of sound varies within the cross-section of the pipe. This profile is obtained by reconstruction of the velocity profile from the local speed of sound measurement simultaneously with the flow velocity. The method of the present invention is real-time tomographic ultrasonic Doppler velocimetry utilizing a to plurality of ultrasonic transmission and reflection measurements along two orthogonal sets of parallel acoustic lines-of-sight. The fluid velocity profile and the acoustic velocity profile are determined by iteration between determining a fluid velocity profile and measuring local acoustic velocity until convergence is reached.

A numerical and experimental investigation of the performance of sound intensity probes at high frequencies

Abstract: The influence of scattering and diffraction on the performance of sound intensity probes has been examined using a boundary element model of an axisymmetric two-microphone probe with the microphones in the usual face-to-face arrangement. On the basis of calculations for a variety of sound field conditions and probe geometries it is concluded that the optimum length of the spacer between the microphones is about one microphone diameter; with this geometry the effect of diffraction and the finite difference error almost counterbalance each other up to about an octave above the frequency limit determined by the finite difference approximation. This seems to be valid under virtually any sound field condition that could be of practical importance in sound power determination. The upper frequency limit corresponds to about 10 kHz for an intensity probe with 12-in. microphones, which means that it should be possible to cover most of the audible frequency range, say, from 50 Hz to 10 kHz, with a single probe conf...

Learning-Based Three Dimensional Sound Localization Using a Compact Non-Coplanar Array of Microphones

Abstract: One of the various human sensory capabilities is to identify the direction of perceived sounds The goal of this work is to study sound source localization in three dimensions using some of the most important cues the human uses Having robotics as a major application, the approach involves a compact sensor structure that can be placed on a mobile platform The objective is to estimate the relative sound source position in three dimensional space without imposing excessive restrictions on its spatio-temporal characteristics and the environment structure Two types of features are considered, interaural time and level differences Their relative effectiveness for localization is studied, as well as a practical way of using these complementary parameters A two-stage procedure was used In the training stage, sound samples are produced from points with known coordinates and then are stored In the recognition stage, unknown sounds are processed by the trained system to estimate the 3D location of the sound source Results from the experiments showed under ±3° in average angular error and less than ±20% in average radial distance error

Particle size distribution and zeta potential using acoustic and electroacoustic spectroscopy

Abstract: A device is described which combines Acoustic and Electroacoustic spectrometers to characterize both particle size distribution and zeta potential for concentrated dispersed systems. The Acoustic Spectrometer measures both attenuation and sound speed for multiple frequencies using each measurement to help optimize and correct the other. The attenuation spectra is used to calculate particle size. The Electroacoustic Spectrometer measures Colloid Vibration Current (CVI), correcting the measured value using attenuation and sound speed data from the Acoustic Spectrometer. The Colloid Vibration Current is used to calculate zeta potential taking into account the particle size calculated from the acoustic measurement as well as particle interaction. Sound speed and multiple frequency CVI measurement provide additional experimental data to check the validity of the data.

A study of the medium frequency response of sound field in a panel–cavity system

Abstract: Vibration and absorption properties of structures which are used to form an enclosure have significant effects on the acoustical response of the enclosed sound field. Boundary structures such as panels and partitions found in real enclosures like buildings and vehicles are often elastic, thus their perturbational/coupling effect cannot be isolated from the vibrational motion of boundary-induced acoustic modes in the enclosed sound field. The effect of acoustic-structural coupling on the transient and steady-state responses of the sound field has been investigated in both low- and high-frequency ranges. In the medium-frequency range, acoustic–structural coupling problems are not well understood. In this paper, acoustic–structural interactions at medium frequencies are investigated using the modal coupling method and the effect of the coupling on the medium frequency response of the sound field in a panel–cavity system is studied. Features associated with the sound field response are then obtained when moda...

Spatial localization of sound sources: azimuth and elevation estimation

Abstract: A model-based bio-mimetic sound localization method has been proposed for concurrent and continuous speech sources located in reverberant environment. However, the method only provides the estimation of azimuths of sound sources. The current paper is to extend the previous method to be available for sound sources existing in the 3D space by using a four microphone set. As the procedure of signal processing, arrival time differences of different microphone pairs are calculated at each available onset of sound components. The locus circles of different microphone pairs in the surface of Gaussian Sphere are then calculated and projected topographically to a horizontal plane, which consists the north pole, by the south pole projection. A two dimensional histogram in the projected plane corresponding to the source direction is created by summing all the projected maps of every onsets. Finally, the directions of sound sources are determined by the position of the major peaks in the two-dimensional histogram.

