bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite-element solution of the inverse problem in bubble swarm acoustics
Authors: Commander Kerry W. , McDonald Robert J.
Published: October 2005

The bubble population near the ocean surface is of considerable interest. This population affects surface scattering strength, propagation near the surface, and the exchange of gases between the atmosphere and the sea. Both optical and acoustical means have been used to measure the bubble population with varying degrees of success. The acoustic method requires measurements at multiple frequencies and their subsequent conversion to bubble densities through either the resonance theory approximation or numerical solution of the resulting integral equation. In this paper, a numerical solution to the integral equation is obtained using the method of weighted residuals with linear B splines as basis functions. A regularization technique is employed to stabilize the solution. A number of plausible bubble distribution functions are generated along with their acoustic properties to test the robustness of the technique. This approach is shown to yield very accurate bubble distributions from high-quality attenuation data.
A parametric study of cochlear input impedance
Authors: Puria Sunil , Allen Jont B.
Published: October 2005

In this paper various aspects of the cat cochlear input impedance Zc(ω) are implemented using a transmission line model having perilymph viscosity and a varying cross-sectional scalae area. These model results are then compared to the experimental results of Lynch et al. [J. Acoust. Soc. Am. 72, 108–130 (1982)]. From the model, the following observations are made about the cochlear input impedance: (a) Scalae area variations significantly alter the model Zc(ω); (b) the use of anatomically measured areas improves the fits to the experimental data; (c) improved agreement between model and experimental phase is obtained when perilymph viscosity and tapering are included in the cochlear model for frequencies below ≊150 Hz; (d) when model scalae tapering and perilymph viscosity are chosen to match physiological conditions, the effect of the helicotrema impedance on Zc(ω) is insignificant; and (e) the cochlear map, which is defined as the position of the basilar membrane peak displacement as a function of stimulus frequency, can have an important effect on Zc(ω) for frequencies below 500 Hz. A nonphysiological cochlear map can give rise to cochlear standing waves, which result in oscillations in Zc(ω). Scalae tapering and perilymph viscosity contribute significantly to the damping of these standing waves. These observations should dispel the previous notion that Zc(ω) is determined solely by parameters of the cochlea close to the stapes, and the notion that Zc(ω) is dominated by the helicotrema at low frequencies.
Coding of vibrotactile stimulus frequency by Pacinian corpuscle afferents
Authors: Horch Kenneth
Published: October 2005

Psychophysical and electrophysiological techniques were used to study the encoding and processing of information about the frequency content of vibrational stimuli applied to glabrous skin in humans and cats. Trained human subjects were asked to discriminate changes in stimulus frequency and harmonic content for pairs of mono- and diharmonic sinusoidal vibrations applied to the fingertips. These psychophysical tests supplied data on what information is available to the central nervous system about the frequency components of vibratory stimuli. Electrophysiological recordings from nerves innervating the glabrous skin of the paw in cats during presentation of the same stimuli used in the psychophysical study provided data on how the peripheral nervous system encodes information about the physical parameters of cutaneous vibratory stimuli. The two sets of data indicated that the subjects derived information about the frequency of vibrotactile stimuli from the mean interval between action potentials in afferent nerve fibers activated by the stimulus.
Wave-vector-time domain and Kirchhoff integral equation methods to determine the transient acoustic radiation loading on circular cylinders
Authors: Ebenezer D. D. , Stepanishen Peter R.
Published: October 2005

Two new methods are presented to determine the transient acoustic radiation loading on circular cylinders. The acoustic modal forces are expressed as a sum of the convolution of the modal radiation impulse responses and the modal velocities. In the wave-vector-time domain method, the modal radiation impulse responses are obtained by using the radiation impulse responses of an infinite cylinder and the modes in wave-vector space. The approach can thus be easily used for parametric studies on the effects of boundary conditions and normalized lengths on the modal radiation impulse responses. In the Kirchhoff integral equation method, space and time are discretized. The pressure and acceleration in each element are then expressed in the form of a Taylor-series expansion about points at which the pressure is obtained by marching forward in time. The radiation impulse responses of both infinite and simply supported finite cylinders are obtained by the two methods and compared.
Generation of fluctuating normal stress in a viscoelastic layer by surface shear stress and pressure as in turbulent boundary-layer flow
Authors: Chase David M.
Published: October 2005

