bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of monaural frequency selectivity in binaural analysis
Authors: Hall Joseph W. , Fernandes Mariano A.
Published: October 2005

The relation between the monaural critical band and binaural analysis was examined using an NoSm MLD paradigm, in order to resolve ambiguities about the width of the masking spectrum important for binaural detection. A 500-Hz pure-tone signal was presented with a 600-Hz-wide band of masking noise to the signal ear. Bands of noise ranging in width from 25 to 600 Hz, or noise notches (imposed on a 600-Hz-wide band centered on the signal frequency) ranging in width from 0 to 600 Hz were presented to the nonsignal ear. All noise bands and notches were centered on 500 Hz, the frequency of the signal. The effects of varying bandwidth were radically different from those of varying notchwidth: the MLD changed from zero to approximately 8 dB over a bandwidth range of 400 Hz; for notchwidths, however, the MLD changed 8 dB over a range of only 50 Hz. The results support an interpretation that the fine frequency selectivity of monaural analysis is preserved in peripheral binaural interaction, but that a relatively wide frequency range of critical bands is scanned at a later stage of binaural processing. It was suggested that the wide spectral range of binaural analysis may provide a background against which binaural differences due to the signal are detected.
A more rigorous synthesis of echosonde patterns
Authors: Adekola S. Adeniyi
Published: October 2005

Presented here is the echosonde (acoustic echosounding) synthesis based on a more rigorous analytical tool than hitherto available. The basic problem addressed in this paper is that of specifying a pattern and solving for the source distribution capable of reproducing the pattern specified. We focus attention on the determination of suitable practical source fields that can provide acceptable pattern approximations to certain prescribed echosonde beams. Numerical and analytical examples discussed, describe patterns synthesizing into physically realizable source fields confined within finite antenna-aperture regions. Also, other analytical results provided, reveal very clearly that the pattern synthesis problem is not unique. In order to highlight the importance of the present echosonde contribution to the general problem of circular synthesis, we present a brief survey of the synthesis works to date where certain technical problems which still remain unresolved are pointed out. A substantial set of new results for circular echosonde synthesis which has received little attention in the literature, is presented in comprehensive tables for ease of reference. The paper also finally examines an error analysis of certain aspects of the results obtained.
Imaging in a scanning photoacoustic microscope
Authors: Cox I. J. , Sheppard C. J. R.
Published: October 2005

Imaging in a scanning photoacoustic microscope (SPAM) is analyzed using Fourier imaging concepts. In particular, the spatial frequency response and the resolution of the instrument are examined. It is shown that in the general case, the imaging is object dependent. However, for the special cases of negligible thermal diffusion or where the specimen is either optically uniform or acoustically and thermally uniform, explicit expressions for the spatial frequency response are derived. It is shown that a SPAM may exhibit superresolution provided an acoustic lens is used rather than a large area detector.
Reflection of P and S
V waves at the free surface of a prestressed elastic half-space
Authors: Sidhu R. S. , Singh Sarva Jit
Published: October 2005

The propagation of plane waves in a prestressed elastic solid with incremental elastic coefficients possessing orthotropic symmetry is discussed. Two types of plane waves, called quasi-P and quasi-S waves, are shown to exist. An expression for the group velocity of these waves is obtained. The velocities of quasi-P and quasi-S waves are found to depend on the angle of propagation. The reflection coefficients of these waves incident at the free surface of a prestressed elastic half-space are derived. Critical reflection of quasi-P and quasi-S waves has been discussed. It is found that while quasi-S waves always have critical reflection, quasi-P waves can have critical reflection only if incremental elastic coefficients satisfy a certain condition.
Calculation of acoustic wave scattering by means of the Helmholtz integral equation. I
Authors: Tobocman W.
Published: October 2005

For the calculation of wave scattering by targets of complex shape it is suggested that the Helmholtz integral equation be solved in configuration space directly. Expansion in terms of spherical or spheroidal waves is thus avoided. The method is tested by calculating the scattering of acoustic waves by rigid spheroids of various shapes and orientations. The method appears to be particularly well suited to the intermediate wavelength regime where the wavelength is comparable to the dimension of the target.
Theoretical spectra for optimum SNR enhancement of narrow-band signals in surface reverberation
Authors: Symons Frank W.
Published: October 2005

In a recent publication [Symons, J. Acoust. Soc. Am. 74, 851–860 (1983)] theoretical performance capabilities of the optimum filter for maximization of SNR and of a suboptimum approximation were compared to the conventional matched filter in the case of signals masked by surface reverberation. Some representative theoretical spectra are presented in order to give insight into the effects of the filters in a reverberation environment.
A uniformly valid solution for acoustic normal mode propagation in a range varying ocean
Authors: Desaubies Yves
Published: October 2005