Control of position of a particle using a standing wave field generated by crossing sound beams

Abstract: Non-contact control of position of a particle using an ultrasonic standing wave field in water has been studied experimentally. Although a standing wave field generated between a transducer and a reflector makes it possible to trap particles at nodes of the sound pressure distribution and to transport them by changing frequency, the method has several problems such as resonance of the sound field. The present paper describes a method to generate a standing wave field by two transducers whose sound beam axes are crossing to each other without using a reflector. Since the sound field does not resonate, it is stable for any frequency changes. When a particle was put in the region of the crossing sound beams, it was trapped at nodes of the sound pressure. By changing the phase difference between the transducers, the trapped position shifted. By assigning slightly different frequency to each transducer, transportation at constant speed was realized. It is possible to extend this scheme into two or three-dimensional manipulation by adding more transducers.

Simulation of three-dimensional sound propagation with multidimensional wave digital filters

Abstract: The propagation of sound waves is described by partial differential equations for the acoustic pressure and the acoustic fluid velocity. The solution depends on the shape of the enclosure and on the boundary conditions. Among various methods for the discretization of partial differential equations, the multidimensional wave digital filter approach is known to yield robust algorithms for the discrete simulation of continuous problems. This paper describes the derivation of a discrete model for three-dimensional sound propagation according to multidimensional wave digital filtering principles. The correct treatment of boundary conditions for various wall impedances is shown. A numerical example for the sound propagation in three interconnected rooms of a building demonstrates the capabilities of the method.

Measurement of propagation time of sound waves; involves measuring phase shift between transmitted and received signals at two different frequencies

Abstract: Two sound signals, preferably ultrasound signals, of different frequency (F1,F2) are emitted and received by an acoustic transducer. The phase shift of the received signal with respect to the emitted signal is measured for each sound signal and used to calculate the propagation time of sound within defined boundaries. The emitted sound may be transmitted in short bursts that are long enough for the frequency of the transmitted wave trains to reach a stationary state. An Independent claim is included for a device for implementing the method.

Experimental investigations and prediction of aerodynamic sound generated from square cylinders

Abstract: Aerodynamic sound generated from cylindrical objects, such as in pantographs of trains, is a prime noise source in high speed vehicles. Our objective is to understand the generation mechanism of the aerodynamic sound from two-dimensional cylinders in order to contribute to the prediction and control of high speed vehicle noise. Aerodynamic sound generated from a square cylinder with various angles of attack is measured in relation to the surface pressure fluctuations on the cylinder. Coherent length and the phase characteristics of the surface pressure fluctuations are measured and the aerodynamic sound level is predicted based on the theory of LighthillCurle. Flow around a square cylinder changes drastically at the angle of attack at around 13°, when the separated flow from the leading edge re-attaches on a side surface, and shows the lowest sound level. Predicted sound pressure level agrees well with the measured value for the most range of angles of attack.

Acoustic vector sensing sonar system

Abstract: A system for the detection of acoustic signals utilizing an array of acoustic sensors coupled to a beamformer which generates a steered acoustic beam using the output from one or more of the acoustic sensors within the array. The acoustic sensors include a multiaxis vector sensor co-located with a scalar acoustic pressure sensor. The beamformer generates a weighted output for each acoustic sensor by combining the weighted output of the scalar pressure sensor with the scalar field generated by forming the inner product of the vector components measured at each sensor location with a vector component weighting vector. The weighted output signals are delayed to synchronize the phase of the weighted output signal to that of a weighted signal at a reference array location. The resulting delayed weighted output signals are then summed.

