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Journal of the Acoustical Society of America

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Dec 1978

Volume 64, Issue 6, pp. 1561-1735

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Experimental speakerphone system for teleconferencinga)

J. E. West, D. J. MacLean, J. R. Nelson, and J. L. Flanagan

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1561-1565 (1978); (5 pages)

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Travel to distant conferences consumes time, energy, and human resources. An alternative, should it prove an adequate replacement for face‐to‐face communication, is ’’teleconferencing.’’ While the necessary and desirable elements of conferencing by telephone are yet to be quantified, we describe a rudimentary experimental system which provides a communication versatility that belies its simplicity. We establish a dedicated 4‐wire connection between distant conference rooms. We modify conventional speakerphones (Model 4A) by disconnecting the electronic hybrid to give separate transmit (microphone) and receive (loudspeaker) leads. We give each conferee an individual instrument. In a given conference room, we sum the signals from individual transmit leads and connect the results to the transmit path of the 4‐wire circuit. Similarly, we distribute the receive path of the 4‐wire connection to the individual receive leads. The voice operated attenuator (variolosser) and the noise‐operated gain‐adjusting device (NOGAD) in each individual speakerphone are left completely intact. Complementary connections are made in the other conference room. As a result of these features, the teleconferencing system is able to provide effective, interactive conferencing among large groups of users. Because of the distributed configuration of transmitters and receivers, it copes well with room reverberation and background noise.
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43.38.Si Telephones, earphones, sound power telephones, and intercommunication systems
43.72.-p Speech processing and communication systems

Mode locking in nonlinearly excited inharmonic musical oscillators

N. H. Fletcher

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1566-1569 (1978); (4 pages) | Cited 11 times

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Many musical instruments consist essentially of resonant systems having only approximately harmonic normal modes and excited by a force that depends nonlinearly on the velocities associated with those modes. An approximate condition is derived for the resulting sound spectrum to consist of components rigorously locked into harmonic relationship. Such mode locking is favored by nearly harmonic normal mode frequencies, by large mode amplitudes, and by large nonlinearity in the driving force.
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43.75.Ef Woodwinds
43.40.At Experimental and theoretical studies of vibrating systems
43.75.-z Music and musical instruments

Some experiments with the bass drum

Harvey Fletcher and Irvin G. Bassett

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1570-1576 (1978); (7 pages) | Cited 1 time

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Measurements were made of bass drum tones to determine the characteristic properties of the sound. The analysis was performed with computer‐modeled band‐pass filters with 3‐Hz bandwidth. Frequency, peak sound pressure level, and decay rate were determined for each of the major components from 40 Hz up to 1000 Hz. The frequencies of the components were found to change with time, decreasing as amplitude of vibration decreases. Observed frequencies agreed with theoretical values to within 5% in some cases and less than 1% in most. It was found that a blow near the center of the drum puts more energy into the lower‐frequency components, while a blow near the edge emphasizes those of higher‐frequencies. Drum tones were synthesized by summing the contributions of each of the important components. Recordings of synthesized and real tones were presented randomly in listening tests. Synthesis was viewed as successful when the synthetic tones were judged to be real as often as they were judged to be synthetic. In the listening tests, a jury of 31 people correctly identified the synthetic tones only 51% of the times those tones were presented.
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43.75.Hi Drums

A mixed‐source model for speech compression and synthesis

John Makhoul, R. Viswanathan, Richard Schwartz, and A. W. F. Huggins

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1577-1581 (1978); (5 pages)

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This paper presents an excitation source model for speech compression and synthesis that allows the degree of voicing to be varied continuously by mixing voiced (pulse) and unvoiced (noise) excitations in a frequency‐selective manner. The mix is achieved by dividing the speech spectrum into two regions, with the pulse source exciting the low‐frequency region and the noise source exciting the high‐frequency region. The degree of voicing is specified by a parameter Fc, which corresponds to the cut‐off frequency between the voiced and unvoiced regions. For speech compression applications, Fc can be extracted automatically from the speech spectrum and transmitted. Experiments performed with the new model indicate its power in synthesizing natural sounding voiced fricatives and in largely eliminating the ’’buzzy’’ quality of vocoded speech. A functional definition of buzziness and naturalness is given in terms of the model.
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43.72.-p Speech processing and communication systems
43.70.Jt Instrumentation and methodology for speech production research

