bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of a rough seabed on the spectral composition of deep ocean infrasonic ambient noise
Authors: Liu Jin-Yuan , Schmidt Henrik , Kuperman W. A.
Published: October 2005

In deep water, the vertical separation of surface noise sources from the elastic bottom is too large for direct excitation of the experimentally observed seismic interface waves in the frequency regime 1–10 Hz. It is here proposed that these strong seismic components are generated by scattering at rough elastic interfaces in the bottom, thereby coupling the noise field produced by the primary surface sources into evanescent waves in the bottom. This hypothesis is investigated by combining a previously developed perturbation theory of rough interface scattering with a model for surface generated noise in a stratified ocean environment. The resulting theory predicts a spectral composition of the noise field near the seabed that is consistent with the spectral structure of relevant seismic noise data recently collected in the Pacific. The present analysis, in combination with earlier analysis of a data set gathered in a shallow-water region, makes it quite clear that waveguide propagation mechanisms have an extreme coloring effect on the spectral shape of ocean ambient noise; hence, these mechanisms must be subtracted from measured noise data before inferring the spectral level of surface noise sources.
Scattering by an open sphere: Exact solution and comparison with a boundary integral method
Authors: Elias Georges , Malbéqui Patrice
Published: October 2005

The objective of this paper is to extend the amount of exact solutions for acoustic scattering configurations available to validate numerical methods. The configuration chosen is the radiation of an acoustic point source located at the center of a rigid spherical shell having a circular aperture. In comparison to standard scattering problems, like diffraction of a plane wave by a closed sphere, this problem implies a more severe geometry including a sharp edge. The exact solution is derived using an expansion of the pressure field in terms of spherical Bessel functions and Legendre polynomials. The associated coefficients are the solution to an infinite linear system. The truncation of this system as a function of the reduced wave number ka is discussed. It is found that the system is stable with regard to the truncation and that only 4×ka coefficients are needed to get an accurate solution. Comparisons are made with solutions obtained using a boundary integral method developed by Hamdi [‘‘Formulation variationelle par équations intégrales pour le calcul de champs acoustiques linéaires proches et lointains,’’ doctoral thesis, Université de Compiègne (1982)]. A good agreement is obtained for various frequencies and aperture sizes (relative differences in the far field are of about 1%).
Scattering of longitudinal waves by a cylindrical cavity in an attenuating solid
Authors: Kim Yu-Man , Lee Byung-Ho , Ih Jeong-Guon
Published: October 2005

This paper deals with the scattering of plane longitudinal elastic waves incident normally on a cylindrical cavity in a solid medium with attenuation. The scattered fields are found by introducing complex wave numbers whose imaginary parts are given by the attenuation coefficients of the solid medium. The impulse responses of the scattered displacement field at various positions of the receivers are obtained. It is seen that the impulse responses in an attenuating medium are different from those in a medium with negligible attenuation. To verify the accuracy of predicted impulse responses, experiments have been carried out for aluminum and acryl specimens as a typical nonattenuating medium and an attenuating one, respectively. Experimental results are in good agreement with predicted ones. Using the results of this study, once the input waveform and the attenuation coefficients are known, it is possible to predict the waveforms of longitudinal waves scattered by a cylindrical cavity. It is also found that the impulse responses of scattered waves can be applicable to finding the size and the position of the cylindrical cavity in a solid.
Approximations for the two-dimensional Green’s function of a fluid-loaded plate
Authors: Photiadis Douglas M.
Published: October 2005

Simple analytical formulas to predict the acoustic component of the two-dimensional (2-D) Green’s function of a fluid-loaded plate are presented. The formulas do not require any side computations such as numerical zero finding or numerical integrations. The simplest result obtained provides a good estimate of the Green’s function for a very broad range of frequencies, being degraded only near the coincidence frequency. A somewhat more complicated formula, almost uniformly valid in frequency, and yielding reasonable accuracy even at coincidence, is also presented. Numerical results comparing the asymptotic approximations to the ‘‘exact’’ Green’s function are presented, and show significant improvement over a basic steepest descents based approximation. For large values of x, very high accuracy can be achieved with relative errors of less than 0.1%. For other less stringent applications the approximations are accurate to within 10% at fairly small distances from the source, requiring only kfx>1 and k0x>0.5.
Self and mutual time-dependent interaction forces between ultrasonic transducers—Application to the computation of radiation impedances
Authors: Cassereau Didier , Guyomar Daniel
Published: October 2005

