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Journal of the Acoustical Society of America

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Sep 1984

Volume 76, Issue 3, pp. 661-1005

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A theoretical and experimental study of a model piezoelectric membrane headphone

Geoffrey Davies, Preston V. Murphy, and Guy Maurer

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 661-665 (1984); (5 pages)

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The generation of sound by a curved circular piezoelectric polymer diagram has been analyzed theoretically and experimentally. The diaphragm was considered to have zero flexible stiffness and adjustable tension and to drive a coupling volume having significant reaction effects. The analysis was confined to frequencies well below resonance. Measurements of static diaphragm displacement caused by differences in air pressure were used to determine values of Young’s modulus and a film pretension. The sound generated by a 110‐Hz signal was measured as a function of static displacement and found to increase strongly at first, pass through a rather flat maximum, and finally decrease. A theory was developed which correlated with the results and a figure of merit was derived which relates output per unit exciting voltage to the thickness, piezoelectric coefficient, elastic modulus, and Poisson’s ratio of the diaphragm.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.38.Si Telephones, earphones, sound power telephones, and intercommunication systems
43.58.Vb Calibration of acoustical devices and systems

The addition of piezoelectric properties to structural finite element programs by matrix manipulations

Graham F. McDearmon

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 666-669 (1984); (4 pages)

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Piezoelectric properties may be added to structural finite element programs (SFEPs) by matrix manipulations of elastic and heat transfer element matrices. The theory for this addition is contained in this publication.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.38.Ar Transducing principles, materials, and structures: general
43.40.At Experimental and theoretical studies of vibrating systems
77.65.-j Piezoelectricity and electromechanical effects

Measurement of speed and attenuation of ultrasound in egg white and egg yolk

C. Javanaud, R. R. Rahalkar, and P. Richmond

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 670-675 (1984); (6 pages) | Cited 2 times

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Measurements of the speed and absorption of ultrasound in egg white and yolk at 2.10, 4.12, and 6.79 MHz over the approximate temperature range 20°–25 °C have enabled distinct trends to be detected. Further measurements using a different piece of apparatus enabled values for the absorption, every 10 MHz, over the frequency range up to 124 MHz, (from 5 MHz for the yolk and from 15 MHz for the white) to be found. These results tie in well with the more accurate lower frequency data. Egg yolk and egg white have very different ultrasonic characteristics. The temperature coefficient of the speed of sound in the former could not be detected, whereas that of the latter is very close to that of water. On the other hand, the negative temperature coefficient of absorption in the yolk shows up quite clearly, whereas that of the white is small and possibly changes sign near 4 MHz. The frequency dependence of absorption (up to 124 MHz) is close to linear in the white (exponent ∼1.2) and slightly greater in the yolk (exponent ∼1.5). Dispersion in velocity could not be detected over the frequency range of 2.1–6.8 MHz.
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43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

Behavioral vocal response thresholds to mating calls in the bullfrog, Rana catesbeiana

Andrea Megela‐Simmons

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 676-681 (1984); (6 pages) | Cited 1 time

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Male bullfrogs will vocalize in response to playbacks of the mating (advertisement) calls of conspecifics. This behavior was studied in response to playbacks of bullfrog mating calls presented at six different sound intensity levels. The lowest sound intensity level tested (50 dB SPL) was insufficient to evoke calling from any of the animals. Calling was evoked by playback levels of 60 dB SPL and higher. The data suggest that behavioral evoked calling thresholds lie between 50‐60 dB SPL for these animals. Playback intensity levels of 80 dB SPL were more effective in evoking responses than were intensity levels up to 20 dB higher or lower. This was true both in terms of the total number of evoked responses and the trial number at which responding ceased. Moreover, significantly less habituation of evoked calling occurred at levels of 80 dB SPL than at higher or lower levels. The data suggest that a sound pressure level of 80 dB represents a behaviorally preferred intensity level for evoked calling in the bullfrog. Field recordings of bullfrog choruses show that the intensity produced by an individual calling male reaches a level of 80 dB SPL at a distance of 1 m. This intensity level is identical to that producing maximal evoked calling in the laboratory.
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43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing
43.80.Nd Effects of noise on animals and associated behavior, protective mechanisms

