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Journal of the Acoustical Society of America

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Dec 1994

Volume 96, Issue 6, pp. 3375-3837

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Loudness level versus sound‐pressure level: A comparison of musical instruments

Andrzej Miśkiewicz and Andrzej Rakowski

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3375-3379 (1994); (5 pages) | Cited 1 time

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Loudness levels (LL) of musical scale segments played pianissimo and fortissimo were predicted for 11 orchestral instruments, using Zwicker’s and Stevens’ Mark VI procedures for loudness calculation. The results show that the dynamic LL range of musical instruments depends not only on the dynamic sound‐pressure level range, but is also influenced by changes in the spectral envelope that accompany the dynamic gradations of sound. As the sound is played louder, its bandwidth extends to high frequencies, and the increase in sound‐pressure level (SPL) is greater for the high partials than for the low ones. Due to spectral loudness summation, the changes in spectral envelope with playing level enhance the dynamic LL range of the sound. As a consequence, for most instruments the dynamic LL range in a given pitch register is larger than the dynamic SPL range in that register. The difference between the two ranges was found to be greatest for brass instruments and for the clarinet, and approached about 6 dB in certain pitch registers.
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43.75.De Bowed stringed instruments
43.75.Ef Woodwinds
43.75.Fg Brass instruments and other lip-vibrated instruments
43.66.Cb Loudness, absolute threshold

Chemical treatment of wood for musical instruments

H. Yano, H. Kajita, and K. Minato

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3380-3391 (1994); (12 pages) | Cited 2 times

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After a review of the structure of wood concerning its acoustic properties and a discussion of the merits and demerits of wood as a material for making soundboards of stringed instruments, the effects of three chemical treatments (a low molecular weight phenolic resin treatment, a resorcin/formaldehyde treatment, and a saligenin/formaldehyde treatment) on the acoustic properties of Sitka spruce wood are reported and compared with those of formaldehyde treatment. All three chemical treatments increased the specific dynamic Young’s modulus and greatly decreased damping (tan δ) without greatly increasing specific gravity. The range was almost equivalent to that with formaldehyde treatment whose superb effects have already been confirmed in the violin. With saligenin/formaldehyde treatment, the frequency dependence of tan δ could be controlled over a wide range by changing the saligenin concentration. In all treatments, hygroscopicity was reduced and dimensional stability was improved significantly.
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43.75.De Bowed stringed instruments

Nonlinear analysis and classification of speech under stressed conditions

Douglas A. Cairns and John H. L. Hansen

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3392-3400 (1994); (9 pages) | Cited 3 times

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The speech production system is capable of conveying an abundance of information with regards to sentence text, speaker identity, prosodics, as well as emotion and speaker stress. In an effort to better understand the mechanism of human voice communication, researchers have attempted to determine reliable acoustic indicators of stress using such speech production features as fundamental frequency (F0), intensity, spectral tilt, the distribution of spectral energy, and others. Their findings indicate that more work is necessary to propose a general solution. In this study, we hypothesize that speech consists of a linear and nonlinear component, and that the nonlinear component changes markedly between normal and stressed speech. To quantify the changes between normal and stressed speech, a classification procedure was developed based on the nonlinear Teager Energy operator. The Teager Energy operator provides an indirect means of evaluating the nonlinear component of speech. The system was tested using VC and CVC utterances from native speakers of English across the following speaking styles; neutral, loud, angry, Lombard effect, and clear. Results of the system evaluation show that loud and angry speech can be differentiated from neutral speech, while clear speech is more difficult to differentiate. Results also show that reliable classification of Lombard effect speech is possible, but system performance varies across speakers.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.72.Kb Speech communication systems and dialogue systems

Accuracy of quasistationary analysis of highly dynamic speech signals

Roel Smits

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3401-3415 (1994); (15 pages) | Cited 1 time

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In this paper, the accuracy of the analysis of rapidly varying formants using spectrogram and linear prediction is assessed. Analysis of various dynamic signals shows that, when a long analysis window, like 25 ms, is used, the quality of the representation may be impoverished. Obvious unwanted effects are staircaselike formant tracks, flattening‐off of formants close to voicing onset, and bending of the formant towards a strong energy concentration in the release burst. The parameters that have the largest influence on the quality of the representation are the length of the analysis window, the transition rate of the formant, the fundamental frequency, and the position and energy of the release burst. It is shown that the most accurate analysis using a quasistationary method is made when windows are positioned pitch synchronously. Finally, a quantitative analysis of the influence of the mentioned parameters provides evidence that no deviations due to the quasistationarity assumption occur when the effective length of the analysis window is not larger than the pitch period. The wideband spectrogram is expected to be a reliable speech‐analysis tool because it meets this condition for fundamental frequencies up to 370 Hz.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech

Theoretical and experimental study of quasisteady‐flow separation within the glottis during phonation. Application to a modified two‐mass model

X. Pelorson, A. Hirschberg, R. R. van Hassel, A. P. J. Wijnands, and Y. Auregan

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3416-3431 (1994); (16 pages) | Cited 58 times

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Most flow models used in numerical simulation of voiced sound production rely, for the sake of simplicity, upon a certain number of assumptions. While most of these assumptions constitute reasonable first approximations, others appear more doubtful. In particular, it is implicitly assumed that the air flow through the glottal channel separates from the walls at a fixed point. Since this assumption appears quite unrealistic, and considering that the position of the separation point is an important parameter in phonation models, in this paper a revised fluid mechanical description of the air flow through the glottis is proposed, in which the separation point is allowed to move. This theoretical model, as well as the assumptions made, are validated using steady‐ and unsteady‐flow measurements combined with flow visualizations. In order to evaluate the effective impact of the revised theory, we then present an application to a simple mechanical model of the vocal cords derived from the classical two‐mass model. As expected, implementation of a moving separation point appears to be of great importance for the modeling of glottal signals. It is further shown that the numerical model coupled with a more realistic description of the vocal cord collision can lead to signals surprisingly close to those observed in real speech by inverse filtering.
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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

Comodulation masking release for single and multiple rates of envelope fluctuation

David A. Eddins and Beverly A. Wright

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3432-3442 (1994); (11 pages) | Cited 15 times

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Two experiments are presented that investigate the influence of envelope fluctuation rate upon the magnitude of comodulation masking release (CMR). In Experiment 1, thresholds were measured for a tonal signal centered in either one or five masker bands. The maskers were either narrow‐band noises or 100% sinusoidally amplitude‐modulated (SAM) tones. The five masker bands had either the same (coherent) or different (incoherent) envelopes. Envelope rate was varied by manipulating either the noise bandwidth (10–200 Hz) or the SAM rate (10–128 Hz). The CMR values were largest for slow envelope rates. In Experiment 2, envelope coherence was simultaneously manipulated at two rates by amplitude modulating (10 Hz) narrow‐band noises (100 Hz). The modulation depth was 100%, 83%, or 50%. The CMR based on the coherence of the noise carriers was about 5 dB, regardless of the SAM coherence or the modulation depth. The CMR based on the SAM coherence decreased from about 19 to 2 dB as modulation depth decreased, regardless of the noise‐carrier coherence. Thresholds were highest when the envelope fluctuations were incoherent at both rates and were lowest when the envelope fluctuations were coherent at both rates. These data suggest that the auditory system is able to make across‐frequency envelope comparisons at both envelope rates simultaneously.
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43.66.Ba Models and theories of auditory processes
43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Effect of component‐relative‐entropy on the discrimination of simultaneous tone complexes

Robert A. Lutfi and Karen A. Doherty

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3443-3450 (1994); (8 pages) | Cited 5 times

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Results are reported from a number of experiments investigating the effects of stimulus uncertainty on the discrimination of simultaneous multitone complexes. With few exceptions the data were well described by a model in which average threshold for the detection of a change in one or more components varies with the components’ relative entropy (CoRE) in the complex [R. A. Lutfi, J. Acoust. Soc. Am. 94, 748–758 (1993)]. In different experiments, thresholds for the detection of a change in target level were found to be linearly related to CoRE for manipulations in the number of targets, the number of context tones, and the relative degree of level perturbation on tones from trial to trial. The slopes of the functions did not change with measures taken at different points on the psychometric function, and in most cases were close to the theoretical value of b=−1.0, as predicted by strict application of the model. Also as predicted (but for the exception of one listener) increasing the level of the target beyond that of the context had little or no effect on threshold. A correlational analysis of the trial‐by‐trial data revealed a tendency of listeners to give negative weight to frequencies immediately above the target, and to adjust weights in response to changes in the relative degree of level perturbation. Though inconsistent with the basic premise of the model, the variation in weights was not so great as to materially affect the predictions for mean thresholds.
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43.66.Ba Models and theories of auditory processes
43.66.Fe Discrimination: intensity and frequency