In this paper, diffraction theory is used to describe the self and mutual time-dependent interaction forces between ultrasonic transducers. This concept is interesting since it is equivalent, up to a temporal Fourier transform, to the radiation impedance. The formalism allows a description of self and mutual radiation impedances in terms of the aperture functions of the emitter and the receiver, and this description does not suppose that the transducers work in the piston mode. Then, the formalism is used to retrieve the well-known results about the radiation impedance of a circular piston. Finally, the mutual radiation impedance between two transducers is analyzed, and the particular case of small transducers compared to the wavelength is discussed. The results are similar to those obtained by Stepanishen and Pritchard [R. L. Pritchard, J. Acoust. Soc. Am. 32, 730–737 (1960); P. R. Stepanishen, ibid. 49, 283–292, 841–849 (1971)], except that the results here exhibit a correction term that increases the validity domain of the approximations.
Standing wave tube testing of sound intensity probes
Authors: Guy R. W.
Published: October 2005

To ensure correct measurements of sound intensity in standing wave fields with particular respect to probe construction influences, a standing wave field performance test would be a useful addendum to a standard addressing instruments for the measurement of intensity. A recent analytical development describing peak-to-peak (P–P) measurements at discrete frequencies within standing waves is employed here to suggest elements of a suitable test procedure.
Marching acoustic fields in a phase space
Authors: Steinberg Ben Z. , McCoy John J.
Published: October 2005

A novel approach that explicitly incorporates the interpretation of sound propagation as an ordered sequence of local events is presented. The new framework is based on a wedding of two methodologies. The first is the methodology of sequential ordering of events, governed by the marching of a radiation field. The second is the resolution of a wave field to transversely local events, governed by windowed, or phase space, transformations. The advantage of the new approach is that it requires a description of that portion of the environment that affects the localized event and only at the ‘‘time’’ of occurrence of that event. The properties of the new framework are investigated analytically and demonstrated by numerical examples.
Source signature and elastic waves in a half-space under a semicircular source of a normal impulsive cosine load
Authors: Ziv M.
Published: October 2005

The half-space elastic response to a source of a nonuniformly spatially distributed impulsive normal load is presented in this paper. Specifically, an infinite semicircular canyon of a finite radius is embedded in the surface of the half-space where an impulsive cosine load is radially distributed over the entire surface of the canyon. The spatial distribution of this load is such that the load is maximum at the stress-free boundary of the half-space and then descends smoothly to zero at the axis of symmetry of the half-space. In earlier works, the author gave an analytical-numerical method for transient multicurvilinear dimensional boundary-value problems and its employment to nonuniformly spatially distributed loads. Here, the resultant transient deformation of the half-space under a cosine load is described and interpreted. In particular, a detailed discussion is devoted to the appearance of spatially stationary strong discontinuity fronts in the interior of the deformed half-space. These fronts, which disclose the nature of the prescribed source of disturbance, are the source signature. A complete account is then given of the waves emitted from the source signature and those generated by boundary conditions, all revealing themselves explicitly by the solution method.
Active control of acoustical beamforming with an electrode array on a piezoelectric rubber composite
Authors: Park Joseph C. , Neelakanta Perambur S.
Published: October 2005

An ‘‘active’’ method of controlling acoustical beamforming with a linear array of electrodes configured on a composite piezoelectric rubber sheet is demonstrated. The active control is achieved by applying a dc bias on the electrode elements. The electroded regions of the piezorubber sheet exhibit piezoelectric activity proportional to the magnitude of the bias. By selectively biasing the electrodes, the corresponding locales of the array are forced to be active or inactive (piezoelectrically) for electroacoustic synergism. The ability to control the piezoelectric response of individually electroded regions provides a method to change the wave vector response of the electroacoustic transducer array. Tailored beamforming is therefore, made plausible with appropriate dc bias applied to selective electrodes. This ‘‘active’’ method could be useful in ‘‘smart’’ beamforming strategies and ‘‘active’’ control of vibrations. Test results on a prototype sample are presented as the proof of the concept.
Comparison of the Rayleigh and T-matrix theories of scattering of sound from an elastic shell
Authors: Kazandjian Luc
Published: October 2005

The Rayleigh and T-matrix mathematical formalisms of scattering of sound from an elastic shell are established and compared. It is shown that the two formalisms have a unique solution and are theoretically equivalent when used to calculate the pressure field sufficiently far away from the obstacle. From a numerical point of view, the closeness of the results obtained with the two methods does not depend on the validity of the Rayleigh hypothesis. These results enable one to analyze the validity of the wave superposition and retracted boundary integral formalisms when the auxiliary retracted surface is located inside the inscribed sphere. Some comments are made about the numerical results expected from these methods.
Slow wave propagation in air-filled permeable solids
Authors: Nagy Peter B.
Published: October 2005

The propagation of slow compressional waves in air-saturated permeable solids was studied by experimental means between 10 and 500 kHz. The velocity and attenuation coefficient were measured as functions of frequency from the insertion delay and loss of airborne ultrasonic waves transmitted through thin slabs of 1–5 mm in thickness. Porous ceramics of 2–70 Darcy and natural rocks of 200–700 mDarcy permeability were tested. In the low-frequency (diffuse) regime, the experimental results are consistent with theoretical predictions; the phase velocity and attenuation coefficient are essentially determined by the permeability of the specimen and both increase proportionally to the square root of frequency. In the high-frequency (propagating) regime, the experimental results are consistent with the theoretical predictions for the phase velocity but not for the attenuation coefficient. The phase velocity asymptotically approaches a maximum value determined by the tortuosity of the specimen while the attenuation coefficient becomes linearly proportional to frequency instead of the expected square-root relationship. It is suggested that the observed discrepancy is due to the irregular pore geometry that significantly reduces the high-frequency dynamic permeability of the specimens.
Ultrasonic tomography using scanned contact transducers
Authors: Jansen D. P. , Hutchins D. A. , Young R. P.
Published: October 2005