Description of a color spectrogram

G. M. Kuhn

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 682-685 (1984); (4 pages)

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We define a color spectrogram which retains all the information of the standard spectrogram, and which encodes information about the shape of each short‐time spectrum into the chromaticity with which that spectrum is illuminated. The chromaticity for each spectrum is derived by interpreting each spectrum as an energy distribution in the visible light frequencies.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.70.Jt Instrumentation and methodology for speech production research
42.66.Qg Scales for light and color detection

Speechreading supplemented with frequency‐selective sound‐pressure information

M. Breeuwer and R. Plomp

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 686-691 (1984); (6 pages) | Cited 13 times

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The benefit of supplementing speechreading with frequency‐selective sound‐pressure information was studied by auditorily presenting this information to normal‐hearing listeners. The sound‐pressure levels in one or two frequency bands of the speech signal with center frequencies of 500, 1600, and 3160 Hz, respectively, and with 1‐ or 1/3‐ oct bandwidth were used to amplitude‐modulate pure‐tone carriers with frequencies equal to the center frequencies of the filter bands. Short sentences were presented to 18 normal‐hearing listeners under the conditions of speechreading‐only and speechreading combined with the sound‐pressure information. The mean number of correctly perceived syllables increased from 22.8% for speechreading‐only to 65.7% when sound‐pressure information was supplied in a single 1‐oct band at 500 Hz and to 86.7% with two 1‐oct bands at 500 and 3160 Hz, respectively. The latter signal scored only 26.7% correct syllables without accompanying visual information.
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43.71.Rt Sensory mechanisms in speech perception
43.66.Lj Perceptual effects of sound
43.66.Wv Vibration and tactile senses
43.71.Gv Measures of speech perception (intelligibility and quality)

The detection of French accent by American listeners

James Emil Flege

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 692-707 (1984); (16 pages) | Cited 3 times

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The five experiments presented here examine the ability of listeners to detect a foreign accent. Computer editing techniques were used to isolate progressively shorter excerpts of the English spoken by native speakers of American English and French. Native English‐speaking listeners judged the speech samples in one‐ and two‐interval forced‐choiced tests. They were able to detect foreign accent equally well when presented with speech edited from phrases read in isolation and produced in a spontaneous story. The listeners accurately identified the French talkers (63%–95% of the time) no matter how short were the speech samples presented: entire phrases (e.g., ‘‘two little dogs’’), syllables (/tu/ or /ti/), portions of syllables corresponding to the phonetic segments /t/, /i/, /u/, and even just the first 30 ms of ‘‘two’’ (roughly, the release burst of /t/). Both phonetically trained listeners familiar with French‐accented English and unsophisticated listeners were able to accurately detect accent. These results suggest that listeners develop very detailed phonetic category prototypes against which to evaluate speech sounds occurring in their native language.
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43.71.Hw Cross-language perception of speech
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Limits on phonetic accuracy in foreign language speech production

James Emil Flege and James Hillenbrand

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 708-721 (1984); (14 pages) | Cited 9 times

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This study examined the French syllables /tu/ (‘‘tous’’) and /ty/ (‘‘tu’’) produced in three speaking tasks by native speakers of American English and French talkers living in the U. S. In a paired‐comparison task listeners correctly identified more of the vowels produced by French than American talkers, and more vowels produced by experienced than inexperienced American speakers of French. An acoustic analysis revealed that the American talkers produced /u/ with significantly higher F2 values than the French talkers, but produced /y/ with F2 values equal to those of the French talkers. A labeling task revealed that the /y/ vowels produced by the experienced and inexperienced Americans were identified equally well, but that the experienced Americans produced a more identifiable /u/ than the inexperienced Americans. It is hypothesized that English speakers learn French /y/ rapidly because this vowel is not—like French /u/—judged to be equivalent to a vowel of English. The French and American talkers produced /t/ with equal VOT values of about 55 ms, which is intermediate to values commonly observed for monolingual speakers of French and English. It is hypothesized that the bilingual talkers judged the /t/ of French and English to be equivalent, which affected their perceptual target for French /t/ and ultimately their production of this stop.
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43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation
43.71.Hw Cross-language perception of speech
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics

Intensity perception. XIII. Perceptual anchor model of context‐coding

L. D. Braida, J. S. Lim, J. E. Berliner, N. I. Durlach, W. M. Rabinowitz, and S. R. Purks

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 722-731 (1984); (10 pages) | Cited 16 times

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In our preliminary theory of intensity resolution [e.g., see N. I. Durlach and L. D. Braida, J. Acoust. Soc. Am. 46, 372–383 (1969)], two modes of memory operation are postulated: the trace mode and the context‐coding mode. In this paper, we present a revised model of the context‐coding mode which describes explicitly a process by which sensations are coded relative to the context and which predicts a resolution edge effect [L. D. Braida and N. I. Durlach, J. Acoust. Soc. Am. 51, 483–502 (1972); J. E. Berliner, L. D. Braida, and N. I. Durlach, J. Acoust. Soc. Am. 61, 1256–1267 (1977)]. The sensation arising from a given stimulus presentation is coded by determining its distance from internal references or perceptual anchors. The noise in this process, combined with the sensation noise, constitutes the limitation on resolution in the model. In the revised model the probability density functions of the decision variable are not precisely Gaussian (and cannot be expressed analytically in closed form). This paper outlines the predictions of the model for one‐interval paradigms and for fixed‐level two‐interval paradigms and derives estimates of the values of model parameters.
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43.66.Ba Models and theories of auditory processes
43.66.Fe Discrimination: intensity and frequency
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Cb Loudness, absolute threshold

Integration of spectral and temporal cues separated in time and frequency

Blas Espinoza‐Varas and Donald G. Jamieson

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 732-738 (1984); (7 pages)

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Subjects discriminated a ‘‘standard’’ pair of tone bursts (T1, T2) from a ‘‘comparison’’ pair (T1+Δt, T2+Δf), containing increments in the duration Δt of the first burst and/or the frequency Δf of the second burst. The threshold (d′=2.0) for Δt was measured as a function of Δf, and the threshold for Δf as a function of Δt. The integration of increments in duration and frequency was studied as a function of the spectral and temporal separation between T1 and T2. A trade‐off between the values of Δt and Δf required for d′=2.0 performance was observed. This integration takes place when Δt, Δf occur simultaneously in the same spectral region, and when they occur separated by up to 120 ms, or by up to a full octave. The efficiency of integration was similar for all conditions of temporal and spectral separation studied, because the discriminability of Δt and of Δf is also nearly uniform across experimental conditions. The results from all experimental conditions are adequately described by a vector summation model derived from TSD. In a subsidiary experiment, subjects categorized pure tones varying in duration and frequency as ‘‘high’’ or ‘‘low’’ in pitch and ‘‘long’’ or ‘‘short’’ in duration. It was found that combined variations in duration and frequency result in essentially independent perceptual processes, although pitch has a small effect upon the perceived duration. It is concluded that spectral–temporal integration is a general ability operating in a variety of stimulus conditions. Listeners integrate independent evidence provided by the temporal and spectral cues in favor of, or against, particular stimulus states.
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43.66.Ba Models and theories of auditory processes
43.66.Fe Discrimination: intensity and frequency
43.66.Lj Perceptual effects of sound
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

On the growth of masking asymmetry with stimulus intensity

Robert A. Lutfi and Roy D. Patterson

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 739-745 (1984); (7 pages) | Cited 16 times

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Masking asymmetry was investigated over a wide range of stimulus intensities for two signal frequencies, f0=1.0 and 4.0 kHz, using both fixed‐masker and fixed‐signal paradigms. The masker was a notched noise with the upper and lower edges of the notch, fu and fl, respectively, placed asymmetrically about f0. For various notch widths, the asymmetry of masking was measured as the difference between the masked threshold obtained when fl was nearer f0 and that obtained when fu was nearer f0. For maskers with wide notches, (fu−fl)/f0>0.15, masking asymmetry changed with stimulus level; at the highest level, masked threshold was greatest when fl was nearer f0, and, at the lowest level the asymmetry reversed slightly for f0=1.0 kHz so that masked threshold was actually greater when fu was nearer f0. Nonparallel growth of masking functions reveal changes in masking asymmetry with signal level as well as with masker level. It is concluded that the nolinear growth of masking with level is due primarily to changes in the auditory filter, rather than changes in the detector following the filter.
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43.66.Dc Masking
43.66.Ba Models and theories of auditory processes
43.66.Yw Instruments and methods related to hearing and its measurement