A comparison of the effectiveness of across‐channel cues available in comodulation masking release and profile analysis tasks

Deborah A. Fantini and Brian C. J. Moore

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3451-3462 (1994); (12 pages) | Cited 9 times

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These experiments were designed to explore the benefit to signal detection of different types of across‐channel cues, both alone and in combination. Some conditions were similar to those used in profile analysis (PA), and some to those used in comodulation masking release (CMR). Others were designed specifically to eliminate, or render unreliable, a particular across‐channel cue so that the benefit to performance from another cue could be assessed. Thresholds for detecting an increment in level of a sinusoid, or of the carrier of a sinusoidally amplitude modulated (SAM) sinusoid, were measured in the presence or absence of four sinusoids or SAM sinusoids (flankers), two centered above and two centered below the signal frequency. The flankers were always modulated with the same depth as the target component during nonsignal intervals. The flankers, when present, were either equal in level to the nonsignal target sinusoid, or were scrambled in level (different in level both from each other and from the target by an amount that varied randomly from one stimulus to the next). In some conditions the overall level of the stimuli was also varied randomly from one stimulus to the next. The results indicate that about 5–6 dB of benefit arises from the cue of a disparity in level across frequency (a PA‐type cue), and about 1–3 dB from the cue of a disparity in envelope modulation depth across frequency (a CMR‐type cue). For some subjects, slightly less benefit occurred when the flankers were presented to the opposite ear as the signal, requiring across‐ear comparisons. Scrambling the level of the flankers often impaired performance, especially when the overall level of the stimuli was fixed. This appears to reflect an across‐channel interference effect.
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43.66.Dc Masking
43.66.Fe Discrimination: intensity and frequency
43.66.Rq Dichotic listening
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

The effect of burst duration, interstimulus onset interval, and loudspeaker arrangement on auditory apparent motion in the free field

Thomas Z. Strybel and Wayne Neale

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3463-3475 (1994); (13 pages) | Cited 1 time

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The illusion of auditory apparent motion (AAM) was examined in order to determine the burst durations and interstimulus onset intervals (ISOIs) at which AAM is heard when spatial information regarding source location was varied. In the first experiment AAM was examined in the free field under monaural and binaural listening conditions. AAM was heard at the same burst duration‐ISOI combinations for both listening conditions, but the location of the lead source could be determined only under binaural listening. In the second experiment AAM was measured with two and three sound sources. The number of sources did not affect the burst duration‐ISOI combinations that produced AAM, but did affect the determination of the location of the lead source. In the third experiment AAM was tested when the sources were located in the median plane. The sources were located either at 0° and 180° azimuth, or both at 0° azimuth, one in the horizontal plane and one 20° above. The location of the speakers did not affect the timing requirements for the perception of AAM, only the timing requirements for the detection of the lead source. In the fourth experiment, AAM was measured when the vertical separation between the sources was either 2.5° or 20°. AAM was heard at both separations, even though 2.5° is less than the vertical MAA. In each of these experiments only burst duration and ISOI determined whether motion was heard. Localization cues were important only for the determination of the direction of motion.
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43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Pn Binaural hearing
43.66.Qp Localization of sound sources

Auditory brainstem response (ABR) peak amplitude variability reflects individual differences in cochlear response times

Manuel Don, Curtis W. Ponton, Jos J. Eggermont, and Ann Masuda

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3476-3491 (1994); (16 pages) | Cited 11 times

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Previously, it was shown [Don et al., J. Acoust. Soc. Am. 94, 2135–2148 (1993)] that cochlear response times are gender specific and about 13% shorter in females than in males. It is also suggested that one of the possible reasons click‐evoked auditory brainstem response (ABR) waveforms recorded from females are better defined and have larger amplitudes than those of males is due to a sex difference in cochlear response times leading to better synchronization of the cochlear output across the frequency regions. Variability in cochlear response times would also lead to variability in click evoked ABR amplitudes. The high‐pass noise masking derived ABR technique was used to investigate the effect of normalizing the individual temporal variability at the neural and cochlear levels. This involved adjusting for differences in neural conduction time (I–V delay) by a compression or expansion of the derived ABR waveforms and by adjusting for differences in cochlear response times by a shift of the derived ABR waveforms. A summation of the compressed and shifted ABRs results in a normalized unmasked ABR waveform that can then be compared for amplitude variability with the unprocessed unmasked ABRs. Compensation for the neutral I–V variability had little effect while compensation for cochlear response times, particularly the delay between the 5.7‐ and 2.8‐kHz regions, greatly affected the amplitude of wave V of the compounded ABR. This work provides a better understanding of the significant relationship between cochlear response times and variability of the ABR peak amplitudes.
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43.64.Ri Evoked responses to sounds

Detection of a weak sinusoid with drifting phase in non‐Gaussian noise

Luciano Izzo, Luigi Paura, and Mario Tanda

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3492-3498 (1994); (7 pages)

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The problem of detecting by an array of sensors a weak sinusoidal signal with drifting phase embedded in additive white non‐Gaussian noise is addressed. The phase drift at each array element is modeled as a Brownian motion process. The locally optimum array detector is considered first. Then two suboptimum detection structures are examined: The first one is the locally optimum detector synthesized to detect a sinusoid with a random but constant phase; the second one is a version of the so‐called mth‐order noncoherent detector, which has been modified to account for the non‐Gaussian behavior of the noise. The detection performances in terms of deflection are analytically evaluated and compared. Finally, to corroborate the results of the deflection analysis, the performances, in terms of detection probability for a fixed false‐alarm rate, are assessed and compared by computer simulations.
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43.60.Cg Statistical properties of signals and noise
43.60.Gk Space-time signal processing, other than matched field processing

Matched‐phase noise reduction

Gregory J. Orris, B. E. McDonald, and W. A. Kuperman

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3499-3503 (1994); (5 pages)

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A simple method is presented for improving signal‐to‐noise ratios in noise dominated data, given the shape of the noise spectrum. No a priori information about the signal is required, except that its spectrum be distinct from that of the noise. Under the condition that the noise spectrum is sufficiently well known, a numerical example is given in which a signal may be detected despite a signal‐to‐noise ratio less than −100 dB.
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43.60.Cg Statistical properties of signals and noise
43.60.Gk Space-time signal processing, other than matched field processing

Mean‐scatterer spacing estimates with spectral correlation

Tomy Varghese and Kevin D. Donohue

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3504-3515 (1994); (12 pages) | Cited 2 times

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An ultrasonic backscattered signal from material comprised of quasiperiodic scatterers exhibit redundancy over both its phase and magnitude spectra. This paper addresses the problem of estimating mean‐scatterer spacing from the backscattered ultrasound signal using spectral redundancy characterized by the spectral autocorrelation (SAC) function. Mean‐scatterer spacing estimates are compared for techniques that use the cepstrum and the SAC function. A‐scan models consist of a collection of regular scatterers with Gamma distributed spacings embedded in diffuse scatterers with uniform distributed spacings. The model accounts for attenuation by convolving the frequency dependent scattering centers with a time‐varying system response. Simulation results indicate that SAC‐based estimates converge more reliably over smaller amounts of data than cepstrum‐based estimates. A major reason for the performance advantage is the use of phase information by the SAC function, while the cepstrum uses a phaseless power spectral density that is directly affected by the system response and the presence of diffuse scattering (speckle). An example of estimating the mean‐scatterer spacing in liver tissue also is presented.
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43.60.Cg Statistical properties of signals and noise
43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues

Frequency independence property of radiation spatial filters

Giorgio V. Borgiotti and Kenneth E. Jones

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3516-3524 (1994); (9 pages) | Cited 11 times

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It is known that a time harmonic boundary normal velocity field of a radiating object immersed in an acoustic fluid can be decomposed into a (efficiently) radiating and a non (efficiently) radiating components, belonging to two orthogonal ‘‘radiating’’ and ‘‘evanescent’’ subspaces. Numerical results show the validity for a capped cylinder of the conjecture that the ‘‘radiating’’ subspace at a certain frequency f1 is a subspace of the radiating subspace at frequency f2≳f1. The implications are (a) from the output of a bank of spatial filters designed for the max frequency of operation the far field can be identified over the entire frequency band, and, perhaps more importantly, (b) if in an active control scheme the outputs of the filters are driven to zero, broadband cancellation of the radiating noise is achieved.
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43.60.Gk Space-time signal processing, other than matched field processing