Ultrasonic tomographic images have been obtained from objects of rectangular cross section by scanning spring-loaded transducers across the sample faces. Hemispherical brass caps, placed on each transducer, facilitated sliding along the surface. The complete system was under the control of a microcomputer, resulting in an entirely automatic data collection system. Selected images obtained from this system are presented for metal and rock samples, as well as samples with artificial anomalies.
On the existence of stationary nonlinear Rayleigh waves
Authors: Hamilton M. F. , Il’insky Yu. A. , Zabolotskaya E. A.
Published: October 2005

The existence of stationary nonlinear Rayleigh waves is investigated theoretically on the basis of new model equations for the propagation of finite amplitude Rayleigh waves in isotropic solids [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569–2575 (1992)]. The spectral components of the proposed stationary waveforms are governed by coupled quadratic algebraic equations that are similar in form to those used by Parker and Talbot [J. Elast. 15, 389–426 (1985)]. However, whereas the theoretical investigation of Parker and Talbot predicted the existence of stationary nonlinear Rayleigh waves, the present investigation does not, unless artificial constraints are imposed on the frequency spectrum. Differences between nonlinearity in Rayleigh wave propagation in isotropic solids and nonlinearity in sound wave propagation in fluids is briefly discussed.
The determination of the acoustic far field of a radiating body in an acoustic fluid from boundary measurements
Authors: Borgiotti Giorgio V. , Jones Kenneth E.
Published: October 2005

The far field (FF) of a radiating or scattering object immersed in an acoustic fluid can be represented in the frequency domain as a finite dimension linear combination of basis functions, which are determined by the shape and the size of the object in acoustic wavelengths. The coefficients of the linear combination are obtained as the outputs of a bank of spatial filters whose inputs are either the boundary normal velocity—for the radiation problem—or the boundary pressure and the normal velocity—for the scattering problem—measured by a dense set of sensors. The filter outputs provide the information sufficient to reconstruct the radiated or scattered far field, amplitude and phase. The structure of the filters is identified from the singular valve decomposition of the appropriate radiation or scattering operator, mapping the boundary normal velocity, or the combination of normal velocity and pressure, into the FF. Also, from the filter outputs, the efficiently radiating component of the boundary field can be extracted. For example the boundary total normal velocity may have a localized high peak, which however may be completely or almost completely absent in the radiating component. Selected results of an extensive simulation are presented illustrating the accuracy of the reconstruction of the FF from the spatial filtering of the boundary field.
Monostatic and bistatic reverberation results using linear frequency-modulated pulses
Authors: Preston John R. , Kinney Wayne A.
Published: October 2005

Estimates of reverberant scattering strength are presented as a function of range and bearing for selected monostatic and bistatic geometries of a reverberation experiment. Diffuse scattering strengths were found to be comparable (within ∼3 dB) for both monostatic and bistatic geometries. This experiment was performed off the west coast of Sardinia in approximately 2800 m of water during February of 1990. The receiver was a horizontal array of approximately 20 wavelengths. Source and receiver depths ranged from 50 to 120 m. The signals used consisted of linear frequency-modulated (FM) pulses centered near 1 kHz with durations ranging from 8 to 16 s and bandwidths ranging from 32 to 64 Hz. Monostatic and bistatic scattering strength values are estimated using uncorrelated (i.e., not match-filtered) pulses. The scattering strengths presented vary from −29 to −48 dB for ranges up to 40 km (but not data near fathometer returns). A method is described that shows different correlator gains against noise and reverberation. Comparisons of measured and modeled reverberation are presented using the generic sonar model (GSM) and curve fits with the decay in monostatic diffuse backscatter show good agreement with Lambert’s rule using a −32 dB constant. Finally, GSM is used to estimate grazing angles from which plots of measured scattering strength versus grazing angle in the 10°–26° interval are presented. Using this method, a Lambert’s rule constant of ∼−30 dB was a better fit to the data.
Performance stability of high-resolution matched-field processors to sound-speed mismatch in a shallow-water environment
Authors: Smith G. B. , Chandler H. A. , Feuillade C.
Published: October 2005

