bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of amplitude on voicing contrast may not be explained by VIIIth nerve synchrony capture.
Authors: Lotto Andrew J. , Kluender Keith R.
Published: October 2005

Kluender, Lotto, and Jenison [J. Acoust. Soc. Am. 97, 2552–2567 (1995)] reported that overall stimulus amplitude can affect perception of the voicing contrast in syllable-initial stops. Their results supported an hypothesis that a shift in the temporal pattern of neural firing from frequencies near F2 and F3 to F1 and f0 could signal voicelessness. The results of the current study undermine this ‘‘synchrony capture hypothesis.’’ The effect of amplitude (increased voiceless identifications with higher amplitude) maintains when there is no cutback in F1 during the quasiperiodic portion of the syllable and when stimuli are high-pass filtered above the frequency of F1. In a further test of the hypothesis, two ten-step series (/ba/–/pa/ and /ga/–/ka/) were created which maintained period voicing throughout the syllable (with F1 cutback signaling voicelessness). The energy just below the frequency of F2 and the energy above F1 were presented dichotically. Thus, at the periphery, there was no competition between frequencies near F2 and lower frequencies and, as a result, no chance for a change in neural temporal patterns. Subjects continued to label voicelessness as a function of overall amplitude. Alternative models of the encoding of voicelessness will be considered. [Work supported by NIDCD and NSF.]
A novel psychophysical procedure for investigating the syllabic organization of phonemes in speech.
Authors: Bashford James A. , Warren Richard M. , Brubaker Bradley S.
Published: October 2005

When listeners attempted to tap in synchrony with a target phoneme in a repeating phrase or sentence (e.g., ‘‘Most Wisconsin winters are cold.’’), taps to syllable-initial phonemes were accurate, whereas taps to syllable-final phonemes were early. These results indicate that the apparent occurrence of speech sounds depends upon syllabification, and that the synchronous phoneme-tapping task can be used for investigating syllabic structure. The tapping paradigm was used to examine a topic of current interest—the syllabic assignment of intervocalic consonants. The stimuli were six minimal-contrast pairs of bisyllabic CVCVC words differing only in their first vowels, having either a tense V1 (as in ‘‘tunic’’) or a lax V1 (as in ‘‘tonic’’). Tense-V1 and lax-V1 words were presented to separate groups of 24 listeners who provided a sequence of 15 taps to each target phoneme in the repeated words. Intervocalic consonants (IVCs) following tense vowels elicited accurate tapping, indicating their treatment as second-syllable onsets, whereas taps to IVCs following lax vowels were early, indicating their treatment as first-syllable codas. These results are consistent with linguistic theory and explicit judgments of syllabification [see Trieman and Danis, J. Mem. Lang. 27, 87–104 (1988)].
Auditory-visual context effects on the perception of /r/ and /l/ in a stop cluster.
Authors: Norrix Linda W. , Green Kerry P.
Published: October 2005

Context effects in speech perception are thought to reflect knowledge about coarticulatory influences from the surrounding phonetic environment. This study investigated if such effects occur when the context is specified in the visual modality and segmental information in the auditory modality. In the first experiment, two continua were synthesized: one varying from /iri–ili/ and the other from /ibri–ibli/. When presented to listeners for identification as /r/ or /l/, there was a significant shift in the category boundary between the two continua. In a second experiment, the /iri–ili/ tokens were paired with visual tokens of a talker saying /ibi/. When presented in an auditory-visual (AV) condition, these tokens were perceived as ranging from /ibri/ to /ibli/. Observers also identified the /iri–ili/ tokens in a separate auditory-only (AO) condition. Results indicated a similar shift in the /r–l/ boundary between the AO and AV conditions. Analysis of /r/ and /l/ productions revealed that the perceptual adjustments were consistent with the acoustic consequences of articulating /r/ and /l/ in a stop cluster. The findings suggest that the perceptual adjustment reflects cross-modal knowledge of the coarticulatory effects of a bilabial consonant on the acoustic realization of /r/ and /l/. [Work supported by NIDCD, NIH.]
Individual differences and the perception-production link.
Authors: Newman Rochelle S.
Published: October 2005

Several theories (e.g., Motor Theory [Liberman and Mattingly, Cognition 21, 1– 36, 1985]) posit a link between perception and production. One way of examining the interrelationship between production and perception is to look at individual differences in both types of tasks. Previous research has yielded somewhat ambiguous results, but many of these studies looked at the boundaries between categories. The current study examined individuals’ prototypes and related data from production. Subjects participated in a perceptual task modeled on that of Miller and Volaitis [Percept. Psychophys. 46, 505–512 1989]. Subjects heard members of a VOT series centered on /pa/, and rated them according to ‘‘p’’ category goodness. These same subjects were recorded producing stop consonant–vowel tokens, and the VOTs of these productions were measured. A correlation was found between the average VOT for subjects’ productions of ‘‘pa’’ and the VOT of the tokens they rated as the best examples. This supports the idea of a perception-production link, and leaves open the possibility that a common mechanism may be used in both processes. [Work supported by NIDCD Grant No. R01 DC00219 to SUNY at Buffalo.]
An age-based auditory Stroop effect.
Authors: Ralston James V. , Plesser Jarad M. , Lawless Elizabeth A.
Published: October 2005