Method and device for determining a liquid level with the aid of ultrasonic pulses

Abstract: A method for determining a liquid level with the aid of ultrasonic pulses improves the measuring accuracy of the liquid level in a container with an echo time measurement of ultrasonic pulses and a mean sound velocity. The mean sound velocity is extrapolated from at least two reference sound velocities in the liquid. In this way it is possible to achieve a measuring accuracy of less than a millimeter, independently of the liquid level. A device for carrying out the method has a main measuring path, at least one device for transmitting and receiving ultrasonic pulses, at least two reference paths for determining sound velocities, and a computer unit. The computer unit extrapolates from the sound velocities to the mean sound velocity.

Coupled-mode sound propagation in a range-dependent, moving fluid

Abstract: Full-field acoustic methods for current velocity inversion require accurate and efficient mathematical models of sound propagation in a range-dependent waveguide with flow. In this paper, an exact coupled-mode representation of the acoustic field is derived. To account for the physics of the problem, normal modes in a corresponding range-independent waveguide are chosen as the local basis. In the absence of currents, mode shape functions form a complete orthogonal basis. This property is heavily used in coupled-mode theories of sound propagation in motionless fluid. Unlike in the motionless case, however, vertical dependencies of acoustic pressure in individual normal modes are not orthogonal in the presence of currents. To overcome this difficulty, linearized equations of hydrodynamics are rewritten in terms of a state vector. Its five components are expressed in terms of acoustic pressure and particle displacement due to the wave. Orthogonality of the state vectors corresponding to individual normal modes is established. Coupled differential equations are derived for range-dependent mode amplitudes, leading to a remarkably simple result. The mode-coupling equations have the same form as those known for the motionless case, but of course the values of the mode-coupling coefficients differ as long as the range dependence of the flow velocity contributes to mode coupling in addition to the range dependence of sound speed and fluid density. The mode-coupling formulation is verified against known coupled-mode equations for certain limiting cases and an exact analytic solution of a benchmark problem.

A least-squares spectral element method for sound propagation in acoustic ducts

Abstract: This letter presents a novel numerical method and results for sound waves propagating in two-dimensional acoustic ducts without a flow. The method is based on a least-squares finite-element formulation to solve the two-dimensional Helmholtz equation with acoustic boundary conditions. Numerical calculations were obtained for sound waves propagating in an acoustically lined duct and in a rigid duct with a 90-deg bend. The exact solution and the boundary element solution of the acoustically lined duct were also obtained to validate the proposed numerical algorithm. Sound pressures computed by the present method agree very well with the exact and BEM solutions.

Sound propagation over convex impedance surfaces

Abstract: Theoretical calculations for the diffraction of sound by large spheres and cylinders with finite impedance surfaces are reported. The differences between existing two-dimensional and new three-dimensional results are made explicit and are shown to involve a simple correction factor in the case of a large sphere. The results for propagation over an infinitely long cylinder have a bearing on the widely used analogy between sound propagation over a curved surface and sound propagation in a refracting atmosphere above an impedance plane. Specifically, it is found that there is a rigorous analogy between sound propagation above a large circular cylinder and propagation in a medium where the sound speed varies exponentially with height. This differs from the bilinear profile that is often used when exploiting the analogy [see, for example, J. Acoust. Soc. Am. 83, 2047–2058 (1988)]. Predictions for both profiles are found to agree well with each other and with the published data in the shadow zone, but considerable discrepancies are found in the penumbra region.

Sound absorbing method, and device and program recording medium therefor

Abstract: PROBLEM TO BE SOLVED: To suppress even such omnidirectional noise as an entire room is filled therewith. SOLUTION: Outputs of microphones 1, 2 are divided 4 into each frequency bands, and varied according to the positions of the microphones 1, 2. A difference between parameter values of each sound signal reaching the microphones is detected 3, and based on the detected difference, sound sources are separated by selecting a frequency component of each sound signal, and desired sound and undesired sound are discriminated 6 from each other from the difference between both frequency characteristics, and the undesired sound is suppressed on frequency base 7 and the output is synthesized with the sound source signal. The undesired signal is suppressed also on time base by paying attention to the difference in the periodicity of the waveforms between the desired and undesired sound. COPYRIGHT: (C)2000,JPO

Analysis of Aerodynamic Sound Source with Measurement of Static-Pressure Fluctuation.

