bluuebunny/crossref_metadata_2025 huggingface dataset:
The ‘‘overshoot’’ effect and sensory hearing impairment
Authors: Carlyon Robert P. , Sloan Eileen P.
Published: October 2005

The threshold for the detection of a brief tone masked by a longer-duration noise burst is higher when the tone is presented shortly after the onset of the noise than at longer delay times. This finding has been termed the ‘‘overshoot’’ effect [E. Zwicker, J. Acoust. Soc. Am. 37, 653–663 (1965)]. The present letter compared the size of the effect in the better and more impaired ear of six subjects with high-frequency unilateral or asymmetric hearing losses of sensory origin. Thresholds were measured for 5-ms 4-kHz tones presented 10, 200, and 390 ms after the onset of a 400-ms, 2- to 8-kHz noise burst. The better ear of each subject was tested using two noise levels, one equal in sound-pressure level and one equal in sensation level to that used for the impaired ear. Thresholds for all subjects and all ears decreased monotonically with increasing delay time, with the size of the effect typically 5 dB. Thus a small overshoot effect was observed regardless of hearing impairment.
Oscillations of a cloud of bubbles of small and not so small amplitude
Authors: Omta Roelof
Published: October 2005

The oscillations and sound emission of a bubble cloud containing a large number of bubbles in a liquid are studied. Averaged equations are used to describe the behavior of the mixture. Two analytical models are used to describe the behavior of the bubble contents. The oscillations of small amplitude are calculated analytically, those of not so small amplitude numerically. It is shown that the frequency spectrum is determined mainly by the total volume of gas in the cloud. The efficiency of sound emission is determined also by the magnitude of the individual bubbles. The frequency spectrum of the emitted sound has a peak at a frequency much lower than the eigenfrequency of the individual bubbles. At higher amplitudes of the oscillations, very high pressures occur at the center of the cloud that strongly limit the numerical calculations.
Acoustic force measurement in a dual-temperature resonant chamber
Authors: Robey Judith L. , Trinh Eugene H. , Wang Taylor G.
Published: October 2005

The acoustic radiation force was measured for a dual-temperature resonant chamber. This rectangular chamber has its long dimension approximately 8.5 times the square cross-sectional dimension, and the opposite ends are at widely different temperatures. Force profiles were obtained for two hot end temperatures of 520 °C and 760 °C, while the cool end remained at approximately room temperature. The lateral force was measured as a function of the long dimension of the chamber along the temperature gradient, and as a function of the drive voltage. Force magnitudes as high as 17 dyn for a sample 1.2 cm in diameter at 760 °C and at 162-dB input level were measured. Qualitatively, the measured force profiles correspond well with the theoretical curves; the correlation of absolute magnitude, however, is yet to be determined.
The propagation of low-frequency sound in a two-dimensional duct system with T joints and right angle bends: Theory and experiment
Authors: Bruggeman Jan C.
Published: October 2005

The method of matched asymptotic expansions is used to determine a low-frequency approximation of the acoustic pressure in a waveguide system with a T joint. The low-frequency approximation is compared with (a) experimental data of Lippert [Acustica 4, 313–319 (1954)]; (b) new experimental data; and (c) the first approximation of the mode expansion proposed by Miles [J. Acoust. Soc. Am. 17, 259–272 (1946)].
Acoustic wave propagation in a circular cosh duct carrying a mean flow
Authors: Thompson Charles , Sen Rahul
Published: October 2005

An analysis of acoustic wave propagation in a waveguide carrying an incompressible mean flow is presented. The radius of the waveguide is taken to vary slowly as a function of axial location. It is shown that the dynamic behavior of the enclosed fluid can be parametrized by the small parameter ε, where ε is the ratio of the typical duct radius R0 and the wall wavelength L0. An analytical solution for the pressure field in the duct is given in terms of a regular perturbation expansion in ε. The method of matched asymptotic expansions is used to evaluate the refractive effect of a thin mean-flow boundary layer on the acoustic pressure field. It is shown that in the case where the duct geometry conforms to that of a circular cosh duct the effect of higher-order turning points in the wave equation can be effectively handled by a closed-form solution that approximately solves the governing equations. The results of analysis are compared to those obtained using numerical methods.
Edge diffraction of a compressional beam
Authors: Harris John G.
Published: October 2005

The compressional and shear waves reflected from a semi-infinite crack and diffracted from its edge when it is struck by a two-dimensional compressional beam are calculated asymptotically. Both a beam whose amplitude is initially rectangular and one whose amplitude is Gaussian are studied. The crack is positioned perpendicular to the central ray of the incident beam. Further, the crack lies in the near- to farfield transition region of the incident beam. Thus the incident beam is only slightly divergent when it strikes the crack edge. For the incident rectangular beam, approximations representing the reflected and transmitted beams plus their interactions with the diffracted waves at the reflection and shadow boundaries are calculated from integral representations of the scattered waves. However, the diffracted waves outside the boundary regions are omitted. In contrast, for the incident Gaussian beam, all the waves scattered from the crack edge are calculated. However, to calculate the wave fields in the reflection and shadow boundary regions, working with the integral representations was abandoned. Instead, boundary layer equations are derived and solved. One result of these analyses, which was not anticipated, is that the reflection and shadow boundaries must be found as part of the boundary layer analyses.
Generation of sound within a closed cell by an alternating current in a straight wire
Authors: Wright Wayne M.
Published: October 2005

