Showing papers on "Sound intensity published in 1990"

Active localization of virtual sounds.

Abstract: A simple virtual sound display built around a microcomputer and analog hardware is described. The display implements most of the primary cues for sound localization in the ear-level plane. Judging both from informal observations by users and from objective data obtained in an experiment on homing to virtual and real sounds, it is concluded that simple displays like the one described are effective in creating the impression of external sounds to which observers can locomote with ease; in particular, this means that simulation of the direction-dependent spectral shaping effects of the pinnae is not a necessary requirement for extracranial sound localization.

Method of detecting acoustic signal

Abstract: According to a method of detecting an acoustic signal, first and second sound receiving units are located at substantially the same position and are used to output signals having different target signal power to noise power ratios (S/N ratios). When a difference between the powers of the signals output from the first and second sound receiving units or a ratio of the power of the signal from the first sound receiving unit to that from the second sound receiving unit in a given period falls within a predetermined range, reception of the target signal within the given period is discriminated. The first sound receiving unit is an adaptive microphone array capable of controlling directivity characteristics in correspondence with a noise position.

Automatic sound level compensator for a sound reproduction device mounted in a vehicle

Abstract: In an automatic loudness compensator provided in a sound reproduction device in a vehicle, the sound level is compensated to reproduce a sound source with the high fidelity intended by the producer of the source of sound. The level of sound frequency-pressure is increased or decreased relative to a middle range of sound frequency at a sound level lower or higher than a reference sound level, respectively. The level of sound frequency-pressure is also adjusted based on the noise produced by the movement of the vehicle and on the acoustic characteristic of the passenger compartment of the vehicle.

Air conditioning apparatus having audible sound level control function

Abstract: An audible sound radiated from an air conditioning apparatus is decreased when the actual audible sound detected by the sound sensor is greater than a predetermined audible sound value which is modified according to changes in the ambient light or the ambient temperature.

The Self-Noise From Ordered Structures in a Low Mach Number Jet

Abstract: This article is concerned with examining the self-noise produced by instability waves in a round jet. The self-noise is defined here as the noise attributed to the nonlinear sources in Lighthill’s stress tensor. The calculated self-noise is found to be proportional to the fourth order of the velocity amplitude saturation. The self-interaction of the instability waves results in a “super-directivity.” The dependency of the sound intensity on the Strauhal number and on the Mach number is in accordance with observations.

Sound Localization in Intact and One-Eared Crickets

Abstract: This study reports on two different compensatory mechanisms found in the cricket Gryllus bimaculatus after the loss of one auditory organ. These mechanisms enable the one-eared animal to maintain a stable sound-related walking course with an error angle less than 90 degrees relative to the direction of sound incidence.

Marine acoustic aerobuoy and method of operation

Abstract: A marine acoustic detector for use in identifying a characteristic airborne sound pressure field generated by a propeller-driven aircraft including a surface-buoyed resonator chamber tuned to the narrow frequency band of the airborne sound pressure field and having a dimensioned opening formed into a first endplate of the chambver for admitting the airborne sound pressure field. Mounted within the resonator chamber is a transducer circuit comprising a microphone and a pre-amplifier, the microphone functioning to detect the resonating sound pressure field within the chamber and to convert the resonating sound waves into an electrical signal while the pre-amplifier functions to amplify the electrical signal for transmission via a cable to an underwater or surface marine vehicle to undergo signal processing. The sound amplification properties of the resonator air chamber are exploited in the passive detection of propeller-driven aircraft at airborne ranges exceeding thoses ranges of visual or sonar detection to provide 44 dB of received sound amplification at common aircraft frequencies below 100 Hz.

