bluuebunny/crossref_metadata_2025 huggingface dataset:
A test of a simple model of the acoustic velocity in marine sediments
Authors: Nobes David C.
Published: October 2005

A simple physical model is proposed for the dependence of the acoustic velocity of marine sediments on the porosity and lithology. The model is tested for clay-rich marine sediments using data from the Deep Sea Drilling Project, but has also been successfully used to calculate the acoustic velocity in consolidated and unconsolidated carbonate sediments. The model is a combination of the Wood [A. B. Wood, A Textbook of Sound (Macmillan, New York, 1941)] and Wyllie [Wyllie et al., Geophysics 21, 41–70 (1956)] (time average) models: Any medium may be thought of as composed of one fraction that is comparable to a slurry of particles in suspension and a second that consists of a rigid grain matrix. As the porosity decreases, so too does the fraction of slurry that makes up the sample. A slurry has essentially no shear strength, and thus the bulk compressibility is expressed as the weighted mean compressibility of the solid and fluid components. The rigid matrix velocity is determined using the time average equation. The variation of the grain (zero-porosity) velocity with lithology is similarly represented using the time average equation. The net bulk velocity is then taken to be the inverse of the weighted mean travel time for each of the component fractions. This approach could simplify the modeling of acoustic velocity variations given an independent measure of the porosity, or vice versa.
Remote sensing of western boundary currents using acoustic tomography
Authors: Spiesberger John L.
Published: October 2005

The utility of continuous long-range acoustic transmissions between fixed sources and receivers to measure the deflection and speed of a western boundary current front along the transmission paths is discussed in a theoretical context. A signal-processing technique, which utilizes both the amplitude and the phase of the acoustic arrivals, is used to estimate the change in acoustic travel time with more accuracy than is possible by using only the amplitudes of the arrivals. When the transmission path crosses the front only once, and when the rotations of the front are confined to orientations that are within about 60 deg of the normal direction to the transmission path, the deflection of the front can be measured with an accuracy of about 2 km over periods of a few days and its propagation speed can be measured with an accuracy of about 8 cm/s. Errors are imposed by the changes in acoustic travel time that arise from the influence of the random fluctuations of internal waves. The errors of the tomographic estimates of the deflection and speed of the front are small compared with observed deflections and speeds that are of order 10 km/day and 1 m/s, respectively. The spatial (temporal) resolution of the tomographic estimate of the frontal deflection and speed along the transmission path is the same as (is better than) that obtained by satellites.
Calculation of the steady-state oscillations of a clarinet using the harmonic balance technique
Authors: Gilbert J. , Kergomard J. , Ngoya E.
Published: October 2005

The harmonic balance technique is known as a time-frequency simulation technique used for the study of large signal regimes of microwave circuits driven in forced oscillation. The technique can be adapted to self-sustained oscillations, especially for wind musical instruments such as clarinets. The resonator (i.e., the instrument body) is the linear part, treated in the frequency domain, while the driving system (the reed) is the nonlinear part, treated in the time domain. The harmonic balance method is shown to connect the results of two known methods, so-called weakly nonlinear (in frequency domain) and strongly nonlinear (in time domain). The advantages and disadvantages of the method are discussed.
Phase transition and sound velocity measurements in very small solid samples under high pressure by Brillouin scattering
Authors: Bonello Bernard , Fischer Myriam , Polian Alain
Published: October 2005

Brillouin scattering is an ideal tool for accurately determining sound velocities in very small transparent samples (about 20-μm thickness). In particular, Brillouin scattering in a diamond anvil cell is the only method of measuring sound velocities in small single crystals at high pressure (>10 GPa). In this paper, this technique is used to determine sound velocities in SrTiO3 up to 36 GPa.
Theory of acoustic radiation in corners with homogeneous and mixed perfectly reflecting boundaries
Authors: Buckingham Michael J.
Published: October 2005

An exact solution in the form of uncoupled normal modes is derived for the harmonic field from a point monopole source in a corner with perfectly reflecting boundaries (either homogeneous Dirichlet, homogeneous Neumann, or mixed Dirichlet–Neumann). Each mode coefficient is the sum of two integrals, representing the image and diffraction components of the field, neither of which can be expressed explicitly. The image mode integral shows a highly oscillatory spatial dependence in the ensonified region of the mode, a domain that is bounded by a hyperbolic caustic beyond which lies a shadow zone. First- and second-order asymptotic approximations are developed for the image mode integral that are matched in the vicinity of the caustic and that give an extremely accurate representation of the image mode field throughout the ensonified region, across the caustic, and into the shadow. The diffraction mode integral shows a relatively slow spatial dependence. A uniform asymptotic approximation is developed that provides an accurate representation of the diffraction mode integral throughout the domain of the corner. Both the matched and uniform asymptotic approximations are very fast to evaluate compared with numerical computations of the respective integrals. The mode sum yields an expression for the velocity potential consisting of a finite number of image terms plus an intractable integral for the diffracted component of the field, for which an accurate first-order stationary phase approximation is developed.
Stochastic geometrical theory of diffraction
Authors: Mazar R. , Felsen L. B.
Published: October 2005

