bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of the electromechanical properties of ceramic polymer composite materials for hydrophone applications
Authors: Rittenmyer Kurt M.
Published: October 2005

The real and imaginary parts of the complex elastic, dielectric, and piezoelectric properties of two types of commercial piezoelectric composite materials were studied as a function of temperature from − 70°C to + 50°C using an electrical resonance technique described previously [J. Acoust. Soc. Am. Suppl. 1 82, S101 (1987)]. These materials consist of ceramic particles embedded in a polymer material and possess improved hydrostatic sensitivity as well as mechanical flexibility in comparison with conventional piezoelectric ceramics. Measurements of the temperature dependence of the hydrostatic piezoelectric coefficients have also been performed. The interrelationship of the properties is complicated by the presence of the glass transition of the elastomeric phase of the composite material where sharp changes in the electmechanical transition causes typical relaxation behavior in the complex elastic coefficients and a peak in the dielectric properties. The transition was studied further by the use of differential scanning calorimetry in order to corroborate the results of the resonance measurements. The results demonstrate some difficulties in using these particular materials and indicate that other polymeric materials should be investigated for use in these composite materials. [Work supported by ONR.]
Lower symmetry of the elastic and piezoelectric tensors
Authors: Nelson D. F.
Published: October 2005

A long wavelength lattice dynamical calculation of the elastic and piezoelectric tensors that does not use the adiabatic approximation yields linear coupling to rotation as well as to strain in dynamic interactions. This leads in the general anisotropic (triclinic) case to 45 independent elastic components (rather than 21 as believed for over a century) and to 27 independent piezoelectric components (rather than 18). The new contributions to these tensors result from the inertial effects of the optic modes and are proportional to the square of the frequency. Thus they vanish for static interactions and so restore the traditional symmetries in this limit. The new tensor components create an antisymmetric part to the stress tensor; it produces a torque that is balanced by a change in the internal angular momentum density of the optic modes. The new tensor components will be measurably large only for frequencies comparable to optic mode frequencies, which, in most crystals, are well beyond the acoustic region. However, near a second-order phase transition, the frequency of a soft optic mode approaches zero. In some cases, such as chloranil, the soft mode has been observed in the hypersonic region as a distinct (underdamped) resonance. In such eases, the new tensor components can be expected to be measurably large.
Influence of fillers on constrained-layer vibration-damping capabilities of chlorobutyl elastomers
Authors: Capps Rodger N. , Beumel Linda L.
Published: October 2005

A chlorobutyl elastomer formulation has been developed at this laboratory (USRD) for potential vibration damping applications. It combines the attractive engineering properties of low compression set, good weather and ozone resistance, and good tensile and tear properties with desirable viscoelastic behavior for vibration control. An intensive investigation of the effects of plasticizers and different types and loadings of fillers upon physical properties and damping capability of the base polymer was conducted. Measurements of the dynamic Young's modulus and loss tangent over an extended frequency range were used in conjunction with the Ross-Ungar-Kerwin model [Structural Damping, edited by J. E. Ruzicka (American Society of Mechanical Engineers, New York, 1959), Sec. 3] to predict the damping of simple three-layer constrained structures. The model predictions were compared with actual damping measurements of composite plates. The observed differences between elastomers with different types of fillers are discussed in terms of mechanisms of interaction between the fillers and the gum phase of the elastomer. [Work supported by Code 1962 of David Taylor Research Center.]
Interpreting vowel “quality”: The dimension of rounding
Authors: Lisker Leigh
Published: October 2005

