bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of effective medium theories for inhomogeneous continua
Authors: Gaunaurd G. C. , Wertman W.
Published: October 2005

A unified review is presented of two methods for the prediction of the dynamic effective properties of inhomogeneous media, and effective sound speeds and attenuations are calculated in four possible cases by the two methods. The goal is to assess the agreement/disagreement of the methods in a number of relevant physical situations. With the present form of our effective medium theory (EMT), excellent agreement is found in two of the four possible cases, and mild to strong disagreement in the other two. A physical and mathematical interpretation/explanation for the comparison is given, and a prescription is offered to make the disagreeing cases agree. Advantages/disadvantages of both methods and a number of conclusions emerge. The present comparison was prompted as a reply to a letter [L. Anson and R. C. Chivers, ‘‘Ultrasonic propagation in suspensions,’’ (private communication, 1987)] recently received by the authors.
Subsonic axial flow fan noise and unsteady rotor force
Authors: Chiu Wen-Shyang , Lauchle G. C. , Thompson D. E.
Published: October 2005

The noise radiated by a subsonic, axial flow fan at its rotational frequency and harmonics is related to the unsteady blade force created by the rotor blade/fluid interaction. This force is highly dependent on the time-invariant flow distortions that enter the fan. The objectives of this study are to quantify the correlation between the inflow nonuniformity, unsteady blade loading, and the discrete-frequency radiated noise. The inflow field of a typical cooling fan used in the electronic and computer industry was distorted by placing a small cylinder in the inlet plane. The fan was instrumented with a sensor to measure the axial rotor force. The on-axis sound pressure spectra were compared to the coherent output power spectra conditioned on the unsteady rotor force and the radiated sound. Very good coherence at the discrete tones was observed. In the inlet plane, the time-invariant, spatially nonuniform inflow was measured using miniature, five-hole pressure probes. Fourier analysis of the inflow velocity data was used to compute the harmonic content of the unsteady rotor force. A simplified form of Curle’s equation was then used to compute the discrete-frequency radiated noise at the blade passage frequency (BPF) and its lower harmonics. The predicted and measured noise levels are in close agreement at the BPF and the first harmonic, for which the fan is a compact source.
Exact, explicit solutions for diffraction by hard sound barriers and seamounts
Authors: Tolstoy Ivan
Published: October 2005

A new method of obtaining exact, explicit solutions for the diffraction of sound waves by truncated wedges is given which, in conjunction with a previous study [I. Tolstoy, IEEE J. Ocean Eng., in press (1989)], can be applied to problems involving two parallel vertices and arbitrary wedge angles θw, θ′w at these vertices. The method combines exact, explicit representations of the field diffracted by a single vertex with the classic multiple scatter algorithm to formulate the interaction between the line vertices. The previous study had demonstrated the method only for cases in which θw, θw were irrational fractions of π, as well as for the rather special case θw=θ′w =2π, i.e., for the hard strip. In the latter case, the calculations were carried out for wavenumbers k such that 1≲kl≤16, where l was the strip width, and were shown to agree with experimental measurements [H. Medwin et al., J. Acoust. Soc. Am. 72, 1005–1013 (1982)]. The present article extends the theory to cover the important remaining cases for which θ, θw are rational fractions of π; i.e., they are of the form πp/n where p,n are integers. The resulting exact formulas, in combination with previously published ones, thus constitute a complete, exact plane-wave diffraction theory for truncated wedges of any angles θw, θ′w. The formulas have now been applied to the case of a thick rectangular barrier, in the wavenumber range 0.2≲kl≤2.8 and it is shown that the agreement with Medwin et al.’s experimental data is good. The method is quite general and can be extended to more complicated polygonal and broken-line profiles with any number of vertices. As a consequence, there is now a technique for calculating diffraction by realistically shaped seamounts in underwater acoustics as well as by sound barriers in air.
Adaptation of boundary elements to the dynamics of elastic solids
Authors: El-Raheb Michael , Wagner Paul
Published: October 2005

The method of boundary elements is adapted to the dynamics of elastic axisymmetric solids. Three scalar potentials are used, each satisfying the Helmholtz equation and each represented by its own source distribution. The sources are distributed over a surface enclosing the solid boundary. Stress or displacement conditions on the boundary are realized by third-order derivatives of the potentials. Discrete ring elements on the source enclosure combine their influences at discrete ring elements on the solid boundary.
Application of an automated package of pattern recognition techniques to acoustic signature inspection of railroad wheels
Authors: Haran Shivan , Finch Robert D. , Jansen B. H.
Published: October 2005