The localization of high-frequency sound-wave propagation around ray trajectories, and the reflection and(or) diffraction of these local plane-wave fields by boundaries, inhomogeneities, and(or) scattering centers has been combined via the geometrical theory of diffraction (GTD) into one of the most effective means of analyzing high-frequency wave phenomena in complex deterministic environments. These constructs are here incorporated into a stochastic propagation and diffraction theory for statistical moments of the high-frequency field when the propagation medium has weak random fluctuations superimposed upon an inhomogeneous background profile, subject to the assumption that the correlation length ln of the fluctuations is small compared with the scale of variation, but large compared with the local wavelength λ=2π/k=2πv/ω, in the fluctuation-free background, with k being the local wavenumber, v the local wave speed, and ω the radian frequency. Canonical problems of deterministic GTD furnish the propagators and, in the presence of interfaces, boundaries, or other types of scatterers, the local reflection, refraction, and diffraction coefficients that relate incoming to outgoing wave fields.

The major analytical building blocks include propagators described in local coordinates centered on the curved GTD ray trajectories in the deterministic inhomogeneous background environment; multiscale expansions in these coordinates to chart and solve for the propagation properties of statistical measures of the parabolically formulated ray fields; Kirchhoff or physical optics (PO) approximations, generated by stochastic GTD incident fields, to establish initial conditions for fields reflected from, or transmitted across, extended smooth surfaces; and ‘‘point scatterer’’ solutions to establish GTD initial conditions for small scatterers and edges. In addition to the conventional second- and higher-order coherence functions, there are introduced as appropriate statistical objects two-point random functions and corresponding higher-order functions which are useful in treating correlation of incident and of backward reflected or diffracted fields that traverse the same propagation volume. By this solution strategy, one gains access to a much larger class of high-frequency problems in a random medium than at present. Expressions for the average field and higher moments have been obtained for forward propagation in a fluctuating medium with inhomogeneous and caustic-forming background, for reflection and refraction due to a plane or smoothly curved interface in such a medium, and for diffraction due to a wedge and a small scatterer.
Shape perturbation and inertial mode coupling in cavities
Authors: Herzog P. , Bruneau M.
Published: October 2005

The influences of shape perturbation and inertial effects on the modal structure of acoustic fields are studied inside small cavities, taking into account dissipative phenomena near the walls. Both are shown to have similar effects on the acoustic field, leading to coupling and energy transfers between modes. Validity of the analytical model is discussed and compared with accurate experimental results for the lower-order modes. Discrepancies are found to be less than 0.1 dB for small shape perturbations, as well as for rotations up to 1000°/s, which shows a very good agreement between the theoretical and experimental results. Qualitative aspects of the perturbed problem are also discussed and illustrated experimentally.
A method for computing acoustic fields based on the principle of wave superposition
Authors: Koopmann Gary H. , Song Limin , Fahnline John B.
Published: October 2005

A method for computing the acoustic fields of arbitrarily shaped radiators is described that uses the principle of wave superposition. The superposition integral, which is shown to be equivalent to the Helmholtz integral, is based on the idea that the combined fields of an array of sources interior to a radiator can be made to reproduce a velocity prescribed on the surface of the radiator. The strengths of the sources that produce this condition can, in turn, be used to compute the corresponding surface pressures. The results of several numerical experiments are presented that demonstrate the simplicity of the method. Also, the advantages that the superposition method has over the more commonly used boundary-element methods are discussed. These include simplicity of generating the matrix elements used in the numerical formulation and improved accuracy and speed, the latter two being due to the avoidance of uniqueness and singularity problems inherent in the boundary-element formulation.
Comments on ‘‘Acoustic transfer characteristics in human middle ears studied by a SQUID magnetometer method’’ [J. Acoust. Soc. Am. 8
2, 1646–1654 (1987)]
Authors: Goode Richard L. , Nakamura Koshiro , Gyo Kiyofumi , Aritomo Hiroshi
Published: October 2005

The study by Brenkman et al. [J. Acoust. Soc. Am. 82, 1646–1654 (1987)] of malleus umbo and anterior crus of stapes displacement in 14 human temporal bones shows a mean −7.3-dB/oct slope above 1.0 kHz for stapes displacement in response to a 80-dB SPL input at the eardrum. The slope they obtained for midfrequency (1.0–4.0 kHz) stapes displacement is significantly flatter than what was found previously [Gyo et al., Acta Otolaryngol. 103, 87–95 (1987); Gundersen, Prostheses in the Ossicular Chain (University Park, Baltimore, MD, 1971); Kringlebotn and Gundersen, J. Acoust. Soc. Am. 77, 159–164 (1985); Vlaming and Feenstra, Clin. Otolaryngol. 11, 353–363 (1986a)]; in these studies, stapes displacement rolled off at −12.0 to −14.9 dB/oct above 1.0 kHz. It appears that their mean midfrequency stapes displacement slope has been flattened by some unusual results in a small number of ears. Possible reasons for these results are discussed.
Notions of conventional stereo in ‘‘Interaural cross-correlation coefficients in stereo-reproduced sound fields’’ [J. Acoust. Soc. Am. 8
5, 780–786 (1989)]
Authors: Cooper Duane H.
Published: October 2005

