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Sep 1986

Volume 80, Issue 3, pp. 723-1003

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The frequency of flexural vibration of completely free composite piezoelectric polymer plates

Donald Ricketts

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 723-726 (1986); (4 pages) | Cited 2 times

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The frequency expression for flexural vibrations of the completely free composite piezoelectric polymer plate given in an earlier paper [J. Acoust. Soc. Am. 77, 1939–1945 (1985)] for all modes of the type p/q (p, q=2,3,4,...) is extended to cover all modes of this type for p, q=0,1,2,..., where p and q are the number of nodal lines in the coordinate directions x1 and x2, respectively. Because of the stiffening effect of electrodes deposited on the polymer surface, the expressions for the flexural and twisting rigidities of the composite plate given in the earlier paper for 2n layers are rewritten with the electrodes treated as layers separate from the polymer. Expressions are also given for the rigidities of the composite plate for an odd number of layers, a case not considered in the earlier paper. The frequencies of several modes are computed for a completely free composite piezoelectric polymer plate, a configuration which has application to hydrostatic polymer hydrophones.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.40.Dx Vibrations of membranes and plates
43.20.Bi Mathematical theory of wave propagation
43.30.Yj Transducers and transducer arrays for underwater sound; transducer calibration

Attenuation measurement uncertainties caused by speckle statistics

Kevin J. Parker

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 727-734 (1986); (8 pages) | Cited 3 times

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Attenuation measurements can be derived from the decay of backscattered signal with depth in an inhomogeneous material. In cases such as liver tissue, where many small inhomogeneities are likely to be included in sample volumes defined by pulse and beam widths, Rayleigh statistics describe the random nature of the magnitude of backscattered pressure. The statistics of speckle underlie the uncertainties in estimates of attenuation at discrete frequencies, and of the magnitude and frequency dependence of attenuation over a bandwidth. This paper derives expressions for the standard deviations of attenuation magnitude and frequency dependence in terms of parameters such as the dimensions of the region of interest, and the bandwidth of the ultrasonic system. Practical examples are given using published data, and comparisons to other techniques which measure ‘‘attenuation slope’’ are made. The analysis yields insights into trade‐offs among variables such as the dimensions and shape of regions of interest, and the segmenting of data in time and frequency domain.
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43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues
43.80.Ev Acoustical measurement methods in biological systems and media

Sounds, source levels, and associated behavior of humpback whales, Southeast Alaska

Paul O. Thompson, William C. Cummings, and Samuel J. Ha

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 735-740 (1986); (6 pages) | Cited 12 times

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Humpback whales in Southeast Alaskan waters produced five categories of sounds: moans, grunts, pulse trains, blowhole‐associated sounds, and surface impacts. Frequencies (Hz) of moans and grunts were 20–1900. Major energy in low‐frequency pulse trains was in a band of 25–80 Hz with pulse duration of 300–400 ms. Blowhole‐associated sounds, recorded as transiting whales encountered one another, were of two types: shrieks, 555–2000 Hz, and trumpetlike horn blasts with fundamental at 414 Hz (median). Pulses and spread spectrum noise were associated with gas bubble formation and explosive bursts, respectively, in connection with spiral feeding maneuvers. Surface impacts resulted from fluke or flipper slaps in sequences of 3–21 sounds. Source levels ranged from 162 (low‐frequency pulse trains) to 192 dB (surface impacts), re: 1 μPa, 1 m. Songs, commonly heard on winter breeding grounds, were absent from our recordings. Feeding and perhaps certain other whale activities can be monitored based on sound production.
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43.80.Nd Effects of noise on animals and associated behavior, protective mechanisms
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Vowel errors in noise and in reverberation by hearing‐impaired listeners

Anna K. Nábělek and Paul A. Dagenais

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 741-748 (1986); (8 pages) | Cited 7 times