It is shown that the adiabatic approximation usually presented in the literature for acoustic normal mode propagation in a range-dependent ocean has serious limitations and breaks down at rather short ranges. This is because the approximation does not account properly for the phase of the modes. A rigorous, uniformly valid asymptotic expansion is presented which provides a solution with greatly improved range of validity.
Interpretation of sample wave speed measured in an impedance tube
Authors: Dubbelday Pieter S. , Capps Rodger N.
Published: October 2005

The basic measurement in an impedance tube is a complex reflection coefficient, from which the propagation speed and attenuation are computed. This speed is often identified with the dilatational wave speed in the sample material. This is only approximately correct; it depends on the ratio of sample radius to inner radius of the tube. Thus a correction to the measured wave speed is in order. Moreover, by varying the ratio of the radii one may derive two elastic moduli for the sample material from the measurements, as is shown by an experimental example for a Lucite sample.
On the growth of masking asymmetry with stimulus intensity
Authors: Lutfi Robert A. , Patterson Roy D.
Published: October 2005

Masking asymmetry was investigated over a wide range of stimulus intensities for two signal frequencies, f0=1.0 and 4.0 kHz, using both fixed-masker and fixed-signal paradigms. The masker was a notched noise with the upper and lower edges of the notch, fu and fl, respectively, placed asymmetrically about f0. For various notch widths, the asymmetry of masking was measured as the difference between the masked threshold obtained when fl was nearer f0 and that obtained when fu was nearer f0. For maskers with wide notches, (fu−fl)/f0>0.15, masking asymmetry changed with stimulus level; at the highest level, masked threshold was greatest when fl was nearer f0, and, at the lowest level the asymmetry reversed slightly for f0=1.0 kHz so that masked threshold was actually greater when fu was nearer f0. Nonparallel growth of masking functions reveal changes in masking asymmetry with signal level as well as with masker level. It is concluded that the nolinear growth of masking with level is due primarily to changes in the auditory filter, rather than changes in the detector following the filter.
Laryngeal muscles and articulatory control
Authors: Löfqvist Anders , McGarr Nancy S. , Honda Kiyoshi
Published: October 2005

The present study continues earlier work on laryngeal control in speech with particular reference to adjustments in Swedish voiceless consonants and consonant clusters. Electromyographic recordings were obtained from four intrinsic laryngeal muscles together with simultaneous transillumination and acoustic signals. Results indicate that the vocalis and lateral cricoarytenoid muscles participate in the control of both articulation and phonation (F0). The interarytenoid muscle appeared to be involved only in articulatory adjustments. Activity in the cricothyroid was mostly related to F0 change; however, this muscle also showed an increase in activity for voiceless sounds. In addition, the vocalis muscle appeared to participate in glottal adduction without complete closure in voiceless clusters with the lateral cricoarytenoid and the interarytenoid playing no particular roles. The results suggest the need of studying laryngeal behavior in speech within a general systems famework for movement control.
Dolphin biosonar detection in clutter: Variation in the payoff matrix
Authors: Au Whitlow W. L. , Turl Charles W.
Published: October 2005

An Atlantic bottlenose dolphin (Tursiops truncatus) was trained to detect targets in the presence of interference induced by a clutter screen. The screen consisted of forty-eight 5.1-cm-diam cork spheres spaced 15.2 cm apart and arranged in a rectangular array. Hollow aluminum cylinders having the same outer diameter and wall thickness and three different lengths were used as targets. Only one target was presented per target-present trial and it was placed in the plane of the clutter screen at its midpoint. The payoff matrix was manipulated by changing the amount of reinforcement (number of pieces of fish) for correct detections and rejections. In terms of the ratio of correct detections to correct rejections, the payoff matrix was varied over four values—1:1, 4:1, 8:1, and 1:4. As the payoff matrix increased from 1:1 to 4:1 and 8:1, the dolphin became progressively more liberal in reporting on the presence of a target with a subsequent increase in both the correct detection and false alarm rates. However, the animal’s detection sensitivity was approximately constant and independent of the response bias. The dolphin generally emitted the most clicks per trial when the payoff matrix was 4:1 and the least amount of clicks when the payoff matrix was 8:1. The dolphin also typically emitted more clicks for target-present versus target-absent responses.
A theoretical and experimental study of a model piezoelectric membrane headphone
Authors: Davies Geoffrey , Murphy Preston V. , Maurer Guy
Published: October 2005

The generation of sound by a curved circular piezoelectric polymer diagram has been analyzed theoretically and experimentally. The diaphragm was considered to have zero flexible stiffness and adjustable tension and to drive a coupling volume having significant reaction effects. The analysis was confined to frequencies well below resonance. Measurements of static diaphragm displacement caused by differences in air pressure were used to determine values of Young’s modulus and a film pretension. The sound generated by a 110-Hz signal was measured as a function of static displacement and found to increase strongly at first, pass through a rather flat maximum, and finally decrease. A theory was developed which correlated with the results and a figure of merit was derived which relates output per unit exciting voltage to the thickness, piezoelectric coefficient, elastic modulus, and Poisson’s ratio of the diaphragm.
The addition of piezoelectric properties to structural finite element programs by matrix manipulations
Authors: McDearmon Graham F.
Published: October 2005

Piezoelectric properties may be added to structural finite element programs (SFEPs) by matrix manipulations of elastic and heat transfer element matrices. The theory for this addition is contained in this publication.
Cochlear mechanics: Analysis for a pure tone
Authors: Holmes Mark H. , Cole Julian D.
Published: October 2005

A three-dimensional hydroelastic model of the cochlea is analyzed, in which the fluid is viscous and the basilar membrane is an inhomogeneous orthotropic elastic plate. After the solution is obtained using a multiple-scale approximation, comparison is made with experiment for the human cochlea.
High-frequency rolloff in a cochlear model without critical-layer resonance
Authors: Lewis E. R.
Published: October 2005

Zwislocki’s original cochlear model, incorporating axial fluid inertia and shunt basilar-membrane stiffness and viscous resistance, possesses an operating regime not previously emphasized in the literature. Even in the absence of basilar-membrane mass and the consequent critical-layer resonance, this regime provides extraordinarily steep high-frequency rolloff. That rolloff is not associated with a critical frequency at which energy flow velocity goes to zero, but is attributable instead to a combination of two effects; (1) frequency-dependent energy coupling to the basilar-membrane viscous resistance, leading to local attenuation of the traveling wave at a rate (Np/cycle) that is directly proportional to frequency, and (2) wavelength that decreases with increasing frequency, thus increasing the number of cycles per unit length of basilar membrane. This combination leads to local attenuation of the traveling-wave amplitude (hence energy absorption from the traveling wave) that is strongly dependent on frequency, the rate (Np/cm) being proportional to the square of frequency in the long-wave mode. In Ranke’s (two-dimensional, short-wave mode) version of the model, the same operating regime leads to attenuation that is even more intensely dependent on frequency, the rate being proportional to the cube of frequency.
Measurement of nonlinear vibration by signal compression method
Authors: Aoshima Nobuharu
Published: October 2005

The signal compression method [Aoshima, J. Acoust. Soc. Am. 69, 1484–1488 (1981); Aoshima, J. Acoust. Soc. Jpn. (E) 3, 105–109 (1982)] is shown to be useful for analyzing nonlinear systems as well as linear systems. If a nonlinear system can be modeled as a parallel combination of a linear part and elements subject to a power law, such as a squarer, they can be analyzed separately by the signal compression method. As the test signal of the signal compression method has been generated by an ‘‘expanding filter’’ H(ω)=exp(jαω2), the linear response can be detected by a ‘‘compression filter’’ H−1(ω)=exp(−jαω2). Then the nonlinear component generated by the squarer is also compressed by another ‘‘second-order compression filter’’ H−12(ω)=exp(−jαω2/2). The frequency tripled component, which is generated by a third power nonlinear element, is compressed by the ‘‘third-order compression filter’’ H−13(ω)=exp(−jαω2/3). Results of model experiments by an analog squarer and a numerical nonlinear processing are exemplified together with nonlinear effects observed in a floor vibration experiment.
Acoustically generated turbulence and its effect on acoustic agglomeration
Authors: Tiwary Rajiv , Reethof Gerhard , McDaniel Oliver H.
Published: October 2005

Acoustic agglomeration (AA) is an intermediate treatment of aerosols containing submicron- and micron-sized particles so that conventional cleaning devices such as electrostatic precipitators, bag houses, and scrubbers can remove these fine particles more efficiently. The high-intensity acoustic field in the AA causes local velocity fluctuations to move the particles relative to one another, collide, adhere, and grow. This paper addresses the question of whether such highly intense acoustic fields (approximately 160 dB) will cause random velocity fluctuations of such a magnitude that this acoustic ‘‘turbulence’’ significantly affects AA. The experimental study results show that only the acoustic velocity fluctuations at the excitation frequency dominate the local velocity and therefore the particle motions. Although some acoustically generated random motion is noted with increasing acoustic intensity above 160-dB sound pressure level, the energy in turbulent fluctuations is about three orders of magnitude lower than the energy in acoustic frequency and harmonics. The paper concludes that acoustically induced turbulence does not play a significant role in AA.
Intrinsic modes in a nonseparable ocean waveguide
Authors: Arnold J. M. , Felsen L. B.
Published: October 2005

Waveguide structures encountered in underwater acoustics usually lead to nonseparable boundary value problems, which do not admit definition of conventional normal modes. However, it may nevertheless be possible to construct source-free modelike wavefunctions for such configurations, which are intrinsically determined by the waveguide geometry, are mutually decoupled, and therefore propagate independently of one another when used in superposition. We call such wavefunctions intrinsic modes. For the special case of a wedge-shaped ocean with penetrable bottom, we pursue an approach similar to our previous analysis [J. M. Arnold and L. B. Felsen, J. Acoust. Soc. Am. 73, 1105–1119 (1983)] to construct the intrinsic modes explicitly. Leading order asymptotic evaluation of an intrinsic mode for small bottom slope reveals its similarity to the conventional adiabatic mode, but with a uniform transition, through cutoff, between the bound and leaky mode regions. This construction proceeds without reference to any source of the acoustic field, thereby differing from our previous treatment wherein the existence of local modes was inferred from an independently calculated asymptotic form of a line source field. Moreover, by local normal mode expansion of an intrinsic mode, with the expansion coefficients derived from the next higher order asymptotic approximation, we demonstrate explicitly that the intrinsic mode can account for coupling between adiabatic modes, with coupling coefficients that are shown elsewhere to be consistent with those from conventional coupled mode theory.
Effects of second-order scattering on high resolution sonars
Authors: Stanton T. K.
Published: October 2005

To achieve simultaneous high volume coverage and high spatial resolution, sonars employing multiple narrow steered receiver beams in conjunction with a single wide transmitter beam are quite often used. The effects of second-order scattering on multibeam sonars have been calculated. The analysis is in terms of the backscattered energy (or ‘‘integrated echo’’) due to clouds of point scatterers. The work applies to scattering such as from clouds of bubbles or dense schools or ‘‘swarms’’ of swimbladder-bearing fish. Under certain conditions second-order scattering will increase the echo energy an appreciable amount, especially as the ratio of transmitter beamwidth to receiver beamwidth increases. The major conditions are (1) dense clouds of nondirectional scatterers are insonified, (2) the sonar signal suffers measurable attenuation due to the extinction cross section of the scatterers, and (3) the absorption cross section of the scatterers is small. The echo energy due to both first- and second-order scattering are calculated for several beamwidth ratios. It is shown that the backscattered energy is increased by up to 100% due to second-order scattering.
Solitary waves on nonlinear elastic rods. I
Authors: Soerensen M. P. , Christiansen P. L. , Lomdahl P. S.
Published: October 2005

Acoustic waves on elastic rods with circular cross section are governed by improved Boussinesq equations when transverse motion and nonlinearity in the elastic medium are taken into account. Solitary wave solutions to these equations have been found. The present paper treats the interaction between the solitary waves numerically. It is demonstrated that the waves behave almost like solitons in agreement with the fact that the improved Boussinesq equations are nearly integrable. Thus three conservation theorems can be derived from the equations. A new subsonic quasibreather is found in the case of a cubic nonlinearity. The balance between dispersion and nonlinearity in the equation is investigated.
Nonlinear scattering of acoustic waves by vibrating surfaces
Authors: Piquette Jean C. , Van Buren A. L.
Published: October 2005

The problem of the scattering of acoustic waves by a vibrating surface surrounded by a fluid was investigated. Theoretical results were obtained for the specific case of a plane wave (of angular frequency ωp ) normally incident on an infinitely long cylinder vibrating uniformly and harmonically (at angular frequency ωc ) in the radial direction. This problem was previously studied by Censor [J. Sound Vib. 25, 101–110 (1972)], who used the linear equation together with nonlinear boundary conditions to obtain his solution. In addition to ordinary rigid-body scattering, Censor predicted nongrowing waves at the sum and difference frequencies ωp±ωc. However, medium nonlinearities also produce sum- and difference-frequency waves. The amplitudes of these waves tend to grow with increasing distance from the surface and, after a very small distance, dominate those predicted by Censor. In the present study, an expression for the difference-frequency wave was obtained using the simple-source formulation of the nonlinear wave equation subject to the appropriate boundary conditions. The expression was evaluated numerically for specific parameters and the results are presented graphically. Efforts to experimentally confirm the theoretical predictions were inhibited by the presence of previously unsuspected levels of hydrophone nonlinearity.
Nonlinear radial oscillations of a gas bubble including thermal effects
Authors: Miksis Michael J. , Ting Lu
Published: October 2005

A system of integral differential equations determining the nonlinear oscillations of a spherical gas bubble including thermal and viscous damping effects is derived. This system is obtained systematically from the Navier–Stokes equations for the liquid and the gas phases and from the interface conditions by the method of matched asymptotics. The ratio of the thermal length (De/ω)1/2, in the gas and the mean bubble radius is the small expansion parameter. Here De is the reference thermal diffusivity of the gas and ω the frequency of oscillation. By using the well-tested approximate viscosity function in compressible boundary layer theory, the pressure inside the bubble can be related to its radius by an integral equation. Coupling this integral equation with the Rayleigh–Plesset equation gives us a closed system determining the radial oscillations of the bubble. For small oscillations, the system is solved analytically and the results are in agreement with the linear theory. This system is then solved numerically for finite amplitude oscillations.
Method of data reduction for accurate determination of acoustic backscatter coefficients
Authors: Madsen Ernest L. , Insana Michael F. , Zagzebski James A.
Published: October 2005

In previous methods of data reduction used to determine ultrasonic backscatter coefficients, various approximations were made. One frequently used is that there is an abrupt cutoff in the lateral extent of the scattering volume interrogated. Another approximation in all previous methods is that the effect of time gating the received echo signals can be written as a function of the distance along the axis of the interrogating beam. In the present paper we show that the backscatter coefficient can be derived from experimental data without making such approximations. The cases of narrow-band and broadband pulses are treated, and the method is applicable whatever the distance between the interrogated volume of scatterers and the transducer face. It is shown that, for a given pulse form, the gate duration must be sufficiently long in order to attain a specified accuracy for the measured backscatter coefficient. A test of the method was done using a phantom with well-defined scattering properties. Very good agreement was found between measured values of backscatter coefficients and those calculated using a first-principles theory.
The reflection phenomena of plane waves at a free boundary in a prestressed elastic half-space
Authors: Pal A. K. , Chattopadhyay A.
Published: October 2005

In this article the reflection phenomena of plane harmonic elastic waves in a homogeneous, prestressed, orthotropic half-space are discussed. It has been observed that the reflection phenomena of pure mode of P and SV waves in such a medium are different from that of the classical isotropic elastic medium. Apart from the directions parallel to the coordinate axes in the medium there exists a specific direction along which pure modes of P and SV waves may propagate through the medium. It is seen that under certain conditions the P wave propagating in a specific direction will give rise to a reflected wave which is either the superposition of both P and SV waves or an SV wave only, obeying the simple laws of reflection, but it cannot give rise to a pure P mode only. [This phenomenon, i.e., case 3 (as discussed in the paper) may be possible when the denominator of R2 is zero.] Similar phenomena are also observed in the case of an SV wave. Since initial stress generally induces orthotropy in an isotropic medium, similar reflection phenomena should also be observed in a stressfree orthotropic medium. But the reflection pehnomenon of an SH wave is similar to that in the classical elastic medium. Moreover, under equal normal initial stresses, the medium behaves like a classical isotropic one and hence the reflection phenomena are similar to that of the classical case.
Nearfield pressures and surface intensity for cylindrical vibrators
Authors: Stepanishen Peter R. , Chen Huo-Wang
Published: October 2005

A numerical approach is presented to evaluate the acoustic nearfield of cylindrical vibrators with specified harmonic radial velocity distributions. The approach is based on the use of a combined Green’s function and FFT method. The acoustic field is first represented in terms of a Fourier transform of the specified radial velocity. A normalized axial power density at the surface of the vibrator is then introduced. This quantity provides a useful measure of the local power transfer into the fluid per unit length of the vibrator. The resulting spectral representation of the acoustic field and power density can be rapidly evaluated via the use of FFT methods to obtain the spatial characteristics of the acoustic field and the local power transfer into the fluid. Numerical results are presented to illustrate the spatial characteristics of the acoustic fields and power density of finite length vibrators with axisymmetric and nonaxisymmetric distributions.
Place-of-articulation information in the closure voicing of plosives
Authors: Barry William J.
Published: October 2005

Two experiments are presented which examine whether the voice bar in [b] and [d] contains information relevant to the identity of the stop consonant and the following vowel. The results indicate that listeners can exploit consonantal place-of-articulation information contained in the voice bars. The ability of the subjects to ascertain the identity of the vowel following the voice bar was extremely limited, even after a training period; the confusions again point to the influence of consonantal place-of-articulation information.
Effect of the temporal pattern of a given noise dose on TTS in guinea pigs
Authors: Buck K. , Dancer A. , Franke R.
Published: October 2005

To show the effect of the temporal pattern of acoustic stimulation on TTS15 min, guinea pigs were subjected to isoenergetic noises with the same spectrum. The exposures in a first experimental series were continuous noises and noise bursts. The continuous noise was presented with different durations and levels but always with the same energy. The noise burst stimulation consisted of a constant number of bursts with different interstimulus intervals. Both duration and repetition rate were shown to affect the TTS15 min measured for these isoenergetic stimuli. A duration of 225 to 1800 s and a repetition rate of one per second produced the greatest TTS15 min. In a second experimental series continuous noise and acoustic impulses with the same spectrum and 100-Hz repetition rate were presented at different levels. In this case the waveform of the stimulus (phase spectrum) was shown to have an effect on TTS15 min.
Ultrasonic beam structures in fluid media
Authors: Weight J. P.
Published: October 2005

Field patterns of short-pulse ultrasonic transducers are quite different from those of continuous- or quasicontinuous-wave sources and depend critically on the actual waveform emitted. The observed patterns, including those provided by using a small target to probe the field in the transmit–receive mode, are also dependent on the method of detection used—whether full- or half-wave. The structure of the field and the marked difference between the pulsed pressure beam pattern and the corresponding transmit–receive mode beam pattern are explained in terms of the plane and edge waves radiated by the source. The field radiated by a transducer is compared with measurements of the field structure of a circular aperture insonified by a plane wave. Consequences of the pulsed beam structure for ultrasonic pulse-echo evaluation are pointed out.
A comparison of acoustical scattering from fluid-loaded elastic shells and sound soft objects
Authors: Werby M. F. , Green L. H.
Published: October 2005

Comparisons are presented for acoustical scattering from fluid-loaded prolate spheroidal sound soft scatterers and elastic shells of the same shape, ranging in thickness from 0.1% to 2.5% of the semi-major axis. The Ka region being studied varies from 3 to 12, where K is the wavenumber of the incident wave and a is one-half the length of the major axis. Exact theoretical calculations are performed using a modified T-matrix approach which for the first time allows one to perform calculations on very thin nonspherical elastic shells. The calculations show that, with the exception of the very thin shell, one does not observe a sound soft background. Furthermore, resonances for these objects are very broad and tend to dominate the form function plots. Of particular interest is the fact that by the time the thickness reaches 2.5%, the background begins to appear rigid for suitably high Ka with a shift in resonance nulls, which is related to the fact that rigid scattering is out of phase by 180° with sound soft scattering
Refining the measurement of psychophysical tuning curves
Authors: Moore Brian C. J. , Glasberg Brian R. , Roberts Brian
Published: October 2005

Four experiments were performed in an attempt to refine the measurement of psychophysical tuning curves (PTCs). PTCs were determined using sinusoidal signals and narrow-band noise maskers, in both simultaneous and forward masking. In experiment I a fixed low-level notched noise was gated with the masker in order to restrict off-frequency listening and to eliminate ‘‘confusions’’ between the signal and masker in forward masking. In contrast to previous work, this procedure produced PTCs with similar round tips in both simultaneous and forward masking. The PTCs differed mainly in that the high-frequency skirts were steeper in forward masking. Experiment II compared PTCs with and without an additional notched-noise masker, for a number of signal levels. The notched noise had the effect of broadening the tips of the PTCs, this effect being greater in forward masking than in simultaneous masking. With increasing signal level the high-frequency skirt of the PTC became slightly steeper, and the low-frequency skirt slightly shallower. Experiment III studied the effect of signal duration on PTCs determined in simultaneous masking. Duration had little effect when off-frequency listening was restricted with a fixed notched-noise masker, but had a substantial effect in the absence of such a masker. Experiment IV studied the effect of signal delay in forward masking. When off-frequency listening was restricted and the signal levels adjusted to produce similar masker levels at threshold for each delay, the shape of the PTC was not affected by delay. It is concluded that, when PTCs are determined in the presence of notched noise, suppression is probably responsible for most of the differences between simultaneous and forward masking. Previous work may have overestimated the influence of suppression, because it did not control off-frequency listening and/or provide appropriate detection cues in forward masking.
Propagation of sound out of a fluid wedge into an underlying fluid substrate of greater sound speed
Authors: Coppens Alan B. , Humphries M. , Sanders James V.
Published: October 2005

A Green’s function extension of image theory allows the sound field in an absorbing fluid substrate underlying a fluid wedge of slower sound speed to be evaluated on a desktop computer. (1) Solutions based on an end-point approximation, valid at great distances from the apex of the wedge and for absorptions representative of sedimentarylike materials, show a beam peaking at a depth close to that predicted by more complicated models. An additional random-phase assumption provides a functional dependence for this angle identical with that obtained by a more elaborate procedure. (2) Solutions based on a saddle-point approximation are valid below the apex and for arbitrary absorption. At moderate absorption, these solutions are consistent with those observed in the farfield. For small absorption, the sound field displays a heretofore unnoticed structure that is consistent with the mutual interference of sound beams entering the substrate at various distances from the apex. Some previously unreported measurements of the sound field in the substrate support the predictions of the saddle-point approximation.
The probability distribution of intensity for acoustic propagation in a randomly varying ocean
Authors: Macaskill C. , Ewart T. E.
Published: October 2005

Probability distributions of intensity fluctuations from the MATE, AFAR, and S. W. Bermuda underwater acoustics experiments are compared with recently derived theoretical expressions. The limitations and strengths of these expressions are discussed. In particular, it is found that the work of Furutsu [J. Math. Phys. 17, 1252–1263 (1976)] gives a good description of the probability distribution function of intensity or log intensity, requiring only a knowledge of the second- and third-order intensity moments. Furutsu’s description is not asymptotically correct at large range, so a modified form is proposed for the moments of intensity that reduce analytically to the log-normal distribution at short range and to the exponential distribution at large range. This new form also predicts the higher moments well but cannot be inverted analytically. A numerical inversion is used, and the ensuing distribution agrees well with the analytical result of Furutsu. It is expected that the new expression will be applicable at all ranges.
The magnetospatial and electrospatial dispersion effects on elastic wave propagation in crystals
Authors: Kumaraswamy K. , Krishnamurthy N.
Published: October 2005

The effect of electric and magnetic fields on elastic wave propagation is studied for all crystal classes. Similarities in the propagation characteristics of electromagnetic and elastic waves in crystals are brought out. In the S4 type of crystals, there is a rotation of the major and minor axes of the elliptical state of polarization which depends on magnetospatial and electrospatial dispersion terms in the respective fields. A birefringence depending quadratically on an applied electric field is induced in the Th type of crystals for parallel field configurations. In perpendicular field configurations the longitudinal and transverse modes are coupled, exhibiting an elliptical state of polarization.
Noise-induced hearing loss as influenced by other agents and by some physical characteristics of the individual
Authors: Humes Larry E.
Published: October 2005

The interaction of noise with a variety of other agents and with some physical characteristics of the individual to produce noise-induced hearing loss is reviewed critically. The review is restricted, for the most part, to publications since 1970. Other agents interacting with steady-state noise that are reviewed here include: (1) ototoxic drugs (kanamycin, neomycin, ethacrynic acid, furosemide, and salicylates), (2) impulse noise, and (3) whole-body vibration. Physical characteristics of the individual that are reviewed are: (1) age, (2) presence of previous hearing loss from prior noise exposure, (3) eye color, and (4) race. Suggestions for future research in this general area are also made. Some of these suggestions are as follows: (1) to extend studies of the interaction of steady-state noise with impulse noise, salicylates, and whole-body vibration to encompass a broader range of exposure conditions, including exposure conditions typically encountered by the worker, (2) to develop an animal model of presbycusis to explore the interactions of noise-induced hearing loss and presbycusis, and (3) to explore the potential interactions resulting from concurrent exposure to multiple agents, such as impulse noise and ototoxic drugs, in younger, more susceptible animals.
Biomolecular absorption of ultrasound. I: Molecular weight
Authors: Kremkau Frederick W. , Cowgill Robert W.
Published: October 2005

Amino acid solutions have absorptions which are generally small compared to those for proteins. Proteolytic enzyme treatment of proteins in solution reduces their absorption. These observations suggest that absorption increases with molecular weight. However, measurements of sugars, polysaccharides, amino acids, and proteins yield no correlations of absorption with molecular weight within these groups. Therefore, it is concluded that absorption increases in these molecules with increasing molecular weight only in a threshold sense, with absorption increasing significantly only in a restricted molecular weight range. This range may approximate that observed for polyethylene glycol and dextran, viz., 1 to 100 monomer units. However, there is some indication that the transition range may be narrower than a factor of 100 in molecular weight.
Intensity discrimination: A severe departure from Weber’s law
Authors: Carlyon Robert P. , Moore Brian C. J.
Published: October 2005

These experiments were designed to assess the importance of different types of information which might be used in detecting intensity changes for pure tones. Thresholds for detecting an intensity change, expressed as 10 log (ΔI/I), were measured over a wide range of frequencies and levels under conditions where one or more sources of information was either present or was removed. Spread of excitation was restricted by using bandstop noise centered at the signal frequency. Information conveyed by dynamic responses to signal onsets and offsets was eliminated by masking onsets and offsets with bursts of bandpass noise. Phase-locking information was eliminated by using high-frequency signals (above 5 kHz). Dynamic responses to signal onsets and offsets appear to play little role in intensity discrimination. Phase locking does appear to be important since Weber’s law or a near-miss to it was observed at low frequencies, whereas at high frequencies performance deteriorated at moderate sound levels, and improved again at high levels. A preliminary experiment, using 225-ms stimuli revealed only a small midlevel deterioration at high frequencies. However, when 30-ms stimuli were used a large deterioration was observed, performance being worse when bandstop noise was presented with the tone. Hence at short durations and high frequencies spread of excitation seems to be important: When it is restricted by bandstop noise values of 10 log (ΔI/I) observed at moderate levels it can be as large as 14 dB. The results of the experiments are consistent with a bimodal distribution of thresholds in primary auditory neurons; at intermediate levels neither population will operate effectively. The absence of a level effect at low frequencies can be explained by phase-locking cues extending the range over which VIIIth-nerve fibers can signal changes in intensity.
The precedence effect: Revisited
Authors: Yost William A. , Soderquist David R.
Published: October 2005

The precedence effect, as investigated by Wallach et al. [Am. J. Psychol. 62, 324–336 (1949)] was studied in three experiments. Experiment I was a replication of the original work of Wallach et al. Although the first click pair appears to dominate the perception of the position of the lateral image, the effect of the first click pair does not appear to ‘‘offset’’ or ‘‘cancel’’ the effect of the second click pair in terms of producing a lateral image at midline. The data are consistent with Zurek’s [J. Acoust. Soc. Am. 67, 952–964 (1980)] proposal that the binaural system is less sensitive to the interaural temporal difference of the second click pair. Experiment II indicated that the effect of the first click pair on lateral judgments still dominates that of the second click pair when the images are judged to be off midline. In all of these studies, the variability of the data is quite high. Experiment III showed that the first click pair also led to a larger change in masked thresholds (masking-level differences, MLDs) than does the second click pair. These data reconfirm the use of two-click stimuli for demonstrations of the precedence effect and they describe some of the limitations of the procedure and the generalities of the effect.
Interaural time sensitivity of high-frequency neurons in the inferior colliculus
Authors: Yin Tom C. T. , Kuwada Shigeyuki , Sujaku Yasumasa
Published: October 2005