The effects of multichannel compression/expansion amplification on the intelligibility of nonsense syllables in noise

Gary Walker, Denis Byrne, and Harvey Dillon

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 746-757 (1984); (12 pages) | Cited 1 time

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The effects of six‐channel compression and expansion amplification on the intelligibility of nonsense syllables embedded in speech spectrum noise were examined for four hearing‐impaired subjects. For one condition (linear) the stimulus was given six‐channel amplification with frequency shaping to suit the subject’s hearing loss. The other condition (nonlinear) was the same except that low level inputs, to any given channel, received expansion amplification and high level inputs received compression. For each condition, each subject received the nonsense syllables at three different input levels, representing low, average, and high intensity speech. The results of this study, like those of most other studies of multichannel compression, are mainly negative. Nonlinear processing (mainly expansion) of low intensity speech resulted in a significant degradation of speech intelligibility for two subjects and in no improvement for the others. One subject showed a significant improvement in intelligibility for the nonlinearly processed average intensity speech and another subject showed significant improvement for the high intensity input (mainly compression). Clearly, nonlinear processing is beneficial for some subjects, under some listening conditions, but further research is needed to identify the relevent characteristics of such subjects. An acoustic analysis of selected items revealed that the failure of expansion to improve intelligibility was primarily due to the very low intensity consonants /O/ and /k/, in final position, being presented at an even lower intensity in the expansion condition than in the linear condition. Expansion may be worth further investigation with different parameters. Several other problems caused by the multichannel processing were also revealed. These included alteration of spectral shapes and band interaction effects. Ways of overcoming these problems, and of capitalizing on the likely advantages of multichannel amplification, are currently being investigated.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Sr Deafness, audiometry, aging effects
43.66.Dc Masking

Intelligibility ratings of continuous discourse: Application to hearing aid selection

Robyn M. Cox and D. Michael McDaniel

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 758-766 (1984); (9 pages) | Cited 2 times

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Twelve normal‐hearing subjects rated the intelligibility of 35‐s, hearing‐aid‐processed continuous discourse (CD) passages. Three talkers (two male, one female), four hearing aids, and two signal‐to‐babble (S/B) ratios were used in a completely crossed design. Research questions concerned: (1) ability of listeners to rate intelligibility, (2) sensitivity of hearing aid rankings when rankings were based on intelligibility ratings for three CD passages per instrument, and (3) dependence of hearing aid rankings on (a) S/B ratio, and (b) talker characteristics. Results were: (1) listeners were able to rate intelligibility, (2) rankings based on intelligibility ratings of three CD passages per hearing aid were capable of identifying two superior instruments within a group of four hearing aids that were similar in frequency/gain function, (3) listening in a more difficult S/B ratio substantially decreased the sensitivity of the hearing aid rankings for the female talker but had only minor effects on the rankings for the male talkers, and (4) hearing aid intelligibility rankings were found to be different for different talkers. Applications to hearing aid selection are discussed.
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43.66.Yw Instruments and methods related to hearing and its measurement
43.66.Ts Auditory prostheses, hearing aids
43.66.Lj Perceptual effects of sound
43.71.Gv Measures of speech perception (intelligibility and quality)

Cochlear mechanics: Analysis for a pure tone

Mark H. Holmes and Julian D. Cole

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 767-778 (1984); (12 pages) | Cited 2 times

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A three‐dimensional hydroelastic model of the cochlea is analyzed, in which the fluid is viscous and the basilar membrane is an inhomogeneous orthotropic elastic plate. After the solution is obtained using a multiple‐scale approximation, comparison is made with experiment for the human cochlea.
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43.64.Bt Models and theories of the auditory system
43.64.Kc Cochlear mechanics

High‐frequency rolloff in a cochlear model without critical‐layer resonance

E. R. Lewis

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 779-786 (1984); (8 pages)

