bluuebunny/crossref_metadata_2025 huggingface dataset:
Comments on ‘‘On equations for the speed of sound in seawater’’ [J. Acoust. Soc. Am. 93, 255–275 (1993)]
Authors: Millero Frank J. , Li Xu
Published: October 2005

The recent measurements of acoustic arrival patterns [Dushaw et al., J. Acoust. Soc. Am. 93, 255–275 (1993); Spiesberger and Metzger, J. Acoust. Soc. Am. 89, 1697–1700 (1991); 89, 2677–2688 (1991)] indicate that the sound-speed equation of Del Grosso [J. Acoust. Soc. Am. 56, 1084–1091 (1974)] may be more reliable than the equation of Chen and Millero [J. Acoust. Soc. Am. 62, 1129–1135 (1977)] at low temperatures (0° to 15 °C) and high pressures (300 to 1000 bar). In this paper the possible causes of the difference and the resultant effect on the equation of state of seawater are discussed. The error in the sound-speed equation of Chen and Millero originated from the unreliable sound speeds for pure water determined by Wilson [J. Acoust. Soc. Am. 31, 1067–1072 (1959)] at low temperatures and high pressures. This difference does not affect the equation of state of seawater within the standard error of the equation (5×10−6 cm3/g in the specific volume at high pressures, vP). A correction has been derived that is valid from 0° to 15 °C to 1000 bar that can be used to correct the sound-speed equation of Chen and Millero. This correction allows one to use their equation over a much wider range of temperature, pressure, and salinity than the Del Grosso equation.
Acoustic scattering from the seafloor: Modeling and data comparison
Authors: Lyons Anthony P. , Anderson Aubrey L. , Dwan F. S.
Published: October 2005

An existing model of seafloor backscattering [D. R. Jackson, D. P. Winebrenner, and A. Ishimaru, J. Acoust. Soc. Am. 79, 1410–1422 (1986)] was implemented with the additions of volume scattering from a random inhomogeneous continuum and scattering from subbottom interfaces. Results of computer simulations with the extended model were compared with values of scattering strength obtained from processed GLORIA data from the Monterey Fan off the coast of California. Regions of well-delineated high and low backscatter are seen in the GLORIA imagery. The geoacoustic input parameters for the simulation runs were either taken directly from or estimated from core data obtained by ground truth sampling in the image area. From the model simulation results it appears that the main factor causing the observed dichotomous character of the strength of returns in the Fingers Area is the presence or absence of a topmost, inhomogeneous silt-clay layer (with a thickness of around 1–1.5 m). In the high backscatter areas, inhomogeneous continuum volume scattering from the silt-clay layer predominates. In the low backscatter areas interface scattering from an acoustically hard, shallow subbottom sand interface (0–10 cm below the water–sediment interface) predominates. These two additions to the scattering model allow use of the ground truth measurements to constrain the input parameter values.
A generalized target strength model for euphausiids, with applications to other zooplankton
Authors: Macaulay Michael C.
Published: October 2005

A hybrid model has been developed that generates predictions of euphausiid target strengths similar to those observed by direct measurement. The controlling variables of the model account for the size, shape, orientation, and stochastic nature of orientation. Sound speed and density contrast values used are within the range of those directly observed. This suggests that it is possible to produce a generalized target strength prediction for euphausiids like those available for fish. Euphausiids appear to be better generalized as a bent cylindrical or bent spheroid targets rather than spherical targets, at least for frequencies greater than 100 kHz. Although the model is based on a single, limited data set, its predictions compare well with the results, of a number of recently published measurements and models of target strength. The model also resolves some puzzling contradictions of target strength frequency dependency previously observed, but unexplained. A number of items were determined to be needed to complete or further refine such hybrid models: Target strength measurements for more sizes, species, and frequencies (especially below 50 kHz and above 420 kHz) are most prominent among these.
Time-domain and frequency-domain analysis of acoustic scattering by spheres
Authors: Thorne Peter D. , Brudner Terry J. , Waters Kendall R.
Published: October 2005

In recent years the application of resonance scattering theory, RST, to the interaction of underwater sound with elastic bodies, has yielded a description of the scattering process that has provided valuable insight into the underlying mechanisms of scattering. Comparisons of this approach with observations have usually been carried out in the frequency domain, using the form function notation. In the present study results are reported of an examination of the backscattered echo from a selection of spheres conducted both in the time domain and the frequency domain. The structure of the background and resonance components of the backscattered signal are investigated, and examined in both domains. To obtain the measurements a linear frequency-modulated signal or chirp was employed. Using a Fourier analysis approach, with pulse compression, measurements have been taken in the time domain, which readily show the components of the backscattered echo. Using these data, sections of the record have been separately transformed to obtain in the frequency domain the background and resonance form functions. Further, time-frequency plots have been generated to examine the association between the time domain echo and the form function structure. To compare the observations with predictions, resonance scattering theory has been applied both in the time domain and the frequency domain.
Acoustic backscatter measurements in the North Sea: 3–18 kHz
Authors: Nützel Bernd , Herwig Heinz , Koenigs Paul D. , Monti Joseph M.
Published: October 2005