Method and application for measuring sound power emitted by a source in a background of ambient noise

Abstract: The detection of sound emitted from a source in a dynamic environment of ambient background noise employs a sufficiently distributed array of sound intensity probes enclosing a sound source is adapted to collect measurements over the same time interval in a non-specific acoustic environment. Each probe in the array is comprised of a pair of mutually spaced microphones generally unmatched in their gain and phase response. A multi-channel fourier spectrum analyzer is used to provide a direct signal processing determination of sound intensity at each probe from pressure measurements taken at each microphone. Their computation is corrected to compensate for gain and phase mismatch between each microphone pair using independently derived probe calibration factors. These correction factors are linearly applied to the sound intensity determination at each probe of the array. Based on the geometry of the probe array and the sound intensity computed at each probe; an approximation of the net flow of emitted sound power through the closed surface of the probe array is made. This closed surface integral approach to determining the net flow of sound power effectively averages out any contribution due to ambient background noise, retaining only the total sound power emitted by the source exclusive of background noise.

Radiation efficiency of acoustic guitars

Abstract: The transfer functions between acceleration and force (‘‘accelerance’’) at the driving point and radiation efficiencies for the top plates of guitars have been investigated. A vibration exciter was used for driving the guitar at the bridge and the transfer functions and cross‐power spectra were measured at the driving point with the aid of an impedance head. The frequency spectrum of the accelerance function determined in this manner showed good agreement with those reported for the same guitar using a different excitation and measurement method. The output acoustic intensity was measured with a sound‐intensity probe and the radiated sound power from the top plate was determined. The radiation efficiency, determined from the ratio of the top plate radiated sound power and the input power, is presented for different guitars and for a guitar with a modified top plate.

Fireplace sound simulator

Abstract: A fireplace-mountable sonic generator produces random noise pulses of varying amplitude imitative of the crackling of a fire, and is particularly suited to emplacement within fireplaces which simulate a log fire by passing burning illuminating gas over a refractory imitation log. The sounds are produced by a reed repeatedly flexed away from a striker plate and then released to impact against that plate, producing a characteristic crackling sound. A series of such deflections and releases at apparently random times is provided by a motor-driven rotating drum having series of surface-mounted, radially-extending irregularly spaced projections. The end of the reed is disposed to be engaged by the drum projections as they move past. Variations in sound intensity from one sound burst to the next may be achieved by varying the lengths of the projections, or by varying their overlap distance as measured from the center of the reed.

Calibrator and calibration method for computationally compensating for phase mismatch in sound intensity probes

Abstract: A calibrator and the derivation of an associated calibration data base for computationally compensating for gain and phase mismatch in sound intensity probes comprised of two unmatched pressure transducing microphones is described herein. The calibrator utilizes a unique `phase plug` to maintain temporal uniformity (in addition to standard spatial uniformity) in the sound field of the calibration chamber. Gain and phase calibration factors are independently obtained for each probe of interest using the calibrator and these data are compiled into an independent data base for storage and subsequent application. Such linear correction factors as applied to associated signal processing of probe measurements serves to computationally compensate for phase mismatch between the unmatched microphone pair.

Noise source identification on rolling tires by sound intensity measurement

Abstract: The sound radiation characteristics of actually rolling tires with three types of the tread patterns were measured by the 2-microphone sound intensity technique. The measure mentswere performed at a test course in Japan Automobile Research Institute, in which a special trailer equipped with an automatic microphone scanning system was used and the normal sound intensity distribution in a plane parallel to the sidewall of a tire was measured during actual running. The results show that it is possible to identify the source positions on a tire actually rolling on a road surface by means of the soundin tensity technique. In the case of a rib tire, the noise was mainly generated from the leading and the trailing edges, not from the contact patch, while in the case of a lug tire, the main source position was the contact patch. The noise radiation pattern varied according to the difference of tread pattern. Further, the sound power radiated by three kinds of tires were compared. A-weighted sound power level of the lug tire is the biggest among them.

Measurements of Structure-Borne Wave Intensity on Lightly Damped Pipes

Abstract: Measurement of the structure-borne sound energy flow through pipes has been studied for the purpose of transmission path ranking. This paper describes the measuring methods for frequencies below the cut-off frequency of the n = 2 shell mode. The methods show a strong analogy with the two-microphone cross-spectral density method for airborne sound intensity measurements. Experiments on two lightly damped pipe sections of a cooling water circuit are used to illustrate some practical measuring aspects and some procedures for error analysis. Reasonably accurate measurements appear feasible, provided high quality instrumentation is used and the various wave types are separated carefully.