An operational acoustic signature inspection system for railroad wheels is described. The purpose is to inspect the wheels on a train as it goes past an inspection site and analyze the data in real time. The wheels on the train are sensed by magnetic wheel sensors that alert an electromechanical hammer installed on the inside of each rail. The hammers strike the wheels on each axle, and the sound is picked up by a microphone installed in front of each hammer and transmitted to a minicomputer at the remote location via dedicated telephone lines. Studies were performed on data obtained from a test consist, specially assembled for this work, and from revenue service trains. Various features were computed in both time and frequency domains, including the spectral cross correlation, the percentage of common peaks, and a measure based on resonance frequencies, and were analyzed using a pattern recognition package. It was concluded that the use of the package resulted in significant improvement in detection of defective wheels and reduction of false alarms.
Frequency discrimination in the goldfish (C
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s): Effects of roving intensity, sensation level, and the direction of frequency change
Authors: Fay Richard R.
Published: October 2005

The ability of goldfish to detect a change in the frequency of 400-Hz pure-tone bursts was studied using classical respiratory conditioning. The frequency discrimination threshold was measured at 15-, 35-, and 55-dB sensation level (SL), under conditions of (1) constant intensity, (2) roving intensity (plus and minus 6-dB burst-to-burst variation in intensity), (3) upward frequency change, and (4) downward frequency change. There was no overall effect of SL on frequency discrimination, but roving the intensity elevated thresholds by about 6 Hz (33%) and increased variability. Upward shifts in frequency elevated thresholds slightly (by 2 Hz or 10%) relative to downward shifts. These relatively small and statistically insignificant effects suggest that earlier measures of frequency discrimination in the goldfish are not due to the detection of simple changes in spike rate within individual peripheral channels.
Modified Helmholtz integral equation for bodies sitting on an infinite plane
Authors: Seybert A. F. , Wu T. W.
Published: October 2005

This article presents a modified version of the Helmholtz integral equation for bodies sitting on an infinite plane. By using dummy integration elements on the bottom surface, the coefficient C(P) of the Helmholtz integral equation can be evaluated by a closed contour. Two different integral forms for C(P) are derived for P off the infinite plane and on the infinite plane, respectively. Numerical results for radiation and scattering from bodies of several different shapes sitting on a rigid, infinite plane are given to verify this formulation.
Physiological responses to the pulsation threshold paradigm. I: Pulsation threshold patterns do not reproduce physiological rate profiles of high-pass and low-pass noise maskers
Authors: Hellstrom Lisa I.
Published: October 2005

This article compares psychophysical measures of human processing of acoustic stimuli with one neurophysiological representation (normalized discharge rate profiles) of those stimuli. Psychophysical pulsation threshold patterns (PTPs) were derived for high-pass and low-pass noise maskers. Spectral features of both maskers are clearly evident in the PTPs. However, while the representation of high-pass noise in the PTPs becomes sharper with increasing masker level, the representation of low-pass noise degenerates as masker level is increased. One assumption that has been used previously to interpret pulsation threshold data is that PTPs reflect the profile of activity in primary neural elements in response to the masking stimulus. To investigate this hypothesis, normalized-rate profiles of responses to both maskers were derived from populations of auditory-nerve fibers in cats. Normalized-rate profiles do not exhibit the same behavior as PTPs for high-pass noise maskers in that the neural representation of the band edge degenerates as sound level increases. Furthermore, the distinction between the passband and the stop band is lost in the neural rate profiles, whereas the distinction improves in the high-pass noise PTPs.
Comodulation masking release (CMR) as a function of masker bandwidth, modulator bandwidth, and signal duration
Authors: Schooneveldt Gregory P. , Moore Brian C. J.
Published: October 2005

These experiments examine how comodulation masking release (CMR) varies with masker bandwidth, modulator bandwidth, and signal duration. In experiment 1, thresholds were measured for a 400-ms, 2000-Hz signal masked by continuous noise varying in bandwidth from 50–3200 Hz in 1-oct steps. In one condition, using random noise maskers, thresholds increased with increasing bandwidth up to 400 Hz and then remained approximately constant. In another set of conditions, the masker was multiplied (amplitude modulated) by a low-pass noise (bandwidth varied from 12.5–400 Hz in 1-oct steps). This produced correlated envelope fluctuations across frequency. Thresholds were generally lower than for random noise maskers with the same bandwidth. For maskers less than one critical band wide, the release from masking was largest (about 5 dB) for maskers with low rates of modulation (12.5-Hz-wide low-pass modulator). It is argued that this release from masking is not a ‘‘true’’ CMR but results from a within-channel cue. For broadband maskers (>400 Hz), the release from masking increased with increasing masker bandwidth and decreasing modulator bandwidth, reaching an asymptote of 12 dB for a masker bandwidth of 800 Hz and a modulator bandwidth of 50 Hz. Most of this release from masking can be attributed to a CMR. In experiment 2, the modulator bandwidth was fixed at 12.5 Hz and the signal duration was varied. For masker bandwidths greater than 400 Hz, the CMR decreased from 12 to 5 dB as the signal duration was decreased from 400 to 25 ms. For masker bandwidths less than 400 Hz, there was no release from masking when the signal duration was less than 100 ms. The results suggest that, for maskers with correlated envelope fluctuations across frequency, across-channel comparisons can reduce signal thresholds even for short signals, but an extra within-channel process can produce a release from masking for signals with long durations. This second process may reflect the ability of subjects to detect a change in the statistical properties of the envelope of the stimulus when the signal is added to the masker.
The scattering of sound from fluid-loaded plates
Authors: Photiadis Douglas M.
Published: October 2005