Acoustic determinants of phrase boundary perception

Lynn A. Streeter

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1582-1592 (1978); (11 pages) | Cited 3 times

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How three supersegmental variables (amplitude, pitch contour, and duration pattern) influence phrase boundary perception was investigated in two studies. Listeners located the phrase boundary in ambiguous algebraic expressions, such as ’’(A plus E) times O’’ and ’’A plus (E times O).’’ In one experiment, two values of each of three variables (appropriate or neutral) were orthogonally varied, using linear predictive coding analysis–synthesis procedures. There was a total of eight manipulations for each expression. In the other, the three suprasegmental variables were exchanged between the two alternative meanings of an expression, yielding a total of eight manipulations for each expression. Results from the two studies were consistent in showing that listeners use all three cues, and just these three to parse such utterances. That is, it was possible to completely shift the meaning of an expression uttered with one meaning into its alternate meaning by exchanging all three variables. In both studies, the effects of duration pattern and pitch contour were additive in total proportion correct. Possible models of how listeners process pitch and duration information independently in making a parsing decision are discussed.
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43.70.Dn Disordered speech
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Longitudinal study of hearing in children: Baseline data concerning auditory thresholds, noise exposure, and biological factors

A. F. Roche, R. M. Siervogel, J. H. Himes, and D. L. Johnson

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1593-1601 (1978); (9 pages) | Cited 3 times

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Serial auditory thresholds are being recorded at six‐month intervals from 224 children and youths aged 4–18 years. The data from the first year show girls have lower threshold levels than boys, especially from 12–17 years, and, in both sexes, those aged 12–17 years have lower thresholds than those aged 6–11 years. Median total noise exposure scores tend to be higher in boys than girls, especially after 10 years of age, but these scores are not significantly correlated with auditory threshold levels. The incidence of exposure to events associated with noise increases markedly in teenage boys and is related to auditory threshold levels. There are no significant associations between auditory threshold levels and responses to general health questions or attained stature, but there are associations with meatal abnormalities. There is suggestive evidence, particularly in girls, that rapid maturation is associated with lower threshold levels, especially at lower frequencies.
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43.66.Cb Loudness, absolute threshold
43.50.Qp Effects of noise on man and society
43.66.Dc Masking

Optimum estimation of signal parameters in non‐Gaussian noise

Jerome J. Sheehy

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1602-1612 (1978); (11 pages)

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The purpose of this paper is to derive optimum estimators for the estimation of signal parameters when the signal is emersed in an additive, not necessarily Gaussian noise field. Also, expressions for evaluating their performance are derived and, for the nonrandom signal case, the results compared with the familiar Cramer–Rao equation which provides a lower bound for the variance of an unbiased estimate. A new lower bound is derived for the variance of an unbiased estimate of the signal power for the case where the signal is a zero mean, random process and again the performance of the estimator, which is optimum for this type of signal, is compared with this new bound. In general it is found that the performance of the optimum estimator when operated in a non‐Gaussian noise field is superior to that which can be obtained when the noise is Gaussian.
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43.60.Cg Statistical properties of signals and noise

Cross‐spectral method of measuring acoustic intensity without error caused by instrument phase mismatch

J. Y. Chung

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1613-1616 (1978); (4 pages) | Cited 13 times

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The theory of a new method of measuring acoustic intensity is presented. The method uses measurements of the cross spectrum of the pressures at two closely spaced microphones. To eliminate the measurement error due to instrument phase mismatch, a circuit switching procedure is used. The method is applicable to any acoustic field subject to the condition that the product of the wave number and the microphone spacing remains small. The method has been verified by laboratory experiment.
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43.50.Yw Instrumentation and techniques for noise measurement and analysis
43.58.Dj Sound velocity