Comparison of concert hall measurements of spatial impression

J. S. Bradley

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3525-3535 (1994); (11 pages) | Cited 5 times

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Two different types of measures of spatial impression, lateral energy fractions and interaural cross correlations, were measured at a number of locations in 14 different concert halls. The mean and range of the hall‐average values of these quantities give an indication of typical conditions to be expected in other larger concert halls. Comparisons of hall‐average values of the two types of quantities showed them to be significantly related at medium and lower frequencies in good agreement with theoretical expectations. Individual position measurements were less well related and showed that other factors had a major influence on the individual position measurements. In some halls the two types of quantities varied quite differently with increasing source–receiver distance. At a particular seat location, the two types of measures cannot always give similar indications of expected spatial impression. Calculating hall‐average values from a small number of measurement locations is shown to introduce significant errors.
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43.55.Mc Room acoustics measuring instruments, computer measurement of room properties
43.55.Gx Studies of existing auditoria and enclosures

Bragg‐modulated hybrid ray‐mode algorithm for sound scattering from a periodically ribbed submerged elastic cylindrical shell: Theory and asymptotics

L. B. Felsen and R. Shaya

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3536-3547 (1994); (12 pages)

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A wave‐based hybrid ray‐mode algorithm has recently been developed to parametrize mid‐ and high‐frequency sound scattering from submerged empty and simply loaded cylindrical shells [Felsen et al., J. Acoust. Soc. Am. 87, 554–569 (1990)]. The present study extends the hybrid ray‐mode scheme to acoustic scattering from a submerged infinite cylindrical elastic shell with annular ribs attached internally at periodic intervals. Assuming thin shell dynamics, the problem is solved by adapting to the nonperiodic azimuthally unbounded domain (−∞<ϕ<∞) the azimuthally periodic harmonic series procedure used by Burroughs [J. Acoust. Soc. Am. 75, 715–722 (1984)] for this problem; the unbounded azimuthal (ϕ) domain with its continuous wave‐number spectrum is the essential starting point for the wave‐based ray‐acoustic analysis. The solution in the spectral domain is separated into the previously derived contributions for the nonloaded shell and into contributions from the infinite array of periodic ring forcings on the shell surface that account for the internal loads. Spectral synthesis furnishes the formal integral representation that is then manipulated by integration path deformations into a form amenable to reduction by saddle point asymptotics and residue calculus so as to yield the desired hybrid ray‐mode combination. The final algorithm for the scattered field contains (a) specular and Bragg‐modulated diffracted ray fields; (b) new unmodulated and Bragg‐modulated helically traveling shell‐guided trapped, creeping and leaky modes, which are phase‐matched to the fluid, in all wave species (compressional, flexural, shear) that the loaded thin shell geometry can support; (c) helically resonant shell‐guided modes, formed by phase coherent circumnavigations of the loaded cylinder by the traveling modes in (b). The dispersion equations for the various Bragg‐modulated wave types and species are determined from the internal impedance functions for the periodically distributed loadings.
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43.40.Ey Vibrations of shells
43.20.Fn Scattering of acoustic waves

Effect of dynamic fluid compressibility and permeability on porous piezoelectric ceramics

Olivier Lacour, Michel Lagier, and Didier Sornette

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3548-3557 (1994); (10 pages) | Cited 4 times

