Showing papers on "Acoustic source localization published in 1991"

Method and apparatus for measuring acoustic wave velocity using impulse response

Abstract: The transit time of acoustic waves between a generator and a receiver positioned across a fluid chamber is determined by generating acoustic waves using a self-purging pneumatic sound generator, a transducer adjacent the outlet of the sound generator, and a receiving transducer positioned away from the sound generator outlet so that the acoustic waves received by the receiving transducer pass through a portion of the fluid. The electrical signals generated by the transmitting transducer and the receiving transducer are processed to obtain the impulse response of these electrical signals, and the point of maximum value is determined. This point of maximum value corresponds to the arrival time of the acoustic waves at the receiving location. The transit time determination may be used to calculate the fluid temperature or other parameters. The pneumatic sound generator is driven by a compressed air source so that the generator is automatically purged of any contaminants in the process of generating the random acoustic noise.

An Acoustic Variable Specifying Time-to-Contact

Abstract: The acoustic intensity structure generated by the rectilinear convergence of a compact sound source and a point of observation is analyzed. It is shown that an acoustic variable specifying the time-to-contact with the source is available at the point of observation, given certain assumptions about the source, the distance between the source and observation point, and the environment. This variable is T = 2I/(dI/dt), where I is the time-averaged intensity. Possible extensions of the analysis are discussed.

Energetics of the deep ocean’s infrasonic sound field

Abstract: Simultaneous measurements of infrasonic (0.5–20 Hz) acoustic particle velocity and acoustic pressure made by the Marine Physical Laboratory’s set of freely drifting Swallow floats are analyzed in terms of the energetics of acoustic fields. Results from a recent deep-ocean deployment indicate that the midwater column’s acoustic potential and kinetic energy density spectra are equal above 1.7 Hz since, away from the ocean boundaries, the sound field is locally spatially homogeneous. Near the ocean bottom, the vertical spatial inhomogeneity is statistically significant between 0.6–1.4 Hz and 7–20 Hz. In the lower band, the pressure autospectrum decreases with increasing distance from the ocean bottom, whereas in the upper band, it increases due to the deep sound channel’s ability to trap acoustic energy at the higher infrasonic frequencies. For ship signals, the signal-to-noise ratio in the active intensity magnitude spectrum is 3–6 dB greater than in either of the two energy density spectra due to the vector nature of acoustic intensity. Although smaller than the net horizontal flux above a few hertz, a statistically significant net vertical flux density of energy occurs across the whole frequency band, from the ocean surface into the bottom. The direction of the net horizontal flux density for various discrete sources, e.g., a magnitude 4.1 earthquake, a blue whale, and commercial ships, is discussed. The net horizontal flux density of the background sound field between 5 and 12 Hz may have been determined by the surrounding ocean bottom topography in one experiment; its direction approximately coincides with the center of a topographic window. However, it also matches the heading toward a 4000-km-distant hurricane. A third possibility of an unknown, broadband source cannot be eliminated with the available data.

Acoustic signal reproducing apparatus

Abstract: An acoustic signal reproducing apparatus for reproducing acoustic signals through headphone devices is disclosed. The left channel and right channel acoustic signals are provided by a device for processing the transmission characteristics with constant transmission characteristics representing the location of an imaginary sound source relative to both of the listener's ears. The left channel and right channel acoustic signals, processed in this manner by the device for processing the transmission characteristics, are provided by an acoustic signal processing device with a level difference and a time difference consistent with changes in orientation of the user's head. In this manner, optimum binaural reproduction with respect to the imaginary sound source may be achieved.

Apparatus for the discrimination of chemical liquids via sound speed measurements

Abstract: An apparatus is provided for identifying an unknown liquid by determining the speed of sound in the liquid. A pulse generator provides an excitation pulse to a first acoustic transducer which transmits an acoustic pulse in the liquid. The acoustic pulse is received by a second acoustic transducer at a distance from the first transducer measured by a displacement transducer. A gated clock is enabled by the excitation pulse and disabled when the acoustic pulse received by the second acoustic transducer reaches a predetermined threshold. The clock measures the time it takes the acoustic pulse to travel the distance between transducers. The temperature of the liquid is determined by indirect means and is provided as an input to a digital computer which computes the speed of the acoustic pulse by dividing the distance between the transducers, provided by the displacement transducer, by the elapsed time measured by the clock. The computer compares the speed of the unknown liquid with the sound speeds of known liquids at the temperature of the unknown liquid. A display coupled to the computer presents the identities of any of the known liquids having the sound speeds within a predetermined interval about the calculated sound speed.