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Zwislocki’s original cochlear model, incorporating axial fluid inertia and shunt basilar‐membrane stiffness and viscous resistance, possesses an operating regime not previously emphasized in the literature. Even in the absence of basilar‐membrane mass and the consequent critical‐layer resonance, this regime provides extraordinarily steep high‐frequency rolloff. That rolloff is not associated with a critical frequency at which energy flow velocity goes to zero, but is attributable instead to a combination of two effects; (1) frequency‐dependent energy coupling to the basilar‐membrane viscous resistance, leading to local attenuation of the traveling wave at a rate (Np/cycle) that is directly proportional to frequency, and (2) wavelength that decreases with increasing frequency, thus increasing the number of cycles per unit length of basilar membrane. This combination leads to local attenuation of the traveling‐wave amplitude (hence energy absorption from the traveling wave) that is strongly dependent on frequency, the rate (Np/cm) being proportional to the square of frequency in the long‐wave mode. In Ranke’s (two‐dimensional, short‐wave mode) version of the model, the same operating regime leads to attenuation that is even more intensely dependent on frequency, the rate being proportional to the cube of frequency.
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43.64.Bt Models and theories of the auditory system
43.64.Kc Cochlear mechanics

Monaural and binaural auditory brainstem responses in relation to the psychophysical loudness growth function

Susan W. Howe and T. Newell Decker

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 787-793 (1984); (7 pages)

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Electrophysiological measures of the brainstem response to auditory stimuli permit comparisons to be made between latency shifts across intensity increments and psychophysical measures of loudness growth. Monaural comparisons leave much room for uncertainty in the interpretation of the nature of the relationship between the two response modes. A more definitive method for examining this relationship is to compare the monaural and binaural data obtained from psychophysical and electrophysiological measures. It is shown here that, while the brainstem electrophysiological response to intensity changes can be described by a power function, the latency of the neural response does not provide a direct link to the process of loudness summation or to the psychophysical response to loudness growth.
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43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Ri Evoked responses to sounds
43.66.Pn Binaural hearing

Measurement of nonlinear vibration by signal compression method

Nobuharu Aoshima

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 794-801 (1984); (8 pages)

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The signal compression method [Aoshima, J. Acoust. Soc. Am. 69, 1484–1488 (1981); Aoshima, J. Acoust. Soc. Jpn. (E) 3, 105–109 (1982)] is shown to be useful for analyzing nonlinear systems as well as linear systems. If a nonlinear system can be modeled as a parallel combination of a linear part and elements subject to a power law, such as a squarer, they can be analyzed separately by the signal compression method. As the test signal of the signal compression method has been generated by an ‘‘expanding filter’’ H(ω)=exp(jαω2), the linear response can be detected by a ‘‘compression filter’’ H−1(ω)=exp(−jαω2). Then the nonlinear component generated by the squarer is also compressed by another ‘‘second‐order compression filter’’ H−12(ω)=exp(−jαω2/2). The frequency tripled component, which is generated by a third power nonlinear element, is compressed by the ‘‘third‐order compression filter’’ H−13(ω)=exp(−jαω2/3). Results of model experiments by an analog squarer and a numerical nonlinear processing are exemplified together with nonlinear effects observed in a floor vibration experiment.
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43.60.Gk Space-time signal processing, other than matched field processing
43.40.Ga Nonlinear vibration

An extension of maximum entropy beamforming to arbitrary planar arrays with statistics

R. S. Hebbert and Leha T. Barkakati

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 802-806 (1984); (5 pages)

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The usual formulation of maximum entropy (ME) beamforming assumes no statistics in the spatial correlation matrix of the received signals. In practice the ME method is restricted to uniform line arrays of half‐wavelength spacing. In this paper, an extended maximum entropy (EME) method is presented allowing statistics in the spatial correlation matrix. Also, a method of solution is given for arbitrary arrays. Results are presented for real and simulated underwater acoustic data.
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43.60.Gk Space-time signal processing, other than matched field processing
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics

Noise levels and hearing thresholds in the drop forging industry

William Taylor, Barry Lempert, Peter Pelmear, Ian Hemstock, and Jeffrey Kershaw

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 807-819 (1984); (13 pages) | Cited 3 times