According to one view, speech perception depends crucially on the articulatory interpretation of the acoustic signal, since this would explain the identification of the acoustically different initial portions of two formant pseudospeech patterns such as, e.g., /di/ and /du/: Listeners “know” that their onsets are produced with very similar tongue gestures. Is this relation between perception and articulation versus acoustic signal typical, or is it instead restricted to certain phonetic units? For vowels it appears that different combinations of tongue and lip articulations yield very similar acoustic patterns and auditory qualities. The 18 “cardinal vowels” of Daniel Jones were presented to several groups of listeners asked to decide which had been produced with lip rounding. Error rates varied significantly over the vowel space, and showed a bias toward reporting front vowels as unrounded and back ones as rounded, a tendency that presumably reflects the relative frequencies across languages of front unrounded, back rounded, front rounded, and back unrounded vowels. Thus, if speech perception is crucially dependent on an articulatory interpretation of an acoustic signal, that interpretation need not be correct. [Work supported by NIH Grant HD-01994 to Haskins Laboratories.]
More support for rate-based discrimination of second formant transitions
Authors: Collins M. J. , Cullen J. K. , Porter R. J. , Jackson D. F.
Published: October 2005

Two prior studies [Besing et al., J. Acoust. Soc. Am. 81, 535 (1987); Porter et al., J. Acoust. Soc. Am. Suppl. 1 82, S81 (1987)] investigated differential thresholds for onset frequency of second formants (30-ms transitions) and for transition duration (60- and 120-ms transitions). The extent of both rising and falling (to 1800-Hz) transition was systematically varied to yield differing rates-of-change for stimuli. Transition discrimination was examined for formants isolated and in a first formant context. The question addressed was whether discrimination varied as a function of the simple stimulus dimensions of frequency and time or in relation to the more complex domain of the rate-of-change of frequency over time. Several aspects of the results supported a rate-of-change interpretation. The present study further tests that interpretation by extending observations to discrimination of onset frequency for 60- and 120-ms transitions. Results for six listeners indicate that onset-frequency discrimination of 60-ms transitions is also based on rate-of-frequency change as was the case for 30-ms transitions; discrimination of 120-ms transitions may be, in part, frequency based. In addition, rate-based discrimination appears to be nonlinear in that higher rates-of-change yield smaller difference limens relative to a reference than do lower rates-of-change. [Supported by NIH-NINCDS and the Louisiana Lions Eye Foundation.]
Rate normalization for the /ba-wa/ contrast
Authors: Eilers Rebecca E. , Oller D. Kimbrough , Burns Rebecca
Published: October 2005

A controversial hypothesis in speech perception posits an important role for rate context in determining the boundary location between /ba/ and /wa/. In general, Miller and Liberman (1979) suggest that longer formant transitions are necessary to cue /wa/ when these syllables contain long rather than short vowels while Shinn et al. (1985) suggests that boundary location is influenced by rate context only under special circumstances. The present work reexamines the rate context hypothesis using four synthetic /ba/ to /wa/ continua differing in vowel duration and four continua varying in both duration and auxiliary synthesis parameters. Adult subjects participated in several standard and nonstandard perception tasks including, identification, ABX discrimination, same-different discrimination, and VRISD, a repeating background detection task. Results indicate a small rate effect that may be largely accounted for by the shortest vowel durations. Examination of individual subject data across tasks suggests that the effect may not have important linguistic ramifications. [Work supported by NIH ♯ HD21534.]
Trading relations in intonation
Authors: McRoberts Gerald , Shankweiler Donald
Published: October 2005

Trading relations in the perception of speech have been reported both for segmental aspects of speech [Best et al., Percept. Psychophys. 29, 191–211 (1981)] and for intonation, a suprasegmental aspect of speech [Studdert-Kennedy and Hadding, Lang. Speech 16, 293–313 (1973)]. However, trading relations in speech production have not been reported. Two studies demonstrate this phenomenon in the production of intonation. In experiment 1, male speakers produced two sentences (“November” and “I did it”) both as questions and as statements. For questions, a trading relation between the peak F0 and the amount of F0 rise on the final syllable was found: As peak F0 increased, the amount of F0 rise on the final syllable decreased. This result is consistent with the findings in perception and suggests a link between the perception and production of intonation. In experiment 2, male actors produced questions and statements using the same two sentences. Peak F0 was varied in two ways: linguistically (emphatic/nonemphatic stress), or affectively (simulated happy and sad emotions). Utterance types in each condition were verified by listeners. The existence of a trading relation between peak F0 and F0 final rise for questions was confirmed for the emphatic stress condition, but not for the affective condition. This dissociation confirms indications from perceptual studies of a linguistic origin for the effect. These results demonstrate a perception-production link for linguistically relevant uses of intonation. [Work supported by NIH ♯NS-24655 and ♯HD-1994.]
Factors affecting the integration of auditory and visual information in speech: The level effect
Authors: Kuhl Patricia K. , Green Kerry P. , Meltzoff Andrew N.
Published: October 2005