At low wave numbers, according to recent indications, fluctuating wall shear stress generated by a turbulent boundary layer may be comparable with fluctuating wall pressure. Consideration is given here to the fluctuating normal stress generated within an elastic layer by both shear-stress and pressure excitation on its outer face. The transfer level from surface shear to normal stress is shown to be comparable with or exceed that from surface pressure in a significant range of low to intermediate wave numbers. This transfer from surface shear stress is enhanced by the outer fluid loading and by the imposition of vanishing displacement at an inner rigid surface. Results of computations are presented and analyzed in numerical examples based on a configuration where an elastomer layer is bounded by a fluid half-space at its excited surface and by a thin, damped plate at its inner surface, with a similar fluid half-space below the plate. Results are given also for the limiting cases of a rigid inner surface and of an elastic half-space with and without fluid loading. The transfer level from shear stress is computed also where a concomitant wall pressure is present and related to shear stress as recently determined from a theoretical treatment of the viscous boundary condition at low wave numbers in turbulent boundary-layer flow. It is thus suggested that the contribution of turbulent wall-shear stress to flow noise on recessed hydrophones in the absence of a plate-like element between these and the flow is likely an important one.
Measurement and calculation of acoustic propagation constants in arrays of small air-filled rectangular tubes
Authors: Roh Heui-Seol , Arnott W. Patrick , Sabatier James M. , Raspet Richard
Published: October 2005

An experimental and theoretical investigation of sound propagation in a porous sample composed of capillary tubes with rectangular cross sections is described in this paper. An experimental technique valid for low flow resistivity and high porosity porous samples was developed to measure the attenuation and phase velocity in the porous material. This technique uses transmission of a short pulse in a large tube through the porous sample and subsequent frequency domain analysis in the range 200–1300 Hz. Good agreement was obtained if an anomalous tortuosity factor of 1.1 is used in the theory. A scaling factor for relating cylindrical and square tube capillary theories, known as the dynamic shape factor, was investigated. Propagation constants computed from use of a near unity dynamic shape factor in the cylindrical pore theory agree favorably with calculations based on the square pore theory for the frequencies and pore radii used in the experiment.
Measurements of the effective nonlinearity parameter B/A of water containing trapped cylindrical bubbles
Authors: Wu Junru , Zhu Zhemin
Published: October 2005

The effective nonlinearity paramter B/A of water containing a three-dimensional ensemble of randomly distributed uniform-sized trapped cylindrical bubbles was measured. The experimental results indicate that the dramatic enhancement of the effective nonlinear parameter B/A is due to the nonlinear resonance oscillation of the trapped bubbles. The measured effective B/A for the system is of the magnitude of 104 to 105.
Transmission of sound beams through the interface between two fluids
Authors: Korneliussen Rolf J. , Hobaek Halvor , Lien Gunnar
Published: October 2005

In this article, results from an experiment on the transmission of a sound beam at and above critical incidence onto an interface between two fluids, which are chosen to simulate a water/sand interface, are presented. The incident beam is produced from a parametric array that is arranged to intersect the interface either within the absorption limit of the primary waves, or far outside the same, with the aim to discriminate whether linear or nonlinear processes are responsible for the transmission. Postcritical transmission is found to be basically a linear process, and is observed out to about 10° above the angle of critical incidence. Interference between the transmitted field and evanescent waves is observed just beneath the interface. The asymptotic axis of the main penetrating beam is investigated with respect to refraction angle and beam displacement. The field structure becomes markedly different if the primary waves are intersected by the interface, the main difference being the presence of a strong “underlobe” that has no direct counterpart in the incident field as measured in free field. This change in field structure is attributed to nonlinear effects, the candidates of which are discussed in detail. The most likely of these are the effects of primary beam truncation suggested by D. J. Wingham [“A theoretical study of the penetration of a water sediment interface by a parametric beam,” J. Acoust. Soc. Am. 76, 1192–1200 (1984)] and nonlinearity of the boundary conditions at the interface where the primary beams are intersected.
Effect of tooth backlash and ball bearing deadband clearance on vibration spectrum in spur gear boxes
Authors: El-Saeidy Fawzi M. A.
Published: October 2005

An analytical model is presented for studying the effect of tooth backlash and ball-bearing deadband clearance (clearance between bearing outer ring and its housing) on vibration spectrum of spur gear boxes. Included in the model are coupled torsional-lateral vibrations of the shafts, time-varying tooth backlash (backlash is a function of operating center distance), mesh stiffness (stiffness is calculated based on the bending, shear, axial, and Hertzian contact strain energies of the tooth that is treated as a cantilever of involute shape), and Hertzian damping at mesh, friction between meshing teeth, and interaction between gear box casing and internals. The bearing–housing reaction forces are calculated with consideration of bearing clearance and system vibrations. The above parameters are accounted for with allowance for number of teeth pairs sharing the load to alternate between one and two. The analysis is applied to a single stage gear box and equations of motion are deduced using Newton’s laws of motion and numerically integrated using Runge–Kutta method. The gear box casing velocities in time domain are transformed into frequency domain (vibration spectrum) using Fast Fourier Transform (FFT). This was done for different values of tooth backlash and bearing clearance and samples of the results are shown. This model provides an analysis procedure for predicting effect of tooth wear (wear affects backlash) and bearing deadband clearance on gear box vibration spectrum.
Performance of hearing-impaired persons on auditory enhancement tasks
Authors: Thibodeau Linda M.
Published: October 2005

