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Journal of the Acoustical Society of America

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Dec 1987

Volume 82, Issue 6, pp. 1883-2173

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Digital waveform generation by fractional addressing

W. M. Hartmann

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1883-1891 (1987); (9 pages) | Cited 1 time

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This article concerns the generation of waveforms by a digital oscillator in which sampled data in a memory buffer are recycled. The buffer contains a fixed waveform and the output sample rate is also fixed. Despite these constraints, the oscillator is capable of arbitrarily high frequency resolution if the technique of fractional addressing is used. However, fractional addressing introduces distortion. This article gives a theory of fractional addressing, resembling the theory of diffraction in crystal lattices with a basis. The theory shows how the spectrum of the distortion components can be calculated and how the distortion can be minimized. Attention is called to numerous symmetries in the distortion spectrum. These symmetries are especially interesting if the purpose of the system is to make use of the distortion components to create inharmonic signals. Of particular importance is the γp symmetry theorem, which makes it possible to derive simple formulas for the level of the largest distortion component and for the total distortion power.
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43.58.Jq Wave and tone synthesizers
43.58.Ta Computers and computer programs in acoustics
43.75.Wx Electronic and computer music

The sound emission pattern and the acoustical role of the noseleaf in the echolocating bat, Carollia perspicillata

David J. Hartley and Roderick A. Suthers

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1892-1900 (1987); (9 pages) | Cited 8 times

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Carollia perspicillata (Phyllostomidae) is a frugivorous bat that emits low‐intensity, broadband, frequency‐modulated echolocation pulses through nostrils surrounded by a noseleaf. The emission pattern of this bat is of interest because the ratio between the nostril spacing and the emitted wavelength varies during the pulse, causing complex interference patterns in the horizontal dimension. Sound pressures around the bat were measured using a movable microphone and were referenced to those at a stationary microphone positioned directly in front of the animal. Interference between the nostrils was confirmed by blocking one nostril, which eliminated sidelobes and minima in the emission pattern, and by comparison of real emission patterns with simple computer models. The positions of minima in the patterns indicate effective nostril spacings of over a half‐wavelength. Displacement of the dorsal lancet of the noseleaf demonstrated that this structure directs sound in the vertical dimension.
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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

The 20‐Hz signals of finback whales (Balaenoptera physalus)

William A. Watkins, Peter Tyack, Karen E. Moore, and James E. Bird

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1901-1912 (1987); (12 pages) | Cited 23 times

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The 20‐Hz signals of finback whales (Balaenoptera physalus) were analyzed from more than 25 years of recordings at a variety of geographic locations on near‐surface hydrophones close to whales and on deep hydrophone systems. These signals were composed of 1‐s pulses of sinusoidal waveform with downward sweeping frequency from approximately 23 to 18 Hz at variable source levels up to 186 dB (re: 1 μPa at 1 m), usually with slightly lower levels for the pulses at the beginning and end of sequences. These ‘‘20‐Hz’’ pulses were produced in signal bouts (separated by more than 2 h) lasting as long as 32.5 h. Bouts were composed of regularly repeated pulses at intervals of 7–26 s (typically), either at one nominal pulse rate or at two alternating (doublet) pulse intervals. Signal bouts were interrupted by rests of 1–20 min at roughly 15‐min intervals and by irregular gaps lasting between 20 and 120 min. The distribution of these signals throughout the year and their temporal sequence were analyzed from the continuous drum records of the Bermuda SOFAR Station. Signal bouts occurred during winter, sometimes beginning in September and ending in May. The sound sequences were never exactly replicated. Direct association of the bouts with the reproductive season for this species points to the 20‐Hz signals as possible reproductive displays by finback whales.
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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
43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Piano string excitation IV: The question of missing modes

Donald E. Hall and Peter Clark

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1913-1918 (1987); (6 pages) | Cited 1 time