Abstract: The objective of this investigation is to develop a method to detect the aerodynamic sound source in the wake of a circular cylinder at Reynolds number 4.0×104. We estimate the intensity of surface pressure which is related to vortex shedding in the wake of circular cylinder by using the coherent output power (COP) in terms of static-pressure and surface pressure on the circular cylinder. Then, we obtain vortices distribution which contribute dipole sound source on the cylinder by measuring COP at various positions in the wake of the circular cylinder. Moreover, we can calculate aerodynamic sound by using the Curle's equation with this estimated surface pressure. We also define the spatial distribution of aerodynamic sound source by means of this method. The result shows the aerodynamic sound generate near the formation region of Karman vortices, that is, X/D=1.5 to 2.0, Y/D=±0.4. Therefore, separated shear flow contributes strongly to the aerodynamic sound generation.

Acoustic surveillance apparatus and method

Abstract: An apparatus and method for detecting, locating, tracking, or classifying an acoustic energy source located on a far side of a structure is disclosed. In accordance with the present invention, a receiving device samples a plurality of points on a near side of the structure to detect vibrations that result from sound waves propagated by the acoustic energy source. The location of the acoustic energy source is determined based on the relative time differences of the vibrations and the known positions of the vibrations on the structure. The acoustic energy source may be classified based on identifying characteristics of the vibrations. In addition, a device may be provided to transmit a sound wave through the structure. The receiving devices samples a plurality of points on the near side of the structure to detect vibrations resulting from reflections of the sound wave from the object.

Sound produced by a backward facing step under a wall jet .

Abstract: Sound radiation by a backward facing step under a plane wall jet is examined. The investigation is based on an experiment where the mean velocity, the step heights and the cross-stream extent of the jet are varied. The comparison between the backward facing step flow and the corresponding wall jet shows the existence and some characteristics of a source located at the step. Computations of the sound radiated by the turbulent eddies and existing literature about sound sources near geometric singularities, indicate that the step is involved in the radiation of this source. It is shown that the step diffracts the sound of nearby passing eddies and that the sound level is significantly increased into the upstream directions. Flapping of the separated shear layer does not radiate sound.

Nonlinear behavior of acoustic rays in underwater sound channels

Abstract: The nonlinear behavior of acoustic rays in underwater sound channels is examined using a set of parabolic ray equations. Two sound speed profiles, a Munk canonical and a double-duct profile, are investigated. For range-independent but stratified ocean sound speed profiles, analytical results concerning the sound ray trajectory and wave length are obtained. The stability of the system is found to be marginal stable, which leads to the phenomenon of wave front folding. Next, a perturbed system attributed to a single-mode internal wave is examined. The stability, bifurcation and other nonlinear dynamic issues of the nearly integrable system are explored using a combination of phase plane trajectories, Poincare maps, bifurcation diagrams, Lyapunov exponents and Floquet multipliers.

Time-domain single hydrophone localization in a real shallow water environment

Abstract: Assuming that the time signal emitted by the source is known, a time-domain single-phone localization approach was developed by Clay and was implemented by Li and Clay in an air wedge waveguide. Frazer and Pecholcs performed several numerical simulations of the time-domain single hydrophone localization with an isovelocity ocean model. In this paper, the authors demonstrate the time-domain single hydrophone localization in a real shallow water environment. In November 1995, an experiment was conducted in the Gulf of Mexico. In this experiment, source and receiver were separated by approximately 21 km and were placed on the bottom along a 188-meter isobath line. An M-sequence waveform with center frequency of 150 Hz and a 3-dB bandwidth of 50 Hz was transmitted from the source and received by the receiver. The authors matched-filtered the received signal to get the ocean impulsive response. They used a broadband normal mode code to generate the predicted impulsive response for a source at different ranges and depths. They correlated the measured ocean impulsive response with the predicted impulsive responses and displayed the correlation output as a range-depth ambiguity surface. The peak in the range-depth ambiguity surface represents the location of the source. They successfully localized the broadband source and the dominant surface scattered energy.

Acoustic wave therapy apparatus with reduced noise during acoustic wave emission

Abstract: An acoustic wave therapy apparatus has an acoustic wave source such as shock wave source and an acoustic transmitter that emits such a separate acoustic signal that, during operation of the acoustic wave therapy apparatus, at least partial cancels the air-borne sound caused by the acoustic wave source.