The scattering of sound waves from a finite strip plate under conditions of heavy fluid loading is numerically simulated. Both baffled and unbaffled geometries are considered, and results for the nearfields and farfields are obtained. Under conditions of heavy fluid loading, scattering effects due to the plate elasticity are generally small unless the excitation frequency is close to a resonance frequency of the fluid–plate system. The general behavior of the fluid–plate system and the frequencies, radiation efficiencies, widths, and strengths of the resonances are determined. With these results, one can determine the relevance of such phenomena in a variety of applications. The reliability of predictions for the resonance parameters based on simple modeling techniques is evaluated. The results indicate that the frequencies and effective masses of the resonances can be reasonably approximated. However, the radiation efficiencies are difficult to estimate because of the effects of the strong fluid loading. In the unbaffled case, modeling techniques based on vacuum mode shapes tend to substantially underestimate the radiation efficiency; in the baffled case, such techniques tend to substantially overestimate the radiation efficiency.
Spectrotemporal analysis and cochlear hearing impairment: Effects of frequency selectivity, temporal resolution, signal frequency, and rate of modulation
Authors: Hall Joseph W. , Grose John H.
Published: October 2005

The detection of 500- or 2000-Hz pure-tone signals in unmodulated and modulated noise was investigated in normal-hearing and sensorineural hearing-impaired listeners, as a function of noise bandwidth. Square-wave modulation rates of 15 and 40 Hz were used in the modulated noise conditions. A notched noise measure of frequency selectivity and a gap detection measure of temporal resolution were also obtained on each subject. The modulated noise results indicated a masking release that increased as a function of increasing noise bandwidth, and as a function of decreasing modulation rate for both groups of listeners. However, the improvement of threshold with increasing modulated noise bandwidth was often greatly reduced among the sensorineural hearing-impaired listeners. It was hypothesized that the masking release in modulated noise may be due to several types of processes including across-critical band analysis (CMR), within-critical band analysis, and suppression. Within-band effects appeared to be especially large at the higher frequency region and lower modulation rate. In agreement with previous research, there was a significant correlation between frequency selectivity and masking release in modulated noise. At the 500-Hz region, masking release was correlated more highly with the filter skirt and tail measures than with the filter passband measure. At the 2000-Hz region, masking release was correlated more with the filter passband and skirt measures than with the filter tail measure. The correlation between gap detection and masking release was significant at the 40-Hz modulation rate, but not at the 15-Hz modulation rate. The results of this study suggest that masking release in modulated noise is limited by frequency selectivity at low modulation rates, and by both frequency selectivity and temporal resolution at high modulation rates. However, even when the present measures of frequency selectivity and temporal resolution are both taken into account, significant variance in masking release still remains unaccounted for.
Complex ray methods for acoustic interaction at a fluid–fluid interface
Authors: Westwood Evan K.
Published: October 2005

The development of a systematic method for finding the reflected and transmitted fields due to a point source in the presence of a plane, penetrable interface is presented. This approach is based on the classical method of steepest descent, but the plane-wave reflection and transmission coefficients are allowed to influence the location of the saddle points and their steepest descent paths. As a consequence, saddle points are, in general, complex, and complicated processes such as the reflected lateral wave field and the evanescent field in the bottom are incorporated in the saddle point formulation. The geometric interpretation of the saddle point criterion is derived in terms of eigenrays and their characteristics, from which expressions are obtained for the ray displacement upon reflection and transmission. Summaries of the eigenray structure of the reflected and transmitted fields are given for low-frequency situations.
New methods of sound reproduction from old wax phonograph cylinders
Authors: Ifukube Tohru , Kawashima Toshio , Asakura Toshimitsu
Published: October 2005

Using the Edison-type phonograph over the years from 1902 to 1905, B. Pitsudski, a Polish anthropologist, recorded the voices and songs of the Ainu people in Sakhalin and Hokkaido on 65 wax cylinders to study their culture. It was expected that these cylinders would provide valuable opportunities for investigating the folklore of the Ainu people, which had been lost. Most of these cylinders, however, changed in quality by recrystallization and had many cracks on their surfaces. In this article, replication methods for the cylinders are described to preserve them permanently, and the reproduction methods are shown to be useful for reproducing sound from not only undamaged but also damaged wax cylinders. Two methods of sound reproduction from old wax cylinders were developed using very light pressure styli and laser-beam reflection. A stylus of 250-μm diameter and a spot diameter of the illuminating beam of around 100 μm were found the most suitable for reproducing the sound from the wax cylinder. The reproduction of the sounds from all of Pitsudski’s cylinders was a success. These techniques and findings can be used to reproduce other cylinders that have been preserved elsewhere in the world.
Estimation of depth dependence of compressional velocity from cross correlation of measured and simulated waveforms
Authors: Vidmar Paul J. , Oakley David W.
Published: October 2005