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It is usually said that a force applied to an extended vibratory system is incapable of exciting any normal mode that has a node at that point. Thus piano hammers positioned to strike the strings at certain fractions of their length should produce spectra with ‘‘missing modes.’’ However, this has been disputed by some observers, and it is sometimes suggested that more careful theoretical treatments would justify a restoration of those modes. Spectra of string motion have been measured as a function of hammer position by moving a piano action frame in small increments along the bed of the case. It is found that there are indeed sharp minima in mode amplitudes (on the order of 20 to 30 dB down) as the striking point passes within a few millimeters of the nodal positions. Possible limitations on the theoretical arguments are discussed, and it is concluded that the small residual strengths in the nearly missing modes can be well accounted for by finite soundboard admittance.
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43.75.Mn Pianos and other struck string instruments

Upper lip, lower lip, and jaw interactions during speech: Comments on evidence from repetition‐to‐repetition variability

John W. Folkins and Carl Kice Brown

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1919-1924 (1987); (6 pages) | Cited 1 time

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Six studies purporting to demonstrate complementary covariation in lip and jaw activity during speech are reviewed. The statistical procedures used to assess interactions among the upper lip, lower lip, and jaw movements are discussed for four different experiments analyzing repetition‐to‐repetition movement variation. The findings from two studies analyzing repetition‐to‐repetition variation for interactions in electromyographic activity recorded from either the jaw musculature or the labial musculature also are evaluated. It is concluded that these studies do not provide convincing evidence of complementary covariation among the articulators or the muscles.
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43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics

Effects of pure‐tone forward masker duration on psychophysical measures of frequency selectivity

Sid P. Bacon and Walt Jesteadt

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1925-1932 (1987); (8 pages) | Cited 5 times

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The effects of forward masker duration on psychophysical measures of frequency selectivity were investigated in two experiments. In both experiments, masker duration was 50 or 400 ms, signal duration was 20 ms, and there was no delay between masker offset and signal onset. In the first experiment, growth‐of‐masking functions were measured for a masker whose frequency was below, at, or above the 1000‐Hz signal frequency. From those data, input filter patterns (IFPs) were plotted for masker levels from 40–90 dB SPL. In the second experiment, masking patterns (MPs) were measured for a 1000‐Hz masker presented at 50, 70, and 90 dB SPL. Both measures of frequency selectivity (IFPs and MPs) indicate that frequency selectivity is greater for the 400‐ms masker. These data suggest that there may be a sharpening of frequency selectivity with time at a stage prior to the adaptation observed in forward masking.
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43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Ba Models and theories of auditory processes

Detection of partially filled gaps in noise and the temporal modulation transfer function

T. G. Forrest and David M. Green

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1933-1943 (1987); (11 pages) | Cited 43 times

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Results of experiments on the detection of silent intervals, or gaps, in broadband noise are reported for normal‐hearing listeners. In some preliminary experiments, a gap threshold of about 2 ms was measured. This value was independent of the duration of the noise burst, variation of the noise level on each presentation, or the temporal position of the gap within the noise burst. In the main experiments, the thresholds for partial decrements in the noise waveform as well as brief increments were determined. As predicted by a model that assumes a single fixed peak‐to‐valley detection ratio, thresholds for increments are slightly higher than thresholds for decrements when the signal is measured as the change in rms noise level. A first‐order model describes the temporal properties of the auditory system as a low‐pass filter with a 7‐ to 8‐ms time constant. Temporal modulation transfer functions were determined for the same subjects, and the estimated temporal parameters agreed well with those estimated from the gap detection data. More detailed modeling was carried out by simulating Viemeister’s three‐stage temporal model. Simulations, using an initial stage bandwidth of 4000 Hz and a 3‐ms time constant for the low‐pass filter, generate data that are very similar to those obtained from human subjects in both modulation and gap detection.
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43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Comodulation masking release (CMR): Effects of signal frequency, flanking‐band frequency, masker bandwidth, flanking‐band level, and monotic versus dichotic presentation of the flanking band

Gregory P. Schooneveldt and Brian C. J. Moore

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1944-1956 (1987); (13 pages) | Cited 40 times