The suitability of using a wire carrying an alternating current as a laboratory sound source has been examined. An analysis is outlined in which Joule heating of the wire is assumed to be communicated to the surrounding air, which is enclosed within a chamber having dimensions comparable to the sound wavelength. The predictions are compared with measurements of the sound field set up inside a cylindrical cell (15-cm long × 5.3-cm diam), in response to a biased ac in a straight wire parallel to the cell axis, over a frequency range (3.5–8.5 kHz) which contains the three lowest resonant modes that are independent of the axial coordinate. This acoustic field varies with source wire position according to theoretical predictions for each of these (two azimuthal and one radial) modes. An average electrical source power of 33 mW/cm in ♯40 Nichrome wire results in a maximum sound pressure within the cell of approximately 5 mPa at the 3.9-kHz first azimuthal resonance, which is less than 0.1% of that which should exist if the thermal energy were deposited directly into the air.
Transient response of fluid-loaded elastic plates via an impulse response method
Authors: Ebenezer D. D. , Stepanishen Peter R.
Published: October 2005

A general time domain approach to evaluate the transient velocity and pressure fields of fluid-loaded plates, which are excited by one-dimensional broadband excitations, is presented. A mechanical pressure, which is independent of the acoustic field, is used to excite the plate. The approach is based on the use of a time-dependent in vacuo modal expansion of the velocity of the plate. As a result of the fluid coupling, the time-dependent velocity coefficients of the modes are described by a set of coupled, linear, convolution integral equations which can be solved by marching forward in time. If both symmetric and antisymmetric modes are excited, they are not coupled and the equations are separated into two sets which are solved independently. Typical numerical results are presented showing the impulse responses of the modal admittance of the plate, the coupling coefficients, the modal velocities of the plate when coupling effects are included and are neglected, and the pressure in the farfield.
Some fundamental considerations regarding voice identification
Authors: Shipp Thomas , Doherty E. Thomas , Hollien Harry
Published: October 2005

Several important areas need substantial clarification or expansion before the reported findings of Koenig, ‘‘Spectrographic voice identification: A forensic survey’’ [J. Acoust. Soc. Am. 79, 2088–2090 (1986)], can be readily accepted. They are: (1) the method of ‘‘voiceprint’’ analysis used, (2) ‘‘voiceprint’’ examiners’ qualifications, and (3) the means for determining the FBI’s correct identification.
Acoustic versus electromagnetic backscattering cross section of a sphere
Authors: Schenck Harry A.
Published: October 2005

The scattering of an acoustic or electromagnetic wave by a sphere is a classical problem, and the results are considered to be ‘‘well known.’’ Actually, there are errors in the results presented in several standard references, and the significant quantitative difference between the acoustic and electromagnetic cases has, at times, been ignored. The purpose of this letter is to point out some of these errors and to clarify the difference in simple graphical form.
Vowel and consonant recognition of cochlear implant patients using formant-estimating speech processors
Authors: Blamey P. J. , Dowell R. C. , Brown A. M. , Clark G. M. , Seligman P. M.
Published: October 2005

Vowel and consonant confusion matrices were collected in the hearing alone (H), lipreading alone (L), and hearing plus lipreading (HL) conditions for 28 patients participating in the clinical trial of the multiple-channel cochlear implant. All patients were profound-to-totally deaf and ‘‘hearing’’ refers to the presentation of auditory information via the implant. The average scores were 49% for vowels and 37% for consonants in the H condition and the HL scores were significantly higher than the L scores. Information transmission and multidimensional scaling analyses showed that different speech features were conveyed at different levels in the H and L conditions. In the HL condition, the visual and auditory signals provided independent information sources for each feature. For vowels, the auditory signal was the major source of duration information, while the visual signal was the major source of first and second formant frequency information. The implant provided information about the amplitude envelope of the speech and the estimated frequency of the main spectral peak between 800 and 4000 Hz, which was useful for consonant recognition. A speech processor that coded the estimated frequency and amplitude of an additional peak between 300 and 1000 Hz was shown to increase the vowel and consonant recognition in the H condition by improving the transmission of first formant and voicing information.
An acoustic analysis of fluctuations in the voices of normal adult speakers across three times of day
Authors: Garrett Kathryn L. , Healey E. Charles
Published: October 2005