Measurements were conducted in the North Sea to investigate the influence of near-surface bubbles on acoustic backscatter in the 3- to 18-kHz frequency range. At normal incidence, the scattering caused by bubbles contributes to reverberation. A partial ‘‘screening’’ (or masking) of the surface was observed for short time periods when bubble plumes were introduced into the insonified volume. At lower grazing angles, the contribution to scattering by bubbles increases with wind speed and frequency such that, for a 30-deg grazing angle, the bubbles become the dominant backscattering mechanism at wind speeds of 35 and 18 kn for 10 and 18 kHz, respectively, and mark the onset of saturation. A comparison with other experimental data shows good agreement.
Ray-mode analysis of a random medium waveguide
Authors: Mazar R. , Katz B.
Published: October 2005

Statistical propagation characteristics in a waveguide filled with a randomly fluctuating medium can be modeled in terms of rays and guided modes. In this work, a plane-parallel waveguide filled with a random medium having a characteristic fluctuations scale much smaller than the transverse waveguide dimension is considered. The field approaching the observer in such a waveguide can be approximated as a sum of contributions of a direct ray and the rays reflected by the waveguide walls. The corresponding intensity distribution is presented as a sum of two parts: coherent and incoherent. Using the Poisson summation formula, these portions can be transformed into the sums of guided modes. Numerical examples are presented.
Ray tracing in isotropic and anisotropic materials: Application to tomographic image reconstruction
Authors: Wang Y. Q. , Kline R. A.
Published: October 2005

One of the principal differences between tomographic image reconstruction with acoustic and radiographic data is that sound waves, unlike x-radiation, do not generally travel along straight line ray paths in nonhomogeneous media. In this work, a technique for ray tracing in nonhomogeneous media (both isotropic and anisotropic) is developed. This approach is based upon Fermat’s principle and can be readily incorporated into tomographic reconstruction algorithms. The effect of ray bending on the accuracy of acoustic tomograms is investigated.
A baffle-type directional microphone
Authors: Benson Jonathan W. , Li Yuan-Liang , Swenson George W.
Published: October 2005

A simple and economical directional microphone has been investigated, consisting of a plane, rectangular baffle with an omnidirectional pressure microphone placed directly on its surface. Outdoor experiments and numerical computations using the method of moments give compatible results and show useful directional properties, comparable with or superior to those of commercially available line (end-fire) or parabolic-reflector microphones of similar dimensions. Variations of beamwidth and beam shape with baffle dimensions and microphone placement are presented.
Vibration analysis of elastic coupler in a planar mechanism
Authors: Wu Sean F.
Published: October 2005

This paper presents an analysis of the transverse vibration and stability of an elastic beam simultaneously subject to a periodic axial load, a distributed transverse load, and time-dependent displacement excitations at both ends. The equation of motion derived from Bernoulli–Euler beam theory is a fourth-order partial differential equation with periodic coefficients. To obtain approximate solutions, the assumed-modes method is used. The unknown time-dependent function in the assumed-modes method is determined by a generalized inhomogeneous Hill’s equation. The instability regions possessed by this generalized Hill’s equation are obtained by both the perturbation technique up to the second order and the harmonic balance method. The dynamic response and the corresponding spectrum of the transversely oscillating elastic beam are calculated by the weighted-residual method.
Acoustical finite-difference time-domain simulation in a quasi-Cartesian grid
Authors: Botteldooren D.
Published: October 2005

The finite-difference time-domain (FDTD) approximation can be used to solve acoustical field problems numerically. Mainly because it is a time-domain method, it has some specific advantages. The basic formulation of the FDTD method uses an analytical grid for the discretization of an unknown field. This is a major disadvantage. In this paper, FDTD equations that allow us to use a nonuniform grid are derived. With this grid, tilted and curved boundaries can be described more easily. This gives a better accuracy to CPU–resource ratio in a number of circumstances. The paper focuses on the new formulation and its accuracy. The problem of automatically generating the mesh in a general situation is not addressed. Simulations using quasi-Cartesian grids are compared to Cartesian grid results.
A hierarchic p-version boundary-element method for axisymmetric acoustic scattering and radiation
Authors: Grannell James J. , Shirron Joseph J. , Couchman Luise S.
Published: October 2005

A rapidly convergent boundary-element method that has a high-accuracy capability is developed for the solution of the exterior Neumann problem for the Helmholtz equation. The approach makes use of the boundary-operator combination idea of Burton and Miller [A. J. Burton and G. F. Miller, Proc. R. Soc. London Ser. A 323, 201–210 (1971)] to avoid the classical irregular frequency difficulties together with p-version boundary elements to obtain a high rate of convergence. The entire algorithm is designed to be fully hierarchic to minimize the cost of multiple solutions, which are necessary for a posteriori assessment of accuracy. A new hierarchic singular-kernel quadrature rule is developed for this purpose. Numerical examples demonstrate the accuracy and convergence rate of the method.
An inverse problem in low-frequency scattering by a rigid ellipsoid
Authors: Lucas R. J.
Published: October 2005