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In experiment I, thresholds for 400‐ms sinusoidal signals were measured in the presence of a continuous 25‐Hz‐wide noise centered at signal frequencies ( fs) ranging from 250 to 8000 Hz in 1‐oct steps. The masker was presented either alone or together with a second continuous 25‐Hz‐wide band of noise (the flanking band) whose envelope was either correlated with that of the on‐frequency band or was uncorrelated; its center frequency ranged from 0.5 fs to 1.5 fs. The flanking band was presented either in the same ear (monotic condition) as the signal plus masker or in the opposite ear (dichotic condition). The on‐frequency band and the flanking band each had an overall level of 67 dB SPL. The comodulation masking release, CMR(U−C), is defined as the difference between the thresholds for the uncorrelated and correlated conditions. The CMR(U−C) showed two components: a broadly tuned component, occurring at all signal frequencies and all flanking‐band frequencies, and occurring for both monotic and dichotic conditions; and a component restricted to the monotic condition and to flanking‐band frequencies close to fs. This sharply tuned component was small for low signal frequencies, increased markedly at 2000 and 4000 Hz, and decreased at 8000 Hz. Experiment II showed that the sharply tuned component of the CMR(U−C) was slightly reduced in magnitude when the level of the flanking band was 10 dB above that of the on‐frequency band and was markedly reduced when the level was 10 dB below, whereas the broadly tuned component and the dichotic CMR(U−C) were only slightly affected. Experiment III showed that the sharply tuned component of the CMR(U−C) was markedly reduced when the bandwidths of the on‐frequency and flanking bands were increased to 100 Hz, while the broadly tuned component and the dichotic CMR(U−C) decreased only slightly. The argument here is that the sharply tuned component of the monotic CMR(U−C) results from beating between the ‘‘carrier’’ frequencies of the two masker bands. This introduces periodic zeros in the masker envelope, which facilitate signal detection. The broadly tuned component, which is probably a ‘‘true’’ CMR, was only about 3 dB.
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43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Rq Dichotic listening

Lateralization of dichotic noise bursts: Effect of onset and offset disparity

Arnold M. Small

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1957-1966 (1987); (10 pages)

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Sound image position associated with the interaural onset or offset disparity of a signal was quantified by a scaling procedure in three experiments. Lateralization cues derived from the steady‐state portion of the broadband noise signal that would support a specific image position were minimized by the use of independent noise sources for each ear. Onset disparities produced lateralization toward the ear at which the sound was presented first, while offset disparity produced lateralization toward the ear at which the sound remained on longer. Disparity was systematically varied between 0 and 10 ms and for a given disparity, a greater shift in the sound image position was obtained when the disparity was at the onset rather than the offset. The duration of the shorter signal ranged from 2.5–100 ms and for either onset or offset disparity, the image of stimuli of long duration tended to remain near the center of the head, while those of shorter duration could be moved to more extreme positions. In an attempt to rule out dichotic loudness cues as a basis for the lateralization associated with offset disparity, stimuli were presented with equal energy at each ear. Image position for equal energy was virtually identical to that for equal sound pressure, suggesting that loudness differences are not mediating lateralization associated with offset disparity.
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43.66.Pn Binaural hearing
43.66.Qp Localization of sound sources
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

An evaluation of three adaptive hearing aid selection strategies

Arlene C. Neuman, Harry Levitt, Russell Mills, and Teresa Schwander

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1967-1976 (1987); (10 pages) | Cited 2 times

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Paired‐comparison judgments of intelligibility of speech in noise were obtained from eight hearing‐impaired subjects on a large number of hearing aids simulated by a digital master hearing aid. The hearing aids which comprised a 5×5 matrix differed systematically in the amount of low‐frequency and high‐frequency gain provided. A comparison of three adaptive strategies for determining optimum hearing aid frequency‐gain characteristics (an iterative round robin, a double elimination tournament, and a modified simplex procedure) revealed convergence on the same or similar hearing aids for most subjects. Analysis revealed that subjects for whom all three procedures converged on the same hearing aid showed a single pronounced peak in the response surface, while a broader peak was evident for the subjects for whom the three procedures identified similar hearing aids. The modified simplex procedure was found to be most efficient and the iterative round robin least efficient.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Yw Instruments and methods related to hearing and its measurement
43.38.Si Telephones, earphones, sound power telephones, and intercommunication systems