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The ac piezoelectric properties of porous ceramics in the presence of compressible viscous fluids filling the pores inside the ceramics are studied. Above the Biot frequency fB, the fluid decouples from the solid and does not significantly affect the piezoelectric properties. Our study which is both experimental and theoretical focuses on the frequency domain below the Biot frequency, in which the fluid is in principle strongly coupled to the solid matrix for oscillations parallel to solid–fluid boundaries. Two regimes are found: (1) For frequencies smaller than a cross‐over frequency fc∼(β/η)L−2, where L is the thickness of the sample, β the fluid bulk modulus, and η its viscosity, the piezoelectric coefficients dij are close to those of the dense nonporous ceramics weighted by the filling factor (1−ϕ); (2) for frequencies larger than fc, the dij tend to those of the empty porous ceramics for fluid bulk modulus significantly smaller than that of the ceramics, as is the case in our experiments. These observations are explained in terms of a frequency‐dependent penetration of the acoustic fluid pressure inside the porous ceramics as a result of the interplay between fluid compressibility and viscosity.
The nature of the decoupling between solid and fluid at frequencies larger than fc but still smaller than fB is for motions, not parallel to their common boundaries (for which the Biot mechanism applies), but perpendicular to their common boundaries. This decoupling occurs due to the finite compressibility of the fluid and in details is controlled by the tube‐cavity topological structure of the porous medium. The dependence of the hydrostatic piezoelectric coefficient dH=d33+d31+d32 as a function of frequency observed experimentally is compared to an effective medium theory for the piezoelectric properties coupled to a permeability model. The experimental dependence of the cross‐over frequency fc on sample sizes and on the fluid viscosity are in good agreement with our theory. The study shows that it is thus possible to obtain the desirable property of a high piezoelectric coefficient dH, characteristic of light porous piezoelectric ceramics, and good mechanical properties under applied high hydrostatic pressure with the use of an internal fluid which allows the pressure to equilibrate without destroying the piezoelectric properties of the porous ceramics.
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43.38.Fx Piezoelectric and ferroelectric transducers
43.38.Ar Transducing principles, materials, and structures: general
77.65.Bn Piezoelectric and electrostrictive constants

Electroacoustic properties for deformable antiferroelectric materials

K. Soumahoro and J. Pouget

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3558-3567 (1994); (10 pages)

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A nonmagnetizable and isolating dielectric involving two polarization types that are initially opposed is considered. The principle of virtual powers applied to the deformation movement gives the constitutive equations, which are then linearized. The analysis of the existence conditions of harmonic plane‐wave solutions shows that the acoustic and optic waves, deriving, respectively, from the modes associated with the deformation and polarizations fields are dispersive. The elastic and electric modes are coupled and the corresponding frequencies are perturbated for low wave numbers.
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43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Estimation of Prandtl numbers in binary mixtures of helium and other noble gases

F. W. Giacobbe

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3568-3580 (1994); (13 pages) | Cited 7 times

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This paper describes two different theoretical methods of calculating Prandtl numbers for mixtures of noble gases at moderate temperatures and pressures. In order to limit the scope and length of this work, only binary mixtures containing helium and one other noble gas (neon, argon, krypton, or xenon) were considered during this study. However, with relatively slight modifications, the methods described in this work for calculating Prandtl numbers should be applicable to other binary noble gas systems. In addition, theoretical gas mixture viscosities and thermal conductivities were compared with the corresponding experimentally measured values at 20.0 °C in order to provide a better assessment of the quality of the Prandtl number calculations. The results of this study should be useful to researchers and design engineers involved in optimizing the operation of acoustic refrigeration systems.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
51.10.+y Kinetic and transport theory of gases
51.30.+i Thermodynamic properties, equations of state

A model of a confocal ultrasonic inspection system for interfaces

E. Yogeswaren and John G. Harris

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3581-3592 (1994); (12 pages)

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A mathematical model describing how a confocal arrangement of two focused ultrasonic transducers is used to interrogate a complex interface between two materials by scanning the focal point across the interface is outlined. A complex interface is one that has roughness and partial contact at several length scales, many of which are equal to or smaller than the compressional or shear wavelength in the material. When the focused ultrasound strikes such an interface, though the focal region be small, multiple scattering takes place among the scatterers within and adjacent to the focal region, making it unclear exactly how the interface is being sampled. To clarify this issue a specific interface model, consisting of a planar array of multiple small cracks having arbitrary lengths and spacings, is used. This interface is interrogated by a focused, antiplane shear wave. While the antiplane assumption makes it scalar, the model shows that what is measured are the multiply scattered signals averaged over the aperture of the transducer, and that the dominant contribution comes from the scattered signals that phase match to the interrogating signal. Explicit expressions relating the modeled reflected and transmitted signals to the convolution of the incident wave field with the crack‐opening displacements at the focal region are given. Numerical examples are worked out for similar and contrasting materials on each side of the interface.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
81.70.-q Methods of materials testing and analysis

Shallow‐water acoustic/geoacoustic experiments at the New Jersey Atlantic Generating Station site

Mohsen Badiey, Indra Jaya, and Alexander H.‐D. Cheng

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3593-3604 (1994); (12 pages) | Cited 9 times

