bluuebunny/crossref_metadata_2025 huggingface dataset:
Source localization with horizontal arrays in shallow water: Spatial sampling and effective aperture
Authors: Bogart Christopher W. , Yang T. C.
Published: October 2005

Using vertical line arrays, matched-field processing (MFP) range–depth localization performance in shallow water is often limited by poor sampling of bottom interacting acoustic modes. For off broadside sources, a horizontal array may offer improved mode sampling and localization performance. The relative performance of a horizontal array in mode sampling and localization defines its effective vertical aperture. The MFP performance of several horizontal line array apertures is investigated and compared to a full water column vertical array in a simulated range-independent shallow water environment. It is demonstrated that a horizontal array of sufficient length can equal or exceed the water column vertical array in range–depth localization performance. Expressions are also derived for mode decomposition factors that permit the direct comparison of horizontal and vertical array mode sampling performance. Horizontal array effective aperture can then be computed without the need of extensive MFP test runs. It is shown that the horizontal array effective apertures predicted by these decomposition factors correspond well to actual MFP localization performance for the scenarios considered in this paper. Thus the decomposition factors are a useful tool for array system design for shallow water MFP localization.
Effects of temporal smearing on temporal resolution, frequency selectivity, and speech intelligibility
Authors: Hou Zezhang , Pavlovic Chaslav V.
Published: October 2005

Envelopes of speech were smeared in 23 parallel frequency channels. The smeared speech was presented to normal-hearing listeners, and the effects of different smearing magnitudes on speech intelligibility were measured by obtaining speech recognition scores. It was demonstrated theoretically and experimentally that the system consisting of the computer smearing and the auditory system had reduced temporal resolution but nearly normal frequency resolution. Speech intelligibility of the processed vowel–consonant nonsense syllables was tested for low- and high-pass filter conditions. The overall speech recognition scores as well as the recognition scores of the consonants grouped according to articulatory features were analyzed. The results indicated that smearing with a narrow temporal window did not degrade speech. The larger equivalent rectangular durations (ERDs) of the resultant temporal window (RTW) of the combined system (temporal smearing plus auditory system) produced a small but significant reduction in speech intelligibility for the low-pass filter condition. Scores for the RTWs≳16 ms were significantly different from the score for the 7.7-ms RTW for the high-pass filter condition, but this effect was small and did not differ across articulatory features.
A preliminary study of the effects of cochlear implants on the production of sibilants
Authors: Matthies Melanie L. , Svirsky Mario A. , Lane Harlan L. , Perkell Joseph S.
Published: October 2005

The potential influence of auditory information in the production of /s/ and /■/ was explored for postlingually deafened adults with four-channel Ineraid cochlear implants. Analyses of the spectra of the sibilant sounds were compared for speech obtained prior to implant activation, after early implant use and after 6 months of use. In addition, the output of the Ineraid device (measured at each of the four electrodes) was analyzed with pre- and postactivation speech samples to explore whether the speech production changes were potentially audible to the cochlear-implant user. Results indicated that subjects who showed abnormally low or incorrect contrast between /s/ and /■/ preactivation, and who received significant auditory benefit from their implants were able to increase the distinctiveness of their productions of the two speech sounds.
Group differences in measures of voice production and revised values of maximum airflow declination rate
Authors: Perkell Joseph S. , Hillman Robert E. , Holmberg Eva B.
Published: October 2005

In previous reports, aerodynamic and acoustic measures of voice production were presented for groups of normal male and female speakers [Holmberg et al., J. Acoust. Soc. Am. 84, 511–529 (1988); J. Voice 3, 294–305 (1989)] that were used as norms in studies of voice disorders [Hillman et al., J. Speech Hear. Res. 32, 373–392 (1989); J. Voice 4, 52–63 (1990)]. Several of the measures were extracted from glottal airflow waveforms that were derived by inverse filtering a high-time-resolution oral airflow signal. Recently, the methods have been updated and a new study of additional subjects has been conducted. This report presents previous (1988) and current (1993) group mean values of sound pressure level, fundamental frequency, maximum airflow declination rate, ac flow, peak flow, minimum flow, ac–dc ratio, inferred subglottal air pressure, average flow, and glottal resistance. Statistical tests indicate overall group differences and differences for values of several individual parameters between the 1988 and 1993 studies. Some inter-study differences in parameter values may be due to sampling effects and minor methodological differences; however, a comparative test of 1988 and 1993 inverse filtering algorithms shows that some lower 1988 values of maximum flow declination rate were due at least in part to excessive low-pass filtering in the 1988 algorithm. The observed differences should have had a negligible influence on the conclusions of our studies of voice disorders.
Discrimination of modulation type (amplitude modulation or frequency modulation) with and without background noise
Authors: Moore Brian C. J. , Sek Aleksander
Published: October 2005