Responses of auditory‐nerve fibers to nasal consonant–vowel syllables

Li Deng and C. Daniel Geisler

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1977-1988 (1987); (12 pages) | Cited 5 times

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Responses of single auditory‐nerve fibers in anesthetized cat to spoken nasal consonant–vowel syllables were recorded. Analyses in the form of spectrograms and of three‐dimensional spatial‐time and spatial‐frequency plots were made. Among other features, formant transitions are clearly represented in the fibers’ response synchronization properties. During vocalic segments, especially those in /mu/ and /ma/, at a stimulus level near 75 dB SPL, a strong dominance in the responses by frequencies near the second formant (F2) is found for most fibers whose characteristic frequencies (CFs) are at or above F2. In contrast, at more moderate levels, the same fibers may show response synchrony to frequencies closer to their own CFs. There are significant differences in the response properties of high and low/medium‐spontaneous‐rate fibers.
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43.64.Pg Electrophysiology of the auditory nerve
43.71.Qr Neurophysiology of speech perception

Responses of auditory‐nerve fibers to multiple‐tone complexes

Li Deng, C. Daniel Geisler, and Steven Greenberg

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 1989-2000 (1987); (12 pages) | Cited 4 times

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To relate level‐dependent properties of auditory‐nerve‐fiber responses to nasal consonant–vowels to the basic frequency selective and suppressive properties of the fibers, multitone complexes, with the amplitude of a single (probe) component incremented, were used as stimuli. Quantitative relations were obtained between the systematic increase of fiber synchrony to the probe tone and the decrease of synchrony to CF, as the amplitude of the probe tone was increased. When such relations are interpreted as a measure of fiber frequency selectivity based on a relative synchrony criterion, a breadth of frequency tuning is obtained, at a 70‐dB SPL multitone sound‐pressure level, which is generally broader than that of the fiber’s threshold tuning curve. Quantitative comparisons with the same fiber’s responses to the nasal speech sounds indicate that the fiber’s speech responses share some common features with its probe‐tone responses.
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43.64.Pg Electrophysiology of the auditory nerve
43.71.Qr Neurophysiology of speech perception

A composite auditory model for processing speech sounds

Li Deng and C. Daniel Geisler

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2001-2012 (1987); (12 pages) | Cited 12 times

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A composite inner‐ear model, containing the middle ear, basilar membrane (BM), hair cells, and hair‐cell/nerve‐fiber synapses, is presented. The model incorporates either a linear‐BM stage or a nonlinear one. The model with the nonlinear BM generally shows a high degree of success in reproducing the qualitative aspects of experimentally recorded cat auditory‐nerve‐fiber responses to speech. In modeling fiber population responses to speech and speech in noise, it was found that the BM nonlinearity allows bands of fibers in the model to synchronize strongly to a common spectral peak in the stimulus. A cross‐channel correlation algorithm has been devised to further process the model’s population outputs. With output from the nonlinear‐BM model, the cross‐channel correlation values are appreciably reduced only at those channels whose CFs coincide with the formant frequencies. This observation also holds, to a large extent, for noisy speech.
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43.64.Bt Models and theories of the auditory system
43.64.Pg Electrophysiology of the auditory nerve
43.71.Qr Neurophysiology of speech perception

Wave propagation in a piezoelectric solid cylinder of arbitrary cross section

H. S. Paul and M. Venkatesan

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2013-2020 (1987); (8 pages) | Cited 2 times

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In this article, the wave propagation in an infinite piezoelectric solid cylinder of an arbitrary cross section is studied. In the analysis, the boundary conditions are satisfied by the use of Nagaya’s Fourier expansion collocation method. The frequency equations for symmetric and antisymmetric cases are obtained and analyzed numerically for longitudinal and flexural waves for the piezoceramic material PZT‐4. The vibrations of circular and elliptical cylinders are investigated and the results are tabulated. The results obtained for a circular cross section are compared with the available results. The frequency versus the aspect ratio (the ratio of the semimajor and semiminor axes of the elliptical cylinder) is plotted and the dispersion curve is also presented.
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43.40.Cw Vibrations of strings, rods, and beams
43.20.Bi Mathematical theory of wave propagation