The purpose of this study was to determine the amount of variation for several vocal parameters across three times of the day (morning, noon, and afternoon). Connected speech samples from normal adult males (N=10) and females (N=10) were recorded during morning, early afternoon, and late afternoon. Results showed that males produced a statistically significant increase in speaking fundamental frequency (SFF) from morning to afternoon. Females did not demonstrate a statistically significant change in SFF across the three time periods. Vocal amplitude did not change significantly for either group. The SFF variability was higher for the females than for the males. Analysis of individual data revealed that the patterns of vocal change across the three times of day were not consistent among the subjects.
Factors affecting thresholds for sinusoidal signals in narrow-band maskers with fluctuating envelopes
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

When a signal is higher in frequency than a narrow-band masker, thresholds are lower when the masker envelope fluctuates than when it is constant. This article investigates the cues used to achieve the lower thresholds, and the factors that influence the amount of threshold reduction. In experiment I the masker was either a sinusoid (constant envelope) or a pair of equal-amplitude sinusoids (fluctuating envelope) centered at the same frequency as the single sinusoid (250, 1000, 3000, or 5275 Hz). The signal frequency was 1.8 times the masker frequency. At all center frequencies, thresholds were lower for the two-tone masker than for the sinusoidal masker, but the effect was smaller at the highest and lowest frequencies. The reduced effect at high frequencies is attributed to the loss of a cue related to phase locking in the auditory nerve. The reduced effect at low frequencies can be partly explained by reduced slopes of the growth-of-masking functions. In experiment II the masker was a sinusoid amplitude modulated at an 8-Hz rate. Masker and signal frequencies were the same as for the first experiment. Randomizing the modulation depth between the two halves of a forced-choice trial had no effect on thresholds, indicating that changes in modulation depth are not used as a cue for signal detection. Thresholds in the modulated masker were higher than would be predicted if they were determined only by the masker level at minima in the envelope, and the threshold reduction produced by modulating the masker envelope was less at 250 Hz than at higher frequencies. Experiments III and IV reveal two factors that contribute to the reduced release from masking at low frequencies: (1) The rate of increase of masked threshold with decreasing duration is greater at 250 Hz than at 1000 Hz; (2) the amount of forward masking, relative to simultaneous masking, is greater at 250 Hz than at 1000 Hz. The results are discussed in terms of the relative importance of across-channel cues and within-channel cues.
Effects of auditory fatigue on psychophysical estimates of cochlear nonlinearities
Authors: Norton Susan J. , Mott John B.
Published: October 2005

Two-tone-suppression (2TS) effects and cubic-difference-tone (CDT) levels were measured using a forward-masking procedure, before and after exposure to an intense tonal stimulus. Changes in 2TS effects were consistent with a change in the nonlinearity, such that the system became more linear, in addition to changes due to attenuation of the primary stimuli F1 and F2. Changes in CDT levels could be accounted for on the basis of a temporary threshold shift at F1 and F2. These results indicate at least a partial dissociation of the mechanisms underlying 2TS and CDT generation.
The perceptual attack time of musical tones
Authors: Gordon John W.
Published: October 2005

Perceptual attack time (PAT) is defined as the time a tone’s moment of attack or most salient metrical feature is perceived relative to its physical onset. Experiments are described that measured the PATs of recorded orchestral instrument tones by means of an interactive procedure with a computer and digital music synthesizer. Some PAT prediction models were then developed and tested against the empirical data. The most successful model had a correlation of 0.995 between measured and predicted PATs. The PAT is dependent on both rise time and listening level, indicating that the slope of the rise function is a key factor. Duration and spectrum can also act as cues to PAT, but are much less influential than amplitude or intensity cues. Possible relations to findings in physiology, particularly to the phenomenon of short-term adaptation in the firing of auditory fibers, are discussed.
Encoding voice pitch for profoundly hearing-impaired listeners
Authors: Grant Ken W.
Published: October 2005

The ability of five profoundly hearing-impaired subjects to ‘‘track’’ connected speech and to make judgments about the intonation and stress in spoken sentences was evaluated under a variety of auditory–visual conditions. These included speechreading alone, speechreading plus speech (low-pass filtered at 4 kHz), and speechreading plus a tone whose frequency, intensity, and temporal characteristics were matched to the speaker’s fundamental frequency (F0). In addition, several frequency transfer functions were applied to the normal F0 range resulting in new ranges that were both transposed and expanded with respect to the original F0 range. Three of the five subjects were able to use several of the tonal representations of F0 nearly as well as speech to improve their speechreading rates and to make appropriate judgments concerning sentence intonation and stress. The remaining two subjects greatly improved their identification performance for intonation and stress patterns when expanded F0 signals were presented alone (i.e., without speechreading), but had difficulty integrating visual and auditory information at the connected discourse level, despite intensive training in the connected discourse tracking procedure lasting from 27.8–33.8 h.
The development of skill in producing word-final English stops
Authors: Flege James Emil , McCutcheon Martin J. , Smith Steven C.
Published: October 2005