Recent psychoacoustic experiments have shown that interaural time differences provide adequate cues for lateralizing high-frequency sounds, provided the stimuli are complex and not pure tones. We present here physiological evidence in support of these findings. Neurons of high best frequency in the cat inferior colliculus respond to interaural phase differences of amplitude modulated waveforms, and this response depends upon preservation of phase information of the modulating signal. Interaural phase differences were introduced in two ways: by interaural delays of the entire waveform and by binaural beats in which there was an interaural frequency difference in the modulating waveform. Results obtained with these two methods are similar. Our results show that high-frequency cells can respond to interaural time differences of amplitude modulated signals and that they do so by a sensitivity to interaural phase differences of the modulating waveform.
Short-latency auditory responses obtained by cross correlation
Authors: Dobie Robert A. , Wilson Michael J.
Published: October 2005

Short-latency auditory responses were derived by cross correlation of pseudorandom white noise with averaged scalp potentials in guinea pigs. The cross-correlation functions were characterized by distinct cochlear microphonic and neural components, as distinguished by susceptibility to hypothermia and masking noise. This technique detects only linear, frequency-following responses of the auditory system, and demonstrated neural frequency following up to 3–4 kHz; thresholds were about 30–40 dB spectrum level. While conventional auditory brain stem responses reflect onset neural activity and are most responsive to high-frequency stimuli, cross-correlation responses reflect frequency-following activity, primarily to low frequencies, and thus may represent a complementary method of electrophysiologic assessment of the auditory system. Data are very rapidly acquired, and estimation of responses of limited areas of the cochlea may be possible by off-line digital filtering of cross-correlation functions obtained with broadband noise stimuli.
On the nonlocal aspects of acoustic waves incident on the boundary of a half-space
Authors: Nowinski J. L.
Published: October 2005

Dynamic field equations in terms of Lamé potentials are derived, and by using the appropriate nonlocal moduli are transformed into difference equations whose solution yields wavefunctions with two wave parameters. Dispersion equations involved lead to a generalized Snell’s law. Assumption of the stress-free boundary of the half-infinite space considered furnishes expressions for the ratios of amplitudes of longitudinal and transverse waves. The case of an incident P wave is discussed in more detail.
Calculation of acoustic wave scattering by means of the Helmholtz integral equation. II
Authors: Tobocman W.
Published: October 2005

In Part I [J. Acoust. Soc. Am. 76, 599–607 (1984)] it was suggested that an effective method for calculating the scattering of a wave field by a target of complex shape in the intermediate wavelength regime is the solution of the Helmholtz integral equation for the wave field on the surface of the target. The method was tested by calculating the scattering of acoustic waves by a rigid spheroid. In this paper we present the results of further test calculations employing the Helmholtz integral equation method to calculate the scattering of acoustic waves by fluid spheroids. Two alternative formulations of the method are tested, and they both give satisfactory results for spherical targets. However, the rate of convergence of one of the methods deteriorates rapidly with increasing nonsphericity while the rate of convergence of the other does not.
Analog measurement of intensity for bandlimited noise in a standing-wave tube
Authors: Bartel Thomas W. , Yaniv Simone L. , Cook Richard K.
Published: October 2005

The use of an analog acoustic intensity meter to determine the sound power radiated from an open-ended standing-wave tube [R. K. Cook and T. M. Proctor, J. Acoust. Soc. Am. 65, 1542–1555 (1979)] is extended to bandlimited random noise. Two microphones located along the axis of the tube were used for the sensing elements of the intensity meter. The bandwidth extension was achieved through the use of a two-channel wideband π/2 phase shifting network. Comparison of the power measured in the tube with the radiated power obtained in the free field by integration of the mean-square sound pressure over a spherical surface in the farfield yielded agreement within 0.25 dB for 1/3-oct bandwidths from 200 to 500 Hz.
A simple model for the acoustic cross section of sand grains
Authors: Clarke Thomas L. , Proni John R. , Craynock Julius F.
Published: October 2005

Previous work on determining the acoustic cross section of sand grains [Geophys. Res. Lett. 9(2), 175–178 (1982)] identified a problem with the application of the simple compressible sphere model for the cross section. Use of the complete elastic sphere model [J. Acoust. Soc. Am. 34, 1582–1592 (1962)] failed to remove the conflict with observation. Application of the bistatic cross-section theorem to the angle averaged cross section shows that the appropriate cross section is the total absorption cross section, not the backscatter cross section. The total absorption cross section for the fluid sphere model is found to be in semiquantitative agreement with scattering data for sand grains.