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The effects of noise and reverberation on the identification of monophthongs and diphthongs were evaluated for ten subjects with moderate sensorineural hearing losses. Stimuli were 15 English vowels spoken in a /b–t/ context, in a carrier sentence. The original tape was recorded without reverberation, in a quiet condition. This test tape was degraded either by recording in a room with reverberation time of 1.2 s, or by adding a babble of 12 voices at a speech‐to‐noise ratio of 0 dB. Both types of degradation caused statistically significant reductions of mean identification scores as compared to the quiet condition. Although the mean identification scores for the noise and reverberant conditions were not significantly different, the patterns of errors for these two conditions were different. Errors for monophthongs in reverberation but not in noise seemed to be related to an overestimation of vowel duration, and there was a tendency to weight the formant frequencies differently in the reverberation and quiet conditions. Errors for monophthongs in noise seemed to be related to spectral proximity of formant frequencies for confused pairs. For the diphthongs in both noise and reverberation, there was a tendency to judge a diphthong as the beginning monophthong. This may have been due to temporal smearing in the reverberation condition, and to a higher masked threshold for changing compared to stationary formant frequencies in the noise condition.
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43.71.Ky Speech perception by the hearing impaired
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.50.Qp Effects of noise on man and society
43.55.Hy Subjective effects in room acoustics, speech in rooms

Superior lateral pharyngeal wall movements in speech

Avraham Parush and David J. Ostry

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 749-756 (1986); (8 pages)

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Medial movements of the lateral pharyngeal wall at the level of the velopharyngeal port were examined by using a computerized ultrasound system. Subjects produced CVNVC sequences involving all combinations of the vowels /a/ and /u/ and the nasal consonants /n/ and /m/. The effects of both vowels on the CVN and NVC gestures (opening and closing of the velopharyngeal port, respectively) were assessed in terms of movement amplitude, duration, and movement onset time. The amplitude of both opening and closing gestures of the lateral pharyngeal wall was less in the context of the vowel /u/ than the vowel /a/. In addition, the onset of the opening gesture towards the nasal consonant was related to the identity of both the initial and the final vowels. The characteristics of the functional coupling of the velum and lateral pharyngeal wall in speech are discussed.
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43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
43.70.Bk Models and theories of speech production
43.70.Jt Instrumentation and methodology for speech production research

Testing a model of intonation in a tone language

Mona Lindau

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 757-764 (1986); (8 pages)

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Schematic fundamental frequency curves of simple statements and questions are generated for Hausa, a two‐tone language of Nigeria, using a modified version of an intonational model developed by Gårding and Bruce [Nordic Prosody II, edited by T. Fretheim (Tapir, Trondheim, 1981), pp. 33–39]. In this model, rules for intonation and tones are separated. Intonation is represented as sloping grids of (near) parallel lines, inside which tones are placed. The tones are associated with turning points of the fundamental frequency contour. Local rules may also modify the exact placement of a tone within the grid. The continuous fundamental frequency contour is modeled by concatenating the tonal points using polynomial equations. Thus the final pitch contour is modeled as an interaction between global and local factors. The slope of the intonational grid lines depends at least on sentence type (statement or question), sentence length, and tone pattern. The model is tested by reference to data from nine speakers of Kano Hausa.
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43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Auditory filter shapes in the chinchilla

D. Lynn Halpern and Peter Dallos

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 765-775 (1986); (11 pages) | Cited 2 times

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Auditory filter shapes were determined for the chinchilla using the notched‐noise technique [R. D. Patterson, J. Acoust. Soc. Am. 59, 640–654 (1976)]. Here, the derivative of the curve relating threshold to masker gap width outlines the shape of the auditory filter. Three chinchillas were trained, using positive reinforcement techniques, to provide forward masked thresholds at 1.0 and 10.0 kHz, at three masker spectrum levels. Unexpectedly, the threshold curves contained inflection points and regions of constant or nonmonotonic changes in threshold, so that the derived filters contained dips in their central passbands. Nonmonotonic variations in threshold may be discerned in human threshold versus notch width functions of previously published studies, suggesting that the two types of data are qualitatively similar. The filters computed from the chinchilla data widened with increasing masker level and were more broadly tuned than those obtained in humans. The physiological response to each frequency component of any stimulus is likely a combination of excitation and suppression. Hence, one cannot predict masked threshold from the acoustic spectra of the maskers used here since they differ from their internal representations. Thus the threshold versus notch width function probably reflects the operation of both an auditory filter and a nonlinearity.
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43.66.Gf Detection and discrimination of sound by animals
43.66.Dc Masking
43.66.Ba Models and theories of auditory processes

Sound localization of frequency‐modulated sinusoids by Old World monkeys

Brad May, David B. Moody, William C. Stebbins, and Mary A. Norat

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 776-782 (1986); (7 pages)