The effects of variations in water sound-speed parameters on the performance of four matched-field processing algorithms (Bartlett, maximum-likelihood, sector-focusing, and multiple constraint) have been investigated. The SNAP propagation model was used to generate the replica acoustic pressure field for a shallow water channel with a depth variable sound-speed profile typical of a midlatitude summer environment. It was also used to simulate a ‘‘detected’’ field due to an acoustic source. These were then correlated using the four algorithms for selected degrees of mismatch of the water sound-speed profile. The maximum likelihood and multiple constraint estimators achieved good peak resolution and high accuracy for small degrees of mismatch. The maximum likelihood estimator deteriorated quickly as the mismatch increased. The multiple constraint estimator performed significantly better, but both failed to give correct location estimates at the higher mismatch values. In contrast, the sector focusing estimator continued to give accurate location estimates over the whole range of sound-speed mismatch, with slightly less peak resolution at small mismatch values. It also performed significantly better overall than the Bartlett estimator, which was found to give accurate location estimates over the whole range of mismatch values used, but with poor peak resolution against a background containing many high sidelobes.
Backscattering of chirped bursts by a thin spherical shell near the coincidence frequency
Authors: Kaduchak Gregory , Marston Philip L.
Published: October 2005

Previous ray calculations and observations [L. G. Zhang, N. H. Sun, and P. L. Marston, J. Acoust. Soc. Am. 91, 1862–1874 (1992); G. Kaduchak and P. L. Marston, J. Acoust. Soc. Am. 93, 224–230 (1993)] have shown that tone bursts with a carrier frequency ka close to the coincidence frequency of a thin spherical shell in water exhibit a backscattering enhancement. A distinct feature associated with the a0− guided wave was enhanced relative to the specular reflection by a factor close to 3.1. In the present research, a Fourier synthesis from the partial wave series is used to investigate how chirping the frequency of the incident burst influences the enhancement. An enhancement is still evident even when the incident burst is swept through the entire ka range of interest sufficiently rapidly for the specular and guided wave echoes to remain distinct. The enhancement is larger when ka is swept from high-to-low than from low-to-high. This is a consequence of a decrease in the group velocity with ka resulting in a localization of the echo for the high-to-low sweep. The enhancement can now exceed the aforementioned value of 3.1 and should increase the signal-to-noise ratio. Experimental records confirm the effect on a real shell.
When feeling is failing: The effects of aging on the sense of touch
Authors: Verrillo Ronald T. , Gesheider George A. , Bolanowski Stanley J. , Hoffman Kathryn E.
Published: October 2005

The vast majority of reports in the literature concerning the psychophysical characteristics of touch is based on studies of college-aged persons. If the skin is to be utilized as a surrogate channel of communication for the profoundly deaf, it is essential that one know how aging affects the sense of vibrotaction. Life-span studies are rare indeed although there is a recent intensified interest in the sensory systems of elderly persons. Being reported are the results of a research program showing changes, from childhood to the elderly, of the threshold of detectability, suprathreshold responses, gap detection, and temporal and spatial summation. The Pacinian system shows a general decline with age and ‘‘recruitment’’ in the growth of sensation magnitude. Changes are also noted in gap detection and in the capacity to summate over time and space. [Work supported by NIDCD-DC01243.]
A unified approach to acoustical reflection imaging. III: Extension to the elastic situation
Authors: Wapenaar C. P. A. , Berkhout A. J.
Published: October 2005

The forward model, as derived in part I [A. J. Berkhout, J. Acoust. Soc. Am. 93, xxx (1993)], and the inversion scheme, as derived in part II [A. J. Berkhout and C. P. A. Wapenaar, J. Acoust. Soc. Am. 93, xxx (1993)], are extended to the elastic situation. The elastic forward and inverse problem are formulated in terms of matrices, similar as in the acoustic situation. Unlike in the acoustic situation, the matrices involved in the elastic problem each consist of 3×3 submatrices. For instance, the submatrices of the multi-component data matrix V represent single-component data matrices, each submatrix being related to a specific combination of source and receiver components. On the other hand, the submatrices of the multi-wavetype reflection matrix R± represent single-wavetype reflection matrices, each submatrix being related to a specific combination of incident and reflected wavetypes. In the discussion of the elastic forward model the multi-component data matrix V at the acquisition surface is related to the multi-wavetype reflection matrices R± in the subsurface. In the discussion of the inversion scheme it is shown how R± is obtained step by step from the multi-component data matrix V. Once the multi-wavetype reflection matrices R± have been determined the medium parameters can be much better resolved than in the acoustic situation.
Temporal integration for array processing
Authors: Le Cadre Jean-Pierre , Zugmeyer Olivier
Published: October 2005