A Comparison of Three Methods of Measuring the Volume Velocity of an Acoustic Source

Abstract: Measurement of the volume velocity of an acoustic source allows the acoustic transfer impedance seen by the source and its acoustic power output to be determined. An investigation of three sources is described whose volume velocity can be determined in different ways: using laser velocimetry, using measurement of the internal source pressure, and using a moving-coil loudspeaker as an output transducer (Salava's method)

Method and device for diagnosing contribution of sound source and vibration source

Abstract: PURPOSE:To obtain a method and a device for diagnosing contribution which enable analysis of the degree of the contribution of a sound source or a vibration source to a sound or vibration at an evaluation point, in a state of actual operation and on a real time basis. CONSTITUTION:A method for diagnosing the contribution of a sound source or a vibration source diagnoses the degree of the contribution of one or a plurality of sound sources or vibration sources to a sound or vibration at an evaluation point. Each detection signal of the sound or the vibration detected in the vicinity of each sound source or vibration source is inputted to adapted filters 41, 42, 43 and 44 and the sum of the respective output signals Ea, Eb, Ec and Ed of the adapted filters 41, 42, 43 and 44 is determined. The coefficient of each of the adapted filters 41, 42, 43 and 44 is updated automatically so that a difference between an aimed signal of the sound or the vibration detected at the evaluation point and the sum of the output signals be the minimum, and the degree of the contribution of each sound source or vibration source is diagnosed on the basis of the output signal of each of the adapted filters 41, 42, 43 and 44 at the time point when the difference converges to some definite value.

Acoustics: Waves and Oscillations

Abstract: Simple Harmonic Motion Theory of Forced Vibration and Resonance Theory of Coupled Oscillations Vibration in an Extended Medium Vibration of Strings Vibration of Bars Tuning Forks Vibration of Membranes and Rings Vibration of Air-Columns Transmission of Sound Reflection Refraction Interference and Diffraction of Sound Reception and Transformation of Sound Sound Measurement and Analysis Acoustics of Buildings Recording and Reproduction of Sound Ultrasonics Problems Index.

Sound generation in the vicinity of the sea surface: Source mechanisms and the coupling to the received sound field

Abstract: This paper presents a theory of the mechanisms of sound generation in fluids containing moving fluid interfaces, i.e., discontinuities in density and sound speed, following the approach of Lighthill [Proc. R. Soc. London Ser. A 211, 564–587 (1952)]. It is shown that in addition to the expected volume distributions of quadrupoles, motion of the discontinuities radiate sound equivalent to that from distributed monopoles and dipoles in place of the surfaces. These sources account both for the generation of sound and for the effect of the surfaces on the radiation of that sound. The results are applied to sound generation in the vicinity of the sea surface. All sources are inherent in the theory. The second part of this paper derives a direct relationship between the sound pressure spectrum in the ocean and the frequency wave-number spectra of the near surface fluid processes responsible for generating the sound, on the assumption that these fluid processes are statistically homogeneous in the horizontal plane. The effects of refraction and bottom reflections are ignored. The results are given in terms of “coupling factors” that are measures of the extent to which the source field copules to the received sound field. The coupling factors are evaluated and the results give some insight into the source characteristics required to ensonify the far field.

Effects of absorption on the nonlinear interaction of sound beams

Abstract: Nonlinearity in the propagation and interaction of sound beams in real fluids is considered, with special emphasis on the effects of absorption. Asymptotic formulas are derived for the sum and difference frequency sound generated by two harmonic sound beams. The amplitude and phase conditions of the sources are arbitrary, within the limits imposed by the parabolic approximation. A distinction is made between two main contributions to the nonlinearly generated sound in the far field, the continuously pumped sound and the scattered sound. The relative amplitudes of the pumped and scattered waves are shown to depend critically on the frequency dependence of the absorption coefficients. Numerical results are presented for the noncollinear interaction of Gaussian primary beams, and also for second harmonic generation in the field of a circular uniform piston source.