Characterizations of stereo systems in Tohyama and Suzuki [J. Acoust. Soc. Am. 85, 780–786 (1989)] appear to be largely limited to diagrams of loudspeaker layout, including one for a so-called conventional stereo. Because of this, many readers may be unaware that the conclusions drawn are not generally applicable without further qualification. Omission of signal-format characterizations could, in principle, require the exclusion of certain stereo systems. In particular, one four-channel system could be regarded as excluded because it overturns a conclusion of Tohyama and Suzuki. Further, one stereo system that uses a conventional two-loudspeaker layout, but uses particularly apt signal formats, also overturns a conclusion.
Unidirectional, second-order gradient microphone
Authors: Sessler Gerhard M. , West James E. , Kubli R. A.
Published: October 2005

A second-order gradient microphone with unidirectional characteristics is described. The microphone consists of two commercially available, first-order gradient electret microphones that are properly baffled and arranged in antiphase with their rotational axes in line. The output of one of these transducers is added to the delayed output of the other transducer. The unidirectional microphone shows a directional characteristic that is relatively frequency independent, has a 3-dB beamwidth of the main lobe of 76 deg, and exhibits a toroidal sidelobe 10–20 dB below the main lobe. After equalization, the frequency response of the microphone in its direction of maximum sensitivity is within ±3 dB between 0.3 and 3 kHz. The output of the microphone, including equalization and amplification, is −60 dB re: 1 V/Pa at 1 kHz, and the equivalent noise level for the above frequency range amounts to 28 dB linear or an A-weighted level of 20 dB.
Contraction-related variation in frequency dependence of acoustic properties of canine myocardium
Authors: Wear Keith A. , Milunski Mark R. , Wickline Samuel A. , Perez Julio E. , Sobel Burton E. , Miller James G.
Published: October 2005

Results of experiments performed in several laboratories indicate that contracting myocardium exhibits a cyclic variation of the magnitude of ultrasonic backscatter, with maxima occurring at end-diastole and minima at end-systole. The mechanisms responsible for this variation are not well understood. The purpose of the present study was to determine whether the frequency dependence of backscatter exhibits systematic variation throughout the cardiac cycle, analysis of which may facilitate improved understanding of biologic factors responsible for the cyclic variation of the magnitude of backscatter. In this study, the myocardial backscatter coefficient, as a function of frequency, was measured throughout the cardiac cycle in nine open-chest dogs. The frequency dependence of the backscatter coefficient was computed from a least-squares linear fit to log backscatter coefficient versus log frequency data. A cyclic variation of frequency dependence of backscatter was found with maximum near end-diastole (f2.6±0.1) and minimum near end-systole (f2.2±0.1), a significant variation (p<0.01). These results suggest that mechanisms responsible for the cyclic variation of backscatter may include changes in the effective size of the dominant scatterers throughout the cardiac cycle. An alternative explanation for the observed variation is an increase in the myocardial attenuation coefficient during systole followed by a decrease in diastole.
On sentence-level factors governing segmental duration in Japanese
Authors: Takeda Kazuya , Sagisaka Yoshinori , Kuwabara Hisao
Published: October 2005

In this paper, the durational characteristics of Japanese are statistically analyzed with the aim of establishing a fine duration setting rule. First, a statistical duration control model is formulated through factor analysis on a large-scale isolated-word database (5240 words). Second, using 282 fluently spoken connected speech utterances, segmental durations calculated by this model are compared with measured durations. Error analysis made clear the existence of the following sentence-level duration effects: (1) Prepausal lengthening is greater than simple word-final lengthening; and (2) shorter durations are found in sentence-final position in read sentences than in the other positions. By incorporating these effects into the duration-setting rules, the prediction error for sentences were reduced to the same level as for isolated words.
Results for two children using a multiple-electrode intracochlear implant
Authors: Busby P. A. , Tong Y. C. , Roberts S. A. , Altidis P. M. , Dettman S. J. , Blamey P. J. , Clark G. M. , Watson R. K. , Dowell R. C. , Rickards F. W. , Nicholls G. H.
Published: October 2005