This paper deals with the study of the performance of array processings in the presence of moving sources. A simplified model of the spatial frequencies of a moving source is derived for the first time. It allows one to obtain analytical formulation of the variance of the estimated source bearings and of the probability of detection. A major parameter for the optimization of the (classical) array processing performance is the optimal integration time. It is related to the cinematic parameters of the (moving) source and to the array length. It is thus shown that the gain in array performance expected by increasing the sensor number can be severly degraded by the source motions. This analysis stresses the importance of the use of a suitable integration time. Under very simple hypotheses (e.g., a unique source with known motion parameters) the optimal integration time (for classical criteria) can be analytically calculated. In the general case, i.e., multiple sources with unknown motion parameters, the analytical results cannot be strictly applied; however they are still relevant to a wide class of practical problems such as contact loss, source crossings, sources with partially known parameters, etc. For all these problems, the aim of this paper consists mainly in defining a general frame for incorporating the source motion into the calculation of the array processing performance and trying thus to optimize it.
A life-sized physical model of the human cochlea with optical holographic readout
Authors: Zhou Gan , Bintz Louis , Anderson Dana Z. , Bright Kathryn E.
Published: October 2005

A life-sized physical model of the human cochlea is demonstrated. The model consists of two fluid-filled chambers separated by a polymer membrane and connected through a small hole that serves the same functional purpose as the helicotrema. The dimensions of the two chambers were made identical to those of scala vestibuli and scala tympani in the real cochlea. The membrane’s width and length are the same as the values measured for the biological basilar membranes, and its thickness is chosen to give it appropriate rigidity. A piezoelectric transducer drives the system via an elastic window (acting as the oval window) on one side of the scala vestibuli. The resulting vibration pattern on the basilar membrane is investigated with an optical novelty filter, with detection sensitivity of 0.3 Å at 2 kHz with a 1-Hz bandwidth. The overall response of this model is found to be a good extrapolation of Bekesy’s low-frequency data. However, the tuning curves of this model are not as sharp as those found by Rhode, Johnstone, and others from the in vivo measurements. Possible implications of these results are discussed.
Effect of the acoustic boundary layer on a nonlinear quasiplane wave in a rigid-walled tube
Authors: Makarov Sergey N. , Vatrushina Elene V.
Published: October 2005

A boundary condition for nonlinear quasiplane wave propagation in a wide tube is given taking into account Stokes boundary layer effects. Wave motion is described by the Khokhlov–Zabolotskaya–Kusnetzov equation. An asymptotic scheme for the solution is based on matching acoustic and boundary layer expansions. In the case of plane motion, the model is reduced to the generalized Burgers equation obtained previously by Blackstock. Numerical results and comparison with experiment are demonstrated. The latter shows that there is good agreement in general, although some specific details are still unclear.
Factors influencing the length change of an auditory outer hair cell in a tight-fitting capillary
Authors: Iwasa K. H. , Chadwick R. S.
Published: October 2005

A membrane theory with area and shear moduli is used to interpret an experimental configuration used by Zenner et al. [Acta Otolaryngol. 112, 248–253]. In that experiment an outer hair cell is drawn into a tight-fitting glass capillary and a negative pressure is applied to characterize the elasticity of the cell. Various assumptions concerning membrane permeability and wall friction, which cannot readily be evaluated, are needed to interpret the data obtained in that experiment. For this reason only an upper bound of the elastic moduli, corresponding to vanishing wall friction and basal end flow conductance, can be obtained from their experimental design. In this limit, the experimental data obtained by Zenner et al. do not contradict the values of elastic moduli previously determined by internal pressurization of the cell.
Ultrasonic backscattering from solid cylindrical inclusions in solid elastic matrices: A comparison of theory and experiment
Authors: Beattie P. , Chivers R. C. , Anson L. W.
Published: October 2005

The problem of ultrasonic backscattering of longitudinal and shear waves normally incident on a solid cylindrical scatterer embedded in a solid matrix is studied both theoretically and experimentally. Calculations of the backscatter form function, f∞(θ,ka), as a function of ka are compared in the range 2.0<ka<9.0 with experimental measurements (using a short pulse-echo technique) in the same range for both copper and steel inclusions embedded in an epoxy matrix. The results show very good agreement between theory and experiment highlighting NDE and material characterization applications.
T-matrix implementation of forward scattering from rigid structures
Authors: Sarkissian Angie , Gaumond Charles F. , Dragonette Louis R.
Published: October 2005

The T-matrix method is applied to compute forward scattering from rigid structures. The method requires evaluation of matrix elements Qmmlk whose imaginary parts with l<k are difficult to evaluate for long, slender, nonellipsoidal structures because the evaluation involves integrations of large oscillatory functions. A new approach for the evaluation of these elements is shown for finite cylinders where the antisymmetric part of the matrix is written in a form involving integrals that are easier to compute. Forward scattering results are shown for spheroids and cylinders with spheroidal endcaps where the length of the cylindrical section is shown to have little effect on forward scattering. The magnitude of the forward scattering at the high-frequency limit is seen to be proportional to the cross-sectional area, which is in agreement with the high-frequency Kirchhoff approximation.
Comments on ‘‘A solution to the longstanding problem involving error analysis of Fourier transform-based, diffractive computation’’ [J. Acoust. Soc. Am. 94, 3515 (1993)]
Authors: Hah Zae G.
Published: October 2005