Lamb and creeping waves around submerged spherical shells resonantly excited by sound scattering

G. C. Gaunaurd and M. F. Werby

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2021-2033 (1987); (13 pages) | Cited 9 times

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Acoustic wave scattering by spherical shells in water in the resonance region is studied. The interaction is studied classically and by the resonance scattering theory (RST). The connection between internal resonances and the Lamb waves excited in the shell is analyzed. Conditions are derived that govern the propagation of Lamb waves in a spherical shell when it is fluid‐loaded or in vacuo. These general conditions reduce to the usual conditions for Lamb waves in plates, in the large radii limit. The connection is established between the outer scattering problem and the internal vibrational problem that excites the shell resonances, and it is demonstrated that the creeping‐wave series that synthesizes the Franz waves around the shell, can be obtained quite simply without the use of the Watson–Sommerfeld Method (WSM).
All that is required is suitable one‐term expansions of the denominators of the scattering amplitudes. This eliminates the need for the cumbersome excursions through the complex angular momentum plane ν of the WSM. Calculations are presented for the summed form functions of seven shells of three compositions and thicknesses over quite broad frequency bands. Subtraction of rigid or soft backgrounds permits one to draw many conclusions as to the behavior of the shell response in various spectral regions. The relative phase between the form function and the background is also displayed. This phase is helpful for the identification of actual resonances and for the choice of proper background. It is shown how the poles of the scattering amplitude in the x plane split into two subsets. One set, the Franz set, depends only on shell shape, and is related to the external Franz (creeping) waves in the water. This set does not change with varying shell thickness or composition. The other set, the Lamb set, depends only on material composition, and is related to the Lamb waves in the shell. These poles are displayed in various cases, and it is shown that for thin shells, only one family of Lamb poles (the zeroth‐order symmetric family, s0) is dominant, which explains the relatively simple structure of the form function of a thin shell. For thicker shells, many modes interact, and one is forced to go to the usual partial‐wave analysis of the RST. A very accurate picture of the scattering process taking place around and inside the shell emerges from this analysis.
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43.40.Ey Vibrations of shells
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.60.Pt Signal processing techniques for acoustic inverse problems

Explosive source location by relative arrival times of atmospherically and seismically propagating disturbances

C. H. Dowding, R. D. Hryciw, and J. M. Garretta

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2034-2041 (1987); (8 pages)

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Detonation of explosives during rock excavation in surface mining produces both atmospherically and seismically propagating disturbances. By manipulating the difference in arrival times of the air blast and ground motion, shot‐to‐recorder distance can be determined with only one recording station. This shot‐to‐recorder distance is needed for automatic development of ground motion attenuation curves with automatic recording devices and is generally helpful in mine activity detection. With two recording stations, the location of the blast may be determined even if the stations are not time synchronized. Data from production blasting at a coal mine were evaluated to verify the method proposed herein. The blast location as determined by the difference in arrival times of the atmospherically and seismically propagating disturbances showed excellent agreement with the location of blasts as provided by field personnel. The method may be employed to detect any explosive activity that produces both types of disturbances.
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43.40.Ph Seismology and geophysical prospecting; seismographs
43.28.Tc Sound-in-air measurements, methods and instrumentation for location, navigation, altimetry, and sound ranging

Stochastic simulation and first‐order multiple scatter solutions for acoustic propagation through oceanic internal waves

Bruce J. Bates and Susan M. Bates

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2042-2050 (1987); (9 pages) | Cited 1 time