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Shallow‐water acoustic experiments were conducted at the Atlantic Generating Station site on the New Jersey Continental Shelf as a part of a long‐term study of the shallow‐water physics in this region. A vertical hydrophone array was used to assess the dispersion characteristics of the broadband acoustic field. A geoacoustic data set including bottom impedance profiles were constructed based on previous measurements of geological parameters from sediment core data. Experimental results show that the acoustic wave‐field dispersion is dependent on the azimuth angle. This dependency may be attributed to several factors relating to topography, range, and depth features.
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43.30.Bp Normal mode propagation of sound in water
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
91.50.Cw Beach and coastal processes
92.10.Vz Underwater sound

Sound‐speed measurements near the ocean surface

Eric Lamarre and W. K. Melville

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3605-3616 (1994); (12 pages) | Cited 9 times

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The results of two field experiments conducted in the fall of 1992 on the measurement of sound speed near the ocean surface are reported. The measurement technique makes use of the travel time of short acoustic pulses between a transmitter and a receiver separated by 40 cm [Lamarre and Melville, J. Atmos. and Oceanic Tech. (1994)]. The instrument is capable of making simultaneous measurements of the sound speed at six depths, starting at 0.5 m, over a frequency range from 5 to 40 kHz. Time series of sound speed show dramatic fluctuations over time periods on the order of minutes or less. These are attributed to the formation of bubble plumes or the passage of bubble clouds. In two particular instances, a newly created bubble plume generated a sound‐speed reduction of 800 m/s at a depth of 0.5 m; and a bubble cloud 25‐s old generated a reduction of 400 m/s. Frequent occurrences of sound‐speed reductions greater than 100 m/s are observed during moderate wind conditions (8 m/s). The signals at various depths are highly correlated and mostly coherent at frequencies below 0.05 Hz. The time‐averaged (20 min) sound‐speed profile is found to be significantly more pronounced and shallower than previously reported. The average sound‐speed reduction is found to correlate with wind speed. Simultaneous measurements at several acoustic frequencies show that the sound speed is nondispersive below 20 kHz for moderate wind conditions of up to 8 m/s. Upward‐looking sonar data reveal the presence of bubble clouds which correlate with the large sound‐speed reductions observed. However, even though bubble clouds are present down to a depth of 3 m and greater, significant sound‐speed reductions are confined to the first meter below the surface.
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43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.30.Nb Noise in water; generation mechanisms and characteristics of the field
92.10.Vz Underwater sound

Model experiments related to outdoor propagation over an earth berm

Karsten Bo Rasmussen

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3617-3620 (1994); (4 pages) | Cited 5 times

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A series of scale model experiments related to outdoor propagation over an earth berm is described. The measurements are performed with a triggered spark source. The results are compared with data from an existing calculation model based upon uniform diffraction theory. Comparisons are made in the frequency domain as well as in the time domain and good agreement is obtained.
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43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.50.Vt Topographical and meteorological factors in noise propagation

Statistical and numerical study of the relationship between turbulence and sonic boom characteristics

Richard Raspet, Henry E. Bass, Lixin Yao, Patrice Boulanger, and Walton E. McBride

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3621-3626 (1994); (6 pages) | Cited 5 times

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A statistical analysis of data collected by NASA during supersonic flight operations in the 1960’s shows that turbulence is related to characteristics of the sonic boom. Both convective and mechanical turbulence increase the rise times and produce peaked and rounded waveforms. Convective conditions are especially conducive to the formation of peaked waveforms. A physical model has been developed to investigate the interaction of sonic booms with turbulence. Scattering center‐based calculations demonstrate that scattering from eddies with sizes from 10 to 100 m is effective in producing long rise times and all major types of non‐N boom shapes.
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43.28.Mw Shock and blast waves, sonic boom
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence

Pattern formation in acoustic cavitation

I. Akhatov, U. Parlitz, and W. Lauterborn

J. Acoust. Soc. Am. Volume 96, Issue 6, pp. 3627-3635 (1994); (9 pages) | Cited 11 times

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A new approach for the theoretical description of structure formation in acoustic cavitation is developed. The model consists of two coupled partial differential equations describing the spatiotemporal evolution of the sound field amplitude and the bubble concentration. Linear stability analysis and numerical simulations of the pattern formation are presented. The relation between this approach and streamer formation is discussed.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.25.Ts Nonlinear acoustical and dynamical systems
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