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Directional hearing acuity, as measured by the minimum audible angle (MAA), was determined in four Old World monkeys, Macaca radiata. The acoustic stimuli were linear changes in frequency (sweeps) for different frequency ranges and sweep rates. The sweeps ranged between 0.5 and 1.3 kHz, at two durations, 100 and 200 ms. In upsweeps which began at 0.5 kHz and were 200 ms in duration, MAA decreased as sweep rate and frequency range increased. These thresholds were compared to MAAs of sweeps which traversed the same range of frequencies but at a different rate, to MAAs of sweeps with identical rates but over different frequency ranges, and to the MAAs of downsweeps. These comparisons indicated that range, and not sweep rate, exerts the greatest effect on the MAA. Interaural phase differences derived from the upper limits of the frequency range are discussed as potential FM localization cues.
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43.66.Qp Localization of sound sources
43.66.Gf Detection and discrimination of sound by animals
43.66.Lj Perceptual effects of sound

Acoustics of ear canal measurement of eardrum SPL in simulators

Samuel Gilman and Donald D. Dirks

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 783-793 (1986); (11 pages) | Cited 10 times

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The effect of standing waves on the ear canal measurement of eardrum sound pressure level (SPL) was determined by both calculation and measurement. Transmission line calculations of the standing wave were made using the dimensions of the ANSI S3.25‐1979 ear simulator and three different eardrum impedances. Standing wave curves have been obtained for the standard eardrum impedance at 1‐kHz intervals in the range of 1–8 kHz. The changes in standing wave position due to each of the three eardrum impedances and their effects on ear canal measurements of SPL were computed for each of the eardrum impedances. Ear canal SPL measurements conducted on simulators modified to correspond to the eardrum impedances used in the calculations were compared to the computed values. Differences between eardrum SPLs and those measured at different locations in the ear canal approached a standing wave ratio (SWR) of 10–12 dB as the position of the measuring probe approached the standing wave minimum at each frequency. These maximum differences compared favorably with data developed by other investigators from real ears. Differences due to the eardrum impedance were found to be significant only in the frequency region of 2–5 kHz. Calibration of probes in a standard or modified ANSI simulator at the same distance from the eardrum as in the real ear reduces the eardrum SPL measurement errors to those resulting from differences in eardrum impedance.
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43.66.Yw Instruments and methods related to hearing and its measurement
43.58.Vb Calibration of acoustical devices and systems
43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex

The effect of bandwidth on the performance of a postbeamformer interference canceller

Lal C. Godara and Antonio Cantoni

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 794-803 (1986); (10 pages)

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A postbeamformer interference canceller, PIC, processes the signals derived from an antenna array by forming two beams using fixed beamforming weights. The weighted output of one beam, referred to as the interference beam, is subtracted from the other beam referred to as the target beam. This paper analyzes the performance of PIC in the presence of narrow‐band directional interference by deriving the analytical expressions for the output signal power, the output interference power, and the output signal to interference ratio, and presents the results of a computer study showing how the performance of PIC varies as a function of bandwidth of the directional sources.
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43.60.Gk Space-time signal processing, other than matched field processing

A design for a general digital filter for state estimation of an arbitrary stochastic sound system

Mitsuo Ohta and Eiji Uchino

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 804-812 (1986); (9 pages) | Cited 1 time

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This article describes a new attempt at the design of a general digital filter for the state estimation of a nonstationary nonlinear stochastic sound system. A recursive algorithm for estimating the higher‐order statistics of arbitrary‐function type, mean, and variance is obtained by introducing a new expansion form of Bayes’ theorem. Further, the state probability density function (PDF) can also be estimated in a unified form of orthogonal or nonorthogonal series expansions by using these estimates. This method is widely applicable for cases where the random‐noise fluctuation is non‐Gaussian. The estimation algorithm proposed in this article agrees completely with a well‐known Kalman filtering theory [J. Basic Eng. 82, 35–45 (1960); Kalman and Buchy, J. Basic Eng. 83, 95–108 (1961)], as a simplified special case when the stochastic system is of linear type with Gaussian random excitation. The validity and effectiveness of the proposed theory were confirmed experimentally by applying it to actually observed room acoustic data and road‐traffic noise data.
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43.60.Gk Space-time signal processing, other than matched field processing

Mean path length in random acoustic fields in solids

Dentcho V. Ivanov and Julian I. Burov

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 813-814 (1986); (2 pages)

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An acousto‐optic method is presented for measuring the reverberation times of the diffuse acoustic fields excited in crystal enclosures on the analogy of the diffuse sound fields in large auditoria. It is shown experimentally that the mean path length formula 〈l〉=4 V/S, where V and S are the volume and the surface of the enclosure, holds true in the case of a random acoustic field in a well‐mixing low‐loss enclosure.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.20.Fn Scattering of acoustic waves
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

An investigation of the sound field above the audience in large lecture halls with a scale model

David W. Kahn and Jiri Tichy

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 815-827 (1986); (13 pages)

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Measurements of steady‐state sound pressure levels above the audience in large lecture halls show that the classical equation for predicting the sound pressure level is not accurate. The direct field above the seats was measured on a 1:10 scale model and was found to be dependent on the incidence angle and direction of sound propagation across the audience. The reverberant field above the seats in the model was calculated by subtracting the direct field from the measured total field and was found to be dependent on the magnitude and particularly on the placement of absorption. The decrease of sound pressure level versus distance in the total field depends on the angle (controlled by absorption placement) at which the strong reflections are incident upon the audience area. Sound pressure level decreases at a fairly constant rate with distance from the sound source in both the direct and reverberant field, and the decrease rate depends strongly on the absorption placement. The lowest rate of decay occurs when the side walls are absorptive, and both the ceiling and rear wall are reflective. These consequences are discussed with respect to prediction of speech intelligibility.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Fw Auditorium and enclosure design
43.71.Gv Measures of speech perception (intelligibility and quality)

Space variances in the mean‐square pressure at the boundaries of a rectangular reverberation room

Mikio Tohyama and Akira Suzuki

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 828-832 (1986); (5 pages)

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It was found that it was possible to reduce the number of samples needed for power measurements by sampling at the boundaries in a reverberation room. The space variances in the mean‐square pressure of oblique wave fields in a rectangular reverberation room were calculated. The sound source was assumed to be a narrow‐band noise source. Space variances throughout the room σ2A, on the floor σ2B, on the edge σ2C, and at the corner σ2G were compared with each other numerically. The numerical results confirmed that the relation σ2G <σ2C <σ2B <σ2A holds well. Particularly, in a rectangular reverberation room, under the condition that the receiver position is fixed at the corner of the room (corner method), the number of samples reduces to (1)/(2) – (1)/(3) the number of samples needed under the condition that both receiver positions and source positions are changed throughout the room. Some experimental results regarding the power measurements by the corner method are also shown. The experimental results confirmed the suitable estimation of the power for a noise source at low frequencies.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Cs Stationary response of rooms to noise; spatial statistics of room response; random testing
43.55.Nd Reverberation room design: theory, applications to measurements of sound absorption, transmission loss, sound power
43.50.Cb Noise spectra, determination of sound power

Nonlinear response in evaluating the subjective diffuseness of sound fields

Yoichi Ando and Yoshitaka Kurihara

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 833-836 (1986); (4 pages) | Cited 6 times

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Tests were conducted to determine which horizontal reflection angles are most effective in stimulating subjective diffuseness for a listener in a room. Paired comparison tests were carried out where subjects were asked to judge in which of two sound fields they perceived more diffuseness. Results show that the most effective horizontal angle depends on the frequency of the one‐third‐octave‐band noise, as is indicated by the interaural cross correlation. The remarkable finding in this investigation is that the scale value of subjective diffuseness may be formulated in terms of the (3)/(2) power of the magnitude of interaural cross correlation (IACC) and that the scale value does not vary with the frequency of the bandpass noise source.
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43.55.Hy Subjective effects in room acoustics, speech in rooms
43.66.Lj Perceptual effects of sound

Predictors of speech intelligibility in rooms

J. S. Bradley

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 837-845 (1986); (9 pages) | Cited 26 times

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Three different types of acoustical measures were compared as predictors of speech intelligibility in rooms of varied size and acoustical conditions. These included signal‐to‐noise measures, the speech transmission index derived from modulation transfer functions, and useful/detrimental sound ratios obtained from early/late sound ratios, speech, and background levels. The most successful forms of each type of measure were of similar prediction accuracy, but the useful/detrimental ratios based on a 0.08‐s early time interval were most accurate. Several physical measures, although based on very different calculation procedures, were quite strongly related to each other.
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43.55.Hy Subjective effects in room acoustics, speech in rooms
43.71.Gv Measures of speech perception (intelligibility and quality)

Speech intelligibility studies in classrooms

J. S. Bradley

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 846-854 (1986); (9 pages) | Cited 26 times