The present research investigates the effect of semantic content of an utterance on age perception. On each trial of two experiments, listeners heard either a relatively old or young voice uttering a word or nonword. Listeners rapidly decided whether the speaker was relatively young or old. One experiment included five repetitions of the words ‘‘young’’ and ‘‘old,’’ and a nonword spoken by a college-aged and a middle-aged female. Analyses of reaction times for correct responses revealed a Stroop effect: Responses were quicker when the semantic information and the age of the speaker were consistent than when they were inconsistent. Overall reaction times, but not the Stroop effect, decreased across repetitions. A second experiment utilized the words ‘‘young’’ and ‘‘old,’’ age-associates, age-neutral words, and nonwords, all recorded from a college-aged and a middle-aged female. Analyses of reaction times revealed a Stroop effect for the semantic associates. In addition, there was a strong trend for response times for nonwords to be greater than those for neutral words. The combined results demonstrate that lexical information influences a listener’s perception of age. Results from more recent studies manipulating listener set will also be presented.
Dynamic cues in vowel identification: A training study.
Authors: Neel Amy T. , Kewley-Port Diane
Published: October 2005

The importance of dynamic formant information for vowel identification has been shown by several studies in recent years. Using sine-wave vowel analogs, Neel and Kewley-Port [J. Acoust. Soc. Am. 96, 3284(A) (1994)] demonstrated that vowel duration is an important cue for vowel identity and that dynamic formant information is more effective when duration cues are absent. However, because identification rates for sine-wave stimuli were low, a training study was conducted to determine the impact of training on the effectiveness of dynamic formant and duration cues for vowel identification. Sine-wave stimuli consisted of two tones representing F1 and F2 from 10 vowels produced by a female speaker. Four types of stimuli were constructed by varying two factors: (1) dynamic versus static formants and (2) appropriate versus fixed vowel duration. Listeners were trained to criterion on one set of stimuli and were tested on another. Training significantly improved identification accuracy. In comparison to performance on static formant tokens, listeners were more accurate in identification and improved more from baseline to test when dynamic formant cues were present. Listeners also showed an identification advantage when duration cues were available. [Research supported by NIHDCD Research Grant No. DC-02229.]
Radiation impedance of RUS modes in fused silica and KCl.
Authors: Herro J. , Zhang H. , Hucho C. , Beck D. , Levy M. , Isaak D. , Carnes J. D. , Anderson O.
Published: October 2005

The pressure dependence of the resonance frequency of several RUS modes in samples of fused silica and KCl has been measured at UCLA in atmospheres of air, He, and Ar near ambient temperature. For both compressional and torsional modes the radiation resistance appears to be linearly dependent upon pressure and increases with the molecular mass of the surrounding gas. The effects are larger for breathing modes than for torsional modes. A model will be presented which will attempt to fit some of these data both qualitatively and quantitatively. [Work supported by the Office of Naval Research.]
Electromagnetic excitation and acoustic spectroscopy of the quadrupole elastic mode of an empty nearly spherical shell.
Authors: Hefner Brian T. , Marston Philip L.
Published: October 2005

The lowest quadrupole mode of an empty nearly spherical metallic shell was excited by a novel form of EMAT (electromagnetic acoustic transducer) not having mechanical contact with the shell. An oscillating current is supplied to a coil located near the equator of the shell. The shell vibrates in response to the Maxwell stresses which are distributed over the shell’s surface in a way especially favorable for excitation of the lowest quadrupole mode (a bending mode) which has a natural frequency near 64 kHz. The stresses are associated with the Lorentz forces on eddy currents around the equator. The mode is detected with a small microphone placed near the shell. In one version of the experiment a large dc bias magnetic field is superposed on a weaker oscillating field of frequency near 64 kHz. In another version of the experiment the bias field is removed and the frequency of the oscillating field is near 32 kHz (half of the excited mechanical frequency). The method may have applications to the inference of the contents or elastic properties of shells and to the investigation of the modal structure of open shells. [Work supported by the Office of Naval Research.]
Resonant ultrasound in circular pipes.
Authors: Mueller Fred M. , Sinha Dipen N. , Hasse Roger D. , Springer Kendall N.
Published: October 2005