These experiments compare the ability to detect amplitude modulation (AM) and frequency modulation (FM) with the ability to discriminate AM from FM, using 10-Hz sinusoidal modulation of a 1000-Hz carrier. Initially, psychometric functions were measured for the detection of AM and FM alone, using a two-alternative forced-choice (2AFC) task. In experiment 1, pairs of values of AM and FM were selected that would be equally detectable, and psychometric functions were measured for the discrimination of AM from FM, again in a 2AFC task. Values of d′ for discriminating AM from FM were always lower than the values of d′ for detection of the AM or FM. When the detectability of the AM and FM was low (d′=0.66), two subjects were essentially unable to discriminate AM from FM. This was true both for stimuli presented in quiet and for stimuli presented with continuous noise chosen to mask either the lower or the upper side of the excitation pattern. In experiment 2, subjects were again required to discriminate AM from FM, but the AM depth was fixed within a block of trials, while the FM depth was varied across trials. The discriminability of AM from FM did not show distinct minima at specific FM depths. Again, this was true both for stimuli presented in quiet and for stimuli presented with continuous noise chosen to mask either the lower or the upper side of the excitation pattern. This result suggests that the discrimination of AM from FM was not based on monitoring just one side of the excitation pattern of the carrier. The overall pattern of results is consistent with an excitation pattern model that assumes that modulation detection is based on a nonoptimal summation of information from all supra-threshold parts of the excitation pattern of the carrier. The discrimination of AM from FM probably requires a comparison of changes in excitation level on the two sides of the excitation pattern, and this leads to lower d′ values than for modulation detection.
Vibration monitoring of steel beams by evaluation of resonance frequency decay rates
Authors: Robin Pierre Y. , Jansen Ben H. , Man Xiu Ting C. , Wang Zhijing , Finch Robert D.
Published: October 2005

Defects in steel structures cause relatively small changes in the resonance frequencies, necessitating long observation intervals or the use of powerful shaking mechanisms. Much simpler monitoring procedures could be devised if the rate of decay of the resonance frequencies contains information about the structural integrity. The study presented here was aimed at determining which decay rates are most sensitive to small structural defects in steel beams. A technique, based on time-dependent spectral analysis of acoustic vibrations, has been developed to measure the decay rates for modes 2 through 6. An experimental study was conducted with 36-in. (0.9 m)-long steel beams with a rectangular cross section of 0.75 (19 mm) by 2.0 in. (51 mm). A slot, approximating a real crack, was cut to 0.7 in. (18 mm) in increments, in the center of one beam, so as to evaluate the sensitivity of the decay rates to the crack size. It was found that the logarithm of the amplitude of the resonance frequencies decays linearly with time, so that the resonance frequency decay rates can be quantified in terms of the slope of a linear regression. Significant differences in decay rates from intact and slotted beams were found for slots as small as 0.3 in. (7.6 mm).
Reflection from a corrugated surface revisited
Authors: Chesneaux Jean-Marie , Wirgin Armand
Published: October 2005

The problem of scattering of a plane sonic wave from a soft surface with periodic (sinusoidal) unevenness along one direction is examined by means of the Rayleigh plane-wave expansion and the Waterman extinction methods, numerically implemented by Fourier projection and expansion, respectively. The computations are done with real, double-precision, stochastic arithmetic instead of the usual complex, double-precision floating-point arithmetic in order to precisely evaluate the numerical accuracy of the results conditioned by round-off errors. It is shown that the low-order plane-wave coefficients obtained by the Rayleigh and Waterman methods are identical when obtained from matrix systems that are large enough to give ‘‘convergence’’ of these coefficients. For the same matrix size, the higher-order coefficients differ the higher the diffraction order. It is also shown that the Waterman (Fourier-series) computation of the near field is generally meaningful, whereas that of Rayleigh, involving summation of the plane waves is generally meaningless except near the points of the scattering surface first encountered by the incident wave (i.e., those in the valleys when the incident wave comes from below). Low-order plane-wave scattering coefficients, with at least two-to-three-digit accuracy, and which are identical (to this precision) to the plane-wave coefficients computed by the rigorous integral equation method, are obtained by both the Rayleigh and Waterman methods for scattering surfaces with slopes as large as 2.26 when the number of nonevanescent waves is 5. The number of significant digits decreases as the slope increases.
Estimation of attenuation of A-weighted traffic noise level due to air absorption
Authors: Lane Sam R.
Published: October 2005