The “McGurk effect” is a phenomenon in which an illusory syllable is perceived when discrepant auditory and visual information are combined. For example, an illusory /da/ is perceived when an auditory syllable /ba/ is paired with a video display of a talker saying /ga/. In a series of studies reported here, it was found that the level of the auditory signal substantially affects the illusion. Moreover, this effect of auditory level works in a direction that is counterintuitive. One might have postulated that as the level of the auditory signal is increased, making the auditory signal more pronounced, the illusion would decrease. These results indicate just the opposite. As the level of the auditory signal goes up, rather than it outweighing the visual signal and thereby decreasing the illusion, the effect is to increase the number of illusory responses. Paired were the same auditory syllable /ba/ at three levels, soft (45 dB SPL), moderate (58 dB SPL), and loud (66 dB SPL), with a video display of /ga/. Significant increases in illusory /da/ responses occurred as the auditory signal increased from soft to moderate and again from moderate to loud. The work thus shows that auditory level is an important determinant in the perception of the illusion. The paradox of the situation is that as the auditory signal increases in strength, the resulting percept becomes less veridical rather than more so. [Work supported by NIH.]
Further studies on the auditory-visual articulation index
Authors: Grant Ken W.
Published: October 2005

Previous work on the auditory-visual articulation index [Ken W. Grant, J. Acoust. Soc. Am. Suppl. 1 79, S4 (1987)] showed that filtered bands of speech with different center frequencies but roughly the same auditory intelligibility in quiet also have the same auditory-visual intelligibility. Furthermore, it was shown that these results could be fairly well predicted by articulation theory. The present study extends this work by examing the theory's ability to predict auditory-visual intelligibility for filtered bands of speech in noise as well as for various combinations of nonadjacent 1/3 octave bands in quiet. A comparison of predicted and obtained intelligibility results will be discussed for each filtered band as a function of speech-to-noise ratio. In addition, the assumption that the auditory AI obtained for each separate band can be added to predict the auditory and auditory-visual AI when the bands are combined will be tested. [Work supported by NIH.]
Choosing an appropriate technique for measuring the benefit of lipreading to speech perception in noise
Authors: Summerfield Quentin , MacLeod Alison , Field Diana , Foster John
Published: October 2005

The reliability of two procedures for measuring the benefit provided by lipreading and speech perception in noise were compared. Benefit was measured as the difference between two signal-to-noise ratios (SNRs) giving a criterion level of intelligibility against a fixed level of white noise when speech was presented: (i) in audio-alone and (ii) in audio-visual conditions. In the first technique, sentences were presented using an up-down rule to converge on the SNR giving 50% intelligibility. In the second technique, continuous speech was presented and subjects adjusted the SNR until they could “just understand every word that was spoken.” For the same duration of testing, the sentence-based procedure yielded an estimate of benefit that differed more reliably from zero and that had a greater test-retest reliability. This estimate also correlated more highly with an independent estimate of a subject's ability to lipread sentences with vision alone, probably because the sentence-based procedure places a higher premium on the use of visual cues. Overall, the sentence-based procedure is the better measurement tool, although the self-adjustment procedure may have some value in rehabilitation.
Topographic noise stripping at oblique angles over continental slopes
Authors: Del Balzo Donald R. , Head Deborah L. , Authement Mona J.
Published: October 2005