Resonant ultrasound has found multiple applications, ranging from medical imaging to a variety of nondestructive testing techniques. Here focus is placed on nested cylinders. A series of ultrasonic measurements has been carried out in a geometry with an outer hollow steel cylinder, and a smaller, solid inner steel cylinder. In the interspace were placed several liquids. Ultrasound was introduced by a narrow contact transducer. A second set of narrow transducers was used as pickups and placed at angles ranging from 10 to 150 deg. The frequency of the ultrasound was varied from 1 to 5 MHz and showed a sequence of eight composite and sharp resonances spaced at about 0.5 MHz. The composite resonances showed a strongly skewed behavior as a function of frequency. The velocity potential has been modeled by using combinations of Hankel functions of complex argument. Convergence was achieved by using angular m’s up to 150. These showed that the asymmetry of the composite resonance peaks is primarily a phase or geometrical optics effect.
Benefit of binaural hearing in a multi-source environment. I. Sound localization.
Authors: Litovsky Ruth Y. , Hawley Monica L. , Jones Jennifer K. , Dunton Leah B. , Colburn H. Steven
Published: October 2005

A multi-source listening environment was simulated under headphones by recording signals through KEMAR in a sound-deadened room. Seven loudspeakers were each positioned in the frontal plane 5 ft from KEMAR at 30-deg increments, ranging from +90 (right) to −90 (left). The recorded signals (IEEE Harvard sentences) were digitally mixed and played back under headphones in a sound-proof booth using a Digital Audio Tape (DAT) player. Sound locazation accuracy was measured for ‘‘target’’ sentence in the presence of various ‘‘jammers.’’ Three variables were manipulated. First, the number of ‘‘jammers’’ was either none, one, two or three. Second, the relative location of the targets and jammers was varied, such that they were either in close proximity, widely separated, or some of each. Third, the jammer content comprised of either other sentences, speech-shaped noise, babble or time-reversed sentences. Normal-hearing listeners were tested under binaural and monaural conditions. The content of the target sentence was known. Localization accuracy decreased as the number of jammers increased, and as the proximity of the target and jammers was increased. In addition, performance was worse under monaural than under binaural conditions. [Work supported by NIH DC02696, DC00100-21.]
The fidelity of virtual auditory displays.
Authors: Zahorik Pavel , Wightman Frederic L. , Kistler Doris J.
Published: October 2005

A new method for on-line virtual sound source synthesis has been developed that affords direct comparison of virtual and real sound sources. Using this method, four listeners performed a 2AFC discrimination of real free-field sources and the virtual representations of these sources. The sources consisted of wideband noise bursts presented at a number of spatial positions. Virtual source fidelity was manipulated (on a trial by trial basis) by applying windows of various lengths (20.48, 5.12, 1.28, 0.32 ms) to the impulse responses (20.48 ms in duration) of the filters used to synthesize the virtual sources. When fidelity was highest, listeners could not discriminate virtual from real sound sources. As window length was decreased, discriminability increased. For a 1.28-ms window, performance was above 75% correct on average. These results are consistent with physical measurements of the differences in the acoustic signal at the listener’s ear drum between virtual and real source presentation. In a related experiment, the same four listeners where asked to report the apparent positions of the virtual sound sources synthesized in the previous experiment. Degradation in localization performance was observed as filter window length was decreased. [Work supported by NASA.]
Auditory localization aftereffects.
Authors: Kashino Makio , Nishida Shin’ya
Published: October 2005

It was observed that the perceptual lateralization of a sound (test) having an interaural time difference (ITD) is shifted away from that of a prior sound (adapter) having a different ITD. First, the frequency selectivity of this ‘‘auditory lateralization aftereffect’’ was examined for sinusoids presented through headphones, with various combinations of adapter and test frequencies below 800 Hz, using the method of constant stimuli. The magnitude of the aftereffect was found to be largest when the frequencies of the two sounds were similar. It decreased as the frequency difference increased, and virtually disappeared at a frequency difference of one-half octave. Second, the ITD selectivity of the aftereffect was examined for 400-Hz tones. Subjects’ judgments of lateralization were measured directly in terms of the azimuth of the test signal for various combinations of adapter and test ITDs in the range of ±625 μs. It was found that the magnitude of the aftereffect was rather small when the ITDs of the adapter and test signal were similar, and was largest when ITDs differed by 250 or 375 μs. These results will be discussed in terms of implications for theories of binaural interaction, possible neural sites, and functional roles of the effects.
The influence of grouping and dimensional similarity on interference effects in auditory short-term memory.
Authors: Starr Gary E. , Pitt Mark A.
Published: October 2005

Previous research investigating auditory short-term memory using a tone discrimination paradigm found same-dimension similarity to be the primary source of memory disruption [e.g., C. Semal and L. Demany, J. Acoust. Soc. Am. 89, 2404–2410 (1991)]. However, grouping principles (e.g., Gestalt principles) also provide a possible explanation for the observed effects, because increases in same dimension similarity may also increase the likelihood of the standard tone grouping with additional tones. This project investigated the contribution of grouping to interference effects in short term memory for the dimensions of pitch and timbre. A modified ‘‘captor effect’’ task was used, with participants discriminating either the pitch or timbre of a standard tone (the sixth tone in an 11-tone sequence) from a comparison tone presented 5 s after the standard. Two variables were orthogonally varied, the same-dimension distance between the standard tone and the captor tones (either close or far), and the grouping structure of the sequence, with structures that either promoted or prevented grouping of the standard tone with the captor tones. Results suggest that grouping contributes to the amount of interference because increases in grouping led to increases in interference.
Perceiving source characteristics from complex sounds.
Authors: Farrington Shannon M. , Pastore Richard E.
Published: October 2005