This study examined production of word-final English /p/ and /b/ by subjects whose native language does not possess voiced stops in word-final position. Native Chinese adults resembled native English adults, native English children, and native Chinese children in producing /p/ with greater peak oral air pressure than /b/. However, unlike subjects in the other groups, the Chinese adults’ /b/ was sometimes misidentified as /p/. This may have occurred, at least in part, because the Chinese adults produced a much smaller difference between /p/ and /b/ in labial closure duration and voicing than the other subjects. The English adults sustained voicing in /b/ significantly longer than subjects in the other three groups. To help determine the basis for this ability, the shape of oral air pressure waveforms was examined systematically. The percentage of ‘‘delayed’’ and ‘‘bimodal’’ waveforms, in which pressure stopped increasing, or decreased, prior to the release of labial constriction, was calculated for each group. Only the English adults showed more such waveforms for /b/ than /p/. Voicing continued 18 ms longer in /b/ tokens with delayed and bimodal waveforms than in tokens in which oral pressure increased continuously. The duration of closure voicing was correlated with the rate at which pressure increased in the English adults’ /b/ waveforms. Previous aerodynamic modeling has shown that delayed and bimodal waveforms may result from an active enlargement of the supraglottal cavity. This, together with the pattern of between-group differences observed here, suggests that the English adults learned to enlarge the supraglottal cavity to sustain voicing in /b/. It appears that neither the children nor the Chinese adults had as yet acquired this skill.
Level and age effects in infant frequency discrimination
Authors: Olsho Lynne Werner , Koch Elizabeth G. , Halpin Christopher F.
Published: October 2005

Frequency difference limens (FDLs) were estimated for 3-, 6-, and 12-month-old infants and for adults using pure tones at 500, 1000, and 4000 Hz. Each listener provided an FDL at 40 dB and at a higher (80 dB, in most cases) sensation level (SL). An observer-based behavioral testing technique was used. The FDLs of 3-month-olds were worse than those of adults at all three frequencies, and increased with increasing frequency. The FDLs of 6- and 12-month-olds were worse than those of adults at 500 and 1000 Hz, but not at 4000 Hz. Decreasing the SL led to an increase in the FDL of about the same magnitude at all ages, and the same age differences were found at both SLs. Thus infant–adult differences in FDL are not a simple consequence of differences in absolute sensitivity. Infant FDLs at one SL were also found to be significantly correlated with the FDL at the other SL. The FDLs at one age were, in general, predictive of the FDL at a later age in a longitudinal sample of infants. Models that might account for these age-related differences are discussed.
Community reactions to helicopter noise: Results from an experimental study
Authors: Fields James M. , Powell Clemans A.
Published: October 2005

Reactions to low numbers of helicopter noise events (less than 50 per day) have been studied in a community setting utilizing a new type of study design. Community residents were repeatedly interviewed about daily noise annoyance reactions on days when helicopter noise exposures had, without the residents’s knowledge, been controlled for study design purposes. The effects of maximum noise level and number of noise events on helicopter noise annoyance were found to be consistent with the principles contained in Leq-based noise indices. Although the best estimate of the effect of number of noise events is very nearly the same as that represented by the energy summation principle contained in Leq-based indices, the possibility that the number of noise events has only a small effect on annoyance cannot be rejected at the conventional p<0.05 level. The effect of the duration of noise events was also found to be consistent with Leq-based indices. After removing the effect of differences in duration and noise levels, there is not an important difference between reactions to impulsive and nonimpulsive types of helicopters.
Permanent indentation effects on the impact response of elastic plates
Authors: Chattopadhyay S.
Published: October 2005

The experimental data on permanent indentation due to the impact of an elastic sphere on an elastic beam have been utilized to predict the dynamic response of an elastic plate due to the impact of a mass. The elastic (Hertzian) impact case has also been calculated for comparison purposes. The contact force and the displacement time histories due to impact have been calculated for elastic and inelastic impacts. The values of the energy absorbed in the plate due to elastic and inelastic responses have been obtained to predict the additional energy contribution due to permanent indentation.
General one-dimensional treatment of the layered piezoelectric resonator with two electrodes
Authors: Nowotny Helmut , Benes Ewald
Published: October 2005

A general transfer matrix description of arbitrarily oriented layered piezoelectric structures is presented. Except for the restriction to two electrodes, it is the most general one-dimensional treatment possible. The description is derived as an exact solution of the fundamental differential equations and the boundary conditions at the terminating surfaces and at the electrical port. It allows the calculation of the electrical admittance appearing between the electrodes for any frequency, as well as the determination of the entire resonance frequency spectrum using only simple matrix multiplications. It covers the general case of multimode excitations and its coupling results. Thus it is not restricted to a single displacement direction and can be used for the rigorous analysis of layered structures containing, e.g., doubly rotated Y-cut quartz crystals.
Sound wave propagation in viscoelastic fluids with simultaneous chemical reactions
Authors: Margulies Timothy S. , Schwarz W. H.
Published: October 2005