This article describes an approach for using broadband acoustic data to determine the depth dependence of the compressional (P) velocity in the upper several hundred meters of the seafloor in deep water areas. The technique used here does not rely upon ‘‘picks’’ of arrival time from acoustic data from many ranges or upon deconvolution of the received signal. Rather, the waveform of the first bottom bounce arrival at a single range is simulated and R (the ratio of the P-wave velocity of the sediment to the water sound speed) and g (the gradient of P-wave velocity) are adjusted to maximize the similarity between the measured and simulated signals. A low-frequency band is used to reduce complications caused by small scale layering in the seafloor and a long-range source is chosen to avoid acoustic interaction with the substrate. For an objective measure of similarity, Cmax, the maximum magnitude of the normalized cross-correlation function of measured and simulated time series is used. In the implementation discussed in this article, the simulated time series were produced by a ray-based computational model that includes eigenrays that travel through the seafloor. It was found that the dependence of Cmax on R and g is strong enough to allow precise estimates (within 10%) of their values. The procedure begins with waveforms simulated for the reported experimental geometry, measured sound velocity profile, measured or calculated source waveform, and initial estimates of geoacoustic parameters. First, the geometrical parameters are refined by maximizing Cmax with respect to the range and depth of source and receiver, and then the P-wave parameters are obtained by maximizing with respect to R and g. The method is demonstrated by obtaining R and g from explosive source data collected in an abyssal hills environment in the Pacific Ocean. Maximizing Cmax in the 25- to 250-Hz band yielded estimates of R and g that agree with reported values.
Maximum-likelihood passive localization using mode filtering
Authors: Hinich Melvin J. , Sullivan Edmund J.
Published: October 2005

The maximum-likelihood estimator for passive range and depth estimation of an acoustic point source in a shallow-water waveguide is presented. The data from a vertical array of hydrophones are passed through a modal filter, the output of which is the set of complex modal amplitudes associated with the normal-mode model of acoustic propagation. The range and depth estimates are then found by a maximum-likelihood estimation procedure that uses these modal amplitudes as inputs. This technique is compared to the matched-field procedure and is shown to have better signal-to-noise and sidelobe behavior for a given scenario. Results are given for both synthetic and real data. The results with the real data demonstrate the importance of the mode-filtering property of the maximum-likelihood estimator presented in this work.
Broadband acoustic transmission fluctuations during NAPOLI 85, an experiment in the Tyrrhenian Sea: Preliminary results and an arrival-time analysis
Authors: Uscinski B. J. , Potter J. R. , Akal T.
Published: October 2005

An acoustic propagation experiment was carried out in the Tyrrhenian Sea in October 1985 in which signals from a broadband source were recorded at a range of 5 km with a vertical 62-m hydrophone array over a period of 5 days. The experiment, named ‘‘NAPOLI 85,’’ was designed to investigate the transfer function of the ocean medium over an acoustic frequency range from 250–2000 Hz as a function of time and position down the vertical array. The present article describes the experiment and treats the pulse arrival times for one ray path, the lower refracted path. It is found that internal-wave models are not helpful in describing the environment of this experiment. In contrast to most previous experiments of this type, the sound-speed refractive index is dominated by noninternal-wave features. Some of the implications (regarding input to the scattering theory and acquiring environmental measurements) of this are explored. The experimental spatial structure function of the arrival time down the vertical array is presented and shown to compare well, given the limitations of the data, with theoretical predictions regarding both its magnitude and functional behavior.
An efficient high-resolution method of source localization processing in mode space
Authors: Shang E. C.
Published: October 2005

The matched-field processing proposed by Bucker [J. Acoust. Soc. Am. 59, 368–373 (1976)] can be performed in phone space (matching the total field received by each phone of an array) or in mode space (matching a subset of modes resolved from the array data). For a stratified waveguide, processing in mode space can be more efficient and more robust. However, the method processing in mode space previously proposed as the ‘‘modal beamforming’’ method has the drawback of less inherent resolution. In this paper, the high-resolution modal matching (HRMM) method has been proposed instead of the ‘‘modal beamforming’’ technique. One of the advantages of the HRMM method is that high resolution can be achieved even when only a few modes are available; for depth estimation especially, the first two modes are good enough. Some numerical examples are presented.
Some effects of signal bandwidth and spectral density on the acoustic-reflex threshold in the elderly
Authors: Jakimetz John J. , Silman Shlomo , Miller Maurice H. , Silverman Carol Ann
Published: October 2005