Other than in speech, there have been very few studies investigating the ability of humans to perceive characteristics of events based upon the sounds emitted. However, there is considerable anecdotal evidence that humans often use complex sounds to accurately perceive events in their environment. To investigate this ability, it is important to determine the extent of subjects’ ability to map sounds onto certain event characteristics and then to determine the specific acoustic properties which tend to be used in this mapping process. Once this process has been determined, techniques can be developed to improve this ability. Previous research from our laboratory [X. Li, R. J. Logan, and R. E. Pastore, J. Acoust. Soc. Am. 90, 3036–3049 (1991)] indicated that subjects are able to identify walker gender based upon acoustic properties of four footsteps on a single surface. The current research investigated subjects’ ability to identify specific walkers across different surfaces. Results indicated that, to varying degrees, subjects could reliably identify walkers across different surfaces and could generalize this training to a novel task. Further experiments provide a more detailed analysis of the properties of the acoustic signal which reliably map on to subjects ability to identify a specific walker.
Effects of variable pattern context on temporal acuity.
Authors: Apfelblat Dana , Riess Jones Mari
Published: October 2005

This experiment varied the time pattern of 25 tones sequences to determine its effect on subjects’ abilities to discriminate small time changes within one of two isochronous test regions. A two-alternative forced-choice procedure was used in which a small time change (±Δt=21, 39, or 57 ms) occurred equally often in one of the two test regions. Test regions were distinguished from surrounding context regions, where timing was variable, by higher frequency tones. Both the absolute amount of temporal variability (small, large) and the nature of temporal variability (rate-accelerating, rate-decelerating, and rate-alternating) within context regions were varied. Results showed that listeners’ ability to detect time changes within test regions was poorer with large amounts of contextual variability than with smaller amounts. However, minimal effects of the patterning of tempo (rate) within context regions were found.
Thermodynamic energy flow, modal models, and statistical energy analysis.
Authors: Bernstein Dennis S.
Published: October 2005

The acoustics and vibration of coupled structures can be efficiently modeled by means of energy flow theory, usually known as statistical energy analysis (SEA). SEA is based upon relations derived from the interaction of pairs of coupled modes and is applied empirically to coupled structures possessing multiple interacting modes. This talk investigates the accuracy of SEA models by deriving exact energy flow relations based upon modal models. Using white noise disturbances but otherwise deterministic structural models, we present energy flow relations for multiple coupled structures. These relations are formulated in terms of thermodynamic energy, which is a measure of subsystem energy dissipation relative to subsystem disturbance intensity. The resulting energy flow models are compared to SEA models based upon coupled, uncoupled, and blocked subsystem energy. The results are applied to systems of coupled oscillators as well as coupled beams to demonstrate predicted energy flow under both strong and weak coupling.
Fuzzy structure mass per unit frequency and its asymptotic tendencies.
Authors: Pierce Allan D.
Published: October 2005

The fuzzy structure theory concept of modal mass per unit natural frequency is explored for an elastic substructure attached to a master structure. The passive influence on the master structure vibration is specified by the driving point impedance of the substructure, which in turn is expressed as a sum over terms, each corresponding to a natural mode. Term parameters are a modal mass in the numerator and the natural frequency. The fuzzy structure idealization replaces the sum by a derivative term (dissipative part) plus an integral (reactive part), both involving modal mass per unit frequency. Generic continuum models of the attachment are inhomogeneous rods, beams, and plates. (In the latter cases, the impedance becomes a matrix, with generalized forces incorporated that correspond to torques, and generalized velocities that are angular velocities.) Asymptotic ideas analogous to those that yield modal density predictions yield predictions of the mass per unit natural frequency (and its generalizations) in the limit of high frequencies. [Work supported by ONR.]
Continuous structures as ‘‘fuzzy’’ substructures.
Authors: Strasberg M.
Published: October 2005

It is by now well known that the resistive part of the combined driving-point impedance of a collection of sprung masses with closely spaced frequencies of antiresonance can be expressed by the simple relation R=1/2π2f2m0, where m0 is the resonant mass density, defined so that m0df is the combined mass of the sprung masses in antiresonance in a differential frequency band of width df centered at the cyclic driving frequency f. To apply this relation to a continuous or complicated structure, it is necessary to determine how the value of m0 varies with frequency for a set of sprung masses duplicating the driving-point impedance of the structure. The procedure is illustrated by calculating m0 for several simple continuous structures, including a long uniform rod in axial vibration, and a long uniform beam or large thin plate in flexural vibration. The values of resistance obtained by treating these systems as fuzzy structures agree with well-known values.
Interaction of structural and acoustical waves at a wedge-shaped junction of two fluid-loaded plates.
Authors: Norris Andrew N.
Published: October 2005