Current versions of the U.S. DOT Federal Highway Administration (FHWA) traffic noise model assume 500 Hz as a representative sound frequency and apply an air absorption attenuation rate of 0.54 dB per 1000 ft for the distance associated with the maximum noise level. According to the American National Standards Institute, the air attenuation rate at 500 Hz is approximately 1 dB per 1000 ft for a wide temperature and relative humidity range. However, the rate of decrease of the composite A-weighted traffic noise level depends on the spectral distribution of car and truck noise, and varies with distance. A more representative air attenuation for traffic noise is obtained by including this effect during integration as source distance varies to obtain the attenuated sound exposure level (SEL) since the traffic noise level is determined from single event SEL and number of events. In many cases, an attenuation due to air absorption of 0.5 to 3.0 dB may be warranted, as compared to less than 0.5 dB assigned by the traffic noise model. These considerations are appropriate only for the ‘‘hard site’’ case since the ‘‘soft site’’ attenuation factor assumed by the model includes extra attenuation due to shielding and air absorption. Air absorption and roadway truncation by terrain shielding may account for most of the traffic noise level attenuation now attributed to ‘‘ground absorption’’ in some cases.
A modified ray acoustic algorithm for near-field scattering by submerged elastic cylindrical shells
Authors: Ho Jin-Meng
Published: October 2005

The near-field scattering of plane waves by a submerged thin elastic cylindrical shell witnesses a shadow boundary generated by the geometrical acoustics field, which is not encountered in the far field except in the immediate vicinity of the forward scattering direction. Even in the lit zone, the incident and reflected rays may appear close and are not well separated. Based on these physical observations a modified ray acoustic approach is proposed here that combines the two spectral integrals that would give rise to separate incident and reflected fields when reduced by saddle point evaluation. The resulting single integral descriptive of the geometrical acoustics field can be cast as an integral version of the harmonic series form for the total (incident plus scattered) field, thereby facilitating its numerical computation. Averting the asymptotic integration procedure, and hence the contour deformation involving possible capture of the membrane wave poles, the new algorithm predicts the total near field uniformly over the entire azimuthal domain, which is now synthesized by the geometrical acoustics field and the shell-guided phase-matched compressional and shear wave field. Extensive numerical examples for the field dependency on frequency as well as on azimuthal and aspect angles are presented; they indicate that the modified ray acoustic solution leads to remarkable accuracy for ka≥1 or so (where k is the fluid acoustic wave number and a is the shell mean radius). By reciprocity, the method presented in this paper applies as well to excitation by an axially phased line source located at finite distance (on- or off-surface).
Influence of relative level on modulation discrimination interference
Authors: Shailer Michael J. , Moore Brian C. J.
Published: October 2005

This experiment examines the effects on modulation discrimination interference (MDI) of differences in level between the signal and masker carriers. The task was to detect a change in depth of amplitude modulation of a 1-kHz signal carrier, in the presence of modulated or unmodulated masker carriers that were either reasonably close to the signal carrier frequency (540 and 1380 Hz) or distant from it (230 and 3300 Hz). The relative level of the signal and masker carriers was systematically varied. The results show that modulated maskers can impair the detection of changes in modulation depth even when the maskers are distant in frequency from the signal carrier and 30–40 dB lower in level than the signal carrier. The magnitude of the interference effect changes only slowly with relative level of the signal and masker carriers, suggesting that the interference depends primarily on across-channel processes.
Comments on ‘‘Evaluating a speech-reception threshold model for hearing- impaired listeners’’ [J. Acoust. Soc. Am. 93, 2879–2885 (1993)]
Authors: Plomp Reinier
Published: October 2005

As everyday practice as well as laboratory experiments have shown abundantly, the hearing aid falls short in eliminating the difficulties of many subjects with sensorineural hearing losses in understanding speech in noise. The attempt by Lee and Humes to demonstrate the opposite with only 11 spondees as speech material does not alter this situation. As far as their experiment allows any conclusion, it supports the view that the speech-reception threshold of hearing-impaired listeners is characterized by a distortion factor as well as an attenuation factor.
Optimization of sound field simulations in small enclosures by parametric inversion
Authors: Hoogenboom H. J. , de Vries D. , van der Toorn J. D.
Published: October 2005

A parametric inversion scheme is introduced which optimizes sound field simulations in small enclosures. The parameters are the average admittance and the normal velocity at the surface of a modeled enclosure; they are estimated from a few pilot measurements. This means that a representation of the effective boundary conditions of the actual enclosure is obtained, to be used as input data in the simulation model. The parametric inversion scheme is applied to the sound field in a rectangular enclosure which was modeled with the finite element method. The optimized sound pressure simulations match the measured responses accurately. Around the maxima of the frequency response the simulation remains within the accuracy of the measurements, which is 1 dB. From the results it is concluded that the proposed parametric inversion scheme is a very promising tool for the optimization of sound field simulations in small spaces with moderate model overlap.
Adaptive tunings for musical scales
Authors: Sethares William A.
Published: October 2005

A fixed, octave-based musical scale cannot remain faithful to the consonant simple integer ratio intervals and simultaneously be modulated to all keys. It is possible to reconcile these competing criteria, however, if the notes of the scale are allowed to vary. This paper presents a method of adjusting the pitches of notes dynamically, an adaptive tuning, that maintains fidelity to a desired set of intervals and can be modulated to any key. The adaptive tuning algorithm changes the pitches of notes in a musical performance so as to maximize consonance, which is calculated based on recent perceptual work. The algorithm can operate in real time, is responsive to the notes played, and can be readily tailored to the timbre (or spectrum) of the sound. This can be viewed as a generalization of the methods of just intonation, but it can operate without specifically musical knowledge such as key and tonal center and is applicable to timbres with nonharmonic spectra as well as the more common harmonic timbres.
Growth-of-masking functions for several types of maskers
Authors: Glasberg Brian R. , Moore Brian C. J.
Published: October 2005

Growth-of-masking functions were obtained for sinusoidal signals at three frequencies (fs), 0.25, 1.0, and 4.0 kHz, using maskers that were always higher in frequency than the signal. Five different maskers were used, chosen so as to evaluate the influence of temporal fluctuations in the maskers and of combination products produced by the interaction of components within the maskers: A sinusoid (S); a narrow-band noise with a bandwidth of 16 Hz (N); a noise with a slightly wider bandwidth equal to 0.75 times the equivalent rectangular bandwidth (ERB) of the auditory filter at each fs (W); a noise with a very wide bandwidth equal to 0.4fs and with lower cut-off frequency and spectrum level matched to those of masker W (V); and a sinusoidal carrier frequency modulated by a noise, and matched in bandwidth and center frequency to masker N (F). The center frequencies of maskers S, N, W, and F were either 1.1fs or 1.2fs. Masker S generally produced the smallest amount of masking and gave growth-of-masking functions with the shallowest slopes (much less than unity). Results were similar for maskers N and F; both produced slightly more masking than masker S and growth-of-masking functions with slightly greater slopes than masker S. Maskers W and V produced more masking than the other maskers, and gave growth-of-masking functions with steeper slopes. For all maskers, the slopes of the growth-of-masking functions were lower at the greater signal-masker frequency separation. It is suggested that the results for the two maskers with the greatest bandwidth (W and V) were influenced by combination bands produced by the interaction of components within the masker. The results for the maskers with very small bandwidths (S, N, and F), suggest that the upper side of the auditory filter increases in slope with increasing level.
Pitch ranking with nonsimultaneous dual-electrode electrical stimulation of the cochlea
Authors: McDermott Hugh J. , McKay Colette M.
Published: October 2005

It has already been established that simultaneous activation of two intracochlear electrodes can evoke a pitch percept which is intermediate to that of either electrode when activated by itself. In the present study, this result has been extended to nonsimultaneous activation of nearby electrodes. Pitch perception was investigated for electric stimuli presented on one or two intracochlear electrode pairs. All stimuli were pulse trains of period 4 ms. In the dual-electrode stimuli, each period contained two biphasic pulses, separated by 0.4 ms, with one pulse for each electrode pair. These stimuli were compared with loudness-balanced single-electrode stimuli, having one pulse per period, generated on the same electrode pairs. Their pitches were ranked in a two-alternative forced-choice procedure by five experienced users of the 22-electrode implant manufactured by Cochlear Pty Limited. The studies showed that the pitch of a dual-electrode stimulus was intermediate to, and moved monotonically between, those of the component electrode pairs as the relative currents were altered in an orderly fashion. Intermediate pitches were achieved in all subjects at a range of cochlear positions, for electrode separations generally up to 3 mm. In half the cases a significantly different intermediate pitch could be created between adjacent electrodes. Further studies are necessary to establish whether intermediate pitches can be obtained at larger separations, as for simultaneous stimulation, and how they are affected by other factors such as the time between pulses or the spatial extent of the stimulation.
Normal mode propagation on conical shells
Authors: Guo Y. P.
Published: October 2005