The viscothermal problem of infinitesimal, planar acoustic wave propagation in nondiffusive, multicomponent materials that are viscoelastic and reacting is studied. The attenuation and dispersion of the sound wave are determined by solving the linearized (first-order) equations of mass, linear momentum, energy, and chemical kinetics. The analysis assumes the simple fluid theory for the stress tensor that incorporates the memory of the material. General results are obtained in the form of a biquadratic characteristic equation (the modified Kirchhoff–Langevin equation) for the complex propagation constant χ=−(α+iω/c), where α is the attenuation coefficient, c is the phase speed of the progressive wave, and ω is the angular frequency. Approximations needed to interpret results in terms of a linear superposition of chemical reaction and viscoelastic relaxations are examined. Calculations of the absorption and dispersion in cyclohexanol were made and compared to experimental measurements reported by Rasulmukhamedova et al. [Sov. Phys. Acoust. 22, 422 (1976)] over an extended range of frequencies.
The effect of stress and sample shape on the magnitude and frequency of magnetomechanical acoustic emission
Authors: Edwards C. , Palmer S. B.
Published: October 2005

The processes that can generate acoustic waves in a sample subjected to a changing magnetic field are discussed. An applied magnetic field with a fast rise time is found to be most efficient for generating magnetomechanical acoustic emission (MAE). The amplitude of the events correlates with the magnetostriction of the material. The shape of a sample affects both the level of magnetization, which can be achieved in a given applied field, and the acoustic modes, which the sample can support. It is demonstrated that MAE excites the fundamental longitudinal resonance of rodlike samples and the way the sample is held affects both the magnitude and frequency of these resonances. When the sample is subjected to tensile stress, the amplitude of the MAE decreases rapidly. However, it is shown that this decrease can be accounted for by an increase in the degree of clamping of the sample ends and that the normalized MAE actually increases initially with tension.
Acoustical effects of ocean current shear structures in the parabolic approximation
Authors: Robertson J. S. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

In a previous article [Robertson et al., J. Acoust. Soc. Am. 77, 1768–1780 (1985)], the authors developed a family of parabolic equations that includes effects due to the presence of a time-dependent, depth-dependent current. Some of these equations contain a new term that explicitly depends on current gradient. In this article, certain effects of this new term are studied. By transforming the parabolic equations, it is possible to convert them to forms that can be directly solved numerically using existing IFD or FFT implementations. Ocean currents with vertical fine structure present situations that can require these new types of parabolic approximations. Propagation in a shallow isospeed channel is examined, with both rigid and lossy bottoms, and use is made of a shear flow with features of an actual ocean current. The vertical current variation can cause changes in relative intensity that are substantial and that depend on bottom loss, source and receiver locations, and acoustic frequency. Intensity differences are demonstrated and examined for reciprocal sound transmissions.
Subcritical penetration of narrow Gaussian beams into sediments
Authors: Jensen Finn B. , Schmidt Henrik
Published: October 2005

Complete wave-theory solutions have been obtained numerically for both the reflected and the transmitted fields associated with a narrow Gaussian beam incident on a water–sediment interface near the critical grazing angle. Interesting reflectivity phenomena are observed, such as subcritical beam penetration into the sediment, nonspecular beam reflection, and lateral displacement along the interface of both the reflected and the transmitted beams. These results are in qualitative agreement with experimental observations using parametrically (nonlinearly) generated beams. It is demonstrated, however, that the fundamental reflectivity characteristics of narrow beams can be entirely explained within the framework of linear acoustics.
Intensity fluctuations in a quadratic channel
Authors: Beran Mark J. , Mazar Reuven
Published: October 2005

Using previously developed two-scale solutions [S. Frankenthal et al., J. Acoust. Soc. Am. 71, 1124–1130 (1982); B. J. Uscinski, Proc. R. Soc. London Ser. A 380, 137–169 (1982); C. Macaskill, ibid. 386, 461–474 (1983); S. Frankenthal et al., J. Opt. Soc. Am. A 1, 585–597 (1984); A. M. Whitman and M. J. Beran, ibid. 2, 2133–2143 (1985)], the scintillation of acoustic radiation in a random medium with a vertical quadratic mean sound-speed profile is considered. It is assumed that the statistics of the random medium are sufficiently anisotropic that fluctuations in the cross horizontal direction may be neglected. A point source is used as a boundary condition. Numerical calculations are performed for Gaussian and exponential correlation functions. Results are compared to those obtained in the absence of a channel. When the focusing length of the channel is small compared to the distance at which saturation would occur in the absence of a channel, the scintillation index is dramatically affected by the presence of the channel.
Comparison of observed and theoretical responses of a horizontal line array to wind-induced noise in the deep ocean
Authors: Ferguson Brian G. , Wyllie David V.
Published: October 2005