Subjective loudness of N‐wave sonic booms

A. Niedzwiecki and H. S. Ribner

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1617-1621 (1978); (5 pages) | Cited 4 times

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A loudspeaker‐driven simulation booth with extended rise‐time capability (down to 0.22 ms) has been used for subjective loudness tests of N‐wave sonic booms. The test series compared signatures over a range of 0.22–10 ms in rise time, 100–250 ms in duration and 0.5–2.5 psf (24–120 Pa) in peak overpressure. In one sequence, the tradeoff between rise time and overpressure was measured for equal loudness; in another, the tradeoff between duration and overpressure. For equal loudness 10‐ms rise time required 8‐dB higher overpressure than for 1‐ms rise time. Duration had little effect in the range 100–200 ms, but at 250 ms noticeably enhanced the loudness. These results confirm those measured by Shepherd and Sutherland made at 1‐ms rise time and above (except for the anomalous enhancement at 250‐ms duration), and extend the measurements down to 0.22 ms. There is also good agreement with theoretical predictions (Johnson–Robinson, Zepler–Harel methods) except for the 10‐ms rise time and 250‐ms duration cases.
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43.50.Ba Noisiness: rating methods and criteria
43.66.Cb Loudness, absolute threshold
43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
43.28.Mw Shock and blast waves, sonic boom

Subjective loudness of ’minimized’ sonic boom waveforms

A. Niedzwiecki and H. S. Ribner

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1622-1626 (1978); (5 pages) | Cited 10 times

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For very long supersonic aircraft the ’’midfield’’ sonic boom signature may not have evolved fully into an N wave at ground level. Thus in current boom minimization techniques the shape of the aircraft may be tailored to optimize this midfield wave form for reduced subjective loudness. The present investigation tests a family of ’’flat‐top’’ waveforms cited by Darden: all but one have a front shock height (‐pSH) less than the peak amplitude (‐pMAX). For equal subjective loudness, ’’flat top’’ vs N wave (peak overpressure ‐pN), the peak amplitude of the ’’flat top’’ signature was found to be substantially higher than that of the N wave; thus for equal peak amplitude the ’’flat‐top’’ signature was quieter. The results for equal loudness were well fitted by an empirical law ‐pSH+0.11‐pMAX =‐pN; the equivalence shows how the front shock amplitude (‐pSH) dominates the loudness. All this was found compatible with predictions by the method of Johnson and Robinson.
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43.50.Ba Noisiness: rating methods and criteria
43.66.Cb Loudness, absolute threshold
43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
43.28.Mw Shock and blast waves, sonic boom

Growth function for human response to large‐amplitude impulse noise

Paul D. Schomer

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1627-1632 (1978); (6 pages)

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The U. S. Environmental Protection Agency has proposed the use of C‐weighted day/night level for the assessment of impulse noise such as the noise resulting from sonic boom, blast noise (artillery, armor, demolition, etc.) and other large‐amplitude impulse sources. One remaining question pertaining to the use of C‐weighting has been the growth function for human response to impulse noise. This question arises because work by Kryter and by Young using peak values and/or small amplitudes exhibited growth functions of 6−7dB for a doubling of annoyance, while the growth function for human response to common sources (planes, vehicles, etc.) increases by about 10 dB for a doubling of annoyance. Kyter’s and Young’s data are reanalyzed herein by using C‐weighting and by including only large‐amplitude data. This reanalysis results in a growth function for human response to impulse noise which increases by about 10 dB for a doubling of annoyance. This equality of growth function between common A‐weighted noise and C‐weighted impulse noise further supports the use of C‐weighted day/night level for assessment of sonic boom, blast noise, or other large‐amplitude impulse noises having similar spectral content.
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43.50.Ba Noisiness: rating methods and criteria
43.50.Qp Effects of noise on man and society
43.28.Mw Shock and blast waves, sonic boom

A comparison of optically and piezoelectrically sensed acoustic emission signals

Ronald A. Kline, Robert E. Green, Jr., and C. Harvey Palmer

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1633-1639 (1978); (7 pages) | Cited 2 times

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The usual sensor for acoustic emission is the piezoelectric transducer. Although this transducer is readily available, reasonably inexpensive, and very sensitive to ultrasonic transients, it has several serious drawbacks as a transducer: It distorts the signals being measured, it exhibits resonances, it has limited bandwidth, it responds differently to surface acoustic waves and bulk waves (because of its large sensitive area), and its calibration is a matter of considerable uncertainty. Essentially, it is a qualitative transducer. Furthermore, it cannot measure local effects within a millimeter of an emission source, where the mechanisms causing the ultrasonic transient are presumably most clearly distinguishable. Optical transducers, on the other hand, have the great advantage of providing accurate, quantitative, highly localized information; they do not disturb the waves being measured and are not limited by frequency response.
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43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.38.Dv Electromagnetic and electrodynamic transducers
43.38.Fx Piezoelectric and ferroelectric transducers

The electroacoustic sensitivity of radially polarized ceramic cylinders as a function of frequency

J. A. Burt

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1640-1644 (1978); (5 pages)

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The voltage response is derived for radially polarized piezoceramic cylinders when pressure is applied on the cylinder inside surface. Both static and oscillating pressures are considered. A 2.54 cm diameter cylinder of PZT‐4 (Vernitron) material is used as a model in the frequency response which is calculated up to 10 MHz.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
72.50.+b Acoustoelectric effects
73.50.Rb Acoustoelectric and magnetoacoustic effects
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
77.65.-j Piezoelectricity and electromechanical effects
43.38.Fx Piezoelectric and ferroelectric transducers

The application of broadband ultrasonic spectroscopy to the study of layered media

N. F. Haines, J. C. Bell, and P. J. McIntyre

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1645-1651 (1978); (7 pages) | Cited 6 times

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An investigation has been made of the frequency dependence of amplitude and phase information when broadband ultrasonic pulses, in the region 1–30 MHz, are reflected from layered targets. An on line computer performing Fourier analysis of sampled ultrasonic pulses allowed both amplitude and phase information to be studied. Layers of various acoustic impedances, velocities, and attenuation have been investigated, and in particular, layers of magnetite grown on mild steel. In all cases excellent agreement between experiment and theory has been achieved. The possible use of the techniques of deconvolution has also been considered for the measurement of the thickness of layers. The methods developed have found application in the problem of determining the thickness of a corrosion layer on the inside surface of a component where access can only be gained through the outer surface.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.20.Fn Scattering of acoustic waves
43.60.Gk Space-time signal processing, other than matched field processing

Laser‐generated stress waves in liquids

Markus W. Sigrist and Fritz K. Kneubühl

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1652-1663 (1978); (12 pages) | Cited 28 times

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The generation of laser‐induced stress waves in liquids by the vaporization process and the thermoelastic effect was studied experimentally. A high‐speed camera and special high‐sensitivity stress transducers with a response time of a few nanoseconds have been used for these investigations. The experimental results obtained for water, n‐heptane, and carbon tetrachloride are discussed. For the first time, the individual contributions of vaporization and the thermoelastic effect on stress generation are separated. In addition, tunable high‐frequency acoustic waves, with frequencies up to 60 MHz, have been generated in water by the impact of a laser pulse exhibiting longitudinal mode beating. Since existing theories on the thermoelastic generation of acoustic waves do not yield satisfactory agreement with our experimental data, a new spherical model is proposed, where the transient heating caused by the laser impact, is represented by the three‐dimensional heat pole. This solution of the equation of heat conduction corresponds to a Gaussian distribution of the excessive temperature in space, and thus to the TEM00 mode of the incident laser beam. An analytical solution of the thermoelastic pressure wave is derived for this case of temperature distribution. Its good agreement with the experiment is discussed for various liquids and for two different laser characteristics.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.38.Ar Transducing principles, materials, and structures: general