Christopher’s comments have little critique since the paper in question deals with spatial domain and not frequency domain.
Reaction times to unidirectional frequency changes: A test of Zwicker’s excitation-pattern model
Authors: Ellermeier Wolfgang , Emmerich David S.
Published: October 2005

A reaction-time methodology was used to evaluate excitation-pattern models of frequency discrimination. These models assume that in order to detect frequency changes, the auditory system actually monitors intensity changes in the filter array along which the excitation pattern is shifted. According to Zwicker’s model, it is along the steep low-frequency slope of the excitation pattern that small frequency changes will be detected. Consequently, small downward shifts in frequency should produce an increment in excitation in the filter monitored, while upward shifts should be associated with a decrement in activity in that filter. Since simple auditory reaction time (RT) is differentially sensitive to increments and decrements in intensity, it seems particularly suitable to studying this conceptualization. In experiment 1, it was demonstrated that increments in intensity elicit faster responses than decrements of equal magnitude. Experiment 2 found that when subjects had to respond to small changes in frequency on the order of 4–20 Hz, reaction time to upward shifts in frequency was faster than reaction time to downward shifts by about 20 ms. This asymmetry, however, rapidly reduced to zero when the magnitude of the frequency shift was made larger, as demonstrated in experiment 3. While these results are inconsistent with the idea that increments and decrements in excitation level in a single channel tuned to the low-frequency slope of the excitation pattern determine frequency-discrimination performance, they can be accounted for when it is assumed that listeners monitor more than one channel to detect a frequency change. Further support for this notion was found in experiment 4 in which parts of the excitation pattern were selectively masked.
Self-suppression in a locally active nonlinear model of the cochlea: A quasilinear approach
Authors: Kanis Luc J. , de Boer Egbert
Published: October 2005

Mechanical input–output functions of the cochlea for pure-tone stimuli are nonlinear for frequencies around the characteristic frequency. To simulate these functions, a long-wave model of the cochlea containing a saturating pressure generator (located at the site of the outer hair cells) is solved in the frequency domain with a quasilinear method. In this method distortion products in the basilar-membrane (BM) response are treated as perturbations and the nonlinear pressure waveform is approximated by the first-order Fourier component. Because the saturating pressure generator forms part of a feedback loop the solution of the model is achieved in a number of iteration steps. Model results show flattening of the BM response at higher input pressures; this property, called self-suppression, is due to saturation of the pressure generator. The resulting input–output functions display the main features of experimental curves. The third-order distortion product in the BM velocity is always more than 25 dB below the primary BM velocity and does not influence the results of the computation; this justifies the use of the quasilinear method.
A stochastic model for scattering from the near-surface oceanic bubble layera)
Authors: Gilbert Kenneth E.
Published: October 2005

A stochastic scattering model is derived in which the backscatter from the near-surface oceanic bubble layer is written directly in terms of an integral over the wave-number spectrum (‘‘power’’ spectrum) of the sound-speed fluctuations in the layer. A factored form is given for the integral that allows the backscatter cross section per unit area to be expressed as the product of a ‘‘geometric factor’’ and an effective horizontal wave-number spectrum. Because a power spectrum formulation is statistical, there are no assumptions about the geometry of the bubble layer (e.g., hemispherical or cylindrical plumes are not assumed). By dividing measured data for backscatter versus frequency by the geometric factor, scattering data from 12 different deep-ocean reverberation measurements were inverted, and the wave-number spectrum of the sound speed in the bubble layer was directly inferred. For all 12 measurements, the inferred wave-number spectrum is an inverse power law of the form P(K)=AK−β, where A is a strength parameter, K is the horizontal wave number for a Fourier component of the sound-speed distribution, and the mean value of the spectral roll-off exponent β is 3.86±0.45. The consistency in the inferred wave-number spectrum strongly suggests that on scales of less than half an acoustic wavelength (5 to 10 m), the sound-speed structure in the bubble layer is governed by turbulence in the inertial subrange (Kolmogorov subrange) which has a universal value of β=11/3=3.67 for fully developed isotropic turbulence. Using Von Karman’s interpolation formula for Kolmogorov turbulence, together with oceanographically constrained input parameters, theoretical backscatter cross sections were computed and compared with the empirical fits of Ogden and Erskine to Critical Sea Test data. It is shown that with no adjustable parameters, the stochastic scattering model gives a good account of the observed backscatter, as a function of both frequency and grazing angle.
Environmental source tracking
Authors: Collins Michael D. , Fialkowski Laurie T. , Kuperman W. A. , Perkins John S.
Published: October 2005