This paper presents a theoretical study on waves on elastic shells of conical shape. The shell motions are formulated according to thin shell theory and the technique of multiple scales is used to derive solutions for shells with small vertex angles. Solutions are decomposed into angular harmonics in the circumferencial direction, each mode propagating along the shell axis. In contrast to waves on cylindrical shells, waves on conical shells experience amplitude and phase variations as a result of the changing shell radius. Discussed in detail is the case where waves propagate toward the apex of the shell. In this event, the decreasing radius causes different modes to be cut off at different locations where the waves also show strong dispersive behavior. Also, as a result of the shrinking radius, the wave amplitudes grow, the growth being limited by blowup at cutoff. The locations of cutoff for different modes are identified and the nature of the amplitude singularities at cutoff is examined in detail.
Wave propagation in anisotropic laminated hollow cylinders of infinite extent
Authors: Soldatos Kostas P. , Ye Jianqiao
Published: October 2005

This paper deals with a three-dimensional elasticity investigation of wave propagation in an infinitely long hollow cylinder whose homogeneous or layered structure is made by generally orthotropic or monoclinic materials. The analysis is based on a recursive formulation of a successive approximation method employed elsewhere by the authors for the study of axisymmetric and flexural vibrations of homogeneous orthotropic and cross-ply laminated hollow cylinders of finite length. The method has further been applied in connection with static and thermoelastic analyses of orthotropic homogeneous and cross-ply laminated cylinders and cylindrical panels. In all cases considered, results of this approach converge very rapidly toward corresponding exact three-dimensional elasticity results. Hence the present study is based on essentially exact three-dimensional elasticity results and is further expected to serve as a benchmark for corresponding future investigations based on finite element and/or two-dimensional shell theory formulations.
An analytic expression for the transient ultrasonic field radiated by a shear wave transducer in solids
Authors: Lhémery Alain
Published: October 2005

An analytic expression is proposed for the radiation of transient pulses by an ultrasonic shear wave transducer directly coupled to an elastic medium (Y-cut crystal). The expression of the displacement vector is obtained by combination of the impulse-response approach with the approximate integral formula for the transient radiation of elastic waves by an arbitrary transducer proposed by Lhémery [A. Lhémery, ‘‘A model for the transient ultrasonic field radiated by an arbitrary loading in a solid,’’ J. Acoust. Soc. Am. 96, 3776–3786 (1994)].
Radiative transfer and multiple scattering of diffuse ultrasound in polycrystalline media
Authors: Turner Joseph A. , Weaver Richard L.
Published: October 2005

A model is presented for the multiply scattered incoherent field in a continuous polycrystalline elastic medium. Unlike a previous development based upon energy conservation considerations [J. A. Turner and R. L. Weaver, J. Acoust. Soc. Am. 93, 2312 (A) (1993)] for a medium containing discrete random scatterers, the present model has been developed from the wave equation and first principles. Appropriate ensemble averaging of the wave equation leads to Dyson and Bethe–Salpeter equations which govern the mean Green’s function and the covariance of the Green’s function, respectively. These equations are expanded for weak heterogeneity and equations of radiative transfer are obtained. The result is valid for attenuations that are small compared with a wave number: α/k≪1. Polarization effects are included, as before, through five elastodynamic Stokes parameters, one longitudinal and four shear. The theory is applied to a statistically homogeneous and statistically isotropic half-space composed of cubic crystallites illuminated by a plane wave. Results for the angular dependence of backscattered intensity are presented. It is anticipated that this approach may be applicable to microstructural characterization through the study of the time, space, ultrasonic frequency, and angular dependence of multiply scattered ultrasound in elastic media.
Detection of a weak sinusoid with drifting phase in non-Gaussian noise
Authors: Izzo Luciano , Paura Luigi , Tanda Mario
Published: October 2005

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.
Comparison of concert hall measurements of spatial impression
Authors: Bradley J. S.
Published: October 2005

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.
Bragg-modulated hybrid ray-mode algorithm for sound scattering from a periodically ribbed submerged elastic cylindrical shell: Theory and asymptotics
Authors: Felsen L. B. , Shaya R.
Published: October 2005