Assessments in speech perception, speech production, and language skills were conducted on two children, 5 and 10 years old at the time of surgery, using the Nucleus multiple-electrode cochlear implant. Data were collected pre- and post-operatively to measure changes in performance over time. For closed-set speech perception tests in the audition alone condition, post-operative performance was generally better than pre-operative performance and performance improved post-operatively for both patients. In closed-set vowel and consonant identification and open-set sentence perception for the older patient, post-operative improvements from the vision alone to the auditory–visual condition were recorded and performance improved post-operatively in both conditions. In all measures of speech production for both patients, post-operative scores were higher than pre-operative scores and performance improved post-operatively. In language skills, post-operative scores were higher than pre-operative scores and scores improved post-operatively in all measures for both patients.
The recognition of vowels differing by a single formant by cochlear-implant subjects
Authors: Tyler Richard S. , Tye-Murray Nancy , Otto Steven R.
Published: October 2005

The ability to recognize synthetic, two-formant vowels with equal duration and similar loudness was measured in five subjects with the Cochlear and five subjects with the Symbion cochlear implants. In one set of test stimuli, vowel pairs differed only in the first-formant frequency (F1). In another set, vowel pairs differed only in the second-formant frequency (F2). When F1 differed, four of five Cochlear subjects and four of five Symbion subjects recognized the vowels significantly above chance. When F2 differed, two of five Cochlear subjects and three of five Symbion subjects scored above chance. These results suggest that implanted subjects can utilize both ‘‘place’’ information across different electrodes and ‘‘rate’’ information on a single electrode to derive information about the spectral content of the stimulus.
The speech of a postlingually deafened teenager during the first year of use of a multichannel cochlear implant
Authors: Tartter Vivien C. , Chute Patricia M. , Hellman Sharon A.
Published: October 2005

The speech of a profoundly postlingually deafened teenager was recorded before, immediately after, 3 months after, and 1 year after electrical stimulation with a Nucleus multichannel cochlear implant. Listener tests of target words revealed significant improvement in overall quality over the year. Spectrograms showed less aspiration and better definition of the lower formants. Acoustic measurements indicated immediate change in F0 and gradual changes in syllable duration and some aspects of voicing and manner of articulation. Vowel space shrank steadily over the year, with both first- and second-formant frequencies dropping. Prestimulation results are discussed relative to the literature on the speech of the congenitally hearing impaired. Effects of multichannel electrical stimulation on speech are compared with studies of single-electrode stimulation.
Binaural processing of noisy stimuli: Internal/external noise ratios for diotic and dichotic stimuli
Authors: Siegel Ronald A. , Colburn H. Steven
Published: October 2005

A set of ten digitized statistically similar Gaussian maskers was used in one-internal tone-in-noise detection experiments under diotic (NoSo) and dichotic (NoSπ) interaural conditions. Stimulus/response matrices were generated for each masker in the presence or absence of a target 500-Hz tone. For both NoSo and NoSπ, nonparametric analyses show that response probabilities and sensitivities vary significantly across noise waveforms, indicating a considerable external noise component in subject response variability. A parametric model is developed that maps individual stimulus waveforms onto a decision axis, facilitating evaluation of internal/external noise variance ratios. For both NoSo and NoSπ, internal and external noise variance are of similar magnitude.
Characterization of an EPSP-like potential recorded remotely from the round window
Authors: Dolan David F. , Xi Lin , Nuttall Alfred L.
Published: October 2005

The whole-nerve cochlear action potential (CAP), to tone burst stimulation, was recorded before and after application of tetrodotoxin (TTX) to the intact round window (RW) membrane. TTX abolished the CAP leaving a residual negative potential without altering the summating potential (SP) or the cochlear microphonic (CM). The residual potential retained its polarity when recorded from scala vestibuli. The peak latency, amplitude, and tuning properties of the residual potential showed features similar to the CAP. Application of kainic acid to the RW membrane eliminated the residual potential, leaving the SP and CM unaltered. It is hypothesized that the sources of the residual potential are the excitatory post-synaptic potentials from the peripheral processes of afferent dendrites under the inner hair cells.
Hazard from an intense midrange impulse
Authors: Price G. Richard , Wansack Samuel
Published: October 2005

It has been hypothesized that the ear would become increasingly susceptible to impulses (gunfire) as the spectral peak of the impulse approached the frequency region where the ear was tuned best (about 4 kHz for the cat ear) [G. R. Price, J. Acoust. Soc. Am. Suppl. 1 62, S95 (1977)]. This prediction was counter to the predictions of the world’s damage-risk criteria for impulse noise. It has been supported by experiments using exposures to 100-Hz and 800- to 1000-Hz impulses; but no test had been run at the point of predicted maximum susceptibility. In the present experiment, three groups of cats were exposed to 50 impulses produced by a primer explosion (spectral peak at 4 kHz) at peak levels of 135, 140, or 145 dB. Auditory thresholds were electrophysiologically measured from the vertex to 2-, 4-, 8-, and 16-kHz tone pips and losses were determined 30 min after exposure and more than 2 months post-exposure. Losses were greatest at 4 kHz, began to develop at 134-dB peak pressure, and the immediate losses grew at a rate of about 7 dB for every dB increase in peak pressure. About half of the loss measured immediately became permanent. The energy required to begin producing a permanent threshold shift was only about 0.07 J/m2 , far lower than that required with continuous noises at lower sound pressures. The data were interpreted as supporting the original hypothesis of greater susceptibility in the midrange.
A practical method of predicting noise produced by road traffic controlled by traffic signals
Authors: Yamaguchi Shizuma , Kato Yuichi
Published: October 2005

A new expression of the probability density function for periodic nonstationary noise level fluctuation is first derived in a case where the road traffic flow is controlled by traffic signals. Next, a new practical procedure for estimating and/or predicting the probability distribution form of road traffic noise, on the basis of the simplified time patterns of the statistics on the noise level or number of moving vehicles, is proposed as an application of the above theory. By using the actual road traffic noise data observed in Hiroshima City, it was experimentally confirmed that the theoretical method was valid and effective as a prediction technique.
Excess sound absorption due to periodically arranged absorptive materials
Authors: Takahashi D.
Published: October 2005

Discontinuities, of any kind, in the surface impedance have a tendency to cause the effect of excess absorption. A well-known example of this phenomenon is the so-called ‘‘edge effect,’’ defined as the dependence of sound absorptivity of a test material on its area size. In relation to this problem, the excess sound absorption of periodically arranged flat surfaces composed of different materials is investigated both theoretically and experimentally. The analyses show that excess absorption, having a specific trend of absorption characteristics, clearly occurs over the full frequency range of interest. As a result of parametric survey conducted on the performance of a surface arranged periodically with rigid and porous materials, it is found that flat surfaces with desirable absorption characteristics can be made by adjusting the parameters suitably. The parameters are the period of the surface, width ratio of the two materials, flow resistivity, and thickness of the porous material. Also, it is shown, as an important matter, that the absorptivity is considerably high and smooth over the wide frequency range.
Zeros of a transfer function in a multi-degree-of-freedom vibrating system
Authors: Tohyama Mikio , Lyon Richard H.
Published: October 2005

This paper analyzes a transfer function (TF) of a vibrating system in the complex-frequency domain based on modal theory. There are three cases of zeros in a TF. One is the usual case where a zero is located on the pole line connecting two adjacent poles. Another is the double-zero case; that is, there are two zeros on the pole line between two adjacent poles. Those zeros above are minimum-phase zeros. The third case, however, can contain a nonminimum-phase zero. A pair of minimum- and nonminimum-phase zeros is located symmetrically with respect to each other at equal distances from the pole line because the transfer function has a symmetrical form in a complex domain with respect to the pole line, assuming real residues (i.e., real mode shape functions). One member of this pair of zeros can be a nonminimum-phase zero, under the condition that the damping is small. Such zeros have been numerically confirmed using the TF of a rectangular room.
Impulse response of density contrast wedge using normal coordinates
Authors: Chu Dezhang
Published: October 2005

The exact impulse response of a point source to a rigid wedge was first derived by Biot and Tolstoy in normal coordinates [I. Tolstoy and C. S. Clay, Ocean Acoustics—Theory and Experiment in Underwater Sound (American Institute of Physics, New York, 1987), Appendix 5]. The solution is compact and includes both reflected and diffracted waves explicitly. Kinney et al. [J. Acoust. Soc. Am. 73, 183–194 (1983)] introduced the solution of free wedge (pressure release), which is similar to the rigid case except sign changes for certain terms. The solutions have been verified in laboratory experiments. However, neither model can be applied directly to many actual cases such as ocean floor, where the ratio of density of the base sediment to that of the water is neither infinite (ridge) nor zero (pressure release). The normal coordinate solution presented here is the impulse response to an isovelocity (c=c′) and density contrast (ρ≠ρ′) wedge. It is an extension to the solution given by Biot and Tolstoy. The eigenvalues νn are functions of the wedge angle and the ratio of the density of two media. For either ρ→0,∞ or ρ′→0,∞, the solution reduces to known exact solutions for ideal wedge. The diffracted part of the solution is not the solution for the ideal wedge (ρ′=0 or ρ′=∞) multiplied by an impedance factor.
A multipath calculation of surface-generated underwater acoustic ambient vertical directivity
Authors: Kennedy Robert M. , Szlyk Thomas K.
Published: October 2005

A general calculation of the spatial correlation function due to a distributed acoustic source near the water surface has been done by others using normal-mode theory. In this article, a multiple-ray-path analysis is used to calculate the acoustic ambient vertical directivity function. Multipath propagation and ambient directional functions are physically intuitive concepts in underwater acoustic theory, and direct application of these notions has advantages in the interpretation of data. Existing procedures and computer codes are used to expand the received pressure field, from a distributed source, into a sum of terms interpreted as multiple propagation paths. Standard forms for the source function and a geometric transformation are used to convert the pressure field to a solid-angle density function. Surface roughness, bottom geoacoustic parameters, and sound velocity-depth profiles measured in the Tongue of the Ocean in the Bahamas are used in the calculations to predict hydrophone array performance in that area. Directivity function versus elevation angle and frequency are displayed for observers above and below a seasonal thermocline. A path-by-path contribution to the vertical distribution of energy is discussed.
Equations of the second-order potentials of finite-amplitude waves in elastic solids
Authors: Qian Z. W.
Published: October 2005

The wave equations of the scalar and vector second-order potentials in elastic solids are derived. The source strengths of the equations consist of a local term and two nonlocal terms; the latter include a bulk term and a surface term (if it exists).
An elastodynamic model for compressional and shear wave transducers
Authors: Schmerr Lester W. , Sedov Alexander
Published: October 2005

Elastodynamic models are developed for both contact ultrasonic compressional wave and shear wave transducers radiating into an elastic solid. Explicit high-frequency asymptotic solutions are obtained for the major wave components present in the transducer responses. These solutions are compared, in both the frequency and time domains, with the response of a piston transducer radiating into a fluid. It is demonstrated that, within the main beam of the transducer and in the farfield, the fluid model accurately predicts the response in the elastic solid for both the compressional and shear wave cases. In the nearfield, the elastodynamic models provide a more complete description of the transducer radiated wave field.
Insights into dolphin sonar discrimination capabilities from human listening experiments
Authors: Au Whitlow W. L. , Martin Douglas W.
Published: October 2005

A variety of dolphin sonar discrimination experiments have been conducted, yet little is known about the cues utilized by dolphins in making fine target discriminations. In order to gain insights on cues available to echolocating dolphins, sonar discrimination experiments were conducted with human subjects using the same targets employed in dolphin experiments. When digital recordings of echoes from targets ensonified with a dolphinlike signal were played back at a slower rate to human subjects, they could also make fine target discriminations under controlled laboratory conditions about as well as dolphins under less controlled conditions. Subjects reported that time-separation-pitch and duration cues were important. They also reported that low-amplitude echo components 32 dB below the maximum echo component were usable. The signal-to-noise ratio had to be greater than 10 dB above the detection threshold for simple discrimination and 30 dB for difficult discrimination. Except for two cases in which spectral cues in the form of ‘‘click pitch’’ were important, subjects indicated that time-domain rather than frequency-domain processing seemed to be more relevant in analyzing the echoes.
Chinese subjects’ perception of the word-final English /t/–/d/ contrast: Performance before and after training
Authors: Flege James Emil
Published: October 2005

Chinese words may begin with /t/ and /d/, but a /t/–/d/ contrast does not exist in word-final position. The question addressed by experiment 1 was whether Chinese speakers of English could identify the final stop in words like beat and bead. The Chinese subjects examined approached the near-perfect identification rates of native English adults and children for words that were unedited, but performed poorly for words from which final release bursts had been removed. Removing closure voicing had a small effect on the Chinese but not the English listeners’ sensitivity. A regression analysis indicated that the Chinese subjects’ native language (Mandarin, Taiwanese, Shanghainese) and their scores on an English comprehension test accounted for a significant amount of variance in sensitivity to the (burstless) /t/–/d/ contrast. In experiment 2, a small amount of feedback training administered to Chinese subjects led to a small, nonsignificant increase in sensitivity to the English /t/–/d/ contrast. In experiment 3, more training trials were presented for a smaller number of words. A slightly larger and significant effect of training was obtained. The Chinese subjects who were native speakers of a language that permits obstruents in word-final position seemed to benefit more from the training than those whose native language (L1) has no word-final obstruents. This was interpreted to mean that syllable-processing strategies established during L1 acquisition may influence later L2 learning.
Measurement of the glottal impedance with a mechanical model
Authors: Rösler Stefan , Strube Hans Werner
Published: October 2005

An approximate but realistic model of the human larynx was constructed to gain better knowledge of the complex glottal impedance and its dependence on glottal width, flow, and frequency. The glottal width was adjustable from 0 to 3 mm, the flow from 0 to 500 cm3/s. The model was fitted into a system of tubes, through which compressed air could be conducted. Supraglottally, a broadband signal was fed into the tube, and, with a two-microphone directional coupler, the complex glottal impedance at a given reference plane was directly determined as a function of frequency. Since the calculated impedance is sensitively dependent on the definition of the position of the reference plane, it is difficult to obtain quantitative statements about the frequency dependence. Nevertheless, in the presence of flow, it is possible to achieve reliable results by analysis of the relative position of the measured curves. On the one hand, the glottal inductance decreases linearly with increasing flow velocity; on the other hand, it diminishes nonlinearly with decreasing frequency. Finally, some difficulties in the definition of glottal impedance are pointed out.
Mechanisms underlying the frequency discrimination of pulsed tones and the detection of frequency modulation
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

This paper describes two experiments intended to test excitation-pattern models of frequency discrimination. In experiment I, frequency DLs (DLFs) for pulsed sinusoids were measured in four conditions: (1) in quiet with the level fixed at 70 dB SPL; (2) in quiet with the level of each tone varied randomly over a 6-dB range around 70 dB SPL; (3) in the presence of a bandpass noise designed to mask the upper side of the excitation pattern, with the level fixed; and (4) with bandpass noise and with the level of the signal randomized over a 6-dB range. Center frequencies of 0.5, 1.0, 2.0, 4.0, and 6.5 kHz were used. DLFs for conditions 3 and 4 were somewhat larger than DLFs for conditions 1 and 2, indicating that frequency discrimination is not based solely on information from the low-frequency side of the excitation pattern. DLFs for condition 4 were, on average, 1.65 times as large as those for condition 1 but, except at 6.5 kHz, were considerably smaller than the values predicted on the assumption that the DLFs were based on the detection of changes in excitation level on the low-frequency side of the excitation pattern. It is suggested that phase-locking information plays a role in determining DLFs at 4.0 kHz and below. Experiment II was similar to experiment I, except that thresholds (FMDLs) for detecting frequency modulation (FM) at a 4-Hz rate were measured, and, in conditions 2 and 4, a 4-Hz amplitude modulation (AM) with a peak-to-valley ratio of 6 dB was imposed on all signals; the phase of the AM relative to the FM was random. The FMDLs were affected more by the noise and by the variation in level than were the DLFs; FMDLs for condition 4 were, on average, 2.36 times as large as those for condition 1. Furthermore, the data for condition 4 were not inconsistent with the assumption that the FMDLs were based on the detection of changes in excitation level on the low-frequency side of the excitation pattern. However, neither a single-band nor a multiple-band excitation-pattern model was able to account for the effect of the bandpass noise on the FMDLs.
Instructional laboratory experiment on the effect of a ring baffle on the radiation from a small sonar transducer at an air–water surface
Authors: Wang Congjun , Stumpf Folden B.
Published: October 2005

The axial pressure and directivity pattern in water were measured for a small sonar transducer at an air–water surface. The brass ring baffle placed around the transducer increased the axial pressure. For the directivity pattern, the ring increased the sound-pressure level at all angles except for those at midrange from the radiation axis where decreased levels were observed.
Binaural speech intelligibility in noise for hearing-impaired listeners
Authors: Bronkhorst A. W. , Plomp R.
Published: October 2005

The effect of head-induced interaural time delay (ITD) and interaural level differences (ILD) on binaural speech intelligibility in noise was studied for listeners with symmetrical and asymmetrical sensorineural hearing losses. The material, recorded with a KEMAR manikin in an anechoic room, consisted of speech, presented from the front (0°), and noise, presented at azimuths of 0°, 30°, and 90°. Derived noise signals, containing either only ITD or only ILD, were generated using a computer. For both groups of subjects, speech-reception thresholds (SRT) for sentences in noise were determined as a function of: (1) noise azimuth, (2) binaural cue, and (3) an interaural difference in overall presentation level, simulating the effect of a monaural hearing aid. Comparison of the mean results with corresponding data obtained previously from normal-hearing listeners shows that the hearing impaired have a 2.5 dB higher SRT in noise when both speech and noise are presented from the front, and 2.6–5.1 dB less binaural gain when the noise azimuth is changed from 0° to 90°. The gain due to ILD varies among the hearing-impaired listeners between 0 dB and normal values of 7 dB or more. It depends on the high-frequency hearing loss at the side presented with the most favorable signal-to-noise (S/N) ratio. The gain due to ITD is nearly normal for the symmetrically impaired (4.2 dB, compared with 4.7 dB for the normal hearing), but only 2.5 dB in the case of asymmetrical impairment. When ITD is introduced in noise already containing ILD, the resulting gain is 2–2.5 dB for all groups. The only marked effect of the interaural difference in overall presentation level is a reduction of the gain due to ILD when the level at the ear with the better S/N ratio is decreased. This implies that an optimal monaural hearing aid (with a moderate gain) will hardly interfere with unmasking through ITD, while it may increase the gain due to ILD by preventing or diminishing threshold effects.
The use of nonuniform element spacing in array processing algorithms
Authors: Shanan S. S. , Pomalaza-Raez C. A.
Published: October 2005

Most array signal processing algorithms use uniform element spacing to estimate source bearing. This paper demonstrates the benefit of using nonuniform element spacing in Bartlett, linear prediction (LP), and minimum variance (MV) array processing algorithms. By using optimum element spacing results obtained by previous investigators for sidelobe reduction of the Bartlett method, better MV and LP performances, in terms of array output power, are obtained.
A treatment of three-dimensional underwater acoustic propagation through a steady shear flow
Authors: Robertson J. S. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

The effect of a steady, depth-dependent, horizontal shear current in an underwater sound channel is considered. Because the source–receiver direction and current direction need not lie in the same vertical plane, the propagation problem is inherently three dimensional. A three-dimensional (3-D) parabolic approximation for this channel is formulated by extending a two-dimensional result obtained previously [Robertson et al., J. Acoust. Soc. Am. 77, 1768–1780 (1985)]. It is shown that, if the azimuthal derivatives are small enough to be neglected in the farfield, azimuthal effects appear only as coefficients in the parabolic equation. Therefore, an N×2-D technique can be used to solve the parabolic equation. Numerical examples are used to examine cross-current propagation. It is shown that substantial intensity variations can occur as the angle between the source–receiver direction and current varies from 0 to 180 deg.
Wind effects in shallow-water acoustic transmission
Authors: Weston David E. , Ching Pamela A.
Published: October 2005