Several matched-field processing (MFP) techniques have been developed for localizing a fixed acoustic source. Environmental source tracking (EST) is an approach for determining the track of a moving source. In addition to being attractive from a practical point of view, EST can determine source track in situations in which MFP cannot determine source position. The performance of MFP is limited by the number of propagating modes at the array location. EST can overcome this limitation by exploiting source motion and environmental complexity. For example, EST may be possible when the receiver is placed in a region of the ocean that supports only one propagating mode, a situation in which single-frequency MFP is impossible. MFP requires the use of either an array of receivers or multiple-frequency data. EST requires only a single frequency and a single receiver. Problems such as array deployment and array tilt, which are important with MFP, are therefore irrelevant with EST.
Acoustic scattering by elastic spherical shells that have multiple massive internal components attached by compliant mounts
Authors: Gaunaurd Guillermo C. , Huang Hanson , Wertman William
Published: October 2005

A study of the scattering of sound waves by a neutrally buoyant, submerged, spherical shell that has heavy masses internally mounted by springs to the shell is presented. The presence of the attached oscillating masses substantially changes the scattering cross section of the otherwise empty shell. Furthermore, if the compliance (i.e., the spring constants) of the mounts are varied—all else being the same—then the resulting cross section also varies substantially, often by more than an order of magnitude. It is seen that if the incident plane wave impinges upon the shell at its North pole, where the masses are mounted, then the effect of the spring-mass system on the scattering response is strongest. Away from the North pole, this effect weakens; when the incidence is from the South pole, it is weakest. In general, the cross-sectional distortion produced by the attached masses consists of a set of amplitude-modulated resonance features that are computed and displayed in a number of instances. These features seem to be confined around a frequency band containing the main resonances of the (coupled) oscillator formed by the masses. The shell motions are described by the bending theory and also by the exact elasticity theory. Comparing the two, it is possible to determine the limit of validity of the bending theory, which is seen to begin to fail just below the coincidence frequency for this shell. The ‘‘background’’ contribution is separated from the ‘‘resonance’’ contribution associated with the empty shell and also from that associated with the internal oscillator. This triple split, as emerging from a shell theory, does not seem to have been investigated in the past. (Bistatic) angular plots associated with peaks/dips in the backscattering cross section and some of the isolated and symmetric ‘‘rosettes’’ observable in selected cases are displayed. This analytic model is easily reproducible and does not require any special numerical code for evaluation.
Comparison between theory and model scale measurements of three-dimensional sound propagation in a shear supporting penetrable wedge
Authors: Glegg Stewart A. L. , Deane Grant B. , House Ian G.
Published: October 2005

Laboratory experiments have been carried out to investigate underwater sound propagation over a sloping bottom which can support shear. The model of the seafloor consisted of a sediment layer (modeled experimentally by epoxy) over a hard substrate made of concrete. The sound field was measured in both the across slope and downslope directions for various frequencies and bottom slopes. The experimental results have been compared with a new source image theory for sound propagation in an ocean wedge with an elastic (shear supporting) bottom and have shown very good agreement for both downslope and across slope propagation. In particular the effect of shear waves on across slope propagation has been demonstrated both theoretically and experimentally. Further, the effect of a sediment layer overlying a semi-infinite substrate has been successfully incorporated into the source image theory for comparison with the experimental measurements.
High-frequency forward scattering from the sea surface: Theory and experiments
Authors: Dahl Peter H.
Published: October 2005

Intensity and coherence properties of high-frequency sound forward scattered from the sea surface are discussed. Propagation of high-frequency acoustic energy often involves a sea surface bounce path. In deep water, and for many sonar acquisition geometries, a single surface bounce may be the best path to the target, because the direct path has faded owing to the sound speed structure. In shallow water, interaction with both the sea surface and bottom is often the rule. For frequencies above 10 kHz, incoherent surface scattering in the forward direction will usually dominate over coherent reflection because of the large sea surface roughness. The mean total energy of the scattered field is reduced by the extinguishing effects of the near-surface bubble field through which surface bounce paths must traverse. Coherence properties of the scattered field, e.g., spatial and temporal, can be related to the sea surface slope distribution and are also influenced by near-surface bubbles. Performance of detection and classification systems will depend on coherence properties, and in particular their degradation as a function of sea surface environmental conditions. Published theories on acoustic scattering from the sea surface in the high-frequency limit are discussed in the context of recent experimental measurements of sea surface forward scattering performed by the Applied Physics Laboratory in both inland water (Whidbey Island, Puget Sound) and open ocean conditions (R/P FLIP off California coast).
Sound propagation through a bubble screen
Authors: Hobbs Christopher M. , Kolaini Ali R.
Published: October 2005

Results of a laboratory experiment to characterize the sound propagation through a bubble screen are described. A bubble screen of various void fractions was positioned in the middle of an anechoic water tank. The cloud was driven using a broadband source and the acoustic pressure was measured on both sides of the layer. The results have revealed that there is significant attenuation near the resonance frequency of the bubbles contained within the screen. When the source frequency is near that of one of the ‘‘collective-oscillation’’ frequencies of the screen, sound pressure amplification may occur. In this paper the new findings corresponding to the collective mode amplification, high-frequency attenuation, as a function of the screen’s physical properties are discussed. [Work supported by ONR.]
Evaluating the articulation index for auditory-visual consonant recognition
Authors: Grant Ken W. , Walden Brian E.
Published: October 2005