Predicting method of direction of sound source

Abstract: PURPOSE:To correctly predict the direction of a sound source even in the sound field where many reflecting sounds are present. CONSTITUTION:Outputs from two microphones 21, 21 are respectively divided to M frequency bands by a band splitting part 22. The power of the signals in each band is detected in a power operating part 23. The peak value of the signals is held by a peak hold part 24, logarithmically processed by a logarithmic processing part 25, and differentiated by a time difference processing part 26. The function of correlation between the signals in the corresponding frequency bands of the outputs of the microphones processed in the same manner is obtained in a correlation function operating part 27. The function of correlation in each frequency band is weighted and averaged in a sound source direction predicting part 23 thereby to obtain a weighted mean. The maximum weighted mean is regarded as the time difference of the direct sounds reaching the microphones 21, 21, whereby the direction of the sound source is operated.

Finite Element Analysis of Focusing Field in Nonlinear Acoustic Waves

Abstract: A finite element approach to focusing field calculation in nonlinear acoustic waves is proposed. Under the assumption of weak nonlinearity, a linearized equation for the second harmonic wave is discretized for finite element method in space including the nonlinearities due to both particle velocity and sound pressure. Numerical experiments confirm that the present method is valid for the analysis of focusing source with large aperture angle. The diffraction of the second harmonic field depends on the nonlinearity parameter B/A.

Separating Sound Sources Using their Orientation Obtained by Localization Each

Abstract: We propose a method for sound source separation. The only informations we need for this method is temporal disparities of arrivals of sound sources at every pair of microphones. For this popose we linked our separating system to a localizing system. The localizing system can localize sound sources using temporal disparities at the onsets that are not mixed with ongoing partions of other sound sources. Several experiments were carried out in an anechoic chamber. We could separate two sound sources (speech sounds), located with azimuth difference of 38°, resulting in 25 dB average attenuation ratio, by a DSP system. The separable azimuth difference was more than 15°. And 5°localization error caused about 6 dB reduction in attenuation ratio.

Ultra-sound detector

Abstract: A process for detecting a phase boundary surface between layers of fluids which are not intermixable with one another includes the steps of penetrating at least one of the fluids with sound waves to strike a reflector, receiving the reflected sound waves, comparing the transmitted sound waves to the reflected and received sound waves, using the comparison to determine the acoustic propagation impedance, and using the results to determine the position of the phase boundary layer.

A Multiple Sound Source Localization System Using Temporal Disparity Histograms

Abstract: A method for multiple sound source localization is presented. It is based on the properties of the onsets of sound as the primary cue : (1) most of the onsets will be contributed by only one source. (2) the onsets will be contributed only by the direct sound. Histograms of temporal disparities for several frequency components and its integrated one are calculated to determine the correct temporal disparities. Experiments were carried out in an anechoic chamber and an echoic chamber. The recorded speeches were used as two sound sources. We could localize the two concurrent sound sourcess with reasonable accuracy.

Parameters of the Sound Due to the Impact of a Particle on a Circular Plate

Abstract: The parameters of impact sound due to collision between a circular plate and a particle are investigate in order to apply it to monitoring for a powder industrial process.The waveform of the impact force between a circular plate and a particle is calculated on the basis of the Hertzian theory. The maximum impact force is proportional to the impact velocity of a particle. Furthermore, it is shown that the component more than characteristic frequency decreased in frequency spectrum of the impact force, and the characteristic frequency depends on the diameter of the impact particle. The vibration equation of circular plate is linear, and the parameters of impact sound are also related to the impact velocity and particle diameter.These results show that the diameter and impact velocity of a particle can be measured by the analysis of impact sound from the collision wall of equipment and particles.