Acoustic transmission in shallow water is degraded in the presence of high winds; losses can exceed 40 dB, after which they cannot easily be measured. Multifrequency studies have used pulse frequencies f from 312 Hz to 4.44 kHz, with path lengths 17, 23, and 137 km, and observations to about 15 m/s wind speed W. The main results show a dB attenuation proportional to f1.5W4, with a coefficient that depends on the season. They can be explained by a quantitative theory involving the scattering loss from the waves on the rough sea surface. But the possibility of a component of the scattering or absorption coming from shallow layers of entrained bubbles is not ruled out. Briefer descriptions cover effects of directional dependence, comparison of rising and falling winds, squalls, breakup of fish shoals, swell, fluctuations, and observed effects on sonar displays.
Pressure derivatives of elastic wave velocities from ultrasonic interferometric measurements on jacketed polycrystals
Authors: Niesler H. , Jackson I.
Published: October 2005

A buffer-rod technique is described for the measurement by ultrasonic pulse interferometry of elastic wave velocities in jacketed polycrystalline specimens as functions of pressure to 3 GPa. The technique is tested on a suite of synthetic polycrystalline specimens (alumina and forsteritic olivine) for which bounds on the pressure-dependent wave velocities may be calculated from single-crystal elasticity data. Measurements conducted at pressures below ∼1 GPa with an unbonded buffer-rod configuration are compromised by the behavior of the interface between the buffer rod and the specimen. It appears that complex reflection and transmission coefficients associated with the contact between microscopically rough surfaces give rise to significant travel-time perturbations that decrease markedly with increasing pressure. These complications can be minimized but not eliminated by insertion between the buffer rod and the specimen of a disk of gold foil that amounts to a ‘‘bond’’ with more clearly defined acoustic properties. The range of pressures within which the interface effect is negligible may be significantly increased by the use of this bonded configuration. Measured elastic wave velocities are influenced by the presence of both microcracks and pores.

Very large pressure derivatives measured between 0 and 0.5 GPa on one specimen are attributed to the closure of 0.1% porosity associated with cracks with aspect ratios less than 10−3. Otherwise, pressure derivatives are normal with velocities approximately 1%, 3%, and 4%–6% below the Hashin–Shtrikman bounds throughout the 0- to 3-GPa interval for specimens of 0.3%, 2.1%, and 4.8% porosity, respectively. These modest reductions in velocity and their survival to 3 GPa indicate that essentially all of the porosity in these specimens is contributed by relatively equidimensional pores of aspect ratio ∼0.1—consistent with their origin as sintered aggregates. The measured pressure derivatives are compared with those of the Hashin–Shtrikman bounds calculated from the pressure-dependent single-crystal elastic moduli. With the sole exception of the microcracked specimen at pressure below 0.5 GPa, the measured derivatives of wave velocities reproduce within ±10% the slopes of the Hashin–Shtrikman bounds demonstrating the viability of the technique for measurement of pressure derivatives of elastic wave velocities on fine-grained polycrystals.
Generation of elastic waves from line and point sources by a high-current pulse method
Authors: Kim Kwang Yul , Sachse Wolfgang
Published: October 2005

This paper describes a method of generating both line and point sources of acoustic emission (AE) signals by a powerful, transient Joule heating of a thin, conductive film deposited on an insulating plate or a small diameter metal wire buried inside it. Point-and line-source AE signals are generated by heating a short or a long section of thin film, respectively. The versatility of this method is demonstated by the diversity of AE signals that can be produced by simply changing the rise time, magnitude, and duration of the current pulse that provides the heating. An analysis shows that both the line and the point AE sources are of dipolar type for the case of the heated thin film. The line source resulting from an imbedded long, thin wire appears to be a two-dimensional center of dilatation. Short-duration current pulses generate a step source whose rise time is approximately equal to that of the input electrical power pulse while long-current pulses produce a linear ramp source that resembles the temperature rise of the heated conducting film or wire.
On transducer and bond corrections for velocity measurements using continuous-wave ultrasound
Authors: Mozurkewich George
Published: October 2005

The perturbing effect of an ultrasonic transducer on determination of sound velocity by continuous-wave methods is reanalyzed. The Bolef–Menes (1+δ) formula is found usually to apply only within a very narrow frequency range around the transducer’s resonant frequencies. Thus it should be regarded as a ‘‘near-transducer’’ rather than a ‘‘thin-transducer’’ correction. Outside the applicable frequency range, it is more appropriate to multiply δ by the square of the ratio of the specimen’s mechanical impedance to that of the transducer. The effect of the bond between specimen and transducer is assessed.