The ANSI standard for calculating the articulation index [ANSI S3.5-1969 (R1986)] includes a procedure for estimating the effects of visual cues on speech intelligibility. This procedure assumes that listening conditions with the same auditory articulation index (AIA) will have the same auditory-visual AI (AIAV) regardless of the spectral composition of the signal. In contrast, other studies have suggested that the redundancy between A and V speech cues might be a better predictor of AV performance than either the AIA or the overall (e.g., percent correct) auditory recognition score. In the present study, the ANSI procedure is evaluated by measuring A, V, and AV consonant recognition under a variety of different signal-to-noise and bandpass-filtered speech conditions. The results indicate that auditory conditions having the same AIA do not necessarily result in the same AIAV, and that low-frequency bands of speech tend to provide more benefit to speechreading than high-frequency bands of speech. Analyses of the auditory error patterns produced by the different filter conditions showed a strong negative correlation between the degree of A and V redundancy and the AV benefit obtained. These data indicate that the ANSI procedure is inadequate for predicting AV consonant recognition performance under conditions of severe spectral shaping. [Work supported by NIH Grant No. DC00792.]
Relationship between identification errors and spectral details of naturally produced diphthongs
Authors: Nabelek Anna K. , Czyzewski Zbigniew , Crowley Hilary
Published: October 2005

In an earlier study [A. K. Nabelek etal., J. Acoust. Soc. Am. 92, 1228–1246 (1992)], identification errors were collected for 15 English vowels, monophthongs, and diphthongs. The vowels were produced in a /b–t/ context by six male talkers who uttered five tokens of each vowel. There were 20 normal-hearing and 20 hearing-impaired subjects. Listening conditions were quiet, noise, and reverberation. Large differences in number of errors were observed among the 30 tokens of each vowels. The goal of the current study was to determine relationships between the spectral details of the diphthongs /open ayei, open ohi, open ayeu/ and identification errors. Spectral analyses indicated that all three diphthongs had two distinct segments. In the first segment F1 and F2 were relatively steady state and in the second segment F2 changed over time. For each token of each diphthong, frequencies and levels of F1 and F2 were traced along the duration of the diphthong. The results of this analysis seem to indicate a relationship between the number of identification errors for these diphthongs and the relative levels of the F2 transition segment. Examples of highly identifiable and high confusable diphthongs will be shown. [This work was supported by NIDCD.]
The separate contribution of head-shadow and binaural interactions to directional hearing in noise
Authors: Nilsson Michael J. , Jayaraman Sriram , Soli Sigfrid D.
Published: October 2005

A replication of Bronkhorst and Plomp [J. Acoust. Soc. Am. 83, 1508–1516 (1988)] was undertaken to study the separate contributions of interaural level differences (ITDs); produced by head shadow, and interaural time differences (ITDs), which produce binaural interactions, to directional hearing in noise. Digital filtering of speech and noise signals was performed using head-related transfer functions (HRTFs) measured on a KEMAR mannequin to simulate sound field conditions under headphones. Speech materials from the hearing in noise test (HINT) were presented at a simulated 0-deg azimuth, while a noise signal matched to the spectral shape of the speech was filtered to include the ILDs and ITDs from either a 0-, 90-, or 270-deg presentation, including mixed combinations, e.g., 0-deg ILDs with 90-deg ITDs. Results from 19 normal hearing subjects showed the ILDs alone benefited the listener slightly more [3.97-dB improvement in sentence speech reception threshold (sSRT) versus a 0-deg condition] than ITDs alone (3.22-dB improvement in sSRT), as compared to 6.21-dB improvement in sSRT when both ILDs and ITDs are present. If the sSRT is calculated relative to the noise level in the shadowed ear, the ITDs alone produced the same sSRT as ITDs and ILDs together. Data from hearing impaired listeners will also be presented.
Three-dimensional modeling of acoustic pulse propagation through shallow water
Authors: Chapman Robert T. , McDowell Donald J.
Published: October 2005

A three-dimensional model capable of simulating the propagation, scattering, and reverberation of acoustic waveforms with an arbitrary time dependence is presented. The finite element method is used to model the spatial characteristics of the shallow water domain. An explicit integration scheme is used to obtain the time-dependent pressure field solution, for the entire computational space, due to a prescribed source function. Multiple independent sources, depth- and range-dependent bathymetry, volumetric scattering, fluid sediments, and scattering from irregular bottom topography may be considered with this modeling technique. As implemented, the computational scheme utilizes enhanced supercomputer vector processing, and an element-by-element storage strategy to enhance the computational efficiency and feasibility for the three-dimensional, time-dependent problems of interest. Computational results will be presented for the propagation of a finite duration pulse from a point source in deep water, up a sloping bottom, into shallow water. [Work supported by the NUWC IR and IED programs.]