bluuebunny/crossref_metadata_2025 huggingface dataset:
Bistatic cross sections and the resonance order: The Rayleigh wave dipole resonance
Authors: Werby Michael F. , Überall Herbert
Published: October 2005

The shape of the bistatic cross section at the resonances of an elastic scattering object has been used experimentally [G. Maze and J. Ripoche, J. Acoust. Soc. Am. 73, 41–43 (1983)] to determine the order of the resonance. The basic principle of this approach is demonstrated here theoretically; for the case of an elastic sphere, it is used to identify the dipole resonance of the Rayleigh surface wave, which previously could not be determined with certainty from backscattering measurements alone.
Frequency-dependent self-induced bias of the basilar membrane and its potential for controlling sensitivity and tuning in the mammalian cochlea
Authors: LePage Eric L.
Published: October 2005

A displacement-sensitive capacitive probe technique was used in the first turn of guinea pig cochleas to examine whether the motion of the basilar membrane includes a displacement component analogous to the dc receptor potentials of the hair cells. Such a ‘‘dc’’ component apparently exists. At a given location on the basilar membrane, its direction toward scala vestibuli (SV) or scala tympani (ST) varies systematically with frequency of the acoustic stimulus. Furthermore, it appears to consist of two parts: a small asymmetric offset response to each gated tone burst plus a progressive shift of the basilar membrane from its previous position. The mean position shift is cumulative, increasing with successive tone bursts. The amplitude of the immediate offset response, when plotted as a function of frequency, appears to exhibit a trimodal pattern. This displacement offset is toward SV at the characteristic frequency (CF) of the location of the probe, while at frequencies either above or below the CF the offset is relatively larger, and toward ST. The mechanical motion of the basilar membrane therefore appears to contain the basis for lateral suppression. The cumulative mean position shift, however, appears to peak toward ST at the apical end of the traveling wave envelope and appears to be associated with a resonance, not of the basilar membrane motion directly, but coupled to it. The summating potential, measured concurrently at the round window, shows a more broadly tuned peak just above the CF of the position of the probe. This seems to correspond to the peak at the CF of the mechanical bias. As the preparation deteriorates, the best frequency of the vibratory displacement response decreases to about a half-octave below the original CF. There is a corresponding decrease in the frequency of the peaks of the trimodal pattern of the asymmetric responses to tone bursts. The trimodal pattern also broadens.

In previous experiments the basilar membrane has been forced to move in response to a low-frequency biasing tone. The sensitivity to high-frequency stimuli varies in phase with the biasing tone. The amplitudes of slow movement in these earlier experiments and in the present experiments are of the same order of magnitude. This suggests strongly that the cumulative shift toward ST to a high-frequency acoustic stimulus constitutes a substantial controlling bias on the sensitivity of the cochlea in that same high-frequency region. Its effect will be to reduce the slope of neural rate-level functions on the high-frequency side of CF.
Analytical and experimental investigation on vibrating circular plates with stepped thickness over a concentric circular region
Authors: Avalos D. , Laura Patricio A. A. , Bianchi A. M.
Published: October 2005

Transverse vibrations of the structural elements described in the title are studied for the case where the edges are elastically restrained against translation and rotation. Since finding an exact solution is a difficult task, it was considered convenient to approximate the response of the plate in the case of free, axisymmetric vibrations by means of a summation of simple polynomial coordinate functions that satisfy the governing boundary conditions. The Ritz method is used in order to generate the frequency equation. The natural frequency coefficients are optimized by minimizing each eigenvalue with respect to an undetermined exponential parameter included in each coordinate function.
Potentials evoked by the sinusoidal modulation of the amplitude or frequency of a tone
Authors: Picton Terence W. , Skinner Christopher R. , Champagne Sandra C. , Kellett Adrian J. C. , Maiste Anita C.
Published: October 2005

Steady state responses to the sinusoidal modulation of the amplitude or frequency of a tone were recorded from the human scalp. For both amplitude modulation (AM) and frequency modulation (FM), the responses were most consistent at modulation frequencies between 30 and 50 Hz. However, reliable responses could also be recorded at lower frequencies, particularly at 2–5 Hz for AM and at 3–7 Hz for FM. With increasing modulation depth at 40 Hz, both the AM and FM response increased in amplitude, but the AM response tended to saturate at large modulation depths. Neither response showed any significant change in phase with changes in modulation depth. Both responses increased in amplitude and decreased in phase delay with increasing intensity of the carrier tone, the FM reponse showing some saturation of amplitude at high intensities. Both responses could be recorded at modulation depths close to the subjective threshold for detecting the modulation and at intensities close to the subjective threshold for hearing the stimulus. The responses were variable but did not consistently adapt over periods of 10 min. The 40-Hz AM and FM responses appear to originate in the same generator, this generator being activated by separate auditory systems that detect changes in either amplitude or frequency.
Instantaneous and time-averaged energy transfer in acoustic fields
Authors: Mann J. Adin , Tichy Jiri , Romano Anthony J.
Published: October 2005

The fundamentals of energy transfer in an acoustic field are addressed and it is shown that describing the flux of energy in an acoustic field with the active intensity alone is inaccurate. A single active intensity vector describes only the time-average energy flux at a point in space, but not where the energy came from nor where it is going. Consequently, the instantaneous intensity must be used to properly describe energy flux as a time-dependent process. The phenomenon of the acoustic vortex is examined and, from the perspective of active intensity, it is seen to represent a resultant wave rotating around a zero pressure line or point at which the pressure phase is discontinuous. It is shown that this resultant wave travels with a phase speed cp, which is generally different than the plane-wave phase speed c. The instantaneous intensity, however, shows that energy is flowing through the vortex and not with the resultant waves. Although the complex intensity vector is normally separated into the active and reactive components (i.e., rotational and solenoidal parts), the active intensity can be further represented by two parts, one with zero and another with nonzero curl, which permits the representation of the coupling between sources or parts of a source. In general, this article emphasizes the physical meaning and interpretation of energy related quantities.
The influence of wind on the underwater sound generated by light rain
Authors: Nystuen Jeffrey A. , Farmer David M.
Published: October 2005

The dominant feature of the underwater sound generated by light rain is a broad spectral peak at 15 kHz. The spectral location of this feature is proportional to raindrop impact velocity. Wind adds a horizontal component to the raindrop velocities, increasing their net impact velocities and shifting the spectral peak to a higher frequency. The surface velocities of waves generated by the wind distribute the raindrop impact velocities and thus broaden the spectral peak. Observations show that the spectral level of the peak drops as the wind increases, suggesting that the efficiency of the drop impact as a sound source has been reduced.
Effects of moisture content on soil impedance
Authors: Cramond A. J. , Don C. G.
Published: October 2005

An impulse technique has been used to investigate the effect of up to 40% by weight moisture content on the impedance of grassland, barren earth, and sand. Layering of the soil after the addition of water causes resonances in the impedance values at frequencies around 5 kHz which are found to be position dependent. Comparison with layer theory is made although the predicted resonances are much broader than the experimental peaks. The variation of the peak height of the reflected impulse has been used to determine the change of effective flow resistivity of the top surface with moisture content. This may change from 200 cgs rayl at 10% moisture to 1500 cgs rayl at 35% moisture content. Results taken over grassland and sand follow the same trend if normalized to their saturation value.
Propagation of medium strength shock waves through the atmosphere
Authors: Bass Henry E. , Layton Bruce A. , Bolen Lee N. , Raspet Richard
Published: October 2005

The rise times and overpressures for shock waves from supersonic projectiles have been measured under a variety of atmospheric conditions. These measurements extend the overpressure for which weak shock theory adequately predicts measured values to 3 kPa. Predicted shock rise times agree reasonably well with theory for shock overpressures between 0.04 and 0.5 kPa with differences increasing at higher overpressures. At overpressures greater than 0.5 kPa, measured rise times might be limited by the experimental apparatus. No correlation between measured rise times and atmospheric turbulence was observed.
Noncollinear interaction of two sound beams from displaced Gaussian sources, with application to parametric receiving arrays
Authors: Hamilton Mark F. , Tjo/tta Jacqueline Naze , Tjo/tta Sigve
Published: October 2005

We consider the noncollinear interaction of two sound beams in a nondissipative fluid, one formed by a high-frequency (pump) wave and the other by a low-frequency (source) wave. It is assumed that both waves are generated by Gaussian-shaded sources. However, the sources may possess linear phase shading and different spot sizes, and their centers may be displaced relative to each other. The analysis is based on the fundamental theory developed in earlier papers [G. S. Garrett, J. Naze Tjo/tta, and S. Tjo/tta, J. Acoust. Soc. Am. 75, 769–779 (1984); and M. F. Hamilton, J. Acoust. Soc. Am. 76, 1493–1504 (1984)], and it is valid throughout the paraxial field. Numerical results are presented for application of the analysis to a parametric receiving array when the pump is located in the nearfield of the sound source. The results show the effect of the pump’s position, size, and frequency on parametric measurements when diffraction of both interacting waves is important. Asymptotic formulas are derived for the case where the receiving hydrophone is located in the farfield of the source, but with the pump still in the nearfield.
Discrimination in neonates of very short CVs
Authors: Bertoncini Josiane , Bijeljac-Babic Ranka , Blumstein Sheila E. , Mehler Jacques
Published: October 2005

The experiment reported here explores the ability of 4- to 5-day-old neonates to discriminate consonantal place of articulation and vowel quality using shortened CV syllables similar to those used by Blumstein and Stevens [J. Acoust. Soc. Am. 67, 648–662 (1980)], without vowel steady-state information. The results show that the initial 34–44 ms of CV stimuli provide infants with sufficient information to discriminate place of articulation differences in stop consonants ([ba] vs [da], [ba] vs [ga], [bi] vs [di], and [bi] vs [gi]) and following vowel quality ([ba] vs [bi], [da] vs [di], and [ga] vs [gi]). These results suggest that infants can discriminate syllables on the basis of the onset properties of CV signals. Furthermore, this experiment indicates that neonates require little or no exposure to speech to succeed in such a discrimination task.
Comodulation masking release (CMR): Effects of signal frequency, flanking-band frequency, masker bandwidth, flanking-band level, and monotic versus dichotic presentation of the flanking band
Authors: Schooneveldt Gregory P. , Moore Brian C. J.
Published: October 2005

In experiment I, thresholds for 400-ms sinusoidal signals were measured in the presence of a continuous 25-Hz-wide noise centered at signal frequencies ( fs) ranging from 250 to 8000 Hz in 1-oct steps. The masker was presented either alone or together with a second continuous 25-Hz-wide band of noise (the flanking band) whose envelope was either correlated with that of the on-frequency band or was uncorrelated; its center frequency ranged from 0.5 fs to 1.5 fs. The flanking band was presented either in the same ear (monotic condition) as the signal plus masker or in the opposite ear (dichotic condition). The on-frequency band and the flanking band each had an overall level of 67 dB SPL. The comodulation masking release, CMR(U−C), is defined as the difference between the thresholds for the uncorrelated and correlated conditions. The CMR(U−C) showed two components: a broadly tuned component, occurring at all signal frequencies and all flanking-band frequencies, and occurring for both monotic and dichotic conditions; and a component restricted to the monotic condition and to flanking-band frequencies close to fs. This sharply tuned component was small for low signal frequencies, increased markedly at 2000 and 4000 Hz, and decreased at 8000 Hz. Experiment II showed that the sharply tuned component of the CMR(U−C) was slightly reduced in magnitude when the level of the flanking band was 10 dB above that of the on-frequency band and was markedly reduced when the level was 10 dB below, whereas the broadly tuned component and the dichotic CMR(U−C) were only slightly affected. Experiment III showed that the sharply tuned component of the CMR(U−C) was markedly reduced when the bandwidths of the on-frequency and flanking bands were increased to 100 Hz, while the broadly tuned component and the dichotic CMR(U−C) decreased only slightly. The argument here is that the sharply tuned component of the monotic CMR(U−C) results from beating between the ‘‘carrier’’ frequencies of the two masker bands. This introduces periodic zeros in the masker envelope, which facilitate signal detection. The broadly tuned component, which is probably a ‘‘true’’ CMR, was only about 3 dB.
Responses of auditory-nerve fibers to multiple-tone complexes
Authors: Deng Li , Geisler C. Daniel , Greenberg Steven
Published: October 2005

To relate level-dependent properties of auditory-nerve-fiber responses to nasal consonant–vowels to the basic frequency selective and suppressive properties of the fibers, multitone complexes, with the amplitude of a single (probe) component incremented, were used as stimuli. Quantitative relations were obtained between the systematic increase of fiber synchrony to the probe tone and the decrease of synchrony to CF, as the amplitude of the probe tone was increased. When such relations are interpreted as a measure of fiber frequency selectivity based on a relative synchrony criterion, a breadth of frequency tuning is obtained, at a 70-dB SPL multitone sound-pressure level, which is generally broader than that of the fiber’s threshold tuning curve. Quantitative comparisons with the same fiber’s responses to the nasal speech sounds indicate that the fiber’s speech responses share some common features with its probe-tone responses.
Wave propagation in a piezoelectric solid cylinder of arbitrary cross section
Authors: Paul H. S. , Venkatesan M.
Published: October 2005

In this article, the wave propagation in an infinite piezoelectric solid cylinder of an arbitrary cross section is studied. In the analysis, the boundary conditions are satisfied by the use of Nagaya’s Fourier expansion collocation method. The frequency equations for symmetric and antisymmetric cases are obtained and analyzed numerically for longitudinal and flexural waves for the piezoceramic material PZT-4. The vibrations of circular and elliptical cylinders are investigated and the results are tabulated. The results obtained for a circular cross section are compared with the available results. The frequency versus the aspect ratio (the ratio of the semimajor and semiminor axes of the elliptical cylinder) is plotted and the dispersion curve is also presented.
Lamb and creeping waves around submerged spherical shells resonantly excited by sound scattering
Authors: Gaunaurd G. C. , Werby M. F.
Published: October 2005

Acoustic wave scattering by spherical shells in water in the resonance region is studied. The interaction is studied classically and by the resonance scattering theory (RST). The connection between internal resonances and the Lamb waves excited in the shell is analyzed. Conditions are derived that govern the propagation of Lamb waves in a spherical shell when it is fluid-loaded or in vacuo. These general conditions reduce to the usual conditions for Lamb waves in plates, in the large radii limit. The connection is established between the outer scattering problem and the internal vibrational problem that excites the shell resonances, and it is demonstrated that the creeping-wave series that synthesizes the Franz waves around the shell, can be obtained quite simply without the use of the Watson–Sommerfeld Method (WSM).

All that is required is suitable one-term expansions of the denominators of the scattering amplitudes. This eliminates the need for the cumbersome excursions through the complex angular momentum plane ν of the WSM. Calculations are presented for the summed form functions of seven shells of three compositions and thicknesses over quite broad frequency bands. Subtraction of rigid or soft backgrounds permits one to draw many conclusions as to the behavior of the shell response in various spectral regions. The relative phase between the form function and the background is also displayed. This phase is helpful for the identification of actual resonances and for the choice of proper background. It is shown how the poles of the scattering amplitude in the x plane split into two subsets. One set, the Franz set, depends only on shell shape, and is related to the external Franz (creeping) waves in the water. This set does not change with varying shell thickness or composition. The other set, the Lamb set, depends only on material composition, and is related to the Lamb waves in the shell. These poles are displayed in various cases, and it is shown that for thin shells, only one family of Lamb poles (the zeroth-order symmetric family, s0) is dominant, which explains the relatively simple structure of the form function of a thin shell. For thicker shells, many modes interact, and one is forced to go to the usual partial-wave analysis of the RST. A very accurate picture of the scattering process taking place around and inside the shell emerges from this analysis.
Scattering from an object in a stratified medium
Authors: Ingenito F.
Published: October 2005

An expression is derived for the acoustic field scattered by a rigid sphere in an isovelocity fluid layer overlying a horizontally stratified medium. The result, valid when multiple scattering can be neglected, is expressed in terms of normal modes and plane-wave scattering functions. It allows simple physical interpretation and straightforward numerical implementation. Sample numerical calculations are given for two cases typical of shallow-water environments. Generalizations to a depth-dependent sound velocity fluid layer and to nonrigid spheres are indicated. A second derivation is given for objects of nonspherical shape in a form similar to that of the rigid sphere. Hence, if the plane-wave scattering functions for the object are known, the scattered field in a stratified medium can be calculated.
Physical optics theory of scattering from the ice canopy
Authors: McDaniel Suzanne T.
Published: October 2005

The method of physical optics is applied to treat high-frequency acoustic scatter from Arctic ice. The development takes into account that the under-ice surface is not statistically homogeneous, but consists of two types of ice: undeformed first year and multiyear ice, and very rough ice due to pressure ridge formation. Expressions are obtained both for the mean scattering strength and the spatial coherence of the scattered field. Measured ice statistics are used to evaluate the expressions derived for the spatial coherence and to estimate the variability of the mean backscattering strength.
Sound wave propagation from a point source over a homogeneous surface and over a surface with an impedance discontinuity
Authors: Enflo B. O. , Enflo P. H.
Published: October 2005

The sound field from a point source above an infinite plane with an impedance discontinuity is studied by considering the Helmholtz equation. With boundary conditions the Helmholtz equation is transformed into a singular integral equation and an exact solution formula is given. The formula is evaluated for the case when the source and the receiver are close to the boundary, many wavelengths from the discontinuity. The evaluation gives, among other things, information on the dependence of the surface wave structure on the impedances and—in the case of no surface waves—information on the farfield solution. If one of the impedances gives a surface wave in the case of a homogeneous boundary, then a surface wave appears also in the nonhomogeneous case and is modified depending on the other impedance. In the case of no surface waves, the rapid decay of the sound field in the homogeneous case does not appear in the nonhomogeneous case since the discontinuity acts as a weak source of slowly decaying waves. A number of experiments are suggested by the results. A new treatment of the special case of a homogeneous boundary is also given, with a new asymptotical expansion of the solution.
The effect of speechreading on the speech-reception threshold of sentences in noise
Authors: Middelweerd M. J. , Plomp R.
Published: October 2005

The monaural speech-reception threshold of sentences in noise, here defined as the 50% correct-syllables threshold, was measured for a female speaker with and without speechreading via a video monitor. The additional visual information resulted in a 4.6-dB lower threshold for a group of 12 young subjects and in a 4.0-dB lower threshold for a group of 18 elderly subjects compared to auditory presentation alone.
Temperature dependence of frog spontaneous otoacoustic emissions
Authors: van Dijk P. , Wit H. P.
Published: October 2005

Spontaneous otoacoustic emissions are recorded from frog ears at various body temperatures. Frequency spectra and amplitude distributions of emissions are determined. Both power and frequency of emission signals show a strong temperature dependence.
Effects of pure-tone forward masker duration on psychophysical measures of frequency selectivity
Authors: Bacon Sid P. , Jesteadt Walt
Published: October 2005

The effects of forward masker duration on psychophysical measures of frequency selectivity were investigated in two experiments. In both experiments, masker duration was 50 or 400 ms, signal duration was 20 ms, and there was no delay between masker offset and signal onset. In the first experiment, growth-of-masking functions were measured for a masker whose frequency was below, at, or above the 1000-Hz signal frequency. From those data, input filter patterns (IFPs) were plotted for masker levels from 40–90 dB SPL. In the second experiment, masking patterns (MPs) were measured for a 1000-Hz masker presented at 50, 70, and 90 dB SPL. Both measures of frequency selectivity (IFPs and MPs) indicate that frequency selectivity is greater for the 400-ms masker. These data suggest that there may be a sharpening of frequency selectivity with time at a stage prior to the adaptation observed in forward masking.
Boundary integral calculations of scattered fields: Application to a spacecraft launcher
Authors: Malbéqui Patrice , Candel Sébastien M. , Rignot Eric
Published: October 2005

The objective of this article is to illustrate the possibilities of the boundary integral method in the analysis of acoustic scattering by the structure of a space launcher. Such an analysis is important in situations where the sound field reaches critical levels at takeoff. In these circumstances an increase in amplitude associated with reflection and scattering must be estimated with precision. The method is based on integral representations of the wave field and only requires a surface mesh of the solid structure. The number of nodes of such surface meshes is much smaller than the 3-D finite difference or finite element equivalents. Another important advantage of the method is that it automatically incorporates the farfield radiation condition. This condition is only approximated in field methods. The calculations are performed with a code originally developed by Hamdi [Doctoral thesis, Universite de Compiègne (1982)]. It is here validated for the scattering of a plane wave by a hard sphere. The convergence properties of the method are examined and are found to be acceptable for most practical purposes. Scattering by the Ariane IV fairings (the payload housing) is then specifically considered. It is found that the geometrical shape of the fairings causes local increases of the sound field. This tendency is confirmed by measurements performed on a (1)/(20) model of the launcher. Effects of geometrical modifications are also discussed.
Modelization of layered sound absorbing materials with transfer matrices
Authors: Allard Jean F. , Champoux Yvan , Depollier Claude
Published: October 2005

A method is presented that allows the prediction of the acoustical properties of layered porous or fibrous materials in normal incidence from simple measurements. Transfer matrices obtained from the Biot theory are used to describe homogeneous layers and screens constituting layered materials. The description of an absorbing material with the method is given.
A comparison of some techniques for corrugated parallel plate waveguides
Authors: Sandström Sven-Erik
Published: October 2005

The method of multiple scales and the rigorous modal technique are compared to the null-field method in some waveguide applications. Periodically corrugated parallel plate waveguides (in two and three dimensions) display resonance phenomena at certain frequencies (in a given direction). The three methods are compared with respect to their ability to correctly describe these acoustic (Bragg) resonances and their influence on the dispersion relation of the waveguide.
Permeability and velocity in simple models with compressible fluids
Authors: Sen Pabitra N. , Schoenberg Michael
Published: October 2005

When a fluid of kinematic viscosity ν and sound velocity αf flows in one direction in rigid-walled ducts and tubes at a radial frequency ω, the slowness s1 of the sound wave propagation or diffusion is directly related to the permeability K=iν/α2fωs21. A similar relation between the dynamic flow permeability and sound wave speed is given for porous media, based on a spatial average over a length scale D of the order of several pore and grain sizes. Model slownesses in ducts and tubes are obtained to calculate K(ω) for compressible fluids. In the long wavelength regime (i.e., channel size much smaller than wavelength) the correction due to compressibility is independent of channel size and is of the order of 2νω/ α2f. This correction is negligible for frequencies below the MHz range for gases and highly viscous fluids and negligible below the GHz range for water.
The radiation of elliptical and bicylindrically focused piston transducers
Authors: Thompson R. B. , Gray T. A. , Rose J. H. , Kogan V. G. , Lopes E. F.
Published: October 2005

Expressions for the radiation of elliptical and bicylindrically focused piston transducers are derived within the Fresnel approximation. For the axial fields, the result takes the form of either a simple analytical expression (small perturbations from the circular piston case), a single quadrature in a real variable (unfocused and some focused cases), or a single quadrature in a complex variable (near focal points). The full fields are represented by a series of localized, Gauss–Hermite eigenfunctions. Numerical examples are used to illustrate the agreement of the two solutions for on-axis fields and to shed light on questions of the convergence and the selection of initial scaling parameters of the Gauss–Hermite expansion.
Fractal finite element mesh generation for vibration problems
Authors: Jeng J. H. , Varadan V. V. , Varadan V. K.
Published: October 2005

A new approach for solving plate vibration problems has been formulated by using the Pascal–Sierpinski gaskets and finite element method. The Pascal–Sierpinski gaskets are geometric fractals that are self-similar under scale transformation. Modeling a finite plate element with the basic Pascal–Sierpinski gasket unit, the equations of motion of the basic unit are derived. A buildup process is formed by linking three identical units together. Finally, systematic recurrence relations are generated. The advantage of this approach is that the dynamic matrix of the system has the same dimension at each buildup step. The basic vibration properties, computation time, and memory requirements are discussed and critically compared with traditional finite element methods by discussing a specific example. In general, finite element mesh generation based on geometric fractals offers much promise in reducing storage requirements and computation times significantly.
Breakdown of echo suppression in the precedence effect
Authors: Clifton Rachel K.
Published: October 2005

A new phenomenon is reported in which a change in spatial location of the leading sound source disrupts the normal echo suppression of the precedence effect. Click trains were presented through two loudspeakers, one leading the other by a few milliseconds. When leading and lagging signals were switched, listeners heard clicks momentarily for as long as several seconds from both loudspeakers before echo suppression was reestablished.
Reply to ‘‘Some fundamental considerations regarding voice identification’’ [J. Acoust. Soc. Am. 8
2, 687–688 (1987)]
Authors: Koenig Bruce E. , Ritenour Donald V. , Kohus Barbara A. , Savoy Kelly Artese
Published: October 2005

This letter is a reply to comments made by T. Shipp et al. on a previous article by B. E. Koenig [J. Acoust. Soc. Am. 79, 2088–2090 (1986)].
Imaging of rough surfaces for impulsive and continuously radiating sources
Authors: Daneshvar M. R. , Clay C. S.
Published: October 2005

Synthetic experiments are employed to investigate the possibility of using focused imaging to reconstruct the subsurface structure. The technique of focusing two arrays of receivers on a subsurface point and cross correlating the outputs is known as the split array cross correlation (SACC) processing. Each point in a subsurface grid is assumed to be the source of scattered Huygens wavelets. The SACC processing gives the relative strengths of the scatterers. A correlation image is constructed from diffracted and reflected signals using the SACC processing. It shows the locations and the strengths of the Huygens sourcelets. Post correlation stack results show the diffraction pattern is enhanced relative to that of the reflection. The SACC processing works for known impulsive sources and continuously radiating random sources. Numerical model experiments were made for an assemblage of wedges, which gives rise to reflections from the facets and diffractions from the apexes and the ‘‘V’’ bottoms. The synthetic seismograms are computed based on the impulse solution for reflection and diffraction from a rigid wedge, adapted from the Biot–Tolstoy impulse theory of diffraction. The controlled source correlation image shows the diffractors and the portions of plain surfaces where reflections occur. The correlation image region is bounded by the ellipse of constant travel time from source to scatterer to receiver. The source and the receiver are at the foci of the ellipse. The correlation image of continuously radiating sources shows high intensities at the diffractors and the mirror images of the sources in the reflecting planes.
A method of range and depth estimation by modal decomposition
Authors: Yang T. C.
Published: October 2005

Normal mode amplitudes are definite functions of depth and have a characteristic phase as a function of source range rs [i.e., exp(−ikirs), where ki is the ith mode wavenumber]. The range and depth of an acoustic source in the ocean can then be determined by decomposing array data and beamforming on the mode amplitudes. In particular, the product of the normal mode amplitudes with the steering vector Ui [where Ui=exp(ikir) ] is maximum for the true source range (r=rs). Similarly, the correlation of the measured (decomposed) mode amplitudes with the theoretically calculated mode amplitudes is maximum at the source depth. Accurate range and depth estimation with this approach, however, requires reliable estimates of the mode amplitudes. In this article, an eigenvector decomposition technique is used to extract the mode amplitudes for data received on a long (1-km) vertical array. Range and depth are successfully estimated both for simulated data and for data from the 1982 FRAM IV experiment in the Arctic Ocean. The effect of the number of modes on the estimates is also illustrated.
Effects of periodic rest on physiological measures of auditory sensitivity following exposure to noise
Authors: Sinex D. G. , Clark W. W. , Bohne B. A.
Published: October 2005

Whole nerve action potential (AP) and single auditory-nerve fiber thresholds were measured in chinchillas exposed to noise. The exposure stimulus was a 500-Hz octave band of noise presented at 95 dB SPL for 15 min/h, for 4 or 40 days. The AP thresholds were elevated by about 40 dB on day 4, between 0.5 kHz and approximately 8 kHz. On day 40, AP thresholds at the same frequencies were lower by 10–25 dB, even though the noise exposure had continued. Single fiber threshold tuning curves exhibited pathologies similar to those previously observed following noise exposure. Tuning curves measured on day 40 were more normal in appearance. These results confirm that similar recovery of threshold observed in psychophysical experiments [Clark et al., J. Acoust. Soc. Am. 82, 1253–1264 (1987)] can be understood in terms of the sensitivity of the peripheral auditory system.
Infrasonic ocean noise sources: Wind versus waves
Authors: Nichols Rudolph H.
Published: October 2005

Published theories on the mechanism of generation of infrasonic (1- to 20-Hz) ambient ocean noise attribute the sources variously to wind, waves, turbulent currents, or combinations thereof. In an effort to investigate the relative importance of wind and waves as noise generators, a 40-day series of concurrent measurements of wind speed, waveheight, and noise spectrum level at eight frequencies from 2.5–20.0 Hz was made at each of three deep-water sites. One was in a high-wind area, another in a low-wind area, and the third in an intermediate weather zone. Cross correlations of the overall 40-day series of noise levels with those of wind speed and of waveheight indicated that wind speed is the factor more related to infrasonic noise level. Detailed examination of the data disclosed shorter periods in which wind speed and waveheight were not correlated, and their effects could be separated. In these, the noise level variations definitely followed those of the wind speed and not those of the waveheight. The behavior of the ambient noise levels with increasing wind speed appeared similar to that reported for higher frequencies by other observers. The nature of the data suggests that breaking waves may be a source of VLF ambient noise.
A simulation model for high-frequency under-ice reverberation
Authors: Bishop Garner C. , Ellison William T. , Mellberg Leonard E.
Published: October 2005

A model has been developed to evaluate reverberation produced by the backscatter of a high-frequency acoustic pulse from pack ice regions characteristic of the interior Arctic. The model uses measured two-dimensional under-ice acoustic profile data and several empirical results that relate geometric parameters of the large-scale under-ice relief features, e.g., ice keels to construct a three-dimensional bimodal under-ice surface consisting of first-year ice keels and sloping flat ice regions. A first-year keel is modeled as an ensemble of randomly oriented ice blocks on a planar surface inclined at some slope angle with respect to a horizontal plane at sea level. The keel is characterized by length, draft, width, ice thickness, and aspect angle. A region of flat ice is modeled as a smooth planar surface whose slope angle is less than some critical angle that serves to distinguish a flat ice feature from an ice keel. The Kirchhoff approximation is used to evaluate the target strength of a facet of an ice block. The target strength of a keel is calculated in range increments as the coherent sum of the backscatter from all scattering facets contained within one-half the pulse length projected onto the keel. Reverberation at each range increment is calculated and compared with measured results from several Arctic sites. The model is used to show the effects of various ice and acoustic parameters on reverberation and target strength frequency distributions.
Rate-intensity functions and their modification by broadband noise for neurons in the guinea pig inferior colliculus
Authors: Rees Adrian , Palmer Alan R.
Published: October 2005

Rate-intensity functions (RIFs) were generated in response to characteristic frequency (CF) tones presented alone and in the presence of broadband noise for neurons in the central nucleus of the inferior colliculus (IC) of the anesthetized guinea pig. Seventy-six percent of the RIFs to CF tones were monotonic (some showing incomplete saturation), and 24% were nonmonotonic. The RIFs to continuous noise were more nonmonotonic than those to CF tones. In continuous or gated noise, the dynamic portion of the RIF to a tone was shifted to a higher tone level, with little change in the dynamic range. Above a threshold noise level, the shift was a linear function of noise level with slope 0.97. Little shift occurred when the noise was inversely gated with respect to the tone burst, suggesting that the underlying mechanism is suppression rather than adaptation. For 63% of units, the maximum discharge rate to a tone in low levels (<0-dB spectrum level) of noise (including inversely gated) was greater than to the tone alone. Although many of the effects of noise in the IC reflect peripheral mechanisms, they are supplemented by centrally based processes which enhance the detectability of tone intensity increments in the presence of noise.
Noise-induced hearing damage caused by metabolic exhaustion: A mathematical model
Authors: Oftedal Gunnhild
Published: October 2005

A mathematical model for noise-induced hearing loss is based on the assumption that hair cells are damaged, temporarily or permanently, by metabolic exhaustion, and that the number of damaged hair cells and the hearing loss are monotonically increasing functions of an energy deficiency. The purpose of the model is to focus on the influence of sound intensity, exposure duration, and temporal pattern of the sound exposure on the noise-induced hearing loss from long-duration exposures. The model is restricted to the range of sound levels where metabolic exhaustion probably is the main reason for the hair cell damage. Only exposures with similar frequency spectra and producing moderate hearing losses are considered; frequency dependence is not discussed.
Minimum audible movement angle as a function of signal frequency and the velocity of the source
Authors: Perrott David R. , Tucker Juliana
Published: October 2005

Thresholds for the detection of the direction of travel of a moving sound source were determined in a single-interval, forced-choice paradigm. Both the rate at which the sound source is displaced (8°–128°/s) and the frequency of the signal to be localized (500–3700 Hz) affect dynamic spatial resolution. There is an inverse relationship between spatial resolution and the rate of travel, a finding that replicates an earlier observation on performance with sources displaced at high velocities [Perrott and Musicant, J. Acoust. Soc. Am. 62, 1463–1466 (1977)]. However, the magnitude of this effect depends on the actual velocities employed. Relatively small changes in spatial resolution are apparent for velocities below approximately 32°/s. The significant frequency effect can be summarized as follows: Dynamic spatial resolution is better for signals below 1000 Hz than for signals above this value (within the range tested). Particularly poor resolution is evident for signals between 1300–2000 Hz. The present results indicate that signal frequency affects dynamic spatial resolution in a fashion similiar to that which has been observed in the more common ‘‘static’’ localization test situation. There is no indication of an interaction between these two variables. These results provide additional support for the hypothesis that both static and dynamic spatial discrimination functions are dependent upon the same underlying mechanisms. The effects of velocity upon the spatial resolution problem, a unique aspect of the dynamic paradigm, can probably be explained without the necessity of additional hypothetical mechanisms in the auditory system (e.g., a specialized motion detector).
The reliability of auditory thresholds in the 8- to 20-kHz range using a prototype audiometer
Authors: Stelmachowicz Patricia G. , Beauchaine Kathryn A. , Kalberer Ann , Langer Theresa , Jesteadt Walt
Published: October 2005

This study was designed to evaluate both intra- and intertester reliability of auditory thresholds in the 8- to 20-kHz range using a recently developed high-frequency audiometer [Stevens et al., J. Acoust. Soc. Am. 81, 470–484 (1987)]. With this device, signals from a high-frequency transducer are introduced into the ear canal via a plastic tube. A calibration function is calculated for each ear and used to estimate the sound-pressure level (SPL) at the tympanic membrane. Twenty normal-hearing listeners were tested four times, twice by each of two examiners. In the higher frequencies, accurate calibration functions could not be obtained for many subjects; in these cases, values extrapolated from lower frequencies were used to estimate SPL. Findings reveal that the standard error of measurement for both intra- and intertester measures increases as a function of frequency. Intertester variability was only slightly higher than intratester variability. In most cases, variability of threshold estimates in dB SPL was higher than that observed for the uncorrected attenuator settings. Exclusion of extrapolated values improved reliability substantially.
The physics of small-amplitude oscillation of the vocal folds
Authors: Titze Ingo R.
Published: October 2005

A theory of vocal fold oscillation is developed on the basis of the body-cover hypothesis. The cover is represented by a distributed surface layer that can propagate a mucosal surface wave. Linearization of the surface-wave displacement and velocity, and further small-amplitude approximations, yields closed-form expressions for conditions of oscillation. The theory predicts that the lung pressure required to sustain oscillation, i.e., the oscillation threshold pressure, is reduced by reducing the mucosal wave velocity, by bringing the vocal folds closer together and by reducing the convergence angle in the glottis. The effect of vocal tract acoustic loading is included. It is shown that vocal tract inertance reduces the oscillation threshold pressure, whereas vocal tract resistance increases it. The treatment, which is applicable to falsetto and breathy voice, as well as onset or release of phonation in the absence of vocal fold collision, is harmonized with former treatments based on two-mass models and collapsible tubes.
Segmental durations in connected-speech signals: Syllabic stress
Authors: Crystal Thomas H. , House Arthur S.
Published: October 2005

Analyses into the effect of syllabic stress on the durations of speech sounds have been performed on the recordings produced by six talkers reading two scripts of approximately 300 words each. The texts, the combined visual–auditory marking technique, and preliminary results were reported earlier in Crystal and House [J. Acoust. Soc. Am. 72, 705–716 (1982)] and further results were reported in Crystal and House [J. Acoust. Soc. Am. XX, XXX–XXX (1988a)]. The average durations and standard deviations of various classes of speech sounds, as well as individual speech sounds, have been determined in syllables where the stress characteristic is known. Measurements are compared to earlier data and to various pertinent published reports.
Stimulus factors influencing the identification of voiced stop consonants by normal-hearing and hearing-impaired adults
Authors: Lindholm Julie Mapes , Dorman Michael , Taylor Bonnie Ellen , Hannley Maureen T.
Published: October 2005

The effects of mild-to-moderate hearing impairment on the perceptual importance of three acoustic correlates of stop consonant place of articulation were examined. Normal-hearing and hearing-impaired adults identified a stimulus set comprising all possible combinations of the levels of three factors: formant transition type (three levels), spectral tilt type (three levels), and abruptness of frequency change (two levels). The levels of these factors correspond to those appropriate for /b/, /d/, and /g/ in the /æ/ environment. Normal-hearing subjects responded primarily in accord with the place of articulation specified by the formant transitions. Hearing-impaired subjects showed less-than-normal reliance on formant transitions and greater-than-normal reliance on spectral tilt and abruptness of frequency change. These results suggest that hearing impairment affects the perceptual importance of cues to stop consonant identity, increasing the importance of information provided by both temporal characteristics and gross spectral shape and decreasing the importance of information provided by the formant transitions.
A practical approach to ultrasonic imaging using diffraction tomography
Authors: Witten Alan , Tuggle Joe , Waag Robert C.
Published: October 2005

A technique for ultrasonic imaging based on the theory of diffraction tomography is presented. The method utilizes a fixed, circular configuration of transmitters and detectors. This configuration was selected because it avoids many practical limitations associated with the design of a medical imaging device. Practical considerations also motivated the inclusion of effects associated with the transmitter beam pattern rather than pursuing the more conventional approach in which plane-wave illumination is required. In addition, the problem of separately imaging both density and compressibility variations is considered.
Small acoustic tubes: New approximations including isothermal and viscous effects
Authors: Zuercher Joseph C. , Carlson Elmer V. , Killion Mead C.
Published: October 2005

Algebraic expressions are given (in fortran format for convenient use) that accurately approximate the value of the per unit-length acoustic impedance of small tubes (radii less than (1)/(16) acoustic wavelength) including isothermal and viscous effects. Their accuracy of typically 3% or better was obtained as a result of adding a shunt conductance term to the traditional approximations and including frequency-dependent multiplicative factors. The multiplicative factors are simple expressions for the real or imaginary terms, providing a factor of 40 increase in calculational speed over the full Bessel-function solution. Experimental verification is presented for various combinations of small tubes and cavities relevant to hearing aid applications, and the differences between the present approximations and previous approximations are illustrated using a 1-mm-diam tube as an example. Normalized complex series impedance and shunt admittance, characteristic impedance, time delay, and attenuation constant plots are provided as a reference utilizing the more nearly exact Bessel solution.