Various noise models consisting of distributions of surface or volume sources with different directional properties have been proposed to describe the ambient noise in the ocean. The theoretical response of a conventional beamformer steered towards broadside, and then towards endfire, is calculated for a number of these mathematical models. The predicted response for each model is then compared with the observed response for data recorded under conditions in which the ambient noise consisted only of noise generated by the action of wind and waves at the ocean surface. Good agreement between theory and experiment is obtained by using the surface model of Cron and Sherman [J. Acoust. Soc. Am. 34, 1732–1736 (1962)] with the directionality index m set to unity. This provides strong support for modeling wind-induced noise as a uniform distribution of independent vertical dipole sources extending over the surface of the ocean, with each source having an amplitude directionality function given by cos α, where α is the angle measured from the downward-pointing vertical axis. The surface model of Cox [J. Acoust. Soc. Am. 54, 1289–1301 (1973)] is also found to provide good agreement with the experimental results, but other models—two- and three-dimensional isotropic noise models, Cron and Sherman’s model with increased directionality (m=2,3), and Cox’s traffic noise model—are shown to be inappropriate in reproducing the observed response.
Application of high-resolution processing to range and depth estimation using ambiguity function methods
Authors: Fizell Richard G.
Published: October 2005

For many environments, a target’s acoustic field incident on a hydrophone array segment is not representable by a plane wave, but is a function, generally, of three coordinates: range, depth, and bearing. This complexity in the received field causes a conventional plane-wave beamformer to suffer a degradation in its performance. Techniques have been developed recently to exploit the complexity of the field to estimate the source location coordinates by correlating the received field on the array with accurate replicas of the acoustic field, derived from knowledge of the environment. The potential utility of such techniques has been demonstrated in determining range and depth; however, they can exhibit excessive sidelobes for low-SNR sources. To alleviate this problem, two high-resolution techniques, the maximum likelihood method (MLM) and ‘‘approximate orthogonal projection’’ (AOP), or linear predictor, are applied to the simulated case of one target in white noise in a Pekeris environment. The MLM is seen to produce stable main peaks that localize targets precisely with low sidelobes, while AOP is shown to be unstable in the presence of random noise and to produce false peaks even when the noise fields are stable.
Comments on ‘‘Speed of sound in standard air’’ [J. Acoust. Soc. Am. 7
9, 1359–1366 (1986)]
Authors: Greenspan Martin
Published: October 2005

In the subject paper, Wong recommended that the commonly used value for the speed of sound in air at STP be revised. The method he used to allow for gas imperfection, which is the only question at issue, is incorrect; the correct method, which has been described in many papers, texts, and reference books, is here briefly summarized. Wong’s problem is used as an example. The ‘‘old’’ value c10=331.44 m/s, is ‘‘correct.’’
Response to ‘‘Frequency dependence of the speed of sound in air’’ [J. Acoust. Soc. Am. 8
2, 375–376 (1987)]
Authors: Wong George S. K.
Published: October 2005

This response addresses the comments of Howell and Morfey on the misinterpretation by this author of their prediction of the effects of humidity on the velocity of sound in air [J. Acoust. Soc. Am. 68, 1525–1527 (1980)]. The misunderstanding has arisen due to the fact that the above authors superimposed their theoretical prediction curves, which have an ordinate unit of (cφa/ cφ−1) ×104, onto Harris’ experimental data [J. Acoust. Soc. Am. 49, 890–893 (1971)], which has an ordinate unit of ch/ c0, and with no information given on their zero-frequency curve [J. Acoust. Soc. Am. 82, 375–376 (1987)]. The misinterpretation is clarified, and this author now concludes that the theoretical prediction given by Wong and Embleton [J. Acoust. Soc. Am. 77, 1710–1712 (1985)] as well as the theoretical predictions of Howell and Morfey are in agreement to within 50 ppm.
Eddy current loss factor series for magnetostrictive rods
Authors: Butler John L. , Lizza Nicholas L.
Published: October 2005

Ordinarily the Kelvin ber and bei functions are utilized to model the eddy current loss factor in magnetostrictive rods. We show here that this loss factor can also be represented by a rapidly convergent series of simpler terms which lends itself to effective computer modeling of rare earth magnetostrictive transducers.
The lower limit of detectable sound pressures
Authors: Tarnow Viggo
Published: October 2005

The electronic thermal noise in a classical condenser microphone and the associated preamplifier has been studied experimentally and theoretically. A new method was used to compute the electronic noise in the microphone. It is shown that the electronic noise in some microphones dominates the noise in the preamplifier. Therefore, the lowest sound pressure that may be detected by those microphones is determined by the thermal noise in the condenser microphones alone.
Surface roughness induced attenuation of reflected and transmitted ultrasonic waves
Authors: Nagy Peter B. , Adler Laszlo
Published: October 2005

The problem of ultrasonic transmission and reflection at a randomly rough interface is considered in connection with ultrasonic NDE of rough surface samples by immersion method. A simple first-order phase perturbation technique is used to calculate both transmitted and reflected components for comparison with experimental results. The transmitted wave is shown to be attenuated in a similar way to the reflected one, and their attenuation ratio is found to be independent of frequency in the considered cases of slight surface roughness. For instance, the surface roughness induced attenuation of the wave reflected from a water–aluminum interface is about seven times higher than that of the transmitted component. Experimental results are presented to show good agreement with calculated predictions of the suggested simple technique.
Theory of three-dimensional acoustic propagation in a wedgelike ocean with a penetrable bottom
Authors: Buckingham Michael J.
Published: October 2005

A new analytical solution is presented for the three-dimensional acoustic field due to a monotonic point source in an ocean wedge with a penetrable bottom. The field consists of a sum of normal modes which depend weakly on range (out from the apex) and frequency. The mode coefficients depend strongly on range, on z (cross range parallel to the apex), and on frequency. A dispersion relation is derived which gives the range-dependent mode shapes. Then a notional ‘‘effective’’ wedge is constructed with perfectly reflecting boundaries whose apex is displaced from that of the penetrable wedge. The offset is such that the range-independent modes in the effective wedge match the range-dependent modes in the penetrable wedge. A known solution for the perfect wedge is then modified, by excluding rays which intersect the bottom at greater than the critical grazing angle, to give the spatial and frequency dependence of the mode coefficients in the penetrable wedge. The new solution, which satisfies the Helmholtz equation and the boundary conditions, exhibits prominent 3-D features uniquely associated with the penetrable bottom. These features conform with ray-theoretic predictions. Toward the end of the article the transient field in the penetrable wedge due to an impulsive point source is derived by Fourier transforming the cw solution. The Green’s function for the velocity potential is a transient of extended duration which contains evidence of image smearing, a phenomenon due directly to the phase shift experienced by rays undergoing total internal reflection from the penetrable interface.
Bearing determination in a waveguide
Authors: Wang Y. Y. , Clay C. S. , Shang E. C.
Published: October 2005

Laboratory studies of source bearing determinations were made in an air waveguide having rigid boundaries. The waveguide height was 0.12 m. The signal transmissions were 12-kHz gated sine waves. Modes 0–8 were possible, however, most of the received signals were in the first four modes. Without mode filtering, theory shows that beamforming in the end fire direction should be poor and it is. This is the first kind of trouble. The analysis shows that beamforming of unfiltered signals also depends on range. As the source changed range at constant bearing (end fire), the apparent direction changed by as much as 25°. This is trouble 2. As expected, beam steering on mode-filtered signals performed well.
Pitch perception by cochlear implant subjects
Authors: Townshend Brent , Cotter Neil , Van Compernolle Dirk , White R. L.
Published: October 2005

Direct electrical stimulation of the auditory nerve can be used to restore some degree of hearing to the profoundly deaf. Percepts due to electrical stimulation have characteristics corresponding approximately to the acoustic percepts of loudness, pitch, and timbre. To encode speech as a pattern of electrical stimulation, it is necessary to determine the effects of the stimulus parameters on these percepts. The effects of the three basic stimulus parameters of level, repetition rate, and stimulation location on subjects’ percepts were examined. Pitch difference limens arising from changes in rate of stimulation increase as the stimulating rate increases, up to a saturation point of between 200 and 1000 pulses per second. Changes in pitch due to electrode selection depend upon the subject, but generally agree with a tonotopic organization of the human cochlea. Further, the discriminability of such place-pitch percepts seems to be dependent on the degree of current spread in the cochlea. The effect of stimulus level on perceived pitch is significant but is highly dependent on the individual tested. The results of these experiments are discussed in terms of their impact on speech-processing strategies and their relevance to acoustic pitch perception.
The application of a capacitive probe technique for direct observation of electromechanical processes in the guinea pig cochlea
Authors: LePage Eric L.
Published: October 2005

The demonstration of evoked mechanical responses of the outer hair cells in the mammalian cochlea by indirect measurements introduces a new range of problems into direct mechanical measurements. Direct and indirect measurements indicate that the frequency spectra of evoked electromechanical responses may extend well into the range of audio frequencies, revealing a need to develop terminology and protocols for distinguishing evoked mechanical responses from the traditional traveling wave when both are apparently superimposed on the motion of the basilar membrane in the normally functioning cochlea. Details are presented of a frequency-modulation capacitive probe technique for measurement of vibrating structures of the guinea pig ear. Considerations include the design of the transducer, calibration, sensitivity, linearity, and sources of noise, as well as the influence of the technique upon the animal preparation, and in particular the issues associated with draining scala tympani for the measurement. Relative advantages and disadvantages of the technique are compared with salient features of other techniques currently available. In view of the apparent complexity of cochlear mechanics some preliminary experiments are required to elucidate some of the key questions about reverse-transduction processes in general. A ‘‘simple’’ first experiment is to test existence of any rectifying or motile response.
A spatial template for the shape of tuning curves in the mammalian cochlea
Authors: LePage Eric L.
Published: October 2005

The shape of the tuning curve of primary auditory neurons of four mammals is characterized using a simple exponential model. The regression analysis formalizes a distinction between the characteristic frequency of a neuron and its ‘‘nominal’’ characteristic frequency in cases of temporary threshold loss in high-frequency neurons. Second, the model offers a stronger quality test for sharpness of tuning than the Q10 dB since it takes into account the threshold of the neuron at its characteristic frequency and its ‘‘characteristic place’’ of origin along the cochlear partition. Third, the model reveals that the low-frequency side of the tip segment of the tuning curve is bounded by a constraint or template which is most simply expressed in spatial terms. The template describes the basal-side boundary of an ‘‘excitatory region’’ whose length along the cochlear partition is proportional to the square root of the sound pressure. Tuning curve variability arises because biological dependencies influence the basic template. A ‘‘spatial-filter’’ hypothesis is developed and its generality is discussed, particularly in regard to the case of the acoustic ‘‘fovea’’ of the horseshoe bat. Finally, the possibility is discussed that the template possesses a simple physiological correlate in the form of a spatially localized region marked by a ‘‘dc’’ shift of the mean position of the basilar membrane which sets the sensitivity of the tuning mechanism [E. L. LePage, J. Acoust. Soc. Am. 82, 139–154 (1987)].
Maximum directivity proof for three-dimensional arrays
Authors: Parsons Alan T.
Published: October 2005

A proof is presented for the following theorem: Given all possible three-dimensional (3-D) configurations of n omnidirectional acoustic sensors with vanishingly small separations, and given all possible weighting schemes and steer directions, the directivity index achieves an overall maximum value of n2 when the sensors are configured as a linear array steered to end-fire, it being immaterial whether or not the sensor spacings are equal.
Effect of frequency dependence of sea-bottom attenuation on the optimum frequency for acoustic propagation in shallow water
Authors: Zhou Ji-xun , Zhang Xue-zhen , Rogers Peter H.
Published: October 2005

The optimum frequency for acoustic propagation in shallow water is controlled by a number of physical effects and environmental parameters. This article concentrates on the effect of a nonlinear frequency dependence of the sea-bottom attenuation on the optimum frequency. Experimental data on low-frequency acoustic propagation in shallow water are presented, for which, over the frequency range where the optimum frequency should occur, no apparent optimum frequency is observed. If there is an optimum frequency for these sea areas, it is much lower than predicted by existing theories. It is demonstrated that the nonoccurrence, or lowering, of the optimum frequency can be easily explained if the sea bottom is assumed to have a nonlinear frequency dependence. Excellent agreement between theory and experiment is achieved for a site in the Yellow Sea for three different seasons using values for sediment attenuation (with nonlinear frequency dependence) and sediment sound speed which were measured independently at the same site [J. X. Zhou, J. Acoust. Soc. Am. 78, 1003–1009 (1985)]. The sea-bottom attenuation used for the calculations was proportional to frequency to about the 1.8 power.
A physicochemical evaluation of the nonlinear parameter B/A for media predominantly composed of water
Authors: Yoshizumi Kiyomi , Sato Takuso , Ichida Nobuyuki
Published: October 2005

The relationship between the value of the nonlinear parameter B/A and the ratio of free water and bound water in a medium predominantly composed of water is examined. First, it is shown that in pure water the observed value of B/A can be expressed as (B/A)=vf(B/A)f +vb(B/A)b, where vf and vb are volume fractions of free and bound water, respectively. Next, a small dependency of the values (B/A)f and (B/A)b on temperature is noted. Then, the role of free and bound water in soft tissue is discussed in connection with the application of B/A analysis for medical diagnosis. Finally the additive property is examined for agarose gel.
Acoustic head-wave arrival times in anisotropic media
Authors: Lerche I.
Published: October 2005

The reflection travel times, caused by a flat interface separating two media, are calculated for incident acoustic waves emanating from a point source when both media have anisotropic acoustic velocities. Special attention is given to the effects of anisotropy on the head-wave arrival time and it is found that the critical angle for production of heads, as well as the head-wave travel time and the specularly reflected wave’s travel time, are significantly altered for anisotropies of order 10%–20% as observed in real subsurface situations. In particular, in the case of reflection by an interface separating an upper isotropic medium from a lower anisotropic medium with propagation speed parallel to bedding planes larger than perpendicular, it was found that the critical angle is decreased, and that head-wave arrival prior to specular arrival occurs at smaller offsets than in the isotropic case since the head wave, but not the specular wave, has its travel time decreased by the anisotropic medium. These calculations suggest that head waves arriving prior to specularly reflected waves should be a sharp diagnostic of conditions at the interface. The computations also suggest that mode conversion effects, curvature and roughness effects, and thin bedding effects should be considered together in order to delineate the precise symptoms of the subsurface being carried by the observed head waves.