The inverse problem for low-frequency plane wave excitation of a small rigid ellipsoid is considered. It is shown that six measurements of the leading-order low-frequency coefficient of the imaginary part of the forward scattering amplitude are sufficient to specify the semiaxes of the ellipsoid and its orientation.
Transient wave propagation through bubbly layers via the Foldy–Twersky integral equation
Authors: Leander Johan L.
Published: October 2005

This work considers transient linear acoustic wave propagation through a layer of small gas bubbles in a liquid. The analysis is based on multiple scattering theory and the Foldy–Twersky integral equation is used. The transmitted coherent wave for a distribution of uncorrelated scattering bubbles is studied. The case of a weak scattering density is investigated for the regimes of single scattering and Foldy–Twersky multiple scattering. A condition for the column density for the single scattering regime is derived and found to be more restrictive than earlier heuristically derived results. The influence of the low-frequency region of the monopole part of the scattering amplitude of a spherical gas bubble is analyzed. It is shown that a combination of the expression for the wave number for the transmitted coherent wave and the formula used for the low-frequency region of the monopole coefficient yield a well-posed initial-value problem. The effects due to single scattering are shown to be negligible so a pulse propagates essentially undisturbed. For the case of Foldy–Twersky scattering, however, the influence of the bubbles can be substantial. The main characteristics of linear transient wave propagation in bubbly liquids experimentally observed by Kuznetsov et al. are qualitatively predicted by the theory used in this paper.
Lip–larynx coordination in speech: Effects of mechanical perturbations to the lower lip
Authors: Munhall Kevin G. , Löfqvist Anders , Kelso J. A. Scott
Published: October 2005

This experiment investigates the coordination between the larynx and the lips and jaw in voiceless consonant production using an experimental paradigm where a mechanical perturbation is applied to an articulator. Three subjects received unexpected perturbations to the lower lip during the transition between the first vowel and the first stop in /i′pip/. Movements of the upper articulators (lips and jaw) were recorded using an optoelectronic technique. Laryngeal responses were monitored using transillumination; intraoral pressure and the acoustic signal were also recorded. Results showed that laryngeal abduction was delayed following lip perturbation and that the duration of the laryngeal adduction gesture was lengthened. The oral movements toward closure of two of the subjects were modified and all subjects showed modification of the oral release movements in the perturbed conditions. All subjects showed an increased movement velocity and displacement of the upper lip, lower lip, and jaw in the oral opening phase. First trial compensation, however, was not observed in two of the three subjects. The results are discussed with respect to the speech perturbation literature and the notion of coordinative structures.
Auditory and categorical effects on cross-language vowel perception
Authors: Flege James Emil , Munro Murray J. , Fox Robert Allen
Published: October 2005

English monolinguals and native Spanish speakers of English rated the dissimilarity of tokens of two Spanish vowel categories, two English vowel categories, or one Spanish and one English vowel category. The dissimilarity ratings of experienced and inexperienced Spanish subjects did not differ significantly. For both the native Spanish and English subjects, perceived dissimilarity increased as the distance between vowels in an F1−F2 acoustic space increased. This supported the existence of a universal, sensory-based component in cross-language vowel perception. The native English and Spanish subjects’ ratings were comparable for pairs made up of vowels that were distant in an F1−F2 space, but not for pairs made up of vowels from categories that were adjacent in an F1−F2 space. The inference that the differential classification of a pair of vowels augments perceived dissimilarity was supported by the results of experiment 2, where subjects rated pairs of vowels and participated in an oddity discrimination task. Triads in the oddity task were made up of tokens of vowel categories that were either adjacent (e.g., /a/–/æ/–/a/) or nonadjacent (e.g., /a/–/i/–/i/) in an F1−F2 space. The native English subjects’ discrimination was better than the native Spanish subjects’ for adjacent but not nonadjacent triads. The better the Spanish subjects performed on adjacent triads—and thus the more likely they were to have differentially classified the two phonetically distinct vowels in the triad—the more dissimilar they had earlier judged realizations of those two categories to be when presented in pairs. Results are discussed in terms of their implications for second language acquisition.
Selective adaptation in speech perception using a compelling audiovisual adaptor
Authors: Saldaña Helena M. , Rosenblum Lawrence D.
Published: October 2005

A replication of the audiovisual test of speech selective adaptation performed by Roberts and Summerfield [Percept. Psychophys. 30, 309–314 (1981)] was conducted. The audiovisual methodology allows for the dissociation of acoustic and phonetic components of an adapting stimulus. Roberts and Summerfield’s results have been interpreted to support an auditory basis for selective adaptation. However, their subjects did not consistently report hearing the adaptor as a visually influenced syllable making this interpretation questionable. In the present experiment, a more compelling audiovisual adaptor was implemented resulting in a visually influenced percept 99% of the time. Still, systematic adaptation occurred only for the auditory component.
Ultrasonic cell lysis in vitro upon fractional, discontinuous exposure vessel rotation
Authors: Brayman Andrew A. , Miller Morton W.
Published: October 2005