In a previous presentation [D. R. Del Balzo, M. J. Authement, and C. T. Mire, J. Acoust. Soc. Am. Suppl. 1 78, S3 (1985)], the effect of a 2.8-deg slope on the noise field generated by 100-Hz sources was discussed. The sources were located in the deep-water basin and over the shallow-water shelf. Propagation for a summer Sargasso sound-speed profile was considered for sources at various ranges from the coastline and located in the range-depth plane normal to the coastline. The presence of a noise notch, a region of relatively low noise, at shallow depths over the slope, was discovered. In this presentation, the analysis will be expanded to include seasonal effects (summer and winter sound-speed profiles), frequency dependence (30 and 100 Hz), and sources located at oblique angles out of the range-depth plane normal to the coastline. The effect of these parameters on the noise field and noise notch will be discussed.
Analysis of marginal ice zone noise events
Authors: Chen Chi-Fang
Published: October 2005

Underwater ambient noise data from MIZEX 84 were examined and transient noise events were detected and studied. Event locations were determined and their peak values used to calculate the source strength based on a simple vertical dipole model. The results indicate that the source strength is about the same order of magnitude as the strength of sources at corresponding frequency in the central Arctic. Event signatures were classified, but, in contrast to the central Arctic case, are considerably longer than their scaled counterparts. [Work supported by Office of Naval Research.]
Cavitation in lithotripsy
Authors: Carstensen Edwin L.
Published: October 2005

The pressure amplitudes of the shock waves used in lithotripsy far exceed thresholds for transient cavitation. Where appropriate nuclei exist within the body, it is highly probable that bubbles will form and collapse violently, giving rise to potentially undesirable side effects of the treatment. Evidence from basic and clinical studies in support of this conclusion is accumulating rapidly. Drosophila larvae have served as useful biological models for studies of cavitation-related phenomena because of the highly reproducible microbubbles within their respiratory system. Using approximately 100 000, 1-μs pulses from a 2-MHz piezoelectric source, the threshold for killing of larvae occurs at a pressure amplitude of ∼0.7 MPa. With an electrohydraulic (unfocused spark source) lithotripter, three positive spikes of ∼ 1 MPa are sufficient to kill roughly one-half of the exposed larvae. This is two orders of magnitude less than the largest reported pressures for clinical lithotripters.
Acoustic volume scattering in the ocean—Approaching maturity
Authors: Usciuski B. J.
Published: October 2005

Until recently, the approximations of Born and Rytov were the standard methods used to describe the intensity fluctuations that arise when a sound wave is scattered in the body of the ocean. Since these methods are valid only for very small fluctuations, it is not surprising that agreement with experiment was often very bad. Over the last few years new analytical expressions for the moments of the acoustic field, valid even for large intensity fluctuations, have been derived on the basis of the parabolic wave equation. These results have been very successful in explaining experiment observations and have also proved to be a powerful tool in furthering our understanding of fluctuation phenomena. From this point of view, acoustic volume scattering can be regarded as a problem for which some answers are now found. The expressions are for the second moment, or complex coherence, and the fourth moment, which gives the intensity fluctuation spectrum. The same forms have been derived by several independent methods and exist in the general case when a deterministic sound-speed profile leads to curved ray paths. The analytical intensity spectrum has been tested by comparison with accurate numerical solutions of the fourth moment equation and the agreement is excellent even for very strong scatter. The intensity fluctuation spectra observed in the experiments at Cobb Seamount are well described by their new fourth moment expressions, where Rytov's approximation had proved hopelessly inadequate. It is strongly recommended that small amplitude approximations, such as that of Rytov, should no longer be used to describe multiple scatter observations when the newer theory, tested and valid in these conditions, is now available.
Some memories of A. H. Benade
Authors: Li Zili
Published: October 2005

Dr. Benade was my thesis advisor after I got my candidacy for Ph.D. in May 1985 and we have worked together since then. Art's rigorous attitude toward science, profound knowledge of physics and acoustics, unique ability doing both theory and experiment, and the combination of humorous languages and pleasant personality gave me an unforgettable impression, especially for a student from China. I'll recall some of my experiences working with him, starting with my first impression of him to the last days we spent together in our laboratory.
The measurement of sound by the simultaneous use of several time constants
Authors: Nordby Svein Arne , Bohn Steiner , Peppin Richard J.
Published: October 2005