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Speech intelligibility tests and acoustical measurements were made in ten occupied classrooms. Octave‐band measurements of background noise levels, early decay times, and reverberation times, as well as various early/late sound ratios, and the center time were obtained. Various octave‐band useful/detrimental ratios were calculated along with the speech transmission index. The interrelationships of these measures were considered to evaluate which were most appropriate in classrooms, and the best predictors of speech intelligibility scores were identified. From these results ideal design goals for acoustical conditions for classrooms were determined either in terms of the 50‐ms useful/detrimental ratios or from combinations of the reverberation time and background noise level.
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43.55.Hy Subjective effects in room acoustics, speech in rooms
43.71.Gv Measures of speech perception (intelligibility and quality)

A model for insertion loss degradation for parallel highway noise barriers

William Bowlby and Louis F. Cohn

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 855-868 (1986); (14 pages) | Cited 2 times

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An algorithm is developed and validated for the prediction of the reduction, or degradation, of traffic noise barrier insertion loss when a second barrier is placed on the opposite side of the highway. The algorithm combines the basic emission, propagation, and barrier attenuation features of the Federal Highway Administration traffic noise prediction model with a geometrical acoustics approach for multiple reflections. The resultant model can accommodate any number of source lanes or receivers, three vehicle categories, and independently variable barrier heights and absorption coefficients. The model was validated against mathematical, scale model, and full scale field data received from other researchers, and has proved to be a good predictor of insertion loss degradation.
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43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
43.50.Vt Topographical and meteorological factors in noise propagation

Experimental study of a slow‐waveguide barrier on finite impedance ground

J. Nicolas and G. A. Daigle

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 869-876 (1986); (8 pages)

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A slow‐waveguide filter consisting of an open network of rigid strips is used to modify a conventional noise barrier. The acoustical performance of the resulting device relies on the interference between the field diffracted by the barrier edge and the field propagating through the waveguide. The possibilities of enhancing low‐frequency noise reduction with this device is studied experimentally. In addition, limitations in the existing waveguide model are removed and the theory is extended to allow for reflections due to the presence of the ground. Both theory and experiments show that, at frequencies where significant destructive interference occurs between the diffracted field and the field transmitted through the waveguide, there is an enhanced noise reduction. However, at adjacent frequencies there is constructive interference which can degrade the performance of the barrier.
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43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.20.Mv Waveguides, wave propagation in tubes and ducts

Closed‐form solutions for rigorous ray tracing

Edward R. Floyd

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 877-887 (1986); (11 pages)

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Closed‐form solutions and expressions for rigorous ray tracing are presented for the effective sound velocity profile, the generating function, the equations of motion, and the initial conditions. These closed‐form solutions may be expressed in terms of the closed‐form solutions of the corresponding Helmholtz equation. Even if the closed‐form solutions for the corresponding Helmholtz equation are unknown, we may still process rigorous ray tracing in terms of the symbolic solutions of the Helmholtz equation. Comparisons are made to both normal modes and classical ray tracing. An Ermakov invariant for rigorous ray tracing is developed and evaluated with closed‐form solutions. A Green’s function that is couched in terms of closed‐form rigorous‐ray‐tracing solutions is developed for acoustic sources.
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43.30.Cq Ray propagation of sound in water
43.20.Bi Mathematical theory of wave propagation
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.20.Dk Ray acoustics

Acoustic imaging of high‐temperature hydrothermal plumes at seafloor spreading centers

D. R. Palmer, P. A. Rona, and M. J. Mottl

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 888-898 (1986); (11 pages) | Cited 4 times

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We explore the possibility of using active sonar techniques to acoustically image high‐temperature ‘‘black smoker’’ hydrothermal plumes. We examine recent sonar images of a hydrothermal vent field at 11°N on the East Pacific Rise obtained from DSRV Alvin which may show the presence of plumes. For vent fields on the East Pacific Rise estimates are obtained of the minimum detectable concentration of precipitates as a function of the range between the sonar and the plume boundary. These estimates are compared with measured concentrations. Some of the anticipated advantages of acoustic imaging are discussed. We conclude that acoustic imaging techniques have the potential of providing a coherent framework for point sampling of physical and chemical properties of hydrothermal plumes and for determining the dynamics of their injection into the surrounding water mass.
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43.30.Bp Normal mode propagation of sound in water
43.30.Ft Volume scattering
43.30.Vh Active sonar systems
92.10.-c Physical oceanography

Laboratory and marine measurements on the acoustic detection of sediment transport