In polystyrene exposure vessels, a substantial fraction of suspended P388 cells was lysed by exposure to cw, 1-MHz ultrasound (5 W cm−2 spatial peak intensity, 5 min) in stationary vessels or those subjected to a small number of half rotations. Lysis was increased significantly by two half-rotations during exposure relative to stationary vessels. Lysis in stationary exposure vessels is generally considered to be minimal; it is shown that ∼40% cell lysis occurs in 15%–20% of the stationary tubes. This result appears to relate to the distribution of random defects on the exposure vessel walls.
Numerical model for acoustic radiation of an immersed elastic stucture and application to a thin cylindrical shell
Authors: Félix Denise
Published: October 2005

This paper is concerned with a problem of scattering from an elastic target. It presents a three-dimensional numerical model for determining the dynamic response and acoustic radiation of an elastic structure in the medium frequency range. This model is applied to a thin cylindrical shell immersed in a fluid. Comparison with experimental results shows the efficiency of this numerical model.
The effects of elastic edge constraints and fluid loading on the resonant response of thick rectangular plates
Authors: Hammouda Jamel , Burroughs Courtney B.
Published: October 2005

An analytic model of the response of rectangular plates simply supported on two opposing edges and elastically supported on the other edges is derived. Transverse shear and rotary inertia in the plate and adjustable stiffness constants in the elastic supports are included in the model. The elastic stiffness constants are adjusted to simulate classical boundary conditions and results compared to published results. The variation of frequencies of resonance with the stiffness of the elastic supports is shown. The effect of fluid on the resonant responses of simply supported plates is presented.
Analytical and experimental determination of the vibration and pressure radiation from a submerged, stiffened cylindrical shell with two end plates
Authors: Harari A. , Sandman B. E. , Zaldonis J. A.
Published: October 2005

An analytical model of a finite, stiffened cylindrical shell with two end plates submerged in fluid was developed. Results obtained for the pressure at various points in the fluid as well as the drive point and transfer point accelerance are compared with experimental results. Good agreement between the analytical and the experimental results are reported.
Inverse filtering of a loudspeaker and room acoustics using time-delay neural networks
Authors: Chang Po-Rong , Lin C. G. , Yeh Bao-Fuh
Published: October 2005

This paper presents the design of a neural-based acoustic control used for the equalization of the response of a sound reproduction system. The system usually can be modeled as a composite system of a loudspeaker and an acoustic signal-transmission channel. Generally, an acoustic signal radiated inside a room is linearly distorted by wall reflections. However, in a loudspeaker, the nonlinearity in the suspension system produces a significant distortion at low frequencies and the inhomogeneity in the flux density causes a nonlinear distortion at large output signals. Both the linear and nonlinear distortions should be reduced so that high fidelity sound can be reproduced. However, the traditional adaptive equalizer which is only capable of dealing with linear systems or specific nonlinear systems cannot compensate these nonlinear distortions. The time-delay feedforward neural network (TDNN) which has the capability to learn arbitrary nonlinearity and process the temporal audio patterns are particularly recognized as the best nonlinear inverse filter of the composite system. The performance of a TDNN-based acoustic controller is verified by some simulation results.
Robust Fourier descriptors for characterizing amplitude-modulated waveform shapes
Authors: Pinkowski Ben
Published: October 2005

Fourier descriptors (FD’s) have traditionally been used to characterize the boundary shape of closed curves in computer-based images. This study examines the usefulness of FD’s for characterizing the shape of amplitude-modulated waveform boundaries. Twenty-eight bioacoustic waveforms representing 7 species-specific sound groups were examined. Nearest-neighbor classification using 32-point waveform envelopes yielded 85.7% recognition rates when Euclidean distances with 8 or 12 FD’s were employed. With 4 or 16 FD’s, recognition was 82.1% but dropped to 71.4% when the number of FD’s was reduced to 3. Evidently only the low-order 4 or 5 FD’s are required to characterize most signals examined. Four FD’s were adequate representation for linear discriminant analysis, wherein 27 (96.1%) of the samples were classified correctly, and for hierarchical cluster analysis, wherein 26 (92.9%) of the samples clustered into dendrogram subtrees corresponding to the known sound groups. Two sounds accounted for many errors in the classification experiments, and these differed from typical sounds for their respective species groups. In such cases, more than a single FD reference pattern may be required to adequately represent the sounds of a given species.
Detection of mixed modulation using correlated and uncorrelated noise modulators
Authors: Sek Aleksander , Moore Brian C. J.
Published: October 2005