Nonstationary or transient sounds measured by a sound level meter will produce different values of sound level, depending on the time constant, or lack thereof, used. The technique of determining exposure, the so-called “doubling rate” will also result in significant differences in readings. Most investigations of the effects of the different time constants and averaging rates on nonstationary signals required several sound level meters or a predefined signal that was repeated for each different measurement method so that the differences could be compared. This paper presents the results of tests using a sound level meter that can simultaneously measure with various time constants and with several “averaging” techniques allowing the operator to measure Lmax and Lmin using “fast,” “slow,” “impulse” time constants and “peak” detection using a doubling rate of 3, 4, 5, 6, and impulse, all on the same arbitrary source.
Computational studies of the diffraction integral occurring in the MAE theory of sound propagation over hills and valleys
Authors: Kearns James A. , Zhou Ji-xun , Berthelot Yves H. , Pierce Allan D.
Published: October 2005

An important class of problems pertaining to outdoor sound propagation is that of the diffraction that occurs when the ground is neither perfectly flat nor perfectly rigid. Such problems are encountered in the study of long-range propagation of sound over hills and valleys. It has been shown previously [J. Acoust. Soc. Am. Suppl. 1 79, S30-S31 (1986)] that the theory of matched asymptotic expansions allows one to express the diffracted field in terms of a complex integral involving Airy functions of complex argument. In some limiting cases, the diffraction integral reduces to some computationally very efficient forms: an equation based on geometrical acoustics in the illuminated region, a creeping wave series in the shadow zone, and a knife-edge Fresnel diffraction integral far behind the ridge. In the present paper, the transition between these different regimes is investigated numerically by computing the general integral, and particular attention is given to the matching with the creeping waves series solution in the penumbra region. Computational results are compared with data obtained in laboratory scaled experiments. [Work supported by NASA Langley Research Center.]
An analysis of the effects of fluid loading on the vibrational modes of a submerged spherical shell
Authors: Sammelmann Gary S. , Hackman Roger H.
Published: October 2005

Previous analyses of the acoustic scattering from submerged, spherical elastic shells have relied on the subtraction of a “suitably defined” background contribution to isolate scattering resonances of the shell. Unfortunately, there is no universal agreement as to what constitutes a suitable background. In the present work, the acoustic scattering amplitude is analytically continued into the complex-k plane and the poles of this amplitude are directly located using a form of Cauchy's theorem. This procedure alleviates any difficulties associated with a background choice. Dispersion curves are generated for shells with thicknesses ranging from 2% to 50% of the outer radius of the shell. This work verifies the bifurcation of the first symmetric mode of a spherical shell reported earlier [L. H. Green, R. H. Hackman, D. H. Trivett, and L. Flax, J. Acoust. Soc. Am. Suppl. 1 76, S65 (1984)], although the details of the bifurcation differ considerably. Our results call into question the whole concept of the separation of poles into background and elastic categories.
Model calculations of self- and external-tone interactions of otoacoustic emissions
Authors: Sivaramakrishnan Savithri , Long Glenis R. , Tubis Arnold
Published: October 2005

Several different forms of nonlinear, active, cochlear models are used to simulate some of the effects of interactions among spontaneous otoacoustic emissions in the same ear [E. M. Burns, E. A. Strickland, A. Tubis, and K. Jones, Hear. Res. 16, 271–278 (1984)] and interactions of emissions with external tones. The former include mutual suppression, and intermodulation distortion products, while the latter include the suppression, frequency shifting, and frequency locking of spontaneous emissions, and the latencies of click and tone-burst evoked emissions. [Work supported by NIH Grant No. NS22095.]
The numerical approach to understanding rough surface scattering
Authors: Thorsos Eric I.
Published: October 2005

Numerical methods for solving simplified rough surface scattering problems “exactly” provide new insights into the rough surface scattering problem. Exact solutions for 1-D surfaces with the pressure release (Dirichlet) boundary condition are found with integral equation and Monte Carlo techniques. These studies provide a better understanding of the validity of the two basic approximations used in rough surface scattering: the Kirchhoff approximation and first-order perturbation theory. From this work, a resolution can be given for the difference in the Kirchhoff and first-order perturbation theory predictions at small surface heights and at very small surface slopