bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic behavior of glass-filled polymer solutions
Authors: Rahalkar R. R. , Gladwell N. , Javanaud C. , Richmond P.
Published: October 2005

The ultrasonic behavior of glass-filled xanthan solutions was studied in the frequency range 5–105 MHz as a function of filler particle size and filler concentration. The glass beads were characterized by measuring the particle size distributions. Unfilled xanthan solution exhibited one relaxation process in this frequency range. The frequency dependence of excess attenuation exhibited two peaks. One of these peaks was in the same frequency range as the relaxation for the unfilled solution and has been interpreted as being due to a modification of the background molecular relaxation. The other process was a complex combination of thermal, viscous, and scattering effects, with multiple scattering being the dominant mechanism at higher concentrations. Although the system studied here was different from an emulsion or suspension in that the continuous phase was viscoelastic, the ultrasonic behavior could be qualitatively explained using existing theories for emulsions and suspensions.
Acoustic and entropy wave input–output relationships for quasi-one-dimensional gas flows
Authors: Barton J. P.
Published: October 2005

The transmission, reflection, and interaction of linear, one-dimensional acoustic and entropy waves within subsonic, quasi-one-dimensional, finite length gas flows is considered. A numerical analysis is used to relate the time variations in gas properties along the length of the duct. Appropriate equations are derived for the case of a nonviscous, nonheat-conducting, fixed composition, ideal gas with constant specific heats and no external body forces or energy sources, though the general procedure may be applied to more complicated flows. The results are expressed in terms of nine frequency-dependent reflection and transmission coefficients. To demonstrate the analysis, calculations are presented for a 4:1 area ratio, 1-m-length nozzle and for a 1:4 area ratio, 1-m-length diffuser.
Auditorium acoustics measures from pistol shots
Authors: Bradley J. S.
Published: October 2005

Details of a procedure for efficiently and accurately calculating various auditorium acoustics measures from pistol shots are described. Early/late sound ratios, decay times, center time, and modulation transfer functions are calculated in octave bands. Measurements for a wide range of acoustical conditions are compared with simple predictions, and various quantities are found to be strongly intercorrelated.
An analytical technique for reducing the influence of edge diffraction in reflection measurements made on thin acoustical panels
Authors: Piquette Jean C.
Published: October 2005

A theorem is presented that permits analytical reduction of the disturbing influence of the edge-diffracted wave arising in reflection measurements made on thin acoustical panels. This theorem permits a better estimate to be made of the infinite-plane reflection coefficient than is possible by directly using experimental data obtained from a finite sample panel (since such data are contaminated by edge diffraction). It is analytically demonstrated that the theorem is exact for the case of a perfectly rigid sample panel and for the case of a perfectly soft sample panel. This means that, for these two limiting cases, the theorem entirely eliminates the disturbing influence of the edge-diffracted wave. (For the exact form of the theorem the source is required to be a Dirac delta-function point source, and the sample must be of infinitesimal thickness. The cross-sectional shape of the sample, however, is arbitrary.) An approximate form of the theorem is presented for the case of a penetrable panel. In this case the panel may have nonzero thickness, but the theorem is no longer exact. The penetrable case was investigated experimentally using underwater measurements made on a polymethylmethacrylate sample panel of 2.54-cm thickness. The sample was square with a side length of 76 cm. The data demonstrate that the technique is capable of achieving a significant reduction of the edge-diffracted wave arising in thin-panel reflection measurements.
Continuous-wave pressure fields of ultrasonic transducers
Authors: Hutchins David A. , Mair H. D. , Puhach P. A. , Osei A. J.
Published: October 2005

The radiated pressure fields of axisymmetric ultrasonic transducers have been measured experimentally at a single frequency to a high resolution. Results in both the nearfield and farfield have been compared to the prediction of theory in three dimensions, developed to examine transducers vibrating with an arbitrary amplitude and phase distribution across their front face. Good correlation was obtained for polyvinylidene fluoride (PVDF) radiators, assuming plane-piston-type behavior. For lead zirconate titanate (PZT) transducers, marked amplitude variations with radius across the disk face were encountered, and these needed to be modeled theoretically to obtain good agreement with experiment. Other predictions of theory which are of interest to applications involving acoustical imaging are presented.
Absorption corrections for transmission loss measurements
Authors: Warnock A. C. C. , Halliwell R. E.
Published: October 2005

Measurements of sound transmission loss made using nine different methods to estimate the effects of room absorption are reported. A single wall specimen was used in five different positions in the opening of a laboratory sound transmission loss test suite. Four different levels of room absorption were used. The conventional decay method is shown to work well in all cases, as does a method using a sound source with a known power to estimate the room absorption. A method using a sound-pressure level near the source and the room average, the near–far method, did not work as well.
Resonant cylinder for internal friction measurement
Authors: Tverdokhlebov A.
Published: October 2005

Similar to the resonant-sphere method in its experimental aspect, a resonant-cylinder technique is developed for the measurement of the internal friction of solids. The solutions of the theoretical problems of using the cylinder instead of sphere are presented: the computation of the resonance spectrum of the cylinder (axially symmetric modes only); the evaluation of the Q factor from the experimental resonance spectrum, characterized by a low (peak/background) ratio; and the separation of the dilatational and shear oscillation components in the total value of internal friction, measured for a given resonance mode. The anisotropy of viscoelastic parameters in a rolled bar of commercial steel has been measured as a method sensitivity check. Other preliminary experimental data are also presented as illustrative examples.
A hardware cochlear nonlinear preprocessing model with active feedback
Authors: Zwicker Eberhard
Published: October 2005

A hardware model of the nonlinear preprocessing established in the inner ear consisting of 90 sections corresponding to a frequency range from 900 to 8000 Hz is described. The model is based on assumptions described by Zwicker [Biol. Cybern. 35, 243–250 (1979)]: The outer hair cells act as saturating nonlinear mechanical amplifiers which feed back to the vibration of the basilar membrane while only the inner hair cells transfer information towards higher centers. The model shows many effects which correlate very closely to physiological and psychoacoustical counterparts. Quantitative data on the level-dependence of frequency responses and phase responses as well as an example of suppression are outlined.
‘‘Otoacoustic’’ emissions in a nonlinear cochlear hardware model with feedback
Authors: Zwicker Eberhard
Published: October 2005

Spontaneous, simultaneous evoked as well as delayed evoked emissions are studied in a hardware model of peripheral preprocessing with nonlinear feedback. The results suggest many very close parallels to the data found for otoacoustic emissions in man. From these parallels and the additional data measurable only in the model, it can be concluded that: (a) the cochlea acts in a similar way as established in the model; (b) the three kinds of emissions stem from the same source; (c) the phase response of the cochlea’s hydromechanics is responsible for the frequency distance between neighboring emissions as well as for the additional tips in suppression tuning curves; (d) the long delay of the delayed evoked emissions is due to the many decaying contributions from the places along the basilar membrane which cancel each other in the early part but sum up to the delayed emission in the later part; and (e) the double-peaked shape of the suppression-period patterns produced by high-level, low-frequency tones reflects the symmetrically shaped saturating nonlinearity of the feedback loops in the model which correspond to the function of the outer hair cells.
Nearfield noise measurements from an Arctic pressure ridge
Authors: Buck Beaumont M. , Wilson James H.
Published: October 2005

This paper presents initial analysis results of ambient noise measurements from an active ice pressure ridge over a 3-day period in April 1979. The site was a research ice camp 180 miles from the pole in the Eurasian Basin of the Arctic Ocean. The ridge was instrumented with calibrated hydrophones paired in both the horizontal and vertical directions. Their distance from the ridge was about 100 m and their outputs were tape recorded. Dimensional surveys of the active portions of the ridge were made at the surface. Source level linear density is deduced from ambient noise measurements near the pressure ridge by assuming the ridge to be a line source of spatially incoherent point sources. Measured Arctic transmission loss data are used to deduce an active pressure ridge average separation compatable with previously measured omnidirectional ambient noise data statistics for the month of April. The effects of surface/image interference are present in the data and allow a preliminary estimate of acoustic source depth of between 14–18 m. The ridge length was approximately 500 m and was formed when a 1 m-thick refrozen lead was pushed on top of a thicker 4-m ice floe. As such, this ridge was, most likely only one ‘‘subridge’’ along the length of the boundaries of the two interacting floes. Recent SEASAT SAR data from October 1978 have shown that ice pans (defined as groups of separate ice floes that move together) can vary from 10 to 100 km in linear dimension and, unless pan size changes significantly from October to April, extremely long ridges (composed of smaller discrete ridges such as the one analyzed in this study) may exist between pressured boundaries of adjacent pans. A uniform spacing of ridges was assumed for noise model calculations and, with an active ridge spacing of 37 km, model noise level estimates and measured 50 percentile noise levels of April were in good agreement. An average ridge was assumed to be 2 km in length consisting of two active 500-m subridges. It is not known whether this ridge was typical in level, length, etc., since these were the first-known quantitative acoustical measurements of ambient noise from a nearby pressure ridge.
Stationary phase evaluation of the integral for the acoustic field around a conical seamount
Authors: Buckingham Michael J. , Jones S. A. S. , Harriman Peter N.
Published: October 2005

An expression derived recently for the acoustic field from a point source in the channel around a conical seamount involves an integral with a highly oscillatory integrand. This integral is examined here and evaluated using the method of stationary phase. A relatively simple approximate expression for the spatial dependence of the field is obtained whose detailed properties compare very favorably with those of the original formulation.
Transient acoustic scattering from layers and plates
Authors: Maze G. , Izbicki J. L. , Ripoche J. , Nagl A. , Überall H. , Yoo K. B.
Published: October 2005

A recent experimental investigation [Maze et al., J. Acoust. Soc. Am. 77, 1352 (1985)] has shown that the spectrum of the resonance frequencies of plates can be obtained using ultrasonic pulse techniques. The distortion of incident wave trains upon their reflection, when the carrier frequency is near a resonance frequency, is analyzed here; the physical origin of plate resonances can be elucidated, the observed ringing of the resonances being caused by multiple internal reflections. A series of backscattering experiments, employing wave trains with carrier frequencies on and off a resonance, has been interpreted in the mentioned fashion, with very good agreement between theory and experiment.
Frequency discrimination of tones presented in filtered noise
Authors: Emmerich David S. , Fantini Deborah A. , Brown William S.
Published: October 2005

Previous research (Emmerich et al., 1983) in which tones were presented in the center of the notches in band-reject noise backgrounds suggests that information from frequency regions remote from the nominal signal frequency is useful in frequency discrimination. The present work extends the earlier findings by presenting tones on either side of a notch so that only one (or the other) tail of the excitation patterns of the tones would fall into the notch. In addition, tones were presented in high-pass noise, low-pass noise, and various combinations of the two. The results again indicate that remote information affects frequency discrimination, and they are also consistent with the hypothesis that the low-frequency tail of the excitation pattern is more useful for frequency discrimination than is the high-frequency tail.
Sensitivity to amplitude-modulated vibrotactile signals
Authors: Weisenberger Janet M.
Published: October 2005

Temporal modulation transfer functions were measured for sinusoidally amplitude-modulated vibratory stimuli delivered to the thenar eminence of the hand. Results for sinusoidal carriers at 25, 50, 100, and 250 Hz reflected greater sensitivity to modulation than those for either broadband or narrow-band noise carriers. The correspondence of these results to other measures of temporal sensitivity in the tactile system was examined. In addition, findings are discussed in view of their relevance to comparisons across sensory modalities, and to the design of vibrotactile aids for hearing-impaired persons.
Forward scattered waves in random media—The probability distribution of intensity
Authors: Ewart T. E. , Percival D. B.
Published: October 2005

An acoustic wave propagating in a medium with an index of refraction that is random in space and time acquires intensity modulations that can be modeled in terms of a space–time autocorrelation function, a scattering strength parameter γ, and a scaled range X. Over a wide range of γ, X, and medium autocorrelation functions, the probability distributions of intensity vary from lognormal at small X to exponential at large X. The generalized gamma distribution [E. W. Stacy, Ann. Math. Stat. 33, 1187–1192 (1962)] is characterized by three parameters, and reduces to many well-known distributions. It varies smoothly from lognormal to exponential as the parameters change. It is proposed that this distribution is a general analytic form that represents the probability distribution of intensity as a function of range, depth, and time in forward scattering. This proposition is tested with the measured temporal intensity fluctuations from the Mid-Ocean Acoustic Transmission Experiment, MATE. It is also tested wtih depth-range results from Monte Carlo simulations of wave propagation in a random medium with a power law autocorrelation function. The fitted generalized gamma distributions for the data sets chosen lie within the 95% Kolmogorov confidence bands for the true unknown probability distributions. In past treatments of this subject, the intensity moments have been used almost exclusively in modeling the probability distributions. The benefits of using distribution modeling rather than moment methods are described. Also discussed are the anomalies encountered for a medium with Gaussian autocorrelation.
Resonant phase matching of surface waves on impenetrable spheroids
Authors: Merchant Barbara L. , Nagl A. , Stoyanov Y. J. , Überall H. , Brown S. H. , Dickey J. W.
Published: October 2005

It is demonstrated that the complex acoustic eigenfrequencies of impenetrable spheroids correspond to the phase matching of repeatedly circumnavigating surface waves. Here, the phase matching condition must be formulated in the integral form, since the surface wave propagation constants vary during the passage of the waves over a surface with variable curvature, depending to first order on the local curvature along the path. Using the expressions for the propagation constants obtained by Franz and Galle [Z. Naturforsch. 10a, 374 (1955)], it is possible to satisfy this phase matching condition and, simultaneously, to obtain an indication of the correctness of the complex eigenfrequencies as found from a T-matrix calculation, or from a calculation employing spheroidal functions [D’Archangelo, J. Acoust. Soc. Am. 77, 6 (1985)].
Exact boundary conditions for scattering problems
Authors: Ting Lu , Miksis Michael J.
Published: October 2005

Scattering in an unbounded uniform medium when the scatterer is of finite size is considered. The scatterer can, in general, be inhomogeneous and nonlinear. Determination of the exact boundary data on the boundary of a finite computational domain G by using Kirchhoff’s formula is proposed. The integral in the formula is evaluated on a surface containing the scatterer and lying inside of G. This formula is explicit since the integrand depends only on the retarded values.
Phase effects in masking related to dispersion in the inner ear
Authors: Smith Bennett K. , Sieben Ulrich K. , Kohlrausch Armin , Schroeder Manfred R.
Published: October 2005

Phase effects in masking experiments using multitone maskers are usually associated with strong variations in the masker envelope. In this article, psychoacoustic experiments with such maskers that lead to phase-dependent threshold variations of up to 20 dB, although the phase transformation leaves the envelope unchanged, are described. However, after filtering the maskers with a realistic basilar membrane model, the envelopes are different owing to the models phase-dispersive properties. Comparison of model outputs with the experimental results reveals a strong correlation between the two for a wide range of parameters, provided one makes the additional assumption that the ear has a minimum integration time of a few milliseconds.
Decision rules in detection of simple and complex tones
Authors: Buus So/ren , Schorer Edwin , Florentine Mary , Zwicker Eberhard
Published: October 2005

Detection of simple and complex tones in the presence of a 64-dB SPL uniformly masking noise was examined in two experiments. In both experiments, the signals were either pure tones (220, 1100, or 3850 Hz) or an 18-tone complex consisting of equally intense components between 110 and 7260 Hz. In experiment 1, psychometric functions were obtained for detection in a 2I, 2AFC task. Results for eight normal listeners show that the psychometric functions are parallel for simple and complex tones. As expected, the masked thresholds for the pure tones are 43–44 dB SPL independent of frequency; the masked threshold for the complex tone is about 37 dB SPL per tone. These results indicate that the simultaneous presence of signal energy in many auditory channels aids detection. In experiment 2, psychometric functions were obtained with all four signals presented in random order within a block of trials. Results for four normal listeners show that the psychometric functions are parallel to one another and to those obtained in experiment 1. The thresholds are elevated to about 46 dB for the pure tones and to 40.5 dB for the complex tone. These results are nearly, but not quite, consistent with a multiband energy-detector model using an optimum decision rule; it appears that listeners may only make an unweighted sum of decision variables across an optimum selection of channels.
Low-frequency noise fields
Authors: Carey W. M. , Wagstaff R. A.
Published: October 2005

A review of low-frequency (LF) (20–200 Hz) physical noise models and measurements shows long-term persistent directional characteristics associated with distant shipping lanes and density patterns. Short-term averages show a temporally dynamic field composed of resolved distant shipping and uncorrelated background noise. These results emphasize the importance of the coherent contribution from coastal shipping to the midocean noise field. Vertical directionality measurements, such as those by Anderson et al. [Technical note 800, Naval Ocean Systems Center, San Diego, CA (1972)] show a broad angular distribution of noise intensity near the horizontal at low frequencies and a peaked distribution about the horizontal at high frequencies. This broad angular distribution near the horizontal is consistent with sound propagating downslope by means of a bottom reflectivity which favors lower frequencies. Since the frequency variation of the noise intensity near the horizontal was found smooth for basins with diverse geographic locations and variable populations of ships, then, in addition to surface ships, environmental noise such as wind driven noise may influence the vertical directionality.
Simulating the response of multiple microphones to a single acoustic source in a reverberant room
Authors: Peterson Patrick M.
Published: October 2005

A method is presented for simulating the impulse response between an acoustic source and multiple microphones in a reverberant room. The method is similar to the image method described by Allen and Berkley [J. Acoust. Soc. Am. 65, 943–950 (1979)] but includes modifications to simulate received echo arrival time accurately. The essential modification is to represent each received echo as a low-pass-filtered impulse at the correct arrival time. Using this ‘‘low-pass impulse’’ method, reverberant rooms can be simulated with sufficient accuracy to investigate multiple-microphone systems that are sensitive to interchannel phase.
Some further remarks regarding scattering of an acoustic wave by a vibrating surface
Authors: Piquette Jean C. , Van Buren A. L.
Published: October 2005

An earlier letter to the editor [Piquette and Van Buren, J. Acoust. Soc. Am. 79, 179–180 (1986)] commented on an article by D. Censor [J. Acoust. Soc. Am. 76, 1527–1534 (1984)]. In his reply [J. Acoust. Soc. Am. 79, 181–182 (1986)], Censor made some observations that warrant further comment. The present letter considers in detail plane-wave scattering by a vibrating plane and thereby demonstrates analytically that Censor’s theory predicts sum and difference frequency component waves that are of the order of magnitude of pseudosound. This example also illustrates that the parametrically growing sum and difference frequency component waves generated nonlinearly overwhelm those predicted by the Censor theory within a fraction of a wavelength of the scatterer’s surface.
Detection and intensity discrimination of a sinusoid
Authors: Hanna Thomas E. , von Gierke Susanne M. , Green David M.
Published: October 2005

Intensity discrimination thresholds were measured for gated 100-ms, 1000-Hz tones. Discrimination thresholds were measured at several intensities near absolute threshold as well as at 30, 60, and 90 dB SPL. Psychometric functions were obtained for several of these discrimination conditions, and for detection of the signal in quiet. The results showed that Weber’s law is approximately valid for standards as low as 0 dB SL. Small amounts of negative masking were observed even when the data were expressed in terms of increment energy. The psychometric functions for the discrimination conditions had a similar form and were shallower than the psychometric function for the detection of a signal in quiet. A similar set of conditions was run in the presence of a continuous, broadband noise. The results were generally in agreement with those obtained in quiet, but slight differences suggested that the variability which limits performance in the two conditions is different. The results are discussed in terms of the effects of nonlinear transduction, the effects of uncertainty, and contrast mechanisms as proposed by Laming [Sensory Analysis (Academic, London, 1986)].
Basilar membrane mechanics at the base of the chinchilla cochlea. I. Input–output functions, tuning curves, and response phases
Authors: Robles Luis , Ruggero Mario A. , Rich Nola C.
Published: October 2005

Basilar membrane (BM) velocity was measured at a site 3.5 mm from the basal end of the chinchilla cochlea using the Mössbauer technique. The threshold of the compound action potential recorded at the round window in response to tone bursts was used as an indicator of the physiological state of the cochlea. The BM input–output functions display a compressive nonlinearity for frequencies around the characteristic frequency (CF, 8 to 8.75 kHz), but are linear for frequencies below 7 and above 10.5 kHz. In preparations with little surgical damage, isovelocity tuning curves at 0.1 mm/s are sharply tuned, have Q10’s of about 6, minima as low as 13 dB SPL, tip-to-tail ratios (at 1 kHz) of 56 to 76 dB, and high-frequency slopes of about 300 dB/oct. These mechanical responses are as sharply tuned as frequency-threshold curves of chinchilla auditory nerve fibers with corresponding CF. There is a progressive loss of sensitivity of the mechanical response with time for the frequencies around CF, but not for frequencies on the tail of the tuning curve. In some experiments the nonlinearity was maintained for several hours, in spite of a considerable loss of sensitivity of the BM response. High-frequency plateaus were observed in both isovelocity tuning curves and phase-frequency curves.
Salicylate-induced changes in spontaneous activity of single units in the inferior colliculus of the guinea pig
Authors: Jastreboff Pawel J. , Sasaki Clarence T.
Published: October 2005

Changes in spontaneous neuronal activity of the inferior colliculus in albino guinea pigs before and after administration of sodium salicylate were analyzed. Animals were anesthetized with pentobarbital, and two microelectrodes separated by a few hundred microns were driven through the inferior colliculus. After collecting a sufficiently large sample of cells, sodium salicylate (450 mg/kg) was injected i.p. and recordings again made 2 h after the injection. Comparison of spontaneous activity recorded before and after salicylate administration revealed highly statistically significant differences (p<0.001). After salicylate, the mean rate of the cell population increased from 29 to 83 Hz and the median from 26 to 74 Hz. Control experiments in which sodium salicylate was replaced by saline injection revealed no statistically significant differences in cell discharges. Recordings made during the same experiments from lobulus V of the cerebellar vermis revealed no changes in response to salicylate. The observed changes in single-unit activity due to salicylate administration may represent the first systematic evidence of a tinnituslike phenomenon in animals.
Study of the sound transmission class system for rating building partitions—Another view
Authors: Sepmeyer Ludwig W.
Published: October 2005

In an earlier paper, Clark [J. Acoust. Soc. Am. 47, 676–682 (1970)] concluded that the ASTM classification method E413 for determining a single-number rating for sound transmission loss characteristics yields conservative values when there are large dips in the TL curve of the partition. That is, Clark found that the sound transmission class (STC) rating method was more sensitive to dips in sound transmission loss than his subjective experimental responses would indicate. Clark also concluded that the rule which limits the deficiency in TL in any 1/3-octave band to 8 dB is unnecessary. Clark’s experimental method consisted of matching the annoyance produced by sounds filtered in accordance with the ASTM reference transmission loss (TL) contour shape with the annoyance produced by sounds filtered by a similar contour with octave-band or 1/3-octave-band dips of various depths. This was done by adjusting the sound transmitted by the reference STC contoured channel to have the same perceived annoyance as that produced by the sound transmitted by the channel containing the TL characteristic with dip. If instead, the sound transmitted by the STC filtered channel had been held constant at the chosen reference level of annoyance, and the channel simulating the TL characteristic with the dip had been adjusted to match the reference annoyance, quite different results would have been obtained. In this paper, the articulation index has been used to predict the results of Clark’s experiment for speech signals. When the TL filtered channel with notch was adjusted to produce the same articulation index of approximately 5%, the results show that the STC rating procedure is not conservative. Rather it overrates TL characteristics with high-frequency octave-band dips by as much as 5 dB. Instead of abandoning the 8-dB rule completely, it is proposed that it be replaced by a limitation of 16 dB for the sum of the deficiencies in any three adjacent 1/3-octave bands.
A method for solving forced vibration problems of arbitrarily shaped sandwich plates
Authors: Poltorak Krzysztof , Nagaya Kosuke
Published: October 2005

This paper is concerned with a method for solving forced vibration problems of solid sandwich plates with irregular boundaries. The exact, general solution of the equation of motion in terms of Bessel functions is found. The boundary problem is solved by using the Fourier expansion collocation method. Damping properties of an intermediate, viscoelastic layer are taken into consideration by means of a concept of a complex shear modulus. As an application, the numerical calculations for circular, truncated elliptical, and parabolic sandwich plates with clamped edges are carried out. Miscellaneous phenomena occurring in sandwich plates are discussed.
Accuracy of a Lax–Wendroff scheme for the wave equation
Authors: Santosa Fadil , Pao Yih-Hsing
Published: October 2005

In this paper, an investigation of the behavior of a finite difference scheme for solving initial value problems for the wave equation is reported. The scheme is a Lax–Wendroff method, which is second-order accurate. The objective of this work is to assess its accuracy in comparison to the well-known leapfrog method. To this end, spectral analysis is performed, which has a natural interpretation in terms of numerical dispersion relation. It is found that the scheme is highly dispersive, dissipative, and anisotropic. Numerical experiments were carried out to compare the performance of this scheme with the leapfrog scheme. It is apparent from our numerical tests and analysis that the standard leapfrog scheme outperforms a Lax–Wendroff scheme in solving linear wave equations.
Energy streamlines for a spherical shell scattering plane waves
Authors: Skelton E. A. , Waterhouse R. V.
Published: October 2005

Plane sound waves are incident on an elastic spherical shell, submerged in water. Theoretical plots of the flow of sound energy around the shell, based on a thin-shell analysis, are given for the case where the n=2 mode is excited. The shell is made lossy, and the water is lossless. Four conditions are treated: two thicknesses of shell, each with the interior either empty or full of water. It is found that significant amounts of energy are held in ring-shaped vortices centered on or near the shells. Values for the absorption cross sections are calculated.
Detection cues in forward masking and their relationship to off-frequency listening
Authors: Yacullo William S. , Abbas Paul J.
Published: October 2005

Conventional and restricted-listening psychophysical tuning curve paradigms were used to evaluate (1) the masking ability of forward maskers of different envelope characteristics, and (2) the relationship between off-frequency listening effects and the envelope characteristics of both the variable masker and stationary masker used to restrict listening to a narrow region surrounding the probe. Maskers were selected so as to differ widely in the degree of fluctuation in their envelopes. The masker with the largest amplitude fluctuations exhibited greater forward-masking ability than other stimuli; this effect was observed on the high-frequency branch and within the tip region of the tuning curve. It is suggested that differences in masking ability may reflect the use of different signal detection cues. The results are also consistent with previous reports [D. Johnson-Davies and R. D. Patterson, J. Acoust. Soc. Am. 65, 756–770 (1979); B. J. O’Loughlin and B. C. J. Moore, J. Acoust. Soc. Am. 69, 1119–1125 (1981a)] which suggest that off-frequency listening is a factor contributing to the sharpness of psychophysical tuning curves. This effect is largely dependent, however, on the envelope characteristics of both variable and stationary maskers.
Frequency dependence of ultrasonic absorption in egg white
Authors: Choi P.-K. , Bae J.-R. , Takagi K.
Published: October 2005

Ultrasonic absorption in egg white has been measured in the frequency range of 0.2–10 MHz over the temperature range of 10°–50 °C using the plano-concave resonator method. The results show no difference between thick and thin parts, no aging effect, and no individual difference. The absorption coefficient is found to be proportional to the 1.25(±0.02)th power of frequency over the entire temperature range.
Detection of a temporal gap in low-frequency narrow-band signals by normal-hearing and hearing-impaired listeners
Authors: De Filippo Carol Lee , Snell Karen Black
Published: October 2005

Temporal processing ability in the hearing impaired was investigated in a 2IFC gap-detection paradigm. The stimuli were digitally constructed 50-Hz-wide bands of noise centered at 250, 500, and 1000 Hz. On each trial, two 400-ms noise samples were paired, shaped at onset and offset, filtered, and presented in the quiet with and without a temporal gap. A modified up–down procedure with trial-by-trial feedback was used to establish threshold of detection of the gap. Approximately 4 h of practice preceded data collection; final estimate of threshold was the average of six listening blocks. There were 10 listeners, 19–25 years old. Five had normal hearing; five had a moderate congenital sensorineural hearing loss with relatively flat audiometric configuration. Near threshold (5 dB SL), all listeners performed similarly. At 15 and 25 dB SL, the normal-hearing group performed better than the hearing-impaired group. At 78 dB SPL, equal to the average intensity of the 5-dB SL condition for the hearing impaired, the normal-hearing group continued to improve and demonstrated a frequency effect not seen in the other conditions. Substantial individual differences were found in both groups, though intralistener variability was as small as expected for these narrow-bandwidth signals.
Random error versus S/N performance of an automatic broadband bearing/time delay tracking system
Authors: Kroenert J. T.
Published: October 2005

This article derives the formula for random error versus signal-to-noise of an automatic bearing/time delay tracking system. The tracker is essentially a servosystem employing a clipper-type phase detector. Numerical results for the broadband (1 oct) case are presented and compared with the Cramer–Rao lower bound on time delay error. The characteristics of the phase detector and loop transfer function combine to provide a tracking filter that automatically decreases bandwidth with decreasing signal-to-noise ratio while maintaining essentially constant stability.
Use of phase contrast microscopy to determine the height of the organ of Corti in whole-mount preparations
Authors: Baggot Patrick J. , Bohne Barbara A. , Bozzay Denyse G. , Harding Gary W.
Published: October 2005

A technique has been developed to measure the height of the organ of Corti (OC) in the whole-mount preparations of the cochlear duct. The technique corrects for variations in the microscope system, such as the magnification of the objective lens and the mechanical properties of the fine-focus knob, as well as the refractive index of the embedding medium and the angle of specimens with respect to the optical axis of the microscope. At 11 percentage locations from apex to base, the height of the OC in ten chinchilla cochleas was measured at three positions: (1) the lateral edge of the inner hair cell (IHC); (2) the medial edge of the first row outer hair cell (OHC1); and (3) the lateral edge of the third row outer hair cell (OHC3). These measurements were compared to measurements made on radial sections from five other cochleas, with very good agreement at IHC and OHC3, and fairly good agreement at OHC1. The height at OHC3 varied almost linearly with percentage distance along the OC, ranging from 96 μm (apical end) to 51 μm (basal end). The height at the OHC1 varied from 77 to 49 μm, but did not vary linearly. The height of the IHC was relatively constant, from 50 to 60 μm, except at the basal end, where it decreased to 42 μm.
Repeated TTS exposures in monkeys: Alterations in hearing, cochlear structure, and single-unit thresholds
Authors: Lonsbury-Martin B. L. , Martin G. K. , Bohne B. A.
Published: October 2005

The findings of a number of studies investigating the effects of excessive sound on hearing have indicated that the correspondence between behavioral, physiological, and histological measures of noise-induced hearing loss may be markedly dependent upon the sensitivity of the particular measure. Recent studies demonstrating significant changes in the responses of single auditory neurons following brief exposures to pure tones suggest that single-unit activity may be a sensitive indicator of physiological insult to the organ of Corti’s sensory cells. In addition, the long-lasting nature of the changes in neural responsiveness suggests that each temporary threshold shift (TTS) episode may produce an increment of damage to the ear that eventually contributes to a measurable permanent threshold shift (PTS). A logical extension of this implication is the proposal that repeated episodes of TTS would first affect single-unit thresholds, and that such damage would eventually manifest itself as PTS.

A test of this notion was peformed by repeatedly exposing monkeys to short-lasting TTS sounds for many months. Behavioral thresholds were monitored using a reaction-time task before and after each inducement of TTS. Two subjects participated in exposure sessions for 18 months, while the remaining monkey was exposed to identical stimuli for 6 months. At the end of behavioral testing, the monkeys were prepared for chronic recording from single cells of the cochlear nucleus. Following the recording period, cochleas were prepared for examination as plastic-embedded whole mounts. Flat preparations of the cochlear duct were made and the position and extent of damage to the organ of Corti and myelinated nerve fibers was determined. No elevations in behavioral threshold were noted for the monkey receiving 6 months of sound-exposure experience, while for both subjects exposed for 18 months, a significant high-frequency hearing loss became apparent during the final months of exposure. For damaged ears, the thresholds of ipsilateral cochlear nucleus units were elevated for characteristic frequencies (CFs) corresponding to the frequency regions where behavioral thresholds were shifted. Thresholds for units with high-frequency CFs in the animal exposed for 6 months also demonstrated a loss in sensitivity. Histological examination of the cochleas of monkeys with permanent hearing losses revealed corresponding damage to the high-frequency region of the organ of Corti. The monkey exposed for 6 months, which demonstrated only elevated unit thresholds, also had high-frequency lesions. These findings suggest that even with lengthy recovery periods between exposure episodes, each brief exposure contributed to the anatomical damage observed within a given ear.
Comodulation detection differences using noise-band signals
Authors: McFadden Dennis
Published: October 2005

In a variant of the standard paradigm employed to study comodulation masking release (CMR), a narrow noise band was used as a signal in the presence of ‘‘cue’’ bands which had either the same or different temporal envelopes. The number of cue bands present ranged from zero to four; when there were two or four cue bands, they were either all presented at the same overall level or the spectral profile was ‘‘scrambled’’ in a haphazard manner. Different noise samples were presented within and across trials. The result was in the opposite direction from the standard CMR outcome; that is, better performance was obtained when the envelopes of the cue band(s) were uncorrelated with those of the signal band than when they were correlated. These comodulation detection differences (CDDs) ranged from a decibel or two up to 10–12 dB in different conditions, and were generally larger the more cue bands present. Standard CMR conditions, which were run as controls, revealed that the detectability of a tonal signal does not increase as the number of cue bands is increased from one to four—an outcome which differs from those obtained in profile analysis experiments. The data taken with the equal-level and the scrambled-level cues differed little in both the CDD and the CMR conditions. All noise bands were 100 Hz wide, and approximately 250 ms in duration. The signal band in CDD and the masker band in CMR were centered at 2500 Hz. The psychophysical procedure was two-interval forced choice.
Audibility and recognition of stop consonants in normal and hearing-impaired subjects
Authors: Turner Christopher W. , Robb Michael P.
Published: October 2005

The purpose of this study was to examine the effect of spectral-cue audibility on the recognition of stop consonants in normal-hearing and hearing-impaired adults. Subjects identified six synthetic CV speech tokens in a closed-set response task. Each syllable differed only in the initial 40-ms consonant portion of the stimulus. In order to relate performance to spectral-cue audibility, the initial 40 ms of each CV were analyzed via FFT and the resulting spectral array was passed through a sliding-filter model of the human auditory system to account for logarithmic representation of frequency and the summation of stimulus energy within critical bands. This allowed the spectral data to be displayed in comparison to a subject’s sensitivity thresholds. For normal-hearing subjects, an orderly function relating the percentage of audible stimulus to recognition performance was found, with perfect discrimination performance occurring when the bulk of the stimulus spectrum was presented at suprathreshold levels. For the hearing-impaired subjects, however, it was found in many instances that suprathreshold presentation of stop-consonant spectral cues did not yield recognition equivalent to that found for the normal-hearing subjects. These results demonstrate that while the audibility of individual stop consonants is an important factor influencing recognition performance in hearing-impaired subjects, it is not always sufficient to explain the effects of sensorineural hearing loss.
Evidence for mora timing in Japanese
Authors: Port Robert F. , Dalby Jonathan , O’Dell Michael
Published: October 2005

Japanese has long been described as a ‘‘mora-timed’’ language by linguists. Japanese pedagogy has traditionally claimed that moras are constant in duration. Four experiments are reported investigating segmental timing in Japanese in order to test several straightforward hypotheses about mora timing. First, it is demonstrated that words with an increasing number of moras increase in duration by nearly constant increments. The next two experiments explored the mechanisms by which constant mora durations are achieved (a) given that there are large universal differences in the inherent duration of various segment types (e.g., /u/ vs /a/), and (b) given that some syllables are supposed to be two mora long (such as, those with long vowels or final consonants). In each case, it was found that the duration of a word stays very close to a target duration that depends on the number of moras in it. This is achieved by stretching or compressing the duration of neighboring segments and adjacent moras. Thus increasing the number of segments in two-mora syllables results in lengthening, not the expected shortening, of other segments in the heavier syllable.
Vowel identification and vowel masking patterns of hearing-impaired subjects
Authors: Van Tasell Dianne J. , Fabry David A. , Thibodeau Linda M.
Published: October 2005

Confusion matrices for seven synthetic steady-state vowels were obtained from ten normal and three hearing-impaired subjects. The vowels were identified at greater than 96% accuracy by the normals, and less accurately by the impaired subjects. Shortened versions of selected vowels then were used as maskers, and vowel masking patterns (VMPs) consisting of forward-masked threshold for sinusoidal probes at all vowel masker harmonics were obtained from the impaired subjects and from one normal subject. Vowel-masked probe thresholds were transformed using growth-of-masking functions obtained with flat-spectrum noise. VMPs of the impaired subjects, relative to those of the normal, were characterized by smaller dynamic range, poorer peak resolution, and poorer preservation of the vowel formant structure. These VMP characteristics, however, did not necessarily coincide with inaccurate vowel recognition. Vowel identification appeared to be related primarily to VMP peak frequencies rather than to the levels at the peaks or to between-peak characteristics of the patterns.
Intelligibility of average talkers in typical listening environments
Authors: Cox Robyn M. , Alexander Genevieve C. , Gilmore Christine
Published: October 2005

Intelligibility of conversationally produced speech for normal hearing listeners was studied for three male and three female talkers. Four typical listening environments were used. These simulated a quiet living room, a classroom, and social events in two settings with different reverberation characteristics. For each talker, overall intelligibility and intelligibility for vowels, consonant voicing, consonant continuance, and consonant place were quantified using the speech pattern contrast (SPAC) test. Results indicated that significant intelligibility differences are observed among normal talkers even in listening environments that permit essentially full intelligibility for everyday conversations. On the whole, talkers maintained their relative intelligibility across the four environments, although there was one exception which suggested that some voices may be particularly susceptible to degradation due to reverberation. Consonant place was the most poorly perceived feature, followed by continuance, voicing, and vowel intelligibility. However, there were numerous significant interactions between talkers and speech features, indicating that a talker of average overall intelligibility may produce certain speech features with intelligibility that is considerably higher or lower than average. Neither long-term rms speech spectrum nor articulation rate was found to be an adequate single criterion for selecting a talker of average intelligibility. Ultimately, an average talker was chosen on the basis of four speech contrasts: initial consonant place, and final consonant place, voicing, and continuance.
Effect of a transition layer on acoustic transmission from a fluid to an elastic layer
Authors: Pierucci Mauro
Published: October 2005

In order for a compliant surface to be able to interact with a flow field in a constructive manner, it is necessary that energy between the fluid and the compliant layer be exchanged very effectively. In this letter the fluid energy is assumed to be a plane wave traveling in the direction normal to a finite thickness elastic layer. A thin transition layer is placed at the interface between the two media.