A correction to the parabolic approximation

J. A. DeSanto, J. S. Perkins, and R. N. Baer

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1664-1666 (1978); (3 pages) | Cited 1 time

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In a previous paper [J. A. DeSanto, J. Acoust. Soc. Am. 62, 295 (1977)] we showed that the solutions of the Helmholtz and parabolic equations were related by an integral transform. The stationary phase approximation of the transform led to corrections of the parabolic approximation (PA). Based on this analysis, we define in this paper a corrected parabolic approximation (CPA) involving the second range derivative of the parabolic field, numerically compare the results to a normal mode example, and show how the CPA reduces the error of the PA. The error reduction is most marked in the phase.
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43.30.Bp Normal mode propagation of sound in water

The interaction of sound with noise in water

T. K. Stanton and R. T. Beyer

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1667-1670 (1978); (4 pages)

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The nonlinear interaction of a monochromatic ultrasonic signal with audio‐frequency noise has been measured in water. The scattered signal lies in sidebands corresponding to the sum and difference components of the frequencies involved. The intensity of the scattered signal increases linearly with interaction distance and quadratically with the signal frequency in the range 1–5 MHz, in agreement with the theory of Westervelt.
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43.30.Qd Global scale acoustics; ocean basin thermometry, transbasin acoustics
43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves

Propagation of nonlinear acoustic waves induced by a vibrating cylinder. I. The two‐dimensional case

Jerry H. Ginsberg

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1671-1678 (1978); (8 pages)

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This study details the first successful uniformly valid expansion for a multidimensional nonlinear wave in a system described by curvilinear coordinates. The problem of interest is the steady‐state wave motion induced within an inviscid compressible fluid by an infinite circular cylinder executing a harmonic planar vibration in its nth circumferential mode. The solution is achieved by employing a regular perturbation series to obtain an outer expansion for the velocity potential. Then outer expansions for the pressure and the velocity components are derived by the method of renormalization. Finally, uniformly valid expansions for the response are determined by matching the outer solutions with the results of a linearized analysis, which represent the inner solutions. Examples considering the effect of the nondimensional parameters are treated by presenting pressure and velocity profiles, as well as nodal and antinodal lines of radial velocity. The range of validity for farfield approximations is discussed.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.40.Ey Vibrations of shells

Propagation of nonlinear acoustic waves induced by a vibrating cylinder. II. The three‐dimensional case

Jerry H. Ginsberg

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1679-1687 (1978); (9 pages)

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The method derived in Part I for investigating the propagation of weakly nonlinear acoustic waves in systems described by curvilinear coordinates is extended herein to a three‐dimesnional situation. Specifically, this is a determination of a uniformly valid first order approximation to the waves radiating from an infinitely long cylinder vibrating harmonically in a mode having circumferential wave number n and axial wavelength L. The phenomenon of self‐refraction, in which the rays, as well as the wavefronts, are distorted by the wave motion, is shown to be the explanation for some unexpected types of distortion in the profiles of the pressure and velocity component waves. An important development is the disclosure that the three‐dimensional case of large, but finite, L cannot be used to deduce the response in the two‐dimensional case of infinite L studied in Part I. The explanation of this situation is found to lie in the existence of a dispersion relation for the phase velocity of linear waves in the three‐dimensional case.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.20.Bi Mathematical theory of wave propagation
43.40.Ey Vibrations of shells

Nonlinear and thermal acoustic sources

Harold M. Merklinger

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1688-1691 (1978); (4 pages)

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Certain nonlinear acoustic phenomena may be explained in terms of virtual or secondary sources. The parametric array is one classic example [P. J. Westervelt, J. Acoust. Soc. Am. 35, 535–537 (1963)]. It is argued here that there must also exist formally similar sources due to the thermoviscous heating of a fluid by a modulated sound wave. At moderate to high modulation frequencies the nonlinear mechanism dominates, but at sufficiently low modulation frequencies, the thermal phenomenon must become the more significant effect.
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43.25.Lj Parametric arrays, interaction of sound with sound, virtual sources
43.28.Kt Aerothermoacoustics and combustion acoustics
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves

Diffraction of elastic waves by cylindrical cavity in a half‐space

S. K. Datta and Nabil El‐Akily

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1692-1699 (1978); (8 pages) | Cited 2 times

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See Also: Erratum

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Diffraction of two dimensional elastic waves by a cylindrical cavity in a half‐space is considered in this paper. The paper is divided into two parts. In the first part we use an integral representation for the scattered displacement field to derive its asymptotic behavior at large distances from the cavity. We also give a formal derivation of the representation of the displacement field in terms of multipolar potentials. In the second part we use a method of matched asymptotic expansions to calculate the scattered field. Numerical results are presented for the surface displacements due to Rayleigh waves scattered by a circular cylindrical cavity.
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43.20.Fn Scattering of acoustic waves
43.20.Bi Mathematical theory of wave propagation

Natural frequencies of curved elastic arcs

N. J. Kudva, A. H. Nayfeh, and M. P. Kamat

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1700-1702 (1978); (3 pages)

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A perturbation analysis is presented for calculating the inextensional natural frequencies of curved elastic arcs. Variation of the radius of curvature along the arc length is accounted for by considering the curvature to be a perturbation from a constant curvature, and utilizing the method of strained parameters. Frequencies thus derived for hinged parabolic arcs demonstrate good agreement with finite element solutions. The analysis could easily be extended to determine the natural frequencies of noncircular curved plates and shells.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.40.Cw Vibrations of strings, rods, and beams

On an extended parabolic‐coherence function propagation model

John J. McCoy

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1703-1709 (1978); (7 pages)

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A parabolic wave theory is considered in which the energy flux through an elemental aperture is required to lie in directions measured relative to a ’’local’’ principal propagation direction that can be termed narrow angled. This can be compared to the more commonly encountered theory, in which a ’’global’’ principal propagation direction is used. A propagation model is then developed which is formulated in terms of an acoustic field measure termed the acoustic intensity angular spectral density. The relationship between this propagation model and the geometric theory is considered, with the latter being recovered in the appropriate limit. A sample calculation is carried out for the behavior of a beamed signal in the vicinity of a point caustic.
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43.20.Bi Mathematical theory of wave propagation
43.20.Dk Ray acoustics

Acoustic bulk parameters in distributions of pair‐correlated scatterers

Victor Twersky

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1710-1719 (1978); (10 pages) | Cited 12 times

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We develop simple approximations for the bulk acoustic parameters associated with coherent waves in pair‐correlated random distributions of scatterers small compared to wavelength, and indicate their relations to earlier forms. Our initial functional equation for the bulk index of refraction applies for dense gas and liquid‐state statistics in terms of integral analogs of lattice sums involving appropriate pair‐correlation functions. For small‐spaced scatterers (average separation of closest neighbors small compared to wavelength) we obtain explicit closed forms for the radiation loss effects by reducing the integrals to simple correlation‐packing functions based on the scaled‐particle equations of state for impenetrable particles. For uncorrelated sparse distributions, the present results reduce to those obtained by elementary procedures for small perturbations in the properties of the imbedding medium. For random lattice‐gas statistics (a model for uncorrelated distributions which takes into account the space‐occupying property of the obstacles), the results reduce, in general, to those obtained before for scatterers excited by the coherent wave and radiating into the imbedding medium.
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43.20.Fn Scattering of acoustic waves
43.20.Bi Mathematical theory of wave propagation

Moulded piezoelectric transducers using polar polymers

F. Micheron and C. Lemonon

J. Acoust. Soc. Am. Volume 64, Issue 6, pp. 1720-1721 (1978); (2 pages)

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Polar polymer such as PVC, PVF and PVF2 show strong piezoelectric activity after being stretched and poled. They were used up to now in plane or cylindrical configurations. We show that such polymers can be moulded and poled, which constitutes a new generation of piezoelectric transducers. Example is given of a high range loudspeaker using a moulded PVC film.
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43.38.Fx Piezoelectric and ferroelectric transducers
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