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A‐weighted equivalent continuous noise levels for hammer and press operations in a drop‐forging industry were determined using both tape recordings of the noise and personal noise dosimeters. The results indicated average A‐weighted Leq values of 108 dB for hammer operators and 99 dB for press operators. Comparison of hearing level statistics for 716 hammer and press operators and 293 control subjects indicated the severe hazard to hearing of impact noise exposures. For mean exposure times of less than 10 years, hearing levels for the press (99 dB) and hammer (108 dB) operator age groups are nearly identical, and in the latter case are less than those predicted for exposure to equivalent continuous noise. For long‐term exposures of 10 years or more, the results of this study indicate that hearing losses resulting from impact noise in the drop‐forging industry are as great or greater than those resulting from continuous noise.
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43.50.Jh Noise in buildings and general machinery noise
43.50.Qp Effects of noise on man and society
43.66.Ed Auditory fatigue, temporary threshold shift

Scattering in glass beads: Effects of frame and pore fluid compressibilities

Kenneth W. Winkler and William F. Murphy, III

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 820-825 (1984); (6 pages) | Cited 2 times

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Ultrasonic compressional wave phase velocities and attenuation have been measured as functions of frequency in packings of unconsolidated glass beads. External confining pressure was varied so as to modify the physical interactions between grains. Samples were studied when vacuum dry and when saturated with different pore fluids. Pressure/pore fluid combinations were chosen so as to minimize nonscattering loss mechanisms. In each experiment, phase velocity exhibited negative dispersion and attenuation was proportional to the fourth power of frequency. Increasing confining pressure (to 15 MPa) significantly reduced the scattering losses (by an order of magnitude at a given frequency in dry glass beads). Decreasing pore fluid compressibility produced a corresponding decrease in the scattering losses. This work shows that theoretical models based on suspensions are not adequate when the grains are interacting to form a solid frame. The present data, along with previous data for fused glass beads, suggest that the scattering strength is related to the contrast between the acoustic properties of the composite and of the grains, rather than to pore/grain or pore/composite contrasts.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

Magnetoacoustic wave propagation in paramagnetic insulators exhibiting induced linear magnetoelastic couplings

G. A. Maugin and A. Hakmi

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 826-840 (1984); (15 pages)

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The propagation of bulk and surface magnetoacoustic waves is studied in paramagnetic materials on the basis of a phenomenological, fully nonlinear, rotationally invariant, thermodynamically admissible theory of the magnetoelasticity of insulators such as rare‐earth compounds. The work is self‐contained and develops from basic nonlinear equations to solve for propagation modes after linearization of both volume and surface equations about a bias state in accordance with the methods of nonlinear continuum mechanics. The initial nonlinear feature of the theory, associated with rotational invariance, allows one to place in evidence the effects of a bias magnetic field on the dynamical properties of the medium. In particular, among the effects thus exhibited are (1) a symmetry breaking favoring the existence of magnetoelastic couplings (biased piezomagnetism), which would not exist in the absence of bias fields, (2) an alteration in the bulk‐wave speeds (direct magnetoacoustic effects), (3) an acoustical linear birefringence, and (4) in addition to the classical Rayleigh mode, creation of an SH magnetoacoustic surface mode akin to the Bleustein–Gulyaev mode of acoustoelectricity, results from adequate symmetry breaking effects of the bias magnetic field. The influence of viscosity and magnetic relaxation is also examined.
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43.35.Mr Acoustics of viscoelastic materials
43.35.Rw Magnetoacoustic effect; oscillations and resonance
75.80.+q Magnetomechanical effects, magnetostriction

Acoustically generated turbulence and its effect on acoustic agglomeration

Rajiv Tiwary, Gerhard Reethof, and Oliver H. McDaniel

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 841-849 (1984); (9 pages)