Peter D. Thorne

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 899-910 (1986); (12 pages) | Cited 4 times

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This paper describes a series of measurements taken both in the laboratory and at sea, to examine the feasibility of monitoring marine gravel transport, by measuring the acoustic self‐generated noise (SGN) produced by the interparticle collisions of bedload material. This study is a continuation of work previously reported on the SGN of agitated artificial sediments. Laboratory measurements are presented on the relationship between the SGN spectrum and particle size for naturally occurring gravels undergoing interparticle collisions. The dependence of the acoustic intensity level upon the mass of agitated material is also studied. Attempts are made to utilize the acoustic spectrum to obtain information on the particle size distribution for poorly sorted gravel samples. Using the laboratory results, a marine system was developed consisting of two hydrophones to monitor the SGN, an underwater TV camera to independently assess bedload transport, and electromagnetic current meters to obtain information on the flow condition. The instrumentation package was deployed on a seabed composed of mobile gravels. The results of an intercomparison between the acoustic and visual data are presented. Also, some discussion on the relationship between flow conditions and gravel movement is pursued. Attempts are also made to obtain the size distribution of the mobile material by an examination of the SGN spectrum taken at sea.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Ft Volume scattering
43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.50.Cb Noise spectra, determination of sound power

Finite amplitude distortion and dispersion of a nonplanar mode in a waveguide

J. H. Ginsberg and H. C. Miao

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 911-920 (1986); (10 pages) | Cited 3 times

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The perturbation method of renormalization is used to study the effect of nonlinearity on a hard‐walled rectangular waveguide. The excitation would induce only the fundamental nonplanar symmetric mode if the system were linear. The analysis develops a solution that satisfies a nonlinear wave equation for the velocity potential, as well as all boundary conditions. The response consists of a pair of oblique planar waves that interact through second‐order excitation of the true planar mode. The investigation discloses that in the high‐frequency limit the signal has a quasiplanar behavior. In contrast, for very low frequencies exceeding the cutoff value, the oblique waves are essentially independent. The distortion is then a result of self‐refraction, in which the particle motion shifts the wave fronts and rays. The transition between the low‐ and high‐frequency limits is marked by the appearance of nonlinear frequency dispersion, which produces asymmetrical distortion of the waveform.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.20.Mv Waveguides, wave propagation in tubes and ducts

Angular dependence of ultrasonic wave propagation in a stressed, orthorhombic continuum: Theory and application to the measurement of stress and texture

R. Bruce Thompson, S. S. Lee, and J. F. Smith

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 921-931 (1986); (11 pages) | Cited 6 times

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A theory for ultrasonic wave propagation in a symmetry plane of a biaxially stressed, orthorhombic continuum is presented. Since many of the material parameters which appear in the analysis are unknown, in particular the third‐order elastic constants of polycrystalline metals, emphasis is placed on the angular dependence of the velocities. An expansion to first order in stress‐induced anisotropy and to second order in textural anisotropy reveals terms with twofold, fourfold, and sixfold symmetry. Scenarios are proposed for using various properties of this symmetry to deduce the difference in magnitude and directions of the principal stresses independent of textural anisotropy and the textural anisotropy independent of the stresses. Experimental results are presented for the cases of aluminum, 304 stainless steel, and copper.
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43.20.Hq Velocity and attenuation of acoustic waves
43.20.Bi Mathematical theory of wave propagation
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Extensional‐wave and flexural‐wave contributions to the sound field radiated by a fluid‐loaded infinite plate

Anthony J. Rudgers, Pieter S. Dubbelday, and Lisa A. Fagerstrom

J. Acoust. Soc. Am. Volume 80, Issue 3, pp. 932-950 (1986); (19 pages) | Cited 1 time

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A structural thick‐plate theory that accounts for the propagation of both extensional and flexural waves in an infinite elastic plate is used to calculate the farfield directional response of the sound radiated by a plate with fluid on one side. The plate is driven by a harmonic point force, and the radiation in the farfield of the driving point is considered. Computations are made for metal plates and plates composed of polymeric materials in water and in air. Anelastic behavior of the plates is considered. The computations, which are made in order to compare the radiated fields of plates in which only flexural waves or only extensional waves can propagate, or in which both wave types can propagate concurrently, show that the radiation caused by extensional waves can make an important contribution to the sound field of an elastic plate.
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43.20.Tb Interaction of vibrating structures with surrounding medium
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.40.Dx Vibrations of membranes and plates
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