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The existing theory of acoustic propagation through an oceanic internal wave field with a Garrett and Munk spectrum is modified and, by numerical computation, is shown to be consistent. The fractional sound speed computation is rederived to satisfy the Garrett and Munk spectrum and used to compute a stochastic simulation of the internal wave sound speed fluctuation field. The Garrett and Munk spectrum in (ω, j) space has been normalized by 4π, and the acoustic scattering is redefined to accommodate scattering from the internal wave phase fronts as in an acoustic phase grating. These modifications are then used to compute the coherent acoustic intensity by two methods: a first‐order multiple scatter approximation and a stochastic simulation. Also, the Rytov approximation is shown to be equivalent to the first‐order multiple scatter approximation in the form of the stochastic parabolic equation method in the unsaturated region. The computational results show agreement in the weak scattering region using typical deep ocean values. The stochastic simulation method is accurate in the saturated and unsaturated regions; however, the method requires long computer execution times. Phase front fragments propagating along rays with sound speeds reduced by the stochastic internal wave field are used to discuss the computational results.
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43.30.Bp Normal mode propagation of sound in water
43.30.Ft Volume scattering
43.20.Bi Mathematical theory of wave propagation
43.60.Cg Statistical properties of signals and noise

Scattering from an object in a stratified medium

F. Ingenito

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2051-2059 (1987); (9 pages) | Cited 31 times

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An expression is derived for the acoustic field scattered by a rigid sphere in an isovelocity fluid layer overlying a horizontally stratified medium. The result, valid when multiple scattering can be neglected, is expressed in terms of normal modes and plane‐wave scattering functions. It allows simple physical interpretation and straightforward numerical implementation. Sample numerical calculations are given for two cases typical of shallow‐water environments. Generalizations to a depth‐dependent sound velocity fluid layer and to nonrigid spheres are indicated. A second derivation is given for objects of nonspherical shape in a form similar to that of the rigid sphere. Hence, if the plane‐wave scattering functions for the object are known, the scattered field in a stratified medium can be calculated.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Bp Normal mode propagation of sound in water

Physical optics theory of scattering from the ice canopy

Suzanne T. McDaniel

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2060-2067 (1987); (8 pages)

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The method of physical optics is applied to treat high‐frequency acoustic scatter from Arctic ice. The development takes into account that the under‐ice surface is not statistically homogeneous, but consists of two types of ice: undeformed first year and multiyear ice, and very rough ice due to pressure ridge formation. Expressions are obtained both for the mean scattering strength and the spatial coherence of the scattered field. Measured ice statistics are used to evaluate the expressions derived for the spatial coherence and to estimate the variability of the mean backscattering strength.
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43.30.Hw Rough interface scattering
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries

Geoacoustic parameters in a stratified sea bottom from shallow‐water acoustic propagation

Ji‐xun Zhou, Xue‐zhen Zhang, Peter H. Rogers, and Jacek Jarzynski

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2068-2074 (1987); (7 pages) | Cited 10 times

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Due to the difficulty of direct measurement, there is a need to develop inverse techniques for remote sensing bottom geoacoustic parameters in the lowan mode measurements are extended to extract acoustic attenuation and speed in a horizontally stratified bottom in shallow water as a function of frequency and depth. The computational and experimental results show that, for a limited frequency band, we can find an equivalent depth profile of sea‐bottom acoustic attenuation with a linear frequency dependence that simulates the effect of nonlinear frequency dependence (without depth structure) on some field characteristics, such as the attenuation rate of individual mode, the frequency response of long‐range sound propagation, and the amplitude ratio of mode 2 to mode 1. However, the resultant equivalent negative gradient for the sea‐bottom attenuation is too strong to be accepted in light of available data. The conclusion is that nonlinear frequency dependence of the acoustic attenuation in the upper sedimentary layer is required to explain many aspects of shallow‐water sound propagation.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Bp Normal mode propagation of sound in water

High‐intensity tone generation by aeroacoustic sources

P. Shakkottai, E. Y. Kwack, Y. I. Cho, and L. H. Back

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2075-2085 (1987); (11 pages) | Cited 1 time