The acoustic-reflex thresholds (ART) for multicomponent tonal complexes of varying bandwidth and spectral density were obtained from 20 normal-hearing (air-conduction thresholds less than or equal to 20 dB HL at 250–8000 Hz) young adults ranging in age from 20–30 years and 20 normal-hearing, old subjects ranging in age from 60–71 years. The results revealed that the ART decreased with spectral density, plateauing after seven components in the young group and after five components in the old group; the decrease in the acoustic-reflex threshold as a result of the increase in spectral density was less in the old than in the young group. The bandwidth effect (when bandwidth was plotted in hertz or octaves) on the acoustic-reflex threshold was present in the young adults, but substantially reduced in the elderly, as evidenced by the statistically significant interaction between subject group and signal bandwidth. The spectral density results are discussed in terms of their theoretic implications for the energy summation capacity and frequency resolution of the auditory system. The bandwidth results are discussed in terms of their theoretic implications for the frequency-resolving power of the auditory system.
A finite-element model for ocean acoustic propagation and scattering
Authors: Murphy Joseph E. , Chin-Bing Stanley A.
Published: October 2005

The finite-element technique has the potential to provide a very accurate treatment of the physics of acoustic-wave propagation in inhomogeneous media. This article describes the development of a finite-element model for acoustic propagation in complex ocean environments and its validation. The computational model can handle range and depth dependence in both sound speed and density, as well as rapid variations in bottom topography.
Stimulus step size and heterogeneous stimulus conditions in adaptive psychophysics
Authors: Green David M. , Richards Virginia M. , Forrest T. G.
Published: October 2005

This paper reports on simulations of repeated estimates of stimulus thresholds using a two-down, one-up adaptive procedure and forced-choice procedures using 2, 3, and 4 response alternatives. In the first section of the paper, the selection of an initial and final step size for the stimulus is the main focus. For a 2-alternative forced-choice psychometric function, a step size of roughly one-quarter the useful range (60%–90%) provides a reasonable initial step size. A final step size of roughly half that value is recommended. The increase in the variability of threshold estimates is, however, not very great if values near those recommended are selected instead. The change in the variability of the threshold estimates with the change in the number of alternatives used in the forced-choice procedure can be predicted by considering the sweat factor associated with the psychometric function. In the second part of the paper, the focus is on how the variability in threshold estimates increases if the stimulus set is heterogeneous; that is, the stimuli produce different psychometric functions. Stimuli that differ only in their means increase the variability of threshold estimates more than do stimuli that differ only in the slopes of their psychometric functions. Stimuli that contain both forms of heterogeneity, however, increase the variability in threshold estimates by only about 50%.
Unification of perturbation measures in speech signals
Authors: Pinto Neal B. , Titze Ingo R.
Published: October 2005

Voice perturbation measures, formerly defined in a somewhat ad hoc fashion, are discussed within the framework of signal theory. An attempt is made to unify a variety of existing jitter, shimmer, and noise measures on the basis of common underlying perturbation functions and their derivatives. Some simple modulations (sinusoid, Gaussian noise, linear trend) are imposed on cyclic parameters in phonation (e.g., amplitude and fundamental frequency) to test the ability of perturbation measures to detect or reject these types of modulations. It is expected that this systematic approach to perturbation analysis will be helpful in identifying the sources of irregularity in the voice and, thereby, in the detection of laryngeal disorders.
Ultrasonic heating of the skull
Authors: Carstensen Edwin L. , Child Sally Z. , Norton Stephanie , Nyborg Wesley
Published: October 2005

Comparatively simple analysis shows that diagnostic ultrasound devices, in some cases, may approach output levels that can produce significant heating of tissues, particularly if the propagation path includes bone. Experimental tests of these predictions using rodents show that temperature increments of the order of 3 °C/W/cm2 are produced in skull bone with sharply focused fields at medically relevant frequencies.
Interference patterns in shallow-water reverberation
Authors: Weston David E. , Hocking Peter D.
Published: October 2005

Echo-ranging experiments off Perranporth, England, have shown diffuse patterns in the reverberation, a major cause being interference between the normal modes of propagation. There are interference modulations in the strength of the echoes from close-range areas of bottom roughness, from daytime fish shoal tracks, and from general reverberation due to fish at night—the latter two effects going out about 56 km. At 1 kHz we can get regular patterns, with typical spacing 6.0 km at 20-km range, and good agreement is demonstrated between experiment and a theory based on two modes. At 2 kHz we can get only irregular patterns, with typical spacing 3.0 km, due to a multiplicity of modes. These patterns follow the tidal variation in water depth, but are sometimes confused by other patterning that follows the tidal streaming. Changes in the phase of the patterns due to the vertical movement of fish in the water column have also been observed; this together with other phenomena can provide a crude measure of echoer depth.
Modeling microsegments of stop consonants in a hidden Markov model based word recognizer
Authors: Deng L. , Lennig M. , Mermelstein P.
Published: October 2005