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.
Using singing whales to track nonsingers
Authors: Makris Nicholas C. , Cato Douglas H.
Published: October 2005

The ability to track vocalizing whales over large distances (≳100 km) using horizontal arrays has recently received much attention in the underwater acoustics community [‘‘Use of Naval Facilities for Ocean Acoustic Research,’’ J. Acoust. Soc. Am. 95, 2851–2854 (1994)]. The high source levels of the whales, up to 190 dB re: 1 μPa at 1 m, make this possible. However, tracking vocal whales may provide an incomplete behavioral picture because a significant proportion of whales may be nonvocal at any given instance. (Visual observations are limited to the small proportion of time that whales surface.) Alternatively, the high source levels invite the possibility of treating the vocalizing whale as an active source. Sound from this source of opportunity that is scattered by other members of the herd may be sufficient to locate nonvocal whales with a towed array. Historical data are used to model the spatial distribution of vocal and nonvocal humpback whales migrating off the Eastern Continental Shelf of Australia. A spectral model for scattering from an object in a waveguide based on Ingenito’s method is used to determine the scattered field from the whales. Waveguide noise is modeled via the Kuperman and Ingenito approach. Simulations indicate that localization of nonvocal whales is plausible for towed arrays within roughly 10 km of the herd in typical ambient noise conditions. This range may be extended significantly with time-domain matched filtering.
Acoustic scattering losses in the Greenland Sea marginal ice zone during the 1988–89 tomography experiment
Authors: Jin Guoliang , Lynch James F. , Pawlowicz Richard , Worcester Peter
Published: October 2005

Using arrival amplitude data from the 1988–89 Greenland Sea tomography experiment, the effects of ice scattering at 250 Hz in the marginal ice zone (MIZ) are estimated. The resolution of the arrivals is examined first, showing that arrivals are resolved as rays from about 8° to 13° launch angle and a normal modes for low angles, below about 4° launch angle. The under-ice reflection losses of resolved rays and modes are then considered using two methods. First, the ratio of arrival amplitudes during ice-free and ice-covered periods is estimated. Second, the ratio of members of a ray group with different reflection numbers is used, showing similar (but not identical) results to the first method. For higher grazing angle reflections, fast field calculations using the program SAFARI are observed to model the data reasonably, using a combination of measured and historical ice parameter values. For the low angle arrivals, the amplitudes of the arrivals are observed to depend strongly upon both the details of the surface mixed layer and the ice cover itself. Using reasonable mixed layer estimates from both data and model inputs, it is observed that part of the amplitude reduction seen in the data is indeed due to ice, though the exact amount is sensitive to the details of the mixed layer.
A study of reflection loss. I. A multilayered viscoelastic seabed at very low frequencies
Authors: Kibblewhite A. C. , Wu C. Y.
Published: October 2005

Recent investigations of wave-induced seismoacoustic noise in the ocean have involved a parallel study of the reflection coefficient of complex seabeds at very low frequencies. Because of the nature of the wave–wave interaction source responsible for the main peak in the ULF noise spectrum, it was necessary to examine the behavior of the reflection coefficient to both the homogenoeus and inhomogeneous components of the wave-induced noise field. The results of these studies have revealed aspects of the reflection loss process not previously recognized. This contribution discusses the reflection loss for a multilayered viscoelastic structure. Companion papers examine the effect of introducing porosity into the sedimentary layers.
Experimental characterization of elastic waves in a floating ice sheet
Authors: Yang T. C. , Giellis G. R.
Published: October 2005

Frequency–wave-number analysis is applied to geophone data to study phase velocities of ice waves as a function of frequency. Previous measurements of phase velocities were based primarily on initial arrival time of individual waves which were valid only for the frequency components associated with the initial arrival. By processing the geophone array data coherently, this frequency–wave-number analysis measures the phase velocity as a function of frequency for a wide frequency band. This processing is applied to geophone data collected on a line array of three-axis geophones; the data were generated by striking sledge hammers against a steel pipe frozen into the ice during an Arctic experiment in 1988. As expected, the longitudinal and horizontal shear waves travel with constant phase velocities below 100 Hz. Applying this analysis to vertical-axis geophone data, we find two families of dispersion curves for the flexural waves. Only one dispersion curve is expected for the flexural wave for a uniform sheet of ice. The origin of the additional (flexural) wave is not established. Time-frequency analysis was applied to individual time series to estimate the group velocities of the flexural wave and use the line array data to estimate ice attenuations. Frequency–wave-number analysis is used to identify ice waves in a complex signal in which the various ice waves are no longer separated by travel time. This is demonstrated by the analysis of a noise event. The origin of this noise event based on the analysis of the hammer blow data is discussed.
Temporal pattern discrimination and speech recognition under electrical stimulation
Authors: Collins Leslie M. , Wakefield Gregory H. , Feinman Gail R.
Published: October 2005

Discrimination of temporal patterns has been suggested as a relevant process in speech recognition by subjects with normal hearing [Sorkin, J. Acoust. Soc. Am. 87, 1695–1701 (1990)]. This paper investigates whether performance of Nucleus multichannel cochlear implant subjects on a temporal pattern discrimination task is an efficient and valid psychophysical measure of speech recognition ability. Stimuli consisted of temporal sequences defined by twelve 35-ms tones and eleven randomly generated temporal gaps separating the tones. A fixed-level same/different paradigm was used to measure the discriminability of these sequences as a function of their average correlation across a block of trials. On each trial, the ‘‘standard’’ sequence was generated randomly by drawing gap durations from a Gaussian distribution. The gaps of the comparison sequence were generated in a similar fashion with a specified average correlation with the gaps of the first sequence. Performance of implanted and normal hearing subjects decreased monotonically with increasing average sequence correlation. However, performance across implanted subjects ranged from that observed for acoustically stimulated subjects with audiometrically normal hearing to levels near chance. Comparing these data with measures of speech recognition in the same subjects, we have found that performance on standard speech recognition tests correlates with ability to discriminate among such random temporal patterns.
A three-dimensional analysis of sound propagation in facetted geometries
Authors: Deane G. B.
Published: October 2005

An analytical technique is presented for computation of the three-dimensional sound field due to an harmonic, point source in a range-dependent waveguide formed with two or more plane facets. The waveguide is assumed to be homogeneous with ideal (perfectly reflecting) boundaries. The theory is based on a development of the method of source images. The idea of a source image is abstracted into a set of reflections (a generating sequence) and a criterion for determining whether an image contributes to the sound field (a visibility criterion). These generalizations allow a solution to be built up without reference to a specific plane geometry. The sound field in a parallel-sided duct terminated by a wedge is calculated as an example of the technique.
Reception at Ascension of the Heard Island Feasibility Test transmissions
Authors: Palmer D. R. , Georges T. M. , Wilson J. J. , Weiner L. D. , Paisley J. A. , Mathiesen R. , Pleshek R. R. , Mabe R. R.
Published: October 2005

At Ascension, about 9200 km from the source ship, all transmissions from the Heard Island Feasibility Test were recorded on at least eight hydrophones and, for many transmissions, on 11 hydrophones. The depths of most of these hydrophones are near the depth of the sound channel axis but some are considerably deeper. All are bottom mounted. Signal-to-noise ratios were found to be surprisingly high. Averaged over the continuous wave (cw) transmissions and in a 1-Hz band, signal-to-noise ratios for the axial hydrophones south of the island range from about 19 to 30 decibels (dB), adjusted to a source level of 220 dB (referenced to 1 μ Pa at 1 m). The average signal-to-noise ratio for a hydrophone at a depth approximately 0.8 km below the axis is about 16 dB, suggesting acoustic energy was not restricted to a narrow interval in depth centered about the sound channel axis as had been anticipated. The travel time of the earliest arrival was found to be about 1 h, 44 min, 17 s. A late, scattered signal was observed for at least 23 min after termination of the direct signal. An unexpected combination of phase stability and amplitude variability was observed in the received signals. Continuing analysis of the Ascension data set is likely to provide considerable information about the characteristics of acoustic signals that have propagated global distances.
On the dipole acoustic source level of breaking waves
Authors: Ding Li , Farmer David M.
Published: October 2005

Wave breaking is believed to be the primary physical mechanism for generation of ambient noise. Yet previous measurements of ambient noise have been based on averaged results of noise sources randomly distributed in space and related primarily to wind speed. Recent progress in direct measurement of breaking waves has made it possible to examine the sound radiated from individual sources and relate it to breaking wave parameters. Here we present field observations of dipole acoustic source levels of breaking waves obtained during the surface wave processes program. The acoustic source level is related to measured breaking wave speed, which is believed to be an important parameter relevant to wave energy dissipation. It is found that the source level has a much better correlation with the breaking wave speed than with the wind speed. The data also indicate that the acoustic source level can be modeled as an exponential distribution. These results are explained using laboratory observations of acoustic radiation and wave energy dissipation due to breaking.
Theoretical and experimental study of quasisteady-flow separation within the glottis during phonation. Application to a modified two-mass model
Authors: Pelorson X. , Hirschberg A. , van Hassel R. R. , Wijnands A. P. J. , Auregan Y.
Published: October 2005