An auditory enhancement effect was evaluated in normal and hearing-impaired persons using a paradigm similar to that used by Viemeister and Bacon [J. Acoust. Soc. Am. 71, 1502–1507 (1982)]. Thresholds for a 2000-Hz probe were obtained in two forward-masking conditions: (1) the standard condition in which the masker was a four-component harmonic complex including 2000 Hz, and (2) the enhancing condition in which the same harmonic complex except for the exclusion of the 2000-Hz component preceded the four-component masker. In addition, enhancement for speech was evaluated by asking subjects to identify flat-spectrum harmonic complexes that were preceded by inverse vowel spectra. Finally, suppression effects were evaluated by measuring forward-masked thresholds for a 2000-Hz probe as a function of suppressor frequency added to a 2000-Hz masker. Across all subjects, there was evidence of enhancement and better vowel recognition in those persons who also demonstrated evidence of suppression; however, two of the normal-hearing persons demonstrated reduced enhancement yet normal suppression effects.
Effect of different types of auditory stimulation on vowel formant frequencies in multichannel cochlear implant users
Authors: Svirsky Mario A. , Tobey Emily A.
Published: October 2005

Two experiments investigating the effects of auditory stimulation delivered via a Nucleus multichannel cochlear implant upon vowel production in adventitiously deafened adult speakers are reported. The first experiment contrasts vowel formant frequencies produced without auditory stimulation (implant processor OFF) to those produced with auditory stimulation (processor ON). Significant shifts in second formant frequencies were observed for intermediate vowels produced without auditory stimulation; however, no significant shifts were observed for the point vowels. Higher first formant frequencies occurred in five of eight vowels when the processor was turned ON versus OFF. A second experiment contrasted productions of the word “head” produced with a FULL map, OFF condition, and a SINGLE channel condition that restricted the amount of auditory information received by the subjects. This experiment revealed significant shifts in second formant frequencies between FULL map utterances and the other conditions. No significant differences in second formant frequencies were observed between SINGLE channel and OFF conditions. These data suggest auditory feedback information may be used to adjust the articulation of some speech sounds.
Auditory perception is not special: We see the world, we feel the world, we hear the world
Authors: Fowler Carol A.
Published: October 2005

The literature on “contrast” provides no evidence that durational contrast should occur in the speech and nonsence signals used in research cited by Diehl et al. [J. Acoust. Soc. Am. 89, 2905–2909 (1991)]. Moreover, there is evidence that, in comparable signals, it does not occur. Accordingly, their own account of the collection of findings on rate normalization is not viable. Their comments on my research do not imperil my interpretation of it or challenge my criticism that classification judgments of acoustically analogous speech and nonsense signals do not permit interpretation, by themselves, in terms of underlying auditory-system mechanisms. Their arguments that in auditory perception, uniquely, we hear proximal stimulation, not its physical causal sources, is implausible. Their theoretical perspective generally, I argue, is unrealistic.
Evaluating the articulation index for auditory–visual input
Authors: Grant Ken W. , Braida Louis D.
Published: October 2005

An investigation of the auditory-visual (AV) articulation index (AI) correction procedure outlined in the ANSI standard [ANSI S3.5-1969 (R1986)] was made by evaluating auditory (A), visual (V), and auditory–visual sentence identification for both wideband speech degraded by additive noise and a variety of bandpass-filtered speech conditions presented in quiet and in noise. When the data for each of the different listening conditions were averaged across talkers and subjects, the procedure outlined in the standard was fairly well supported, although deviations from the predicted AV score were noted for individual subjects as well as individual talkers. For filtered speech signals with AIA<0.25, there was a tendency for the standard to underpredict AV scores. Conversely, for signals with AIA>0.25, the standard consistently overpredicted AV scores. Additionally, synergistic effects, where the AIA obtained from the combination of different bandpass-filtered conditions was greater than the sum of the individual AIA’s, were observed for all nonadjacent filter-band combinations (e.g., the addition of a low-pass band with a 630-Hz cutoff and a high-pass band with a 3150-Hz cutoff). These latter deviations from the standard violate the basic assumption of additivity stated by Articulation Theory, but are consistent with earlier reports by Pollack [I. Pollack, J. Acoust. Soc. Am. 20, 259–266 (1948)], Licklider [J. C. R. Licklider, Psychology: A Study of a Science, Vol. 1, edited by S. Koch (McGraw-Hill, New York, 1959), pp. 41–144], and Kryter [K. D. Kryter, J. Acoust. Soc. Am. 32, 547–556 (1960)].
Hearing thresholds for periodic 60-kHz tone pulses in the beluga whale
Authors: Johnson C. Scott
Published: October 2005