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Acoustic agglomeration (AA) is an intermediate treatment of aerosols containing submicron‐ and micron‐sized particles so that conventional cleaning devices such as electrostatic precipitators, bag houses, and scrubbers can remove these fine particles more efficiently. The high‐intensity acoustic field in the AA causes local velocity fluctuations to move the particles relative to one another, collide, adhere, and grow. This paper addresses the question of whether such highly intense acoustic fields (approximately 160 dB) will cause random velocity fluctuations of such a magnitude that this acoustic ‘‘turbulence’’ significantly affects AA. The experimental study results show that only the acoustic velocity fluctuations at the excitation frequency dominate the local velocity and therefore the particle motions. Although some acoustically generated random motion is noted with increasing acoustic intensity above 160‐dB sound pressure level, the energy in turbulent fluctuations is about three orders of magnitude lower than the energy in acoustic frequency and harmonics. The paper concludes that acoustically induced turbulence does not play a significant role in AA.
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43.35.Ty Other physical effects of sound
82.70.Rr Aerosols and foams

Intrinsic modes in a nonseparable ocean waveguide

J. M. Arnold and L. B. Felsen

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 850-860 (1984); (11 pages) | Cited 2 times

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Waveguide structures encountered in underwater acoustics usually lead to nonseparable boundary value problems, which do not admit definition of conventional normal modes. However, it may nevertheless be possible to construct source‐free modelike wavefunctions for such configurations, which are intrinsically determined by the waveguide geometry, are mutually decoupled, and therefore propagate independently of one another when used in superposition. We call such wavefunctions intrinsic modes. For the special case of a wedge‐shaped ocean with penetrable bottom, we pursue an approach similar to our previous analysis [J. M. Arnold and L. B. Felsen, J. Acoust. Soc. Am. 73, 1105–1119 (1983)] to construct the intrinsic modes explicitly. Leading order asymptotic evaluation of an intrinsic mode for small bottom slope reveals its similarity to the conventional adiabatic mode, but with a uniform transition, through cutoff, between the bound and leaky mode regions. This construction proceeds without reference to any source of the acoustic field, thereby differing from our previous treatment wherein the existence of local modes was inferred from an independently calculated asymptotic form of a line source field. Moreover, by local normal mode expansion of an intrinsic mode, with the expansion coefficients derived from the next higher order asymptotic approximation, we demonstrate explicitly that the intrinsic mode can account for coupling between adiabatic modes, with coupling coefficients that are shown elsewhere to be consistent with those from conventional coupled mode theory.
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43.30.Bp Normal mode propagation of sound in water
43.20.Bi Mathematical theory of wave propagation
43.20.Mv Waveguides, wave propagation in tubes and ducts

Effects of second‐order scattering on high resolution sonars

T. K. Stanton

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 861-866 (1984); (6 pages) | Cited 1 time

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To achieve simultaneous high volume coverage and high spatial resolution, sonars employing multiple narrow steered receiver beams in conjunction with a single wide transmitter beam are quite often used. The effects of second‐order scattering on multibeam sonars have been calculated. The analysis is in terms of the backscattered energy (or ‘‘integrated echo’’) due to clouds of point scatterers. The work applies to scattering such as from clouds of bubbles or dense schools or ‘‘swarms’’ of swimbladder‐bearing fish. Under certain conditions second‐order scattering will increase the echo energy an appreciable amount, especially as the ratio of transmitter beamwidth to receiver beamwidth increases. The major conditions are (1) dense clouds of nondirectional scatterers are insonified, (2) the sonar signal suffers measurable attenuation due to the extinction cross section of the scatterers, and (3) the absorption cross section of the scatterers is small. The echo energy due to both first‐ and second‐order scattering are calculated for several beamwidth ratios. It is shown that the backscattered energy is increased by up to 100% due to second‐order scattering.
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43.30.Vh Active sonar systems
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect

The propagation of plane waves in a thermally stratified atmosphere

W. K. Van Moorhem and Gregory K. Landheim

J. Acoust. Soc. Am. Volume 76, Issue 3, pp. 867-870 (1984); (4 pages) | Cited 1 time

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The behavior of a plane wave reflecting from a finite impedance surface with a realistic atmospheric temperature profile is investigated. An approximate solution has been implemented on a digital computer and this solution is presented graphically for a number of cases at low incidence angles.
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43.28.Kt Aerothermoacoustics and combustion acoustics
43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.20.Bi Mathematical theory of wave propagation
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