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.
Recent developments in the in-situ measurement of sediment geoacoustic properties
Authors: Richardson Michael D. , Griffin Sean R.
Published: October 2005

The latest version of the in-situ sediment acoustic measurement system (ISSAMS) allows direct, in-situ measurement of sediment geoacoustic properties. Geoacoustic probes, which are mounted on a rigid frame, are inserted into the sediment hydraulically. The entire operation is controlled and monitored in real-time from the surface. Data is collected and processed by a wet-side computer and transmitted to the surface for waveform display and analysis. Video cameras both monitor insertion of probes and provide preliminary indication of sediment type. A seabird CTD is used to measure bottom water temperature, salinity, and sound speed. Sediment compressional wave velocity and attenuation are measured over pathlengths of 40 to 110 cm and at depths of between 0 to 50 cm below the sediment–water interface. Pulsed sine waves are transmitted at 58-kHz and time delays and voltages are used to determine values of velocity and attenuation between identical radial-poled ceramic cylinders (two transmit and two receive). Shear wave velocity and attenuation are measured using a similar pulse technique. Bimorph bender elements mounted in flexible silicone rubber mounts and driven at 100 to 2000 Hz to generate shear waves. Values of sediment geoacoustic properties from muddy sediments of Eckernförde Bay, Baltic Sea and carbonate sediments of the Florida Keys presented used to illustrate the operation and utility of the new system.
The effects of multilayering piezoelectric plates with implication to 1–3 piezocomposite materials
Authors: Powell David J. , Howarth Thomas R. , Ting Robert Y.
Published: October 2005

This paper discusses the considerations of stacking piezoelectric plates mechanically in series (on top of each other) and electrically in parallel or series. Benefits include increased displacement for projectors and increased signal-to-noise ratio (SNR) for hydrophones (because of self-shielding and decreased electrical impedance). The presentation will show why these enhancements are realized by using a mathematical solution of the one-dimensional (1-D) wave equation to describe how each layer is related to that in adjacent layers via continuity of particle displacement and force. The resultant set of simultaneous equations is solved using matrix manipulation algorithms over a specified frequency range in terms of the free-field voltage sensitivity (FFVS), transmitting voltage response (TVR), and electrical immitance characteristics. A temporal transient response is obtained through the inverse fast Fourier transform (IFFT). This computational efficient model is capable of piezoceramic or 1–3 piezocomposite transducer layers, as well as inactive layers. The 1–3 piezocomposites are input by using the Smith expressions for representing the piezocomposite as a homogeneous material. Application of 1–3 piezocomposites for multiple layering will be introduced and discussed. [Work sponsored by the Office of Naval Research.]
Estimation of the uncorrelated and correlated spatial components of the self-noise in towed arrays
Authors: Ferguson Brian G. , Speechley Gary C. , Wyllie David V.
Published: October 2005

The self-noise in towed arrays can be divided into two components on the basis of its spatial correlation properties. In this paper, optimal estimates of the uncorrelated and correlated self-noise components are obtained using an adaptive frequency-wave-number analysis technique. The results of applying the technique to real data from various towed-array types are presented. The spatially uncorrelated contribution to the total self-noise is often ignored in the presence of the correlated structure-borne vibrations that travel in both axial directions along the array with a phase speed that is less than the speed-of-sound propagation in the underwater medium. The increasing importance of the uncorrelated component at higher tow speeds is discussed and, under some circumstances, the uncorrelated component is shown to dominate.
Acoustic coupling in directional loudspeaker arrays
Authors: Vu-Maesto Hahn , Chakravarty Ananda , Mehta Vineet , Thompson Charles
Published: October 2005

The performance of directional loudspeaker and microphone arrays is of interest with regard to conferencing applications. Transducer arrays can be steered to enhance transmission and or reception at a prescribed location. In reverberant environments, directional microphone arrays have shown promise in enhancing speech intelligibility in hand-free applications. Steerable loudspeaker arrays, on the other hand, have met with limited success. The differentiating feature is the input impedance of the loudspeaker. In this presentation the role of the acoustic coupling between adjacent transducers in a loudspeaker array will be examined. The acoustical interaction between transducer elements is modeled. The impact of this interaction on beamforming is examined.