Masked thresholds for periodic 60-kHz tone pulses were measured for the beluga whale (Delphinapterus leucas) for tone pulse durations of 0.025, 0.1, 0.3, 0.8, and 1.6 ms, and with repetition times ranging from 770 ms to continuous tones. In addition, masked thresholds were also measured for single pulse stimuli of 0.025, 0.1, 0.3, 0.8, 1.6, 10, 50, 200, and 1000 ms in duration. The data analysis used with human data was not adequate for the three shortest periodic tone stimuli and a rectangular filter, energy detection, model was used for these cases. The integration time estimated from the single tone pulse data (20 ms) was much longer than those obtained from the periodic tone pulse results. Whale integration times for periodic pulses were found to vary almost directly with pulse duration, unlike those reported humans, which are constant and independent of pulse duration. A system bandwidth of 1000 Hz was found to fit the data, a bandwidth much smaller than the critical ratio (2400 Hz) previously reported for the beluga whale.
Sound field in a rectangular cavity in the presence of a thin, flexible obstacle by the integral equation method
Authors: Ouellet D. , Guyader J.-L. , Nicolas J.
Published: October 2005

This paper is concerned with the prediction of the sound field in a cavity enclosing a thin, flexible obstacle and having finite impedance boundaries. The formulation uses the integral equation method adapted to consider a thin obstacle. It also makes use of the equation of motion of the obstacle, but the only form given here is for the case of a limp panel. The solution is achieved by expressing all the required functions as modal expansions in the equations defining the problem. The set of eigenfunctions of an empty, rigid-walled rectangular cavity is used as a basis for the expansions, which restricts the final solution to rectangular cavities. A few numerical results are presented to validate the theory on some aspects related to simple cases of plane obstacles in rigid-walled cavities.
Azimuthal variation of low-frequency acoustic propagation through asymmetric Gulf Stream eddies
Authors: Mellberg Leonard E. , Robinson Allan R. , Botseas George
Published: October 2005

A numerical modeling study of the azimuthal variation of 25-Hz acoustic propagation through radially asymmetric Gulf Stream eddies is presented. Both a cold-core (cyclonic) and a warm-core (anticyclonic) eddy, which are quasi-elliptical in shape, are investigated. Sources located both inside and outside the eddies are considered with transmission out to 240 km. The source is at a depth of 150 m where there are substantial environmental variations due to eddies. Receivers are at depths of 100, 150, and 300 m. The dimensions of the first four convergence zones (CZ) are utilized as indicators of the azimuthal variation of propagation. Propagation conditions assumed an absorbing bottom and no azimuthal coupling of energy. Sensitivity to change in azimuth is dependent upon the orientation of the eddy relative to the direction of transmission. It is increased for transmission paths parallel to the major axis relative to those parallel to the minor axis. For propagation parallel to the major axis, a 15° change in azimuth can result in a change of as much as 13 km in width and 15 km in range for the third CZ. An irregularity in the shape of a quasi-elliptical eddy is shown to effect an appreciable difference in transmission. A 30° shift in the direction of propagation to the right side of the major axis of a cold-core eddy produced a 20% change in the width of the third CZ, while a 30° shift to the left side of the axis gave a 64% change in the width. Sensitivity can depend upon the direction of propagation along a major axis for a source located within the eddy. Propagation in one direction can produce a sensitivity for a 20° change in azimuth of more than double the shift in range to the third CZ, as the opposite (180°) direction yielded over a 75° change in azimuth.
Acoustical radiation from thermally stressed sea ice
Authors: Xie Yunbo , Farmer David M.
Published: October 2005

Observations of the sound generated by cracking ice in the Canadian Arctic during a cooling period provide an opportunity for studying the response of different types of ice to thermal stress. Synthetic aperture radar (SAR) images and air photographs of ice around the experimental site allow mapping of cracking events back to their points of origin, thus providing a correlation between ice type and acoustical activity. It is shown that there are only a few cracking events in the first-year ice during periods of air temperature variation, whereas multiyear ice produces a large number and is responsible for most of the ambient sound recorded. Analysis of several individual events including both natural and artificial sources reveals that failure processes cause acoustic emissions with an angularly dispersive radiation pattern in which higher frequencies tend to be radiated downward and lower frequencies radiated toward the horizontal. This pattern can be explained in terms of two types of eigenmodes used in plate vibration theory. The theory is extended to the case of a shallow surface crack representative of thermal stress effects. Comparisons are made between theoretical predictions and ice cracking events, including artificial sound sources, and the results interpreted in terms of sea-ice properties.
Field experiments to study seafloor seismoacoustic response
Authors: Stoll R. D. , Bryan G. M. , Mithal R. , Flood R.
Published: October 2005

Results of a 5-year program to measure the seismoacoustic properties of unlithified sediments in the seafloor are presented. A field technique utilizing an impulsive source and a geophone array located on the seafloor was used to obtain detailed travel-time curves which permit a number of different kinds of analysis. A new signal source powered by electrically detonated, 8-gauge shotgun shells was used to focus energy into the bottom and eliminate much of the high-frequency water-borne noise that accompanies the usual explosive sources. Both interface waves and wide-angle refractions were analyzed. A variety of data inversion techniques including slant stacking and cross multiplication were used to obtain dispersion curves, and constrained, least-squares inversion using partial derivatives was used to develop an iterative inversion method to obtain velocity and attenuation as a function of depth. Examples of data from a wide angle of different kinds of sediment ranging from soft Holocene mud to stiff overconsolidated clay are presented. The resulting geoacoustic models reflect the influlence of geologic history, which largely determines the in situ porosity, and the additional effect of the present overburden pressure.
A posteriori probability source localization in an uncertain sound speed, deep ocean environment
Authors: Richardson A. M. , Nolte L. W.
Published: October 2005

The a posteriori source position probability density function for a narrow-band source in an uncertain acoustic environment is derived. The implementation of this probability density function (pdf) is termed the optimum uncertain field processor (OUFP). It is shown that the OUFP is a generalization of matched-field processing to situations in which there is uncertainty about the environment. The robustness of the OUFP is illustrated through performance comparisons to a matched-field algorithm.
Musical frequency tracking using the methods of conventional and “narrowed” autocorrelation
Authors: Brown Judith C. , Zhang Bin
Published: October 2005

In two recent papers, a description is given of a means of obtaining an arbitrarily narrow peak in the calculation of the autocorrelation function [J. C. Brown and M. S. Puckette, “Calculation of a narrowed autocorrelation function,” J. Acoust. Soc. Am. 85, 1595–1601 (1989)] or of a narrow valley in the calculation of an inverse autocorrelation [J. C. Brown and M. S. Puckette, “Musical information from a narrowed autocorrelation function,” Proceedings of the 1987 International Conference on Computer Music, Urbana, Illinois, 84–88 (1987)]. These calculations are applied to the determination of the fundamental frequency of musical signals produced by keyboard, wind, and string instruments. These results are compared to frequency tracking results obtained on these sounds with conventional autocorrelation. In so doing it is determined first whether the method of autocorrelation is well-adapted to the problem of tracking the frequency of musical signals, and, second, under what conditions “narrowed” autocorrelation is advantageous.
Ear canal cross-sectional pressure distributions: Mathematical analysis and computation
Authors: Rabbitt R. D. , Friedrich M. T.
Published: October 2005

Cross-sectional pressure distributions, natural acoustic modes, and associated cutoff frequencies are determined for real ear-canal geometries using an asymptotic theory in combination with a numerical method. The technique is particularly well suited to obtain the higher modes, which are trapped near both ends of the ear canal. Results detail the influence of the canal geometry and frequency on the spatial distribution of the pressure. Adult ear-canal geometries are determined near the concha from ear-mold sections using a light microscope interfaced to a video-data-acquisition system. Computed results compare favorably to the exact solutions for circular and square acoustic waveguides. The cutoff frequency of the two adult ear canals studied averaged 20% less than the cutoff frequency of a circular tube of identical cross-sectional area. Inserting a probe microphone into the canal decreases the rate of decay of circumferential nonplanar modes while increasing the rate of decay of radial modes. Relative to the pressure beyond the tube, insertion increases the plane-wave component of the pressure around the tube by a multiplicative factor approximately equal to the square root of the original area divided by the occluded area. Eccentric placement of the probe tube has a relatively small influence on the cutoff frequency. The transition of the pressure distribution at the entrance to a simple plane wave in the core region of the canal is calculated and shown graphically for the actual geometry of two adult subjects.
Dissociation of pitch from timbre in auditory short-term memory
Authors: Semal Catherine , Demany Laurent
Published: October 2005

In three experiments, untrained listeners made same/different judgments on pairs of pure or complex tones with periods that eventually differed by ±4%. On each trial, the two test tones were separated by 4.3 s, during which other tones (I) were heard but had to be ignored. The period (p) of the first test tone was randomly selected between 1/600 and 1/300 s. The period of each I tone was randomly selected among four possible values, close to p (±3% or 6% apart) in some conditions, and remote from p in other conditions. In addition, from condition to condition, the spectral content of the I tones was varied independently of their periods: The I tones could have the same harmonic content as the test tones, or a very different harmonic content. Subjects’ performances were much better when the periods of the I tones were remote from p than when they were close to p, as expected from previous findings by D. Deutsch [e.g., Science 175, 1020–1022 (1972)]. But, more importantly, the relation between the spectral contents of the I tones and the test tones had, by itself, practically no effect on performance. Thus performance was affected by the pitches of the I tones, but not by their timbres. These results suggest that pitch is processed independently of timbre in auditory short-term memory.
Absorption of finite amplitude focused ultrasound
Authors: Dalecki Diane , Carstensen Edwin L. , Parker Kevin J. , Bacon David R.
Published: October 2005

Predictions of the absorption of focused finite amplitude waves based on weak shock theory have been tested experimentally. The characteristics of this absorption are qualitatively different from those associated with small signal losses. Under appropriate conditions, the absorption of finite amplitude ultrasound is determined largely by source amplitude, field geometry, and the nonlinear properties of the medium and is only weakly dependent upon the small signal absorption coefficient of the material. These effects are seen most dramatically in sharply focused sound fields. To emphasize nonlinear absorption in an experimental test of these predictions; measurements of heating were made in agar which has a very small linear absorption coefficient. Under appropriate conditions, nonlinear losses can make the effective absorption coefficient of this poorly absorbing material somewhat greater than the soft tissues of the body.
Plane acoustic waves in linear viscoelastic porous media: Energy, particle displacement, and physical interpretation
Authors: Rasolofosaon Patrick N. J.
Published: October 2005

The poroviscoelastic model, which is asynthesis of the well-known viscoelastic model and Biot’s poroelastic model, is presented in the context of the propagation of plane acoustic waves in linear viscoelastic porous media. Except for the propagation of a second compressional P2 wave in such media, results concerning particle displacement, maximum attenuation, and direction of maximum energy flow are very similar to that obtained by Borcherdt [J. Geophys. Res. 78, 2442–2453 (1973)] in simple viscoelastic media. The energy conservation relation is given explicitly in the case of time harmonic radiation field. From this, expressions of the energy flux, energy densities, dissipated energy, and Q−1 are derived. Furthermore it is demonstrated that the total attenuation Qtotal−1 is equal to the sum of the viscoelastic attenuation Qvisco−1 and Biot’s poroelastic attenuation Qporo−1. This allows a direct comparison between energy dissipated by viscoelasticity and that dissipated by Biot mechanism. For propagation of acoustic waves in infinite natural porous media the latter is always negligible compared to the former. Computed curves and physical interpretations are proposed to illustrate the theoretical derivations.
The propagation of time harmonic Rayleigh–Lamb waves in a bimaterial plate
Authors: Scandrett Clyde , Vasudevan Naresh
Published: October 2005

The time harmonic elastodynamic response of two semi-infinite elastic plates of dissimilar material properties perfectly bonded along their lateral faces is studied. The wave field in either half-plate can be written as a superposition of the so-called Rayleigh–Lamb eigenmodes of an infinite plate. The interaction of a time harmonic incident wave with the interface results in reflected and transmitted fields that contain contributions from all of the real, imaginary, and complex eigenmodes of an infinite plate. Attention is focused on the distribution of energy among the various reflected and transmitted eigenmodes over a range of frequencies. The fundamental symmetric and the fundamental antisymmetric Lamb modes are each used as input excitations. Such excitations can be approximately realized in experiments. It is assumed that the solution of such a canonical problem will facilitate the solution of problems with complicated time-dependent sources.
Numerically efficient evaluation of intrinsic modes in wedge-shaped waveguides
Authors: Ansbro A. P. , Arnold J. M.
Published: October 2005

Evaluation of intrinsic modes in wedge-shaped oceans overlying a fluid bottom is via a spectral domain integral. Here, a numerical technique, centered around the FFT, is applied in the spectral domain, which generates a numerically efficient algorithm. This numerical efficiency permits a demonstration of the intrinsic mode conserving power across a local transverse cross section. Comparisons between the parabolic equation method and the beam propagation method, with respect to the intrinsic mode, are commented upon.
Lamb and creeping waves around submerged spherical shells resonantly excited by sound scattering. II: Further applications
Authors: Gaunaurd G. C. , Werby M. F.
Published: October 2005

The scattering of plane sound waves from an air-filled steel spherical shell submerged in water in the frequency band 0⩽k1a⩽500 is studied. This analysis is based on a methodology [Ayres et al., Int. J. Solids Struct. 23, 937–946 (1987) and G. Gaunaurd and M. F. Werby, J. Acoust. Soc. Am. 82, 2021–2033 (1987)] proposed that uses the exact three-dimensional equations of dynamic elasticity to describe the shell motions and to predict its sonar scattering cross section. This approach is valid at all frequencies, for shells of any thickness, of any (constant) curvature, and it accounts for their fluid-loaded condition. The methodology is used to predict the cross sections, which are later interpreted on the basis of the various resonance features that manifest themselves in the frequency response. The spectral locations of these resonances depend on the various types of elastic waves propagating along the shell, or in the surrounding fluid. The exact plots are generated for the phase (cp) velocities of these (Lamb) waves always accounting for the curvature and fluid-loading effects present on the shell, without appeals to plate waves or theories. Some of the dispersion plots were generated using the Donnell shell-theory approximation, which seems to yield accurate results up to the coincidence frequency. Aside from the broad resonance lobe present at the coincidence frequency, there is another high-frequency resonance lobe, due to a thickness-resonance effect, which was also predicted and displayed. A partial-wave analysis of the resonance response curve for a thin shell, around its coincidence frequency, serves to identify the origins of the various types of observed resonance features and to relate them to the elastic and acoustic waves that propagate along the shell or the outer fluid. Many computer-generated graphs are displayed to illustrate the above points.
New estimates of sound speed in water
Authors: Spiesberger John L. , Metzger Kurt
Published: October 2005

Measured travel times of acoustic pulses, propagated across a 3000-km section of the North Pacific, are inconsistent with travel times predicted with the internationally accepted algorithm for the speed of sound in water. The sound-speed algorithm predicts a speed that is too fast at oceanic pressures found below about 1-km depth. An accurate algorithm of sound speed is important for deriving temperature from measurements of acoustic travel time across oceans. Accurate estimates of the temperature field are probably important for better understanding the ocean’s role in determining weather, climate, and the distribution of marine organisms.
Adaptive beamforming in the presence of correlated arrivals
Authors: Godara Lal C.
Published: October 2005

The constrained least-mean-square (LMS) algorithm updates the weights of an antenna array by estimating the gradient of the mean output power surface. In its standard form an estimate of the required gradient is made by multiplying the array output with the sensor outputs. This form of LMS algorithm is not suitable for updating the weights in the presence of correlated arrivals. The correlation between the desired signal and an unwanted interference may exist in situations of multipath and deliberate jamming. This paper investigates the performance of two algorithms, namely, the structured gradient algorithm and the improved LMS algorithm, in the presence of correlated narrow-band arrivals. Theoretical analysis and computer simulation are presented to demonstrate the capability of these algorithms to estimate the weights of a linear array of equispaced elements, to cancel the correlated directional sources.
Simultaneous linearized inversion of velocity and density profiles for multidimensional acoustic media
Authors: Özbek Ali , Levy Bernard C.
Published: October 2005

In this paper, the multidimensional inverse scattering problem for an acoustic medium is formulated as a generalized tomographic problem. The medium is probed by wide-band plane-wave sources, and the scattered field is observed along straight-line receiver arrays. The objective is to reconstruct, simultaneously, the velocity and density profiles of the medium. Using the Born approximation and applying a proper filter to the observed scattered field, generalized projections of the velocity and density scattering potentials are obtained. The generalized projections are weighted integrals of the scattering potentials; in two dimensions, the weighting functions are concentrated along parabolas, in three dimensions, they are concentrated over circular paraboloids. The resulting problem of generalized tomography (or inverse generalized Radon transform, or integral geometry) is solved in exact analytical form. The solution is expressed as a backprojection operation followed by a two- or three-dimensional space-invariant filtering operation. In the Fourier domain, the resulting image is a linear combination of the velocity and density scattering potentials, where the coefficients depend on the angle of incidence of the probing wave. Therefore, in principle, two experiments with different angles of incidence are necessary to reconstruct the velocity and density scattering potentials separately. It is shown that this involves a numerically unstable procedure, especially for bandlimited data, necessitating the use of several angles of incidence to regularize the inversion.
The significance and measurement of head position during speech production experiments using the x-ray microbeam system
Authors: Westbury John R.
Published: October 2005

Head position and orientation are important variables during experiments conducted on the University of Wisconsin x-ray microbeam system, a nationally shared imaging facility for speech production research. Normally, the head is not restrained during experiments, in order to maximize the naturalness of speech performance, even though free head movements may have an adverse effect on the accuracy of kinematic data that are obtained. The basis for this effect is explained, and techniques for dealing with temporal variations in head position are described. Results obtained from a novel method for three-dimensional measurement of head position, applied to data sets recorded from six normal adult speakers during otherwise typical x-ray microbeam experiments, are summarized to convey some sense of the measurement error that can arise from deviations from a required head position. These measurements suggested that among these speakers, errors attributable to improper positioning of the head, and/or inadvertent head movements within or between trials, never exceeded 5%.
Properties of an ultrasonically driven rotor in water
Authors: Manning Gavin N. , Curzon Frank L. , Koblanski John
Published: October 2005

A nylon disk supported on a horizontal axis in a water bath and irradiated by a 1-MHz focused ultrasonic beam, rotates at a constant angular speed which depends on the acoustic power, the viscosity of the water, and the geometry of the system. It is shown that the acoustic torque is caused by the radiation force, and that the viscous torque is well described by Schlichting’s model, except at low speeds when the boundary layer thickness becomes larger. The placement of the disk in the acoustic beam is specified for maximum angular speed, and scaling laws for the dependence of the speed on the beam power and disk radius are given. It is pointed out that the rotor has desirable attributes as an ultrasonic intensity meter.
A thin film technique for spatial apodization of disc-shaped piezoceramic transducers
Authors: Hayward Gordon , Hamilton Robin , Kanani Behroos , Reilly David A.
Published: October 2005

Conventional piezoelectric disc transducers suffer from some inherent disadvantages as a result of diffraction and multimode wave interaction within the radiated sound field. It is shown that significant improvements may be achieved by employing a continually varying resistive taper as a front or rear face electrode, thereby minimizing the influence of aperture diffraction, radial mode coupling, and electric field variations on the spatial response. The theoretical operation of such devices is discussed and good agreement is obtained from a selection of experimental observations on different transducer materials.
Slips, SLIPS, and the rhyme.
Authors: Stuart Laubstein Ann
Published: October 2005