The motivation of this study is the poor performance of speech recognizers on the stop consonants. To overcome this weakness, word initial and word final stop consonants are modeled at a subphonemic (microsegmental) level. Each stop consonant is segmented into a few relatively stationary microsegments: silence, voice bar, burst, and aspiration. Microsegments of certain phonemically different stops are trained together due to their similar spectral properties. Microsegmental models of burst and aspiration are conditioned on the adjacent vowel category: front versus nonfront vowels. The resulting context-dependent microsegmental hidden Markov models (HMMs) for six stops possess the desired properties for a compromise between modeling accuracy and modeling robustness. They allow the recognizer to focus discrimination onto those regions of a stop that serve to distinguish it from other stops. Use of these models in recognition experiments for word lists consisting of CVC words reduces the error rate by 35% compared with the result obtained by using one HMM for each stop phoneme.
Goupillaud layers and construction of wave speed and density of a layered acoustic medium
Authors: Hooshyar M. A.
Published: October 2005

The problem of finding the density and the wave speed of an acoustic medium from the observed reflection response at two different angles of incidence is studied. Based on results for finding impedance from normal incidence reflection data, existence of a modified Goupillaud method to our problem is motivated. A possible modified Goupillaud approach applicable to finding density and wave speed from reflection response at different angles of incidence is presented and studied.
Reflection and transmission of compressional waves: Some exact results
Authors: Lekner John
Published: October 2005

Exact results are derived for the reflection and transmission of acoustic compressional waves by an arbitrary stratification. These results include conservation and reciprocity theorems, low-frequency and high-frequency limiting forms, and analytic solutions for two special stratifications, both having exponential variation of density with depth, and linear or exponential variations of sound speed.
Use of the magnitude estimation technique for assessing the performance of text-to-speech synthesis systems
Authors: Pavlovic Chaslav V. , Rossi Mario , Espesser Robert
Published: October 2005

As text-to-speech systems develop, it becomes necessary to compare various solutions and to evaluate whether a change in the synthesis procedure has an effect on the listener’s attitude to the system. The possibility of directly scaling intelligibility, naturalness, and user’s satisfaction (i.e., acceptability) with the magnitude estimation technique is investigated. A magnitude estimation protocol suitable for this purpose is described. In general, within the limits of the methodological constraints discussed in this paper, the procedure appears to be reliable and valid for quantifying the perceived attributes of synthesized speech.
Comodulation detection differences with multiple signal bands
Authors: Wright Beverly A.
Published: October 2005

Detection thresholds were determined for signals consisting of one, two, or five noise bands embedded in eight ‘‘cue’’ bands. All of the noise bands were 100 Hz wide. The center frequencies of the signal bands ranged from 1250–3250 Hz in 500-Hz steps, and those of the cue bands ranged from 500–4000 Hz in 500-Hz steps. The multiple-band signals either all had the same temporal envelope, or all had different temporal envelopes. Similarly, the cue bands either all had the same temporal envelope or all had different temporal envelopes. In separate listening conditions, signal thresholds were determined for various combinations of the temporal envelope patterns of the signal and cue bands. The results were analyzed both in terms of differences in threshold across listening conditions, and in terms of changes in threshold within a listening condition, as the number of signal bands was increased. For both the single- and multiple-band signals, performance was best when the signal band(s) had a different envelope from the common envelope of the cue bands, and performance was worst when either the cue bands all had different envelopes, or the signal and cue bands all shared the same envelope. The thresholds of the multiple-band signals were better fitted by an independent-thresholds model than by a statistical-summation model. However, neither model predicted thresholds uniformly well in all listening conditions. The results are discussed in terms of both ‘‘within-channel’’ and ‘‘across-channel’’ models.
Application of Twersky’s boss scattering theory to laboratory measurements of sound scattered by a rough surface
Authors: Chu D. , Stanton T. K.
Published: October 2005

One of the many challenges in describing the scattering of sound by rough surfaces is to address the fact that most surfaces are three-dimensional. Furthermore, only their statistical properties may be known. Twersky’s model [V. Twersky, J. Acoust. Soc. Am. 29, 209–225 (1957)], by using a method of images and taking multiple scattering into account, established a general solution involving distributions of three-dimensional ‘‘bosses’’ (protuberances) on a base plane. A prominent advantage of the theory over others is that it can describe bosses of arbitrary orientation. In this present article the theory is compared with laboratory measurements of sound scattered by a continuously rough pressure-release surface. The mathematical surface in Twersky’s theory does not rigorously resemble the laboratory surface. Thus this study serves to assess the potential applicability of Twersky’s 3-D boss surface to continuously rough 3-D surfaces that may occur in nature. In the model, use is made of prolate hemispheroidal bosses oriented in a randomized range of directions and randomly packed to approximate the rough surface. These bosses and their distribution were chosen to resemble the general size, shape, orientation, and spacing of the major features of the rough surface. The data were taken from Horton et al. [C. W. Horton, S. K. Mitchell, and G. R. Barnard, J. Acoust. Soc. Am. 41, 635–643 (1967)] and Welton [P. J. Welton, report ARL-TR-75-30, University of Texas at Austin (1975)] and involve backscattered sound versus grazing angle for several frequencies. The comparisons of the numerical computations with Welton’s data show a reasonable agreement with respect to not only the boss orientation parameters but also the surface statistical parameters (rms roughness and correlation length). An interesting phenomenon is that the number of spheroidal modes required to fit the data increases as the frequency of the incident plane wave increases.
Dipole scattering and background mobility
Authors: Werby Michael F. , D’Archangelo J. M. , Überall Herbert
Published: October 2005