Two semi-infinite elastic plates are joined along a line forming a wedge structure with unilateral fluid loading in the sector of angle 2Φ. The structure is modeled using thin plate theory, allowing freely propagating flexural and longitudinal waves. The junction is mechanically connected with an applied force and moment acting there to simulate a possible internal connection. The general 2-D solution is described for incidence of time harmonic structural or acoustical waves. The method of Osipov is used to express the total pressure as a Sommerfeld integral, the integrand comprising Malyuzhinets functions and particular solutions of certain difference equations. The junction conditions reduce to a system of eight linear equations. Numerical examples indicate the coupling between the modes for different wedge angles, specifically Φ=112.5°, 135°, and 157.5°, for steel plates in water. Acoustic plane wave incidence on the flatter junction (112.5°) is converted almost equally, in terms of energy, among diffracted flexural and longitudinal waves. The coupling to flexural energy increases with the wedge angle, at the expense of the longitudinal energy which vanishes as Φ→180°. An incident longitudinal wave generates relatively little acoustic sound for all values of Φ considered, with most of its energy redistributed among structural modes. The acoustical diffraction is generally greater for flexural incidence. [Work supported by ONR.]
Effects of component interfacial boundary conditions on component mode synthesis estimates for natural frequencies and modes.
Authors: Farstad Jerry E. , Singh Rajendra
Published: October 2005

Several formulations for component mode synthesis have been proposed in the literature, with the principal differences among them being the types of boundary conditions imposed on individual components at the interfaces where they later will be joined when component natural frequencies and modes are computed. Formulations based on component modes with fixed interfacial conditions, free interfacial conditions, and mixtures of fixed and free conditions have be en proposed. While all formulations yield reliable results when all component modes are included, modal truncation errors are introduced if incomplete sets of component modes are used. In this communication, a new procedure for determining modal truncation errors in modal synthesis formulations is presented and applied to two formulations, one with mixed interface conditions and one with fixed interface conditions. Errors in estimated natural frequencies and local errors in mode shapes are investigated for the case of a two component joined beam system. The results indicate that formulations using component modes with free interface conditions are inherently susceptible to modal truncation errors because of nonzero forces and moments acting at the joints after assembly.
Modal impedances for nonaxisymmetric vibrations of a thin spherical shell.
Authors: Evans Richard B.
Published: October 2005

Modal impedances are found by solving the equations of motion of a thin spherical shell in terms of nonaxisymmetric modes of vibration. These mechanical impedances relate the modal expansion coefficients of the applied force per unit area and the velocity of the shell. The application and interpretation of these modal impedances require an awareness of the lack of orthogonality of certain modes. In proper combinations, the modal impedances in the nonaxisymmetric case are found to be identical to known modal impedances in the axisymmetric case. The analysis is restricted to extensional effects of a thin shell with radial forcing. An application of the modal impedances is given in the prediction of the radiation pattern of a three-dimensional array of closely spaced interacting spherical shells.
The perception of stop consonants in silent-center syllables by listeners with high-frequency hearing loss.
Authors: Stack Janet W.
Published: October 2005

This study investigated whether stop consonant perception in listeners with high-frequency hearing loss could be improved by eliminating nonsimultaneous masking effects of high-amplitude vowels on consonants in consonant–vowel–consonant (CVC) syllables. Full syllables (FS) contained the consonants /b,d,g/ in all combinations with eight vowels (/■,I,ε,æ,■,■,u/). Syllables were produced by a male speaker. Silent-center (SC) syllables were created by attenuating vowel steady-state portions to silence. Stimuli were presented to 12 normal-hearing (NH) and 36 hearing-impaired (HI) adults under the age of 60. HI listeners had steeply sloping high-frequency hearing losses. FS and SC conditions were presented at 50 and 80 dB HL. All subjects showed more accurate vowel and consonant identification in the FS vs SC condition and at 50 vs 80 dB. Errors were significantly higher on initial than on final consonants. Acoustic analysis suggested the possibility of both temporal and spectral explanations for this final consonant advantage. In spite of experimental failure to improve consonant perception in the HI listeners, suggestions for future research emerged which might enhance the effect of the SC condition and the decrement of nonsimultaneous masking effects. [Work supported by Veterans Administration.]
Vowel recognition by cochlear implant patients using a large database of speakers.
Authors: Loizou Philipos C. , Dorman Michael F. , Spanias Andreas S.
Published: October 2005