Visualizing apparatus of sound source

Abstract: PURPOSE:To obtain a method for investigating and visualizing a sound source inside a flow field, by using the results of measurement of changes in the vorticity and the velocity of the flow field, regarding a method for investigation of a turbulent flow noise source. CONSTITUTION:The title apparatus is constructed of a vorticity sensor 3 for detecting a change in vorticity and a change in velocity in a flow field, a traverse device 2 for moving the sensor, a velocity change detecting device 4 provided at a fixed position in the flow field, a condition extracting device 5 for detecting the condition of the flow field, a phase average processing device 6 which computes a phase space average value of the flow field from data obtained from the vorticity sensor, and a sound source computing device which detects a turbulent flow noise source from the space distribution of the changes in the vorticity and the velocity. It is possible to investigate the source of generation of turbulent flow noise from the measured vorticity of the flow field and to visualize a sound source.

Measurement and projection of acoustic fields

Abstract: The 3-D reconstruction of an acoustic field provides extensive information which can be applied to the study of radiation and scattering problems, and the information obtained provides a comprehensive analysis of the acoustic vibrator under study. Emphasis is mainly on the inverse aspects of the problem, that is, the backwards propagation of the pressure field from the measurement contour to the surface of the source. A survey of the various approaches which allow the extension of measured data into three dimensions is given. In the simplest approaches, the 2-D measurement contour is planar or cylindrical, best suited for vibrators which conform closely to these geometries. The measurement contour can be generalised to arbitrarily shaped bodies, expanding considerably the types of sources which can be studied with near-field acoustic holography techniques. >

Sound emitting object e.g. military helicopter location method - by measuring angles of incidence of sound waves on sound detectors

Abstract: The process locates sound emitting objects and has two, detectors connected to each other and separated by a defined distance. The location of the sound source is determined from the distance between the detectors and the angles between the incident direction of the sound waves, the normal through the detectors and a horizontal reference plane. USE/ADVANTAGE - For locating moving vehicles; air, sea and land vehicles particularly helicopters and tanks. Enables reliable location of moving objects using acoustics in horizontal plane.

The polarization of acoustic particle motion in the ocean.

Abstract: Acoustic particle velocity is rarely measured in the ocean even though it is a fundamental property of the sound field. The Marine Physical Laboratory’s Swallow floats are capable of simultaneously measuring both acoustic particle velocity and pressure in the 0.5‐ to 25‐Hz band. Previous work has focused on the relationship between the pressure and the particle velocity measurements. The purpose of this talk is to discuss the properties of the particle velocity cross spectral matrix in terms of the polarization of the motion and the relationship of these properties to the energy flow in the sound field. The measurements indicate that the infrasonic background sound field in the midwater column can be modeled as the superposition of three mutually uncorrelated, rectilinearly polarized waves. This is because the particle velocity cross spectral matrix is purely real since the spatial inhomogeneity of the sound field is negligible. However, the particle motion can be strongly elliptically polarized for sound...

Active power minimization of a sound source in a reverberant closed space

Abstract: Sound power output from a source can be decreased in a closed space by using secondary sources. The minimum power response from sound sources (both primary and secondary sources) is analyzed based on modal theory. The power reduction is observed experimentally for a pure tone source in a large reverberation room. The corner method for sensor location is also discussed. >

Estimation of position and waveform of a specified sound source decreasing the effect of other sound sources and reflection

Abstract: A method is described to estimate, using many sensors (microphones) both the position and the waveform of individual sound sources by decreasing the effects of other sound sources and reflection from walls and/or ceilings. Some experiments using two sound sources and 16 sensors have been carried out in a room with a reverberation time of 0.5 s, and it is found that the waveform of the specified sound source could be estimated by decreasing the effect of other sound sources by about 20 dB. >

Study of Volume Measurement using Sound Signal. Measurement of Volume using a Speaker as Sound Source and Sound Frequency.

Abstract: A new accurate measurement of variation of cavity volume in the container has been investigated. It is difficult to obtain stable measurement with the air jet due to variable factors such as the compressed air pressure and pipe dimensions. This paper deals with a new resonance method using the radiated sound from a speaker. The sound frequency obtained by the experiment is compared with the calculation result of the frequency found by the theoretical analysis in which the cavity system is connected with two acoustic pipes. This method of measuring the volume is available to measure the volume of a solid, animal, etc.