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An experimental investigation has been carried out on the production of high‐intensity tones by axisymmetric ring cavities. Maximum sound production occurs during an acoustic resonance at Strouhal numbers, which depend only on the local flow velocity independent of cavity location. Values of sound pressure of about 115 dB at 1‐m distance can be generated by axisymmetric ring cavities on projectiles moving at a relatively low flight speed equal to 70 m/s. Frequencies in the audible range up to several kilohertz can be generated aeroacoustically. A simple analytical model has been developed to explain the experimental observations.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence

Measurement of the acoustic nonlinearity parameter in water, methanol, liquid nitrogen, and liquid helium‐II by two different methods: A comparison

H. A. Kashkooli, Paul J. Dolan, Jr., and Charles W. Smith

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2086-2089 (1987); (4 pages) | Cited 3 times

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Light diffraction and finite amplitude loss are used to measure the acoustic nonlinearity parameter for water, methanol, liquid nitrogen, and liquid helium‐II. In all cases, the finite amplitude loss technique yielded higher values than the light diffraction technique or thermodynamic estimates from published data.
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43.25.Ba Parameters of nonlinearity of the medium
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics

One‐dimensional implosions under gravity‐induced hydrostatic pressure

Thomas L. Marzetta, Robert Burridge, and David C. Stickler

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2090-2101 (1987); (12 pages)

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An imploding cavity in a fluid‐filled borehole is potentially attractive as a powerful source of acoustic energy for borehole seismic experiments. It is reasonable to model the fluid pressure response due to the implosion as purely one‐dimensional. A simple analysis based on the assumption that the fluid behaves elastically, with a linear pressure/strain relation, predicts that the fluid pressure response becomes negative at depths less than that of the source. This is an untenable prediction since a fluid cavitates under negative pressure. It is more realistic to assume that the fluid behaves in a linear elastic fashion for negative strains (and positive pressures), and that the fluid pressure is zero for positive strains. This leads to a nonlinear, free‐boundary problem in acoustic wave propagation, which surprisingly has a closed‐form analytical solution. The analysis predicts the existence of several unexpected phenomena which could complicate the interpretation of data taken in borehole seismic experiments utilizing this type of source.
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43.25.Vt Intense sound sources
43.30.Qd Global scale acoustics; ocean basin thermometry, transbasin acoustics
43.40.Ph Seismology and geophysical prospecting; seismographs

Transmit–receive mode responses from finite‐sized targets in fluid media

Stephen McLaren and John P. Weight

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2102-2112 (1987); (11 pages)

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Detailed calculations are made of the transmit–receive mode echo responses arising from solid targets of various size interrogated by short pulses of ultrasound propagating in a fluid medium. The theoretically predicted results are in good agreement with experimentally measured results obtained using transducers typical of those used in nondestructive evaluation. The effects of target size, field position, and material on both the amplitude and shape of the echo responses are investigated. The structure of the responses is explained in terms of the plane and edge waves radiated by the source. Implications for the use of ultrasonic pulse‐echo techniques to characterize real defects are considered.
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43.20.Fn Scattering of acoustic waves
43.20.Px Transient radiation and scattering

Acoustic radiation and reflection from a periodically perforated rigid solid

A. N. Norris and H. A. Luo

J. Acoust. Soc. Am. Volume 82, Issue 6, pp. 2113-2122 (1987); (10 pages) | Cited 6 times

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An exact solution is given for the reflection of a plane wave normally incident on a rigid solid with periodically spaced semi‐infinite circular holes. Analytical considerations, verified by numerical calculations, show that the reflection coefficient is unity at the cutoff frequencies defined by the periodicity of the holes. This result is independent of the volume fraction of the holes. It implies that the porous solid acts like a rigid solid at these frequencies. The problem of plane‐wave incidence from the holes is also solved. A reflection coefficient of unity is obtained at the same frequencies, again implying a rigid effect. Below the first cutoff frequency, the reflection coefficient can be parametrized by a simple scalar frequency dependent quantity. This simple result can be interpreted in terms of a displaced pressure continuity condition.
Show PACS
43.20.Fn Scattering of acoustic waves
43.20.Bi Mathematical theory of wave propagation
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