This article is concerned with the mechanisms underlying the detection of amplitude modulation (AM), frequency modulation (FM), and mixed modulation (MM), i.e., simultaneously occurring AM and FM. In a previous study [B. C. J. Moore and A. Sek, J. Acoust. Soc. Am. 92, 3119–3131 (1992)], psychometric functions were measured for the detection of AM alone and FM alone, using a 10-Hz sinusoidal modulator and a 1-kHz carrier frequency. Detectability was then measured for combined AM and FM, with modulation depths selected so that each type of modulation would be equally detectable if presented alone. The detectability of the MM was better than would be predicted if the two types of modulation were coded completely independently. This study examined the possibility that the good detectability of MM was caused by the fact that the AM and the FM were correlated, so that each was predictable from the other. The design was similar to that of our earlier study, but the 10-Hz sinusoidal modulator was replaced by a narrow-band noise modulator. In the MM conditions, the modulators for AM and FM were either strongly positively correlated or essentially uncorrelated. In experiment 1, the waveforms of the noise modulators were fixed throughout the experiment (frozen noise). In experiment 2, the waveforms of the noise modulators were chosen independently for each trial. In both experiments, for both correlated and uncorrelated modulators, the detectability of the MM was better than would be predicted if the two types of modulation were coded completely independently. Performance was better for the correlated modulators than for the uncorrelated modulators. The results indicate that the high detectability of MM cannot be attributed solely to one type of modulation (e.g., FM) being predictable from the other type of modulation (e.g., AM).
The internal representation of spectral contrast in hearing-impaired listeners
Authors: Summers Van , Leek Marjorie R.
Published: October 2005

Abnormal frequency resolution associated with sensorineural hearing impairment produces a smearing of spectral detail in the internal representation of complex acoustic stimuli. As a result, listeners with hearing loss may have difficulty locating spectral peaks (e.g., vowel formants) within stimuli which cue their identity. This study examined the relationship between frequency separation of peaks in a complex spectrum and the degree of spectral contrast preserved in the internal representations in normal and impaired auditory systems. Hearing-impaired and normal-hearing subjects discriminated a flat-spectrum bandpass stimulus from a stimulus containing a sinusoidal ripple across its frequency range. The peak-to-valley amplitude (in dB) necessary for detection of the ripple was measured for ripple frequencies ranging from 1 to 9 cycles/oct. Auditory filter characteristics were also measured at 1 and 3 kHz in order to examine the internal representations of the stimuli after cochlear processing. There were clear differences between groups in both auditory filter characteristics and spectral contrast detection. However, the amount of contrast in the internal representations predicted from these measurements was nearly the same for all subjects, suggesting that the reduced frequency resolution of the hearing-impaired group was largely responsible for differences in required peak-to-valley amplitude in the input spectra. Further, for all subjects, there was a trade-off between the absolute level of internal contrast necessary for ripple detection and the number of samples of this contrast available to the listener.
The role of resolved and unresolved harmonics in pitch perception and frequency modulation discrimination
Authors: Shackleton Trevor M. , Carlyon Robert P.
Published: October 2005

A series of experiments investigated the influence of harmonic resolvability on the pitch of, and the discriminability of differences in fundamental frequency (F0) between, frequency-modulated (FM) harmonic complexes. Both F0 (62.5 to 250 Hz) and spectral region (LOW: 125–625 Hz, MID: 1375–1875 Hz, and HIGH: 3900–5400 Hz) were varied orthogonally. The harmonics that comprised each complex could be summed in either sine (0°) phase (SINE) or alternating sine-cosine (0°–90°) phase (ALT). Stimuli were presented in a continuous pink-noise background. Pitch-matching experiments revealed that the pitch of ALT-phase stimuli, relative to SINE-phase stimuli, was increased by an octave in the HIGH region, for all F0’s, but was the same as that of SINE-phase stimuli when presented in the LOW region. In the MID region, the pitch of ALT-phase relative to SINE-phase stimuli depended on F0, being an octave higher at low F0’s, equal at high F0’s, and unclear at intermediate F0’s. The same stimuli were then used in three measures of discriminability: FM detection thresholds (FMTs), frequency difference limens (FDLs), and FM direction discrimination thresholds (FMDDTs, defined as the minimum FM depth necessary for listeners to discriminate between two complexes modulated 180° out of phase with each other). For all three measures, at all F0’s, thresholds were low (<4% for FMTs, <5% for FMDDTs, and <1.5% for FDLs) when stimuli were presented in the LOW region, and high (≳10% for FMTs, ≳7% for FMDDTs, and ≳2.5% for FDLs) when presented in the HIGH region. When stimuli were presented in the MID region, thresholds were low for low F0’s, and high for high F0’s. Performance was not markedly affected by the phase relationship between the components of a complex, except for stimuli with intermediate F0’s in the MID spectral region, where FDLs and FMDDTs were much higher for ALT-phase stimuli than for SINE-phase stimuli, consistent with their unclear pitch. This difference was much smaller when FMTs were measured. The interaction between F0 and spectral region for both sets of experiments can be accounted for by a single definition of resolvability.
Comparing the fundamental frequencies of resolved and unresolved harmonics: Evidence for two pitch mechanisms?
Authors: Carlyon Robert P. , Shackleton Trevor M.
Published: October 2005