Acoustic intensity device

Abstract: PURPOSE:To simultaneously and accurately measure the direction and the intensity of each sound source by computing the acoustic intensity vector of every frequency and computing the direction and the intensity level of the sound source every frequency. CONSTITUTION:Digital signals outputted from two microphones are sampled at specified sampling frequency in sampling circuits 40a and 40b and transformed to the spectrum data of a frequency area from the data of a time area by Fourier transformation in FFT arithmetic circuits 42A and 42B. Next, the acoustic intensity of every frequency is computed based on the spectrum data inputted from the circuits 42A and 42B in an intensity arithmetic circuit 50. Then, the intensity level and the direction of the sound source are computed based on the output signal from the circuit 50 in a vector arithmetic circuit 60. The components in X and Y directions of the acoustic intensity vector are computed in X and Y vector arithmetic parts 70A and 70B to be outputted.

Apparatus and method for reducing motion sickness

Abstract: An artificial horizon of sound is maintained in an enclosure which is irregularly moving in a manner which may induce motion sickness of its occupant(s), by positioning sound emitters in spaced locations in the enclosure and continuously varying the sound intensity of selected emitters to create the perception of a relatively stationary sound horizon.

Automatic Acoustic Measurement System by Mechanical Resonance of Continuous Sound Waves

Abstract: Using the mechanical resonance of continuous sound waves with frequency higher than 5 MHz, an automatic measurement system is set up for simultaneous measurements of sound velocity and attenuation coefficient in thin disk samples. It is confirmed that the change of sound velocity Δυs/υ0, can be measured automatically with relative accuracy within 10-5 with changing temperatures at rates from 60 k/h to 3 k/h.

Measuring method for transfer function used for active control over noise

Abstract: PURPOSE: To obtain excellent noise elimination effect by measuring the acoustic transfer function between a sound generator for control and a sound receiver for control while a white noise which has a sound pressure level being a specific level higher than an external noise level measured by an auxiliary sound receiver is inputted, and using the result as the determining element of the transfer function of a computing element. CONSTITUTION: First and second acoustic transfer functions GAM and GAO are measured while the white level having the sound pressure level, for example, 10dB higher than the external noise level measured by a microphone 16 is inputted from a noise signal generating circuit 17, namely, while the white noise signal of sound pressure level which is 10dB higher than the external noise is inputted to a speaker 13. Consequently, the sound pressure level ratio of the external noise to the white level is reduced rela tively and the acoustic transfer functions GAM and GAO can be measured accurately and eventually. The transfer function G of the computing element which is determined according to the measured acoustic transfer functions GAM and GAO becomes accurate and the possibility that the noise elimination effect in the active control over the noise which utilizes the transfer function G comes to insufficient is eliminated. COPYRIGHT: (C)1991,JPO&Japio

System characterization of apodized acousto-optic Bragg cells

Abstract: An acousto-optic cell can be characterized in terms of the spatial impulse response or a transfer function that relates the angular plane-wave spectrum of the output light field to that of the input light field. A general methodology for calculating the acousto-optic impulse response and transfer function is developed. This methodology is then specifically applied to the case of acousto-optic cells with and without Hamming apodization of the sound field. Results are obtained and compared with analytical expressions for the conventional Bragg cell for a typical value of the Klein–Cook Q parameter and sound intensity. Finally, implications of the results relating to beam shaping in the scattered light field are discussed.

Consideration of sample dimension for ultrasonic levitation

Abstract: To study ultrasonic levitation, a high-intensity ultrasound field was generated in air by a new type of sound source using a stepped circular vibrating plate, and the sound pressure level was obtained up to 168 dB at a frequency of 20 kHz. This sound source was equipped with a reflecting plate. It was set in a 1-G environment, and the frequency could be changed by the different plates used. Several shapes of samples were inserted in the sound field, and the sample dimension was varied. As a result, the samples were levitated at the sound pressure nodes and the minimum threshold of sound pressure required for levitating the samples was found to be proportional to sample density, and was also inversely proportional to the ultrasound frequency used. The sample dimension was found to influence the sound pressure. >

Environmental sound controller

Abstract: PURPOSE:To reduce discomfort by controlling the power spectrum distribution of the secondary sound based on a sound detected by a microphone so that a sound mixing primary and secondary sounds can be the desired distribution of the power spectrum. CONSTITUTION:The primary sound like noises is detected by a microphone 1, and inputted to a secondary sound control part 3. In the control part 3, the secondary sound signal is outputted corresponding to the secondary sound to be sent from a loudspeakers 2 arranged around a man 4. In a secondary sound signal generation circuit 7, the power spectrum distribution of the primary sound is analyzed, and the secondary sound signal is generated so that the sound mixing the primary and secondary sounds can be the desired power spectrum distribution. The power spectrum distribution of the complex sound is set to 1/f characteristics which is inversely proportional to the frequency. The output of the circuit 7 is passed through a D/A converter 8 and amplified by an amplifier circuit 9, and the secondary sound is sent out from the loudspeakers 2. Thus, the discomfort can be reduced by changing the complex noise to the 1/f noise close to noise of nature.

Areal sound intensity receiver

Abstract: A system of three or more hydrophone arrays are utilized to measure underwater areal sound intensity. The hydrophone arrays bound at least one plane through which an areal sound intensity measurement is desired. Each hydrophone array comprises three orthogonal pairs of hydrophones with coincident acoustic centers. The output of each hydrophone in the system is simultaneously sampled and the outputs processed to obtain a vectorial sound intensity representation at each of the hydrophone arrays from which a representation of the areal sound intensity across the noted plane may be derived.

Effect of sound on a supersonic jet

Abstract: It is known that under the influence of sound from an external source or the sound emitted by the supersonic jet itself at discrete frequencies in nonoptimal flow regimes the supersonic jet expands more rapidly and its range is reduced [1, 2], However, the mechanism of action of the sound on the supersonic jet has not been adequately investigated and, in particular, no one has determined the intensity of the external source capable of producing a marked change in the gas dynamic parameters of the jet, its characteristics or how the interaction process develops. These questions are examined below. By means of shadow photography with a pulsed light source it is shown that a significant change in the gas dynamic characteristics of the supersonic jet can be achieved by directing at its base along the normal to the jet boundary sound with an intensity corresponding to 0.1–0.2% of the total pressure in the jet. The appearance of large-scale disturbances on the irradiated side of jet and the directional emission of sound by the jet at the frequency of the external source are noted.

Device for measuring sound intensity

Abstract: The utility model relates to a measuring device for sound intensity used for testing the sound power of a (noise) sound source, comprising a sound probe (6) composed of two microphones, a dual channels amplifier (7) and a microcomputer (8). A data sampling plate and a signal processing plate are arranged and inserted in the expansion slot of the microcomputer. The sound signals of the sound source are received by the two microphones at the same time; after being amplified by the amplifier, the two ways of signals are input to the data sampling plate to carry out sampling and analog quantity conversion; the digital quantities which are converted are input in the signal processing plate to be processed by Fourier analysis, and the microcomputer makes calculation and outputs results. The utility model suitable for real-time measurement in job site, having the advantages of simple structure, convenient operation and convenient use.

A non-invasive ultrasonic method for viscosity measurements

Abstract: A method for noninvasive measurement of viscosity, based on acoustic streaming, is described. The induced streaming velocity, which is measured by an ultrasonic Doppler technique, is used as a measure of the viscosity of the liquid. Experiments were performed on a glycerin/water mixture with a transmitted sound frequency of 10.4 MHz. The viscosity was varied from 40 mPa-s to 330 mPa-s by changing the temperature of the experimental liquid. Transmitted sound intensity was varied up to 640 mW/cm/sup 2/, yielding streaming velocities up to 14 mm/s. The streaming velocity is reported to be proportional to the sound intensity and inversely proportional to the viscosity of the liquid. Experiments on milk turning sour are also reported. Since ultrasound propagates through most materials for enclosing liquids, the method is suited for the assessment of the viscosity of liquids in sealed containers. >