There have been numerous arguments from the domains of phonotactics and stress for including the rhyme as an internal constituent of the syllable (Halle and Vergnaud, 1980). The rhyme has also been proposed as a production unit on the basis of slips of the tongue and word games (Fudge, 1987; Treiman, 1985). However, like the syllable itself, this constituent is rarely subject to error in spontaneous slips. In the experiment reported on here, the rhyme is experimentally tested using the error elicitation technique (SLIP) described in Motley, Baars, and Camden (1983). Subjects (n=44) were tested on VC (rhyme), CV, and C1C2 sequences where C1 was either a sonorant (SC) or an obstruent (OC). As predicted CV and VC were indistinguishable from one another: both sequences rarely moved as a unit and they were split apart equally often. On the other hand they were both significantly different from SC and OC sequences (Wilcoxon p<0.01). Besides lending more support to the ecological validity of the SLIP technique (Stemberger and Treiman) these results suggest that when sublexical errors occur, the rhyme is not a unit of syllabic structure on a par with other syllabic constituents. Other syllabic constituents like the onset, peak, and coda are subject to error.
Pressure ridging source spectrum level and a proposed origin of the 20-Hz peak in Arctic ambient noise spectra.
Authors: Greening Michael V. , Zakarauskas Pierre
Published: October 2005

This paper presents evidence that the origin of the low-frequency peak (10–20 Hz) observed in Arctic ambient noise spectra may result from a combination of the source spectrum of pressure ridging and the effects of propagation loss on this spectrum. This peak is often attributed to a hypothetical source spectrum but may also be explained by a minimum in the propagation loss. This paper shows that both measurements and modeling studies indicate a minimum in propagation loss versus frequency near 30 Hz. When combined with the measured spectrum of a nearby forming pressure ridge, a ridging event at 60-km range results in a broadband peak at approximately 20 Hz. a)Also at Defense Research Establishment Pacific.
The latest developments of a multimicrophone system with range-dependent sensitivity.
Authors: Date Hikaru
Published: October 2005

At the 115th ASA meeting, the principle of a spatially selective multimicrophone system was introduced. Work is currently at the hardware development stage. Two types of models were made. One is of an icosahedron shape with analog signal processing; the other is of an octahedron shape with digital signal processing. Both experimental modes show a maximum spatial attenuation of more than 25 dB below 1 kHz compared with that of a nondirectional microphone for plane wave incidence. Although these values are reasonable for most practical applications, computer simulation, assuming that ideal pressure microphones are used as elements, show that far more spatial attenuation, for example, 60 dB, can be expected. Several analytical results on the cause of such small values of measured spatial attenuation will be reported in terms of the positional error and gain error of the microphone elements.
Models of prosthetic devices for the middle ear.
Authors: Brink W. Richard , Finch Robert D.
Published: October 2005

There is a need for an engineering approach to the design of prostheses for the middle ear. This paper discusses one and two degree of freedom models and how well they fit the available data on the transfer function of the middle ear. Newton–Raphson and polynomial regression techniques have been used in performing these fits. Possible control mechanisms for high-amplitude response will be discussed. Constraints on the manufacture and implantation of such devices will also be discussed.
DSP control algorithms for canceling broadband random noise with a single microphone and speaker.
Authors: Harley T. R. , Hendrix J. E. , Shields F. D.
Published: October 2005

Innovative and conventional techniques for making a general purpose controller are described and compared. Here, the controller is a digital signal processor which receives input representing some undesired disturbance and outputs a driving voltage to a transducer in order to counteract the disturbance. The controller is intended to optimally reduce stationary random broadband noise for which no upstream or precursor signal is available. Three different methods are presented for defining a linear IIR filter which is implemented by the controller. For one of these methods, the digital filter yielding the minimum power is calculated numerically by integrating the theoretically predicted power spectrum over frequency space. This power spectrum can be easily modified by an arbitrary frequency dependent weighting factor, such as the sensitivity of the human ear. Experimental results are given. Theoretical analysis of the performance to be expected from a conventional LMS algorithm used in single microphone and speaker systems is given for a specific application which reveals inherent problems associated with the conventional approach.
An adaptive predictive filter for controlling broadband noise or vibration with tightly coupled transducers.
Authors: Hendrix James E. , Harley T. R. , Shields F. Douglas
Published: October 2005

An adaptive predictive filter for controlling broadband noise or vibration when no upstream view of the unwanted signal is possible is disclosed. The transducer configuration consists of a single detector tightly coupled to a controlling transducer. The filter has been used in an active noise reducing earphone, for stabilizing a platform and for controlling a vibrating membrane. The filter in question was designed from the time domain perspective and exhibits better stability characteristics than conventional RLMS single detector systems.