Four experiments measured sensitivity (d′) to differences in fundamental frequency (F0) between two simultaneously presented groups of frequency-modulated harmonics. Each group was passed through a bandpass filter in either a LOW (125–625 Hz), MID (1375–1875 Hz), or HIGH (3900–5400 Hz) frequency region. In the first two experiments, a dynamic F0 difference (ΔF0) was created by introducing a 180° disparity between the frequency modulations imposed on the two groups. Experiment 1 measured sensitivity to such ΔF0’s between a MID group with a baseline F0 of 125 Hz and all components summed in sine phase, and a HIGH group, in four conditions. When the baseline F0 of the HIGH group was also 125 Hz, performance was good when its components were summed in sine phase and bad when they were in alternating phase. Conversely, when the HIGH F0 was 62.5 Hz, performance was better for alternating phase than for sine phase, consistent with alternating phase doubling the internal representation of HIGH group’s F0. Similar results were obtained for a comparison between the LOW and MID groups. Experiment 2 measured sensitivity to ΔF0’s between either the LOW and MID groups or between the MID and HIGH groups, for baseline F0s of 88 and 250 Hz. Sensitivity was best when the combination of frequency region and F0 was such that both groups were resolved or both unresolved by the peripheral auditory system, and worst when the groups differed in ‘‘resolvability.’’

Experiment 3 replicated experiment 2 using a different paradigm, in which the two groups were always modulated coherently, and in which the ΔF0 was constant throughout the signal. Experiments 2 and 3 also measured sensitivity to differences in F0 between successively presented tokens of the same group. Experiment 4 showed that the high sensitivity to (simultaneous) ΔF0’s when both groups were unresolved could be attributed to listeners detecting the pitch pulse asynchronies that inevitably arise from ΔF0’s. Finally, a method for predicting sensitivity to simultaneous, across-frequency ΔF0’s from that to successive within-channel differences, on the basis of optimum combination of information, was applied to the results of experiment 3. The method succeeded in predicting sensitivity to ΔF0’s between two groups of resolved harmonics, but over-estimated performance when one group was resolved and the other unresolved. The results suggest that the F0’s of resolved and unresolved harmonics are processed by separate mechanisms, in contrast to the predictions of ‘‘autocorrelation’’ models of F0 encoding.
Detection of interaural delay in high-frequency sinusoidally amplitude-modulated tones, two-tone complexes, and bands of noise
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: October 2005

Listeners’ ability to detect interaural temporal disparities (ITDs) was investigated for 160-ms, sinusoidally amplitude modulated (SAM) tones, two-tone complexes, and bands of noise at center frequencies of 4, 8, or 12 kHz. Rates of modulation for the 100%-modulated SAM tones and frequency separation for the equal-amplitude, two-tone complexes ranged from 32–768 Hz, depending on center frequency. Noise bandwidths ranged from 50–2000 Hz, also depending on center frequency. The data indicate, consistent with previous results, that sensitivity to ITD with the SAM and two-tone complexes decreases as the rate of envelope fluctuation increases beyond about 400 Hz. The decline in performance is not due simply to reduced depth of modulation produced by critical-band-like filtering, but is consistent with an inability to ‘‘follow’’ or encode high rates of modulation. For bands of noise, sensitivity to ITD was relatively constant as a function of bandwidth. Generally, sensitivity to ITD decreased as center frequency was increased from 4 to 8 kHz, but the relations among the data were essentially unchanged. Increasing the center frequency to 12 kHz resulted in very poor performance.
Detection of interaural delay in bands of noise: Effects of spectral interference combined with spectral uncertainty
Authors: Buell Thomas N. , Trahiotis Constantine
Published: October 2005

This study concerns two situations that could limit a listener’s sensitivity to interaural temporal delay (ITD). The first is having to detect a ‘‘target’’ ITD in one spectral region when diotic energy is also present in remote and/or adjacent spectral regions. In such a situation, sensitivity to ITD is typically degraded, as compared to when no remote and/or adjacent diotic energy is present. Both the outcome and the paradigm are commonly termed ‘‘spectral interference.’’ In the present study, spectral interference was measured using a broadband (100 Hz to 9 kHz) noise that was diotic, save for a restricted spectral region that was interaurally delayed. The portion of the noise that contained the ITD had a center frequency (CF) of either 300, 1200, 2400, or 4800 Hz and a bandwidth that was 40% of the CF. The second situation of interest was ‘‘spectral uncertainty.’’ Here, the center frequency of the portion of the noise containing the ITD was varied (chosen from one of four possible CFs) on a trial-by-trial basis. Consequently, the listener was uncertain about which spectral region could contain the ITD. Data were also collected with one of four narrow bands of noise with the CFs and bandwidths identical to the interaurally delayed spectral regions used in the spectral interference and spectral uncertainty conditions. Within a block of trials, the center frequency of the narrow band of noise was either held constant or was randomly chosen from the set of four CFs. In all cases, threshold ITDs were measured in a single-interval task. Consistent with previous studies, the largest amounts of spectral interference occurred when the portion of the noise containing the ITD was centered at or above 2400 Hz. The novel finding was that spectral uncertainty produced extremely poor performance, rendering some listeners unable to detect even a 1-ms ITD presented within high-frequency regions.
Effects of harmonic content on complex-tone fundamental-frequency discrimination in hearing-impaired listeners
Authors: Arehart Kathryn Hoberg
Published: October 2005