There have been many reports on the recognition of vowels by cochlear implant patients fitted with various devices. Most of these reports, however, used a single male and/or female talker to test vowel recognition. This paper presents results on the recognition of vowels produced by a large number of men, women, and children [Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099–3111 (1995)]. The aim of this study was to investigate why certain groups of speakers, e.g., children, and certain vowels are harder for the cochlear implant patients to identify. A total of 5 Ineraid patients who had been fit with continuous interleaved sampling (CIS) signal processors were used in this study. Patients’ performance on vowel recognition ranged from 54% to 84%. The sex and age of the talker (that is, the talker’s vocal tract size) seemed to have a significant effect on the performance for some of the patients, and in particular the ‘‘poor’’ patients. Individual patient’s results on vowel recognition, and a detailed analysis of the vowel confusions will be presented.
Acoustic time-dependent loading on elastic shells of revolution using the internal source density and singular value decomposition method
Authors: Stepanishen Peter , Chen Huo-Wang
Published: October 2005

A new representation for the time-dependent surface pressure on a fluid-loaded shell of revolution with a prescribed space and time-dependent axisymmetric velocity distribution is presented. This representation, which is based on expanding the surface traction and velocity vectors into in-vacuo modal vector expansions with time-dependent coefficients, results in each time-dependent modal pressure coefficient being expressed as a sum of temporal convolution integrals which involve time-dependent modal radiation impulse responses and modal velocities. After presenting the formulation of the appropriate initial-boundary value problem, Fourier transform methods are introduced to obtain the corresponding Neumann boundary value problem. The solution of this latter problem is formulated as a minimum mean square error problem in which linear monopole harmonic distributions along the axis of the shell are introduced to determine the surface pressures resulting from the normal components of the modal vectors of interest. Singular value decomposition methods are then used to determine the harmonic monopole distributions. Modal decomposition and inverse Fourier transform methods are then used to evaluate the time-dependent modal radiation impulse responses. Numerical results are presented for the self and mutual modal radiation impulse responses for both spherical and spheroidal shells.
Finite-difference time-domain approach to underwater acoustic scattering problems
Authors: Wang Shuozhong
Published: October 2005

The finite-difference time-domain (FDTD) recurrence expressions are formulated, and the numerical algorithm developed for underwater acoustic scattering applications, based upon the basic motion equation and the equation of continuity. The boundary condition implementation for both soft and rigid surfaces, and the absorbing boundary conditions on the truncating surface are described. The algorithm simulates the sound wave propagation in the time domain. As the time-stepping proceeds, boundary conditions are satisfied naturally. The method is particularly suited for scattering from complex objects. Near-field distributions of waves scattered from cylinders with ideal boundary conditions, insonified by a plane incident wave, are first computed. Far-field directional patterns are then derived using a Fourier transform method. The method is then applied to some other objects, including a square cylinder with an arbitrary aspect angle, and wedges with either ideally soft or ideally rigid surfaces. A good agreement between the FDTD and the theoretical results is demonstrated, showing the potential of the method in the studies of underwater scattering problems.
Theory of high-frequency sound propagation in a spatially inhomogeneous medium
Authors: Li Kai Ming
Published: October 2005

This paper examines the propagation of sound in a spatially inhomogeneous medium. The high-frequency sound field due to a monopole source in a range-dependent environment has been derived. The method of Liouville–Green transformation is extended to three dimensions hence enabling simplification of the governing wave equation. This simplification allows the total sound field to be expressed in terms of an inverse Fourier integral which can then be evaluated asymptotically by the method of stationary phase. The present method contrasts sharply with the classical ray method which requires an initial assumption of the form of the asymptotic solution. Nevertheless, it is shown that the amplitude and the acoustical path length of the propagated sound determined by the present method agree with that determined by the classical ray method. This is perhaps not surprising because both methods exploit the asymptotic behavior of the solution. The present method has the further advantage that it enables the sound field in close proximity to caustics to be calculated in a straightforward manner.
Formulas for ambient noise level and coherence
Authors: Harrison C. H.
Published: October 2005

This paper investigates the various approximations commonly made in noise and noise coherence models and shows that in many cases a very simple ray approach can produce the same answers as full wave treatments such as RANDI-2. The solution presented here takes the form of a single angle integral which is valid for range-independent environments. Some closed-form solutions are presented, and the approach makes it very easy to understand such phenomena as the ‘‘noise notch.’’ The method can be extended to range dependence, and demonstrations are given of performance near a boundary (inhomogeneous field) and in the presence of nonuniform horizontal distributions of noise sources.
Decomposition of the time reversal operator: Detection and selective focusing on two scatterers
Authors: Prada Claire , Manneville Sébastien , Spoliansky Dimitri , Fink Mathias
Published: October 2005

The decomposition of the time reversal operator (DORT) method is a selective detection and focusing technique using an array of transmit–receive transducers. It relies on the theory of iterative time reversal mirrors which was presented by Prada et al. [C. Prada, J. L. Thomas, and M. Fink, J. Acoust. Soc. Am. 97, 62–71 (1995)]. The time reversal operator was defined as K*(ω)K(ω), where ω is the frequency, * means complex conjugate, and K(ω) is the transfer matrix of the array of L transducers insonifying a time invariant scattering medium. It was shown that this time reversal operator can be diagonalized and that for ideally resolved scatterers of different reflectivities, each of its eigenvectors of nonzero eigenvalue provides the phase law to be applied to the transducers in order to focus on one of the scatterers. The DORT method consists in determining these eigenvectors and using them for the selective focusing. This paper presents a complete analysis of this method in the case of two scatterers. The mathematical expressions of the eigenvectors are given and several experimental results are described. In particular, the effectiveness of the method to focus selectively through an inhomogeneous medium is established.
Propagation of elastic waves in equiaxed stainless-steel polycrystals with aligned [001] axes
Authors: Ahmed S. , Thompson R. B.
Published: October 2005

The unified theory for elastic wave propagation in polycrystalline materials, developed by Stanke and Kino [J. Acoust. Soc. Am. 75, 665–681 (1984)], has been applied to compute the propagation constants in materials consisting of cubic crystallites with texture. The particular texture considered here is one in which one of the cube axes of each crystallite is aligned in a preferred direction with the other two being randomly oriented, leading to a material with macroscopic transverse isotropy. The calculations are done for plane waves under the assumption that the single crystal anisotropy is not large. Numerical results for the variations of attenuation and phase velocity with direction of propagation and frequency are presented for L, SH, and SV waves.
Ultrasonic characterization of a polymerizing epoxy resin with imbalanced stoichiometry
Authors: Matsukawa Mami , Nagai Isao
Published: October 2005

The effect of the mixing ratio of curing agent to epoxy prepolymer on the isothermal polymerization of common epoxy systems has been characterized by ultrasonic spectroscopy. During polymerization, changes in longitudinal ultrasonic wave properties (velocity and attenuation) were observed. These changes were related to the glass transition temperature of the resins. The profile of velocity and attenuation clearly depended on the mixing ratio. In all resins, the wave attenuation exhibited a peak in the primary relaxation (α).
Measurement of elastic constants in composite materials using air-coupled ultrasonic bulk waves
Authors: Hosten Bernard , Hutchins David A. , Schindel David W.
Published: October 2005

This paper presents numerical simulations and experimental measurements of longitudinal and shear bulk waves in composite materials, generated and detected with an air-coupled ultrasonic system. The transfer function of an anisotropic absorbing layered plate immersed in air is computed with the transfer matrix method, and the waveforms produced by transmission through a plate are simulated from the convolution of a reference waveform and the impulse response of the plate. The calculated waveforms compare well to those recorded experimentally, confirming that the waveforms recorded experimentally have the correct characteristics. It is demonstrated that it is possible to identify longitudinal and shear modes. Results are presented showing how this data may be used to recover the stiffness matrix of composite materials, using the angular variation of velocity of both modes.
Visualization of acoustic particle interaction and agglomeration: Theory and experiments
Authors: Hoffmann Thomas L. , Koopmann Gary H.
Published: October 2005

This paper presents new insights in interaction mechanisms between small particles under the influence of a strong acoustic field. These mechanisms are associated with acoustic agglomeration, an effect that causes relative motion and collisions between fine particles entrained in gaseous media. The agglomeration process has potential use in air pollution control to enhance the performance of conventional particle filtering devices in the fine particle size range. In Sec. I of this paper, a number of existing acoustic agglomeration models are reviewed and implemented into a numerical scheme. A quantitative analysis of the proposed theories is conducted with parameters representing those of the experimental Sec. II. Simulations based on the scattering, orthokinetic, and hydrodynamic agglomeration principles generate numerical trajectories which reflect their importance in the particle interaction process. Most importantly it is shown that a hydrodynamic effect based on asymmetric flow fields around the particles (acoustic wake effect) generates significant particle attraction in the direction of the acoustic velocity vector. To evaluate these theoretical findings, Sec. II of this paper presents new experimental observations of microscopic particle trajectories in an intense acoustic field. The experiments are carried out in a small-scale observation chamber using a CCD camera in conjunction with a high-resolution video system.

A homogeneous acoustic velocity field is generated by two rectangular, flat-membrane loudspeakers which comprise two opposing walls in the observation chamber. Glass microspheres (diameters 8.1 and 22.1 μm) and arbitrarily shaped, quartz particles (diameter <50 μm) are used for the observation of interaction and agglomeration trajectories under the influence of an intense acoustic velocity field (1.2–0.53 m/s @400–900 Hz, respectively). The recorded digitized images show a number of different interaction phenomena as well as one distinct pattern that resembles the shape of a tuning fork (thus called the tuning fork agglomeration). The latter appears to be the predominant agglomeration mechanism leading to rapid particle approach and multiple, subsequent particle interactions at large acoustic velocities.
A parallel processing approach to acoustic tomography
Authors: Sullivan C. , Kline R. , Mignogna R. B. , Delsanto P. P.
Published: October 2005

Acoustic tomography is a widely utilized technique to reconstruct material properties from global wave propagation data. One of the main drawbacks to using tomography is the computationally intensive nature of the reconstruction algorithm. In this work, a new computational approach to acoustic tomography is presented using a computer with a massively parallel architecture (Connection Machine CM200). The objective was to develop a tomographic reconstruction algorithm, including ray tracing, which fully utilized the simultaneous computation capability of the Connection Machine. The modifications necessary to implement tomographic reconstructions in parallel are described. Results are presented for several synthetic reconstructions. The CPU time required for the parallel program remains relatively constant as the problem size increases, whereas the CPU time for a serial program increases rapidly. This illustrates the utility of this approach for complex problems.
A functional model of the hair cell–primary fiber complex
Authors: Ross Strange
Published: October 2005

A model is proposed containing three parallel systems; system 1 is a single channel consisting of an inhibitory circuit being fed by a fixed permeability responsible for spontaneous activity in parallel with a displacement-driven permeability, while systems 2 and 3 each consist of a number of identical permeability–volume–permeability channels with on/off switches activated at levels specific for each channel. The (continuous) output of each system drives a Poisson generator whose output ‘‘events’’ are delivered to a firing mechanism in the form of a ‘‘leaky integrator’’ delivering actual ‘‘firings’’ in simulated real time. The model quite accurately reproduces (1) stimulation and recovery phases of PST histograms obtained at six levels of stimulation for six auditory fibers (including ‘‘dead’’ period after stimulation), (2) single-exponential functions of recovery from adaptation for both onset and steady-state part of probe tone, (3) increments in response as independent of time of application of stimulus increment, (4) a specified hazard function for firings, (5) interval histograms of driven activity, (6) loss of phase locking with increasing frequency of stimulation, and (7) extended dynamic range for onset of response. The model fails in reproducing specific characteristics for response to decrements, and for response to AM.
Linearity of sound transmission through the human skull in vivo
Authors: Håkansson Bo , Carlsson Peder , Brandt Anders , Stenfelt Stefan
Published: October 2005

The linearity of sound propagation through the human skull was investigated. One male subject, equipped with bilateral skin-penetrating titanium fixtures for attachment of bone-anchored hearing aids, was studied thoroughly. Three different methods were used: comparison of the frequency response functions estimated at different signal levels (using stepped sine as well as random noise), comparison of the coherence function at different signal levels (using random noise), and the Hilbert transform of the estimated frequency response function. Frequencies from 0.1 to 10 kHz and signal levels up to 77 dB HL at discrete frequencies were used. No indication of any significant nonlinear behavior was found with the three methods used.
Biophysics of the cochlea II: Stationary nonlinear phenomenology
Authors: Nobili R. , Mammano F.
Published: October 2005

Nonlinearities affecting cochlear mechanics produce appreciable compression in the basilar membrane (BM) input/output (I/O) functions at the characteristic frequency for sound-pressure levels (SPLs) as low as 20 dB (re: 20 μPa). This is thought to depend upon saturation of the outer hair cell (OHC) mechanoelectrical transducer (MET). This hypothesis was tested by solving a nonlinear integrodifferential equation that describes the BM vibration in an active cochlea. The equation extends a previously developed linear approach [Mammano and Nobili, J. Acoust. Soc. Am. 93, 3320–3332 (1993)], here modified to include saturating MET, with a few corrections mainly concerning tectorial membrane resonance and OHC coupling to the BM. Stationary solutions were computed by iteration in the frequency domain for a wide range of input SPLs, generating BM I/O functions, frequency response envelopes, and two-tone distortion products. Traveling-wave amplitude envelopes were also computed for a fixed suppressor and several suppressed tones in order to evidence the phenomenon of two-tone suppression (frequency masking) at the mechanical level. All results accord nicely with experimental data.
Vibrotactile threshold in young and old observers: The effects of spatial summation and the presence of a rigid surround
Authors: Goble Alan K. , Collins Amy A. , Cholewiak Roger W.
Published: October 2005

Human psychophysical detection thresholds for ten frequencies of sinusoidal vibration ranging from 10 to 400 Hz were obtained on the left index fingertip and thenar eminence of young and older observers using a three-alternative forced-choice tracking procedure. The first experiment utilized a 7-mm (0.38 cm2) contactor and rigid surround with 1-mm gap. In the second experiment, three contactor sizes (1.6-, 7.0-, and 25.4-mm diameter) and two surround configurations (1-mm gap between contactor and surround, and no surround) were used. The results indicate that, although the shapes of the threshold versus frequency functions were similar in the two age groups, there was a reduction in sensitivity for the older group at all frequencies. Furthermore, taking into account the difference in sensitivity between the two age groups, spatial summation and the effects of a surround did not seem to differ between the two groups. These results are discussed in the context of physiological models of cutaneous sensitivity and changes in receptor function with age.