In some of the earlier literature, it was suggested that the lowest-order dipole mode of an elastic sphere immersed in a fluid and excited by an incident acoustic wave corresponds to a rigid-body oscillatory motion of the sphere as a whole. The present investigation verifies and corroborates these statements in a quantitative fashion.
Effect of contralateral sound stimulation on the distortion product 2F1−F2: Evidence that the medial efferent system is involved
Authors: Puel J.-L. , Rebillard G.
Published: October 2005

The mechanical nonlinearity of the cochlea that is associated with normal cochlear function, induces distortion products that can be recorded in the external auditory canal. The acoustic cubic distortion product 2F1−F2 (DP) was measured in the external canal in the presence and in the absence of a contralateral white noise. The experiments were carried out on 20 guinea pigs after a section of the middle ear muscles. They showed that the presence of a contralateral white noise induces a significant and reversible reduction of the magnitude of the DPs. This suppressive effect produced by the contralateral white noise was completely canceled out by the midline sagittal section of the brainstem. This report supports the hypothesis that the suppressive effect of a contralateral sound stimulation is mediated by the medial efferent system.
Radiation from a finite array of simple sources
Authors: Akay Adnan
Published: October 2005

Closed-form expressions for farfield intensity and power radiated by finite arrays are derived for cases when the adjacent sources are either in phase or out of phase. The results are generalized for a class of linear arrays made up of simple point sources; specifically, expressions for power radiated from arrays of monopoles, dipoles, and axial quadrupoles are considered. The closed-form solutions obtained are made possible by special trigonometric relationships that simplify the intensity terms in the integrations leading to the power expressions. Normalized radiated power and radiation patterns for several cases are plotted, and the characteristics of radiated power at low and high frequencies are examined.
History of the flextensional electroacoustic transducer
Authors: Rolt Kenneth D.
Published: October 2005

The flextensional electroacoustic transducer is resurging as a candidate for high-power, low-frequency active sonar. It has experienced steady investigation and development since the late 1950s and is popular enough now so that it is even advertised in naval and ocean-related publications. Despite this popularity, the history of its invention and development has remained cloudy. The invention is usually credited to William J. Toulis during the late 1950s. However, at least two flextensional designs were invented, developed, and constructed during 1929–1936 by a pioneer in underwater acoustics, Harvey C. Hayes, at the U. S. Naval Research Laboratories in Washington, DC. These flextensionals were intended as aeroacoustic foghorn sources. The Hayes flextensionals then vanished from development during the mid-1930s, and the concept was not revisited (in the U.S.) until the mid-to-late 1950s by Toulis and Frank R. Abbott at the U. S. Naval Electronics Laboratory, San Diego, CA. This paper will review the history of the flextensional transducer beginning with Hayes’ work, review the classes of flextensional transducers, and discuss modern flextensional transducers.
On the use of adaptive procedures in binaural experiments
Authors: Trahiotis Constantine , Bernstein Leslie R. , Buell Thomas N. , Spektor Zorik
Published: October 2005

Adaptive psychophysical procedures have been routinely used in monaural experiments for many years, but only sparsely used in binaural experiments. In this letter, (1) the increasing use of adaptive procedures in binaural experiments is documented; (2) factors that determine their appropriateness are discussed; and (3) data that attest to their usefulness are presented.
The effect of signal-frequency uncertainty on comodulation masking release
Authors: Grose John H. , Hall Joseph W.
Published: October 2005

The aim of this study was to examine whether the scheme of across-frequency comparison underlying comodulation masking release (CMR) is sensitive to the placement of the signal in the array of comodulating bands. This was addressed using the paradigm of signal-frequency uncertainty. In the first experiment, maskers were constructed of linearly spaced sinusoidally amplitude-modulated tones, and the signal was a pure tone presented at one of five frequencies. A small uncertainty effect was observed for the noncomodulated masker, but no significant effect was observed for the comodulated masker. In the second experiment, the maskers were constructed of logarithmically spaced noise bands, and the signal was a pure tone presented at one of seven frequencies. In these conditions, an uncertainty effect was observed in both noncomodulated and comodulated maskers, which was larger than that observed in experiment 1. The results were interpreted as indicating that the mechanism of across-frequency comparison underlying CMR is sensitive to signal location.
Synchronization of spontaneous otoacoustic emissions to a 2f1−f2 distortion product
Authors: van Dijk Pim , Wit Hero P.
Published: October 2005

