Showing papers on "Acoustic source localization published in 1993"

Radiation modes and the active control of sound power

Abstract: Two formulations for calculating the total acoustic power radiated by a structure are compared; in terms of the amplitudes of the structural modes and in terms of the velocities of an array of elemental radiators on the surface of the structure. In both cases, the sound radiation due to the vibration of one structural mode or element is dependent on the vibration of other structural modes or elements. Either of these formulations can be used to describe the sound power radiation in terms of a set of velocity distributions on the structure whose sound power radiation is independent of the amplitudes of the other velocity distributions. These velocity distributions are termed ‘‘radiation modes.’’ Examples of the shapes and radiation efficiencies of these radiation modes are discussed in the cases of a baffled beam and a baffled panel. The implications of this formulation for the active control of sound radiation from structures are discussed. In particular, the radiation mode formulation can be used to provide an estimate of the number of independent parameters of the structural response which need to be measured and controlled to give a required attenuation of the radiated sound power.

Reproduction of plane wave sound fields

Abstract: The problem of reproducing a desired sound field in space, not just at a number of discrete points, but over a continuous two‐dimensional area, is investigated. In theory, any sound field can be reconstructed perfectly in a given region by using a continuous monopole/dipole layer, but this is obviously not possible in practice. This paper attempts to give some quantitative measures of the extent to which a given sound field can be reproduced by using a number of discrete monopole sources. Some of the physical limitations that apply to any sound reproduction system are illustrated by studying a simple model. The desired sound field is a plane wave, the sources are ideal monopoles in a free field, and the optimal source accelerations are calculated using the traditional least‐squares method. All calculations are undertaken in the frequency domain, and three different loudspeaker arrangements are studied. The results clearly demonstrate that the quality of the reproduced sound field is mainly determined by the size of the receiver area and the angles between the sources as seen from the center of the receiver array.

Structure of Supersonic Jet Flow and Its Radiated Sound

Abstract: The present paper explores the use of large-eddy simulations as a tool for predicting noise from first principles. A high-order numerical scheme is used to perform large-eddy simulations of a supersonic jet flow with emphasis on capturing the time-dependent flow structure representating the sound source. The wavelike nature of this structure under random inflow disturbances is demonstrated. This wavelike structure is then enhanced by taking the inflow disturbances to be purely harmonic. Application of Lighthill's theory to calculate the far-field noise, with the sound source obtained from the calculated time-dependent near field, is demonstrated. Alternative approaches to coupling the near-field sound source to the far-field sound are discussed.

Stereo headphone sound source localization system

Abstract: A system for processing an audio signal for playback over headphones in which the apparent sound source is located outside of the head of the listener processes the input signal as if it were made up of a direct wave portion, an early reflections portion, and a reverberations portion. The direct wave portion of the signal is processed in filters whose filter coefficients are chosen based upon the desired azimuth of the virtual sound source location. The early reflection portion is passed through a bank of filters connected in parallel whose coefficients are chosen based on each reflection azimuth. The outputs of these filters are passed through scalars to adjust the amplitude to simulate a desired range of the virtual sound source. The reverberation portion is processed without any sound source location information, using a random number generator, for example, and the output is attenuated in an exponential attenuator to be faded out. The outputs of the scalars and attenuators are then all summed to produce left and right headphone signals for playback over the respective headphone transducers.

Sound environment simulator using a computer simulation and a method of analyzing a sound space

Abstract: The present invention discloses a sound environment simulator including a sound field analyzing unit, a sound field reproducing unit, and an output unit. The sound environment analyzing unit divides the solid surfaces of a space to be analyzed into a set of sections to compute the volume of reflected sounds with a sound absorption coefficient of walls and form factors. It further computes time series data related to the arrival volume of sounds emanated from a certain sound source to the sound receiving point. An impulse response computing unit in the sound field reproducing unit transduces the time series data into an impulse response. Accordingly, the sound field reproducing unit convolutes the impulse response on a dry source in accordance with data related to a listener's position inputted from an associated virtual reality equipment to generate a reproduced sound over a headphone.

Accurate measurements of the sound velocity in pure water by combining a coherent phase-detection technique and a variable path-length interferometer

Abstract: An automated system for measuring the sound velocity in liquids has been developed by combining a coherent phase‐detection technique and a variable path‐length interferometer, in which a sample liquid is filled between an ultrasonic buffer and a moving reflector, and phase changes of a given echo of the ultrasonic pulse is measured by a phase‐sensitive detector (PSD) as a function of changes in the acoustic path length. For the accurate determination of the changes in the acoustic path length, the displacement of the moving reflector is measured by a Michelson interferometer that is illuminated by a frequency‐stabilized He–Ne laser. The sound velocity is determined from a direct comparison of the acoustic wavelength in the sample liquid with the optical wavelength of the laser. In order to check the performance of the apparatus, measurements were performed for distilled water in the temperature range 20–75 °C under atmospheric pressure with a carrier frequency of 16.5 MHz. The precision of the phase measurements by the PSD and systematic errors in the sound velocity measurement are evaluated. The total uncertainty of the sound velocity is estimated to be 0.001%. The results agree with reliable literature values within 0.003%.

Method for controlling localization of sound image

Abstract: A method for reproducing sounds from signals, which are supplied from a same sound source through a pair of localization filters by using a pair of transducers disposed apart from each other and for controlling the localization of a sound image in such a way to make a listener feel that he hears sounds from a virtual sound source which is localized at a desired sound image location being different from the positions of the transducers. When performing this method, a signal for measurement reproduced at each sound image location is measured at the listener's position as data to be used for estimating head-related transfer characteristics. Then, the head-related transfer characteristics corresponding to each sound image location are estimated from the measured data. Subsequently, transfer characteristics of the pair of the localization filters, which characteristics of which are necessary for localizing a sound image at each sound image location, are calculated on the basis of the estimated head-related transfer characteristics. Next, a scaling processing is performed to obtain the coefficients of the pair of the localization filters as an impulse response. Then, the coefficients obtained by the scaling processing are set in a pair of convolvers. Finally, sound signals are supplied from the sound source to the pair of the convolvers. Further, outputs of the pair of the convolvers are reproduced from the pair of the transducers.

Acoustic output device, and electronic apparatus using the acoustic output device

Abstract: Sound waves from a plate-shaped acoustic source, which generates fundamental waves (sound waves) having at least two frequencies, propagate through a propagating portion. The propagating portion consists of a medium in which a non-linear interaction is induced by the fundamental waves. A secondary sound wave having a frequency conforming to the difference between the two fundamental waves is generated by the medium. Fundamental wave components other than the secondary sound wave are absorbed by an acoustic absorber so that only the secondary sound wave is delivered as an output. The acoustic source, propagating portion and acoustic absorber are substantially transparent and stacked in three layers. This allows the resulting acoustic output device to be incorporated in the display unit of an electronic apparatus.

Structural and Acoustic Noise Produced by Turbulent Flow over an Elastic Trailing Edge

Abstract: An analysis is made of the sound and vibration produced by turbulent flow at low Mach number over the trailing edge of an elastic plate. The trailing edges of airfoils and other flow control surfaces are known to be important sources of high frequency sound. When the surface is compliant the turbulent edge-flow also excites structural modes of vibration. In conditions of heavy fluid loading, which typically occurs in underwater applications, the energy imparted to the structural motions can be large, and the subsequent scattering of ‘surface waves’ at mechanical discontinuities is frequently an important secondary source of sound. In this paper general formulae are developed for the structural and acoustic edge-noise when the control surface is modelled by a semi-infinite, thin elastic plate which can support bending waves. Numerical results are given for steel plates in air and in water. In the latter case it is shown that, when the frequency is smaller than the coincidence frequency the bending wave power exceeds the total sound power generated at the edge by 20–40 dB, independently of the mean flow velocity, so that sound generated by secondary scattering may then be the dominant source of acoustic radiation.

A Three-Dimensional Sound Localization Sensor System Based on the Spatio-Temporal Gradient Method

Abstract: This paper describes a theory, algorithm, and experimental results of a new 3-D sound source localization system which is based on the spatio-temporal derivative method applied to acoustic signals. The principle is outlined as follows. We observe the sound field through amplitude f and its spatiotemporal gradients fx, fy, ft of a single point. An instantaneous distribution of time-varying vectors fx, fy, ft, f in a 4-D gradient space is classified according to its degree of orderness. Each orderness is theoretically related to constraints on possible source locations. Under this classification, we obtain an unambiguous 3-D location of a single source under a second degree of orderness and a co-existing line or plane of double sources under a first degree of orderness. We applied the principle to a sound source visualizer system by which a possibility map of the source locale is accumulated and superposed realtimely on TV images. By several experiments, this system is shown to be able to localize multiple wideband sources such as white noises and human voices while discriminating a number of them.

Finding the direction of a sound source using a vector sound‐intensity probe

Abstract: Good spatial resolution of a sound source can be achieved with the four closely spaced pressure transducers in a vector sound‐intensity probe. In contrast, a receiving array generally requires an extensive distribution of transducer elements. Experimental results are presented that demonstrate the ability of a vector probe to determine the direction of a sound source in water, both without and with noise interference. Measurements of the sound‐intensity vector, or sound‐power flux, were performed using the cross‐spectral method. Spectral subtraction and averaging over the frequency range of a source were found to be effective tools for determining the direction of a source when there is uncorrelated interference and background noise.

Method and sensor for determining the distance of sound generating targets

Abstract: A method and to a sensor for determining the distance of sound generating targets, preferably wheeled or track-laying vehicles, from acoustic signals which are subjected to a Fourier transformation. In order to determine the target distance easily and reliably, it is provided that the acoustic signals received by an acoustic sensor at two successive points in time from a target that is at a distance r 1 and r 2 , respectively, from the acoustic sensor are employed, after the Fourier transformation, for an evaluation of the phase difference in the sound spectrum which yields the difference between the distances of the target from the sensor at the two points in time, from which difference the target distance is then calculated according to the spherical wave model.

Method and apparatus of determining the sound transfer characteristic of an active noise control system

Abstract: A method and apparatus of determining the transfer characteristic in an active-noise-control system, which involves generating white noise at an end of a one-dimensional sound field that is defined by a linear ventilating system in which sound travels essentially parallel to the extended direction of the system; equalizing the transfer characteristic of the one-dimensional sound field and generating cancelling sound, according to an inverse of the transfer characteristic, to cancel the white noise and prevent noise being output from the other end of the one-dimensional sound field; continuously preventing the noise output and measuring the characteristic data of the one-dimensional sound field at, at least, one measuring point in the one-dimensional sound field; and calculating the transfer function of the one-dimensional sound field in the noise-output-prevented state, according to the characteristic data of the sound field.

Sound environment simulator and a method of analyzing a sound space

Abstract: The present invention discloses a sound environment simulator including a sound field analyzing unit, a sound field reproducing unit, and an output unit. The sound environment analyzing unit divides the solid surfaces of a space to be analyzed into a set of sections to compute the volume of reflected sounds with a sound absorption coefficient of walls and form factors. It further computes time series data related to the arrival volume of sounds emanated from a certain sound source to the sound receiving point. An impulse response computing unit in the sound field reproducing unit transduces the time series data into an impulse response. Accordingly, the sound field reproducing unit convolutes the impulse response on a dry source in accordance with data related to a listener's position inputted from an associated virtual reality equipment to generate a reproduced sound over a headphone.

Method for determining the propagation time (delay time) of sound signals, and a sound-wave propagation-time determining device

Abstract: A method for determining the propagation time of sound signals over a measurement path between at least one sound transmitter and at least one sound receiver comprises a reference transmission signal being formed which is equivalent to the measurement sound signal emitted into the measurement path and said signal being applied to the sound receiver after passing through the reference path, such that the effect corresponds to the reception of the measurement sound signal which is passed over the measurement path.

A note on the prediction of sound intensity

Abstract: Modal analysis has long been used to describe the acoustic characteristics of enclosures with absorptive boundaries. However, it is demonstrated in this paper that this analysis fails in predicting the sound intensity distributions in the enclosures. This is due to the boundary damping approximation involved in this analysis, which has a misleading effect upon the sound absorption material locations. To illustrate this point, the sound intensity in a one‐dimensional pipe is calculated by modal analysis and the result is compared with the exact solution.

Method for measuring a differential sound by subtracting a sound just emitted via a loudspeaker from a total sound

Abstract: In a method for measuring a differential sound (DS) by subtracting a predetermined sound (AS) just emitted via a loudspeaker (LS) from a total sound (GS) detected by means of an acoustic sensor, the loudspeaker (LS) is used simultaneously as the acoustic sensor of the total sound (GS).

Performance bounds for passively locating a moving source of a known frequency in oceanic waveguide using a vertical array

Abstract: This work obtains analytical expressions for the Cramer-Rao lower bounds on the accuracy of location and velocity estimates obtainable by observing the signal radiated from a moving acoustic source at a vertical array of stationary sensors in oceanic waveguide using normal mode description of the sound field. The source radiates a continuous wave of a known frequency, and the source motion is assumed to be uniform. The observations are made in a background of spatially incoherent Gaussian noise. The results provide physical insights into how each mode contributes to the localization process, and can be easily evaluated for a wide range of source positions in a sound channel using eigenfunctions, eigenvalues, and the number of modes involved. Simulations of the bounds for an Arctic enviornment illustrates the coupling of ocean environment to localization performance. >

Sound field generated in a water layer of variable depth by a source moving in the atmosphere: I. Time-dependent normal modes

Abstract: The sound velocity in the atmosphere is assumed to be constant, and the sound velocity in the water depends on the depth, the slow horizontal coordinates, and slow time The source radiates a variable amplitude, variable phase signal and moves with a velocity smaller than the sound velocity in the water

Sound field generated in a water layer of variable depth by a source moving in the atmosphere: II. Time variation of the normal-mode characteristics

Abstract: The sound velocity in the atmosphere is assumed to be constant. The depth of the water layer varies smoothly in horizontal directions. The sound velocity in the water layer depends on the vertical coordinate and varies smoothly in horizontal directions and with time. the source radiates a signal of variable amplitude and phase and moves with a velocity smaller than the sound velocity in the water

Detecting state of fluid esp. gas

Abstract: The method involves measuring at least the temp. of the fluid as a state parameter. The speed of sound in the fluid is measured and the temp. derived from it. The speed of sound is measured from he transition time of sound from a source to a receiver at a known distance from it. The sound signal propagation speed is derived from the measured transition time and the known distance. For measuring the speed of sound in a flowing fluid, two transmitter/receiver pairs are used. These are arranged to enable the transition times to be measured in and against the flow direction. The difference in transition times gives the speed of sound.

Acoustic measuring method

Abstract: PURPOSE:To precisely find the ratio (LD) of a reflected sound component from a desired side to components of sounds from all directions which are well matched with human subjective evaluation by separating and extracting the reflected sound from the desired side wall surface from a direct sound which is collected at the same time CONSTITUTION:An impulse acoustic signal having the time base extended is collected by a unidirectional microphone 6 at a listening point so as to include at least the reflected sound from the desired side wall surface, and a computer 1 computes the impulse response of the collected signal and separates the reflected sound component from the desired side from the direct sound components in time as to the computation result

Behavior of Aerodynamic Sound of Spur Gears : Determination of Similarity Law and Source Locations

Abstract: Tooth mesh frequency sound generated aerodynamically in the region of meshing was investigated to determine the general characteristics of the sound emission as well as its detailed source locations. Sound pressure response measurement for various facewidths revealed that emission is expressed in terms of a similarity law as a function of a parameter b/λ, the ratio of facewidth to wavelength of the sound. The effect of dimensions such as the module and number of teeth were derived by means of a dimensional analysis with respect to pumping action of the cavity between driving and driven gears. Throughout several kinds of experiments, one source was located at the middle of the meshing exit, which becomes prominent as the axial air flow reaches a certain speed. Another source is estimated to spread over both faceends, of which the radiation characteristics are closely related to the distribution and the solid boundary of the gear pair.

Analysis of sound field on spatial information using a four‐channel microphone system based on a regular tetrahedron peak point method

Abstract: This paper describes the development of a sound field measurement method that is aimed at analyzing spatial information of the sound field in a room. This measurement system has four microphones and each of them is installed at the apex of a regular tetrahedron. With this method spatial information of an individual wave front is analyzed from the impulse response at four points that are completely synchronized. With the introduction of a deconvolution method, measuring accuracy for waveform analysis is greatly improved and the analysis becomes much faster. By using models for which the image source positions are already known, experimental studies have been conducted on the identification of sound source positions and frequency distortion by repeated reflections. Furthermore, virtual sound sources have been detected and the waveform in actual sound fields have been recomposed. The results of these experiments indicate that the measurements are accurate and the measurement method can be used effectively.

Acoustical measurement & computational & electro-acoustics. Three dimensional transient sound intensity measurements for comprehensive room-acoustic evaluation

Abstract: Contemporary objective room-acoustic indicators are based on the capture and subsequent analysis of room impulse response but subjective criteria are also influenced by the spatial distribution of sound energy. The spatial distribution of sound energy is usually not considered due to lack of an efficient, accurate and easy to perform measurement procedure. This study introduces three dimensional sound intensity measurement for obtaining spatial information of the sound field in an enclosure. The measurement technique is described and its merits and potential are identified. Specular and diffuse sound field quantification is also introduced