Complex-tone (fundamental) frequency discrimination was measured in eight well-trained listeners with moderately severe sensorineural hearing impairments as a function of parametric variations in the rank, number, and sensation level of stimulus components. Results indicate substantial differences in the effects of harmonic content on complex-tone frequency discrimination among hearing-impaired listeners and between hearing-impaired and normal-hearing listeners. Despite large variability among the hearing-impaired subjects, several patterns of results emerged: Performance of two subjects grew worse as harmonic rank increased; performance of three subjects did not change substantially with changes in harmonic rank; and performance of three impaired subjects improved as harmonic rank increased. Performance of all but two subjects was significantly degraded for stimuli containing low-order harmonics. For stimuli containing only high-order harmonics, five subjects showed performance that was comparable to that of normal-hearing subjects, and three showed abnormally poor performance. Performance of impaired subjects generally improved as the number of stimulus components increased. The sensation level of stimulus components influenced the performance of several impaired subjects, but not in a uniform manner. To the extent that complex-tone fundamental-frequency discrimination can be assumed to be a pitch perception task, the present results suggest that, in contrast to normal-hearing subjects, hearing-impaired listeners rely primarily on periodicity cues in the perception of complex-tone pitch.
Quality ratings for frequency-shaped peak-clipped speech
Authors: Kates James M. , Kozma-Spytek Linda
Published: October 2005

Peak clipping is a common form of distortion in hearing aids and can reduce the subjective quality of the amplified speech. In a typical hearing aid, frequency-response shaping precedes symmetric peak clipping. The effect of peak clipping on speech quality ratings was therefore studied using sentence test materials that were processed using different frequency response contours and then clipped at different clipping thresholds. The quality of each processed sentence was rated on a ten-point scale by normal-hearing subjects. The experimental results indicate that the clipping threshold, and the interaction of the frequency-response shaping with the clipping threshold, significantly affect speech quality. It is also shown that the distortion effects on speech quality can be modeled by a distortion index computed from the magnitude-squared coherence of the speech-processing system in response to a shaped-noise input signal.
Analysis of pulse propagation in a bottom-limited sound channel with a surface duct
Authors: Monjo Charles L. , DeFerrari Harry A.
Published: October 2005

Measurements of acoustic transmission in a bottom-limited sound channel with a surface duct, are compared with model predictions using broadband ray, normal mode, fast-field, and parabolic approximation methods. At a range of 42 km, six surface-ducted arrivals are evident in the data set and are predicted by all models except simple ray theory. Surface-ducted propagation is compared to propagation without a surface duct. The surface duct is found to generate a series of modes which display a resonance between the highly dispersive surface reflected bottom reflected (SRBR) propagation and less dispersive refracted bottom reflected (RBR) propagation. The six arrivals contain energy from three types of propagation paths. Faster precursors are purely diffracted energy, while slower precursors have RBR and SRBR contributions. Ray theory predicts the SRBR contribution, but not the diffracted energy. The precursors are generated at discrete ranges where RBR and SRBR phase fronts exchange energy with the RSR phase front in the duct. Energy leaking from the duct also reenforces the slower precursors. Since range-independent models were used, mode coupling cannot be the cause of energy exchange.
Matched mode processing for sparse three-dimensional arrays
Authors: Yang T. C. , Bogart Christopher W.
Published: October 2005

Matched mode processing (MMP) has been demonstrated to localize underwater sound sources with vertical hydrophone arrays. Two new MMP algorithms for arbitrarily shaped three-dimensional arrays in a range-independent environment are presented. The first algorithm, exact matched mode processing (EMMP), is a generalization of vertical array MMP; its mode decomposition depends on source bearing. The second algorithm, approximate matched mode processing (AMMP), ignores bearing dependence during mode decomposition, reinserting it afterward. The AMMP azimuth beam pattern is similar to that of matched field processing (MFP) and conventional beamforming. The performance of the EMMP and AMMP algorithms is investigated and compared with MFP using simulated data. A slanted vertical array, a horizontal array, and a T-shaped array composed of horizontal and vertical segments were considered. It was found that the AMMP and MFP yield similar peak-to-sidelobe ratio (PSR) and peak-to-average-sidelobe ratio (PASR) in range and depth localization. In contrast, the EMMP yields higher PSR and PASR in range and depth localization for known source bearings. Its bearing search properties were not investigated; they may be less robust than AMMP, MFP and conventional beamforming.
Sound emissions by a laboratory bubble cloud
Authors: Nicholas M. , Roy R. A. , Crum L. A. , Og̃uz H. , Prosperetti A.
Published: October 2005