Synchronization of spontaneous otoacoustic emissions to a cubic distortion frequency fs=2f1−f2 has been studied. Stimulus, consisting of two primary tones at frequency f1 and f2, could easily be filtered out of the microphone signal. This enabled us to monitor emission phase with respect to synchronization frequency fs, by recording zero-crossing moments of the microphone signal. When primaries were sufficiently loud (typically 30 dB SPL), phase fluctuated around a constant value: The emission was constantly synchronized to fs. Lowering primary levels (to typically 20 dB SPL) resulted in 2π-phase jumps at random moments: The emission occasionally slipped out of synchronization, trying to maintain its own natural frequency f0. This behavior can be described as synchronization of an oscillator (frequency f0) to a sinusoidal force (frequency fs) in the presence of noise.
Auditory duration discrimination in the European starling (S
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Authors: Maier Elke H. , Klump Georg M.
Published: October 2005

Auditory duration discrimination was studied in the European starling (Sturnus vulgaris, n=3) using a GO/NOGO-procedure. Acoustic signals were presented by the method of constant stimuli. Duration discrimination limens (DDLs) were determined using signal detection theory (threshold criterion d′=1.8). Weber fractions ΔT/T at threshold are reported for pure tones (0.5, 2, and 4 kHz) at a sound-pressure level of 50±2 dB. The starlings had DDLs for an increase in duration of between ΔT/T=0.12 and ΔT/T=0.23 for reference durations of between 800 and 100 ms, respectively. The DDLs for reference durations of 400 and 200 ms did not differ from those of 800 ms. There was no effect of tone frequency. Weber fractions ΔT/T for a decrease in duration were independent of the reference durations and the frequencies tested (average ΔT/T=0.19). Duration discrimination is discussed with respect to data from other animals, and to hypotheses on the perception of signal duration.
Measurements of under-ice broadband coherence
Authors: Meredith Roger W.
Published: October 2005

The Arctic ocean is a unique region acoustically, dominated by the under ice canopy. The ice varies seasonally in coverage, thickness, and roughness, causing varying degrees of acoustic spatial and temporal variability. In this paper, horizontal coherence, from explosive acoustic sources under the arctic ice pack, is examined in the frequency range 90–1400 Hz with a nominal sensor separation of 370 m. Magnitude-squared coherence is computed separately for the direct and ice-reflected propagation paths. Frequency averaging is used to compute the coherence estimate that fluctuates with horizontal range, sensor depth, and frequency. Frequency and depth dependence is associated with background coherence inside and below the acoustic half-channel determined by sound speed. The lowest frequency bands do not always give the highest coherence. Coherence degradation due to ice interaction may be as high as 60% for the higher frequency bands inside the half-channel.
Microbend loss fiber optic direction and amplitude sensors for underwater applications
Authors: Vengsarkar Ashish M. , Murphy Kent A. , Tran Tuan A. , Claus Richard O.
Published: October 2005

Dual purpose fiber optic microbend loss sensors have been developed for measurement of underwater acoustic wave amplitudes and for detection of the direction of wave propagation. Three different construction schemes for cylindrical sensing elements are considered. The dual purpose hydrophones have been characterized for frequencies ranging from 15 to 75 kHz. They exhibit sensitivities in the range of −175 to −200 dB re:1 V/μPa and directionality sensitivity limited by geometrical construction.
Long isotropic buffer rods
Authors: Jen C. K. , Piche L. , Bussiere J. F.
Published: October 2005

Longitudinal acoustic wave measurements performed on isotropic aluminum buffer rods with uniform, notched, and tapered peripheries are presented. The buffer rods considered have diameters between a few and several tens of acoustic wavelengths, and lengths of more than a hundred acoustic wavelengths. The buffer rod with a tapered shape was found to be the most effective for eliminating trailing echoes associated with mode conversion on the outer walls of the rods.
The effects of bandwidth on the detectability of narrow- and wideband signals
Authors: Bernstein Richard S. , Raab David H.
Published: October 2005

The effects of masker bandwidth on the detection of narrow- and wideband signals have been investigated. For both kinds of signals, plots of threshold as a function of masker bandwidth yielded by both narrow- and wideband signals are reasonably described with two intersecting lines. Thresholds initially increase with masker bandwidth and then become independent of further increases. The rate of increase depends on the signal spectrum. The bandwidth at which the lines intersect varies with signal bandwidth and also mode of masker presentation (i.e., whether the masker is gated with the signal or is present continuously). Internal filtering is most accurate when the masker is present continuously. A model is proposed in which a listener’s decisions about the presence of narrow-band signals are based upon estimates of stimulus energy within a critical band. These estimates are degraded by bandwidth-dependent processing errors. When the signal to be detected spans several critical bands (i.e., is wideband), the model forms a test statistic by summing the outputs of the relevant critical bands. The model permits the contribution of each band to the sum to vary with masker bandwidth because it incorporates a form of lateral suppression. Thresholds of narrow-band signals in gated maskers and wideband signals in gated and continuous maskers are predicted by the model. However, the model fails to account for the detectability of narrow-band signals in continuous maskers.