This paper presents the results obtained from a detailed study of the sound field within and around a cylindrical column of bubbles generated at the center of an experimental water tank. The bubbles were produced by forcing air through a circular array of hypodermic needles. As they separated from the needles the ‘‘birthing wails’’ produced were found to excite the column into normal modes of oscillation whose spatial pressure-amplitude distribution could be tracked in the vertical and horizontal directions. The frequencies of vibration were predicted from theoretical calculations based on a collective oscillation model and showed close agreement with the experimentally measured values. On the basis of a model of the column excitation, absolute sound levels were analytically calculated with results again in agreement with the measured values. These findings provide considerable new evidence to support the notion that bubble plumes can be a major source of underwater sound around frequencies of a few hundred hertz.
Ultrasonic nonlinear properties of lead zirconate-titanate ceramics
Authors: Na Jeong K. , Breazeale Mack A.
Published: October 2005

A systematic study of the nonlinear properties of lead zirconate-titanate (PZT) ceramics is presented. The velocity, attenuation, and nonlinearity parameter of PZT ceramics were measured from room temperature to temperatures above the Curie temperature. The velocity goes through a minimum near the Curie temperature. In spite of a maximum in attenuation near the Curie temperature, the nonlinearity parameter exhibits a maximum whose behavior is affected by polarization. Frequency dependence of the nonlinearity parameter at room temperature is reported for the first time. Large third harmonics of an initially sinusoidal ultrasonic wave at room temperature suggest that either the effect of the fourth-order elastic constants is anomalously large or that the nonlinear equation used to describe the behavior of single crystals is only approximately valid for description of PZT. Strain gradients are assumed to cause the frequency dependence of the nonlinearity parameter as well as the large third harmonic.
Attenuated leaky Rayleigh waves
Authors: Qi Quan
Published: October 2005

The propagation of leaky Rayleigh waves under the influence of viscous damping and heat conduction in boundary layers is studied using the matched asymptotic method. Viscosity of the fluid is considered unimportant except in a thin viscous boundary layer at the interface. A new characteristic equation is obtained in which the effect of boundary layer is shown by terms associated with R−1/2=(ων)1/2/ct, where R is the Reynolds number, ω is the frequency, ν is the kinematic viscosity of the fluid, and ct is the shear velocity of the solid substrate. One of the numerically obtained solutions gives the leaky Rayleigh wave speed and the attenuation coefficient. It is shown that, together with radiation, viscosity and heat conduction in the boundary layer also affect the attenuation of the leaky Rayleigh waves. Furthermore, it is shown that, because of the effect of the viscous boundary layer, the attenuated leaky Rayleigh wave speed can be smaller than the Rayleigh wave speed at the interface of a vacuum and a solid substrate. A critical Reynolds number of about 2500 is found beyond which a viscous boundary layer stops influencing leaky Rayleigh wave propagation. Finally, a new wave mode sustained by the viscous boundary layer alone is found in the limit of a small fluid–solid density ratio. This mode exists for appropriate frequency and layer thickness combinations. For air, the corresponding propagation speed is shown to be higher than the sound speed and the corresponding attenuation is significant. These results may be used to improve our interpretation of acoustic signature of materials.
Determinations of anisotropic elastic constants using laser-generated surface waves
Authors: Chai J.-F. , Wu T.-T.
Published: October 2005

This paper studied the recovery of elastic constants of anisotropic solids from measured surface wave energy velocities. The calculations of surface wave phase and energy velocities of anisotropic solids were based on an efficient forward formalism. In the experiment, the surface waves were generated by a pulsed laser and detected by using the PS/PR technique, where the source and receiver were located on the same surface of a specimen. The inverse problem was solved successfully by the simplex optimization method. Following the simplex iteration rules, the orientation and the elastic constants can be recovered from the measured surface wave energy velocities. The wave fronts and the caustic effects of the skimming shear waves have also been observed in the laser ultrasound experiment.
Advanced time domain wave-number sensing for structural acoustic systems. I. Theory and design
Authors: Maillard J. P. , Fuller C. R.
Published: October 2005

This paper discusses new work concerned with developing structural sensors and associated signal processing techniques that provide time domain estimates of far-field pressure or structural wave-number information. The sensor arrangement consists of multiple accelerometers whose outputs are passed through an array of linear filters. The impulse response of each filter is constructed from the appropriate Green’s function for the elemental source area associated with each sensor. The outputs of the filter array are then summed in order to predict far-field pressure or wave-number information somewhat analogous to the well-known boundary element technique. A major significance of the approach is that it provides time domain information and can thus be efficiently applied to active structural acoustic control approaches.
Transient waves in a thick disk
Authors: El-Raheb Michael , Wagner Paul
Published: October 2005

Transient elastic waves in a free thick disk are analyzed by a modal method. Eigenfunctions are determined by applying the Galerkin technique to trial functions which satisfy the differential equations and shear free conditions on all boundaries. The disk is forced concentrically by a trapezoidal pulse of short duration. The excitation is treated in two ways. The first approximates normal pressure by a body force acting over a vanishingly thin layer adjacent to the boundary. The second superimposes an inhomogeneous static problem on a homogeneous dynamic problem. In this way, stress close to the excitation is modeled accurately. Transient stress history matches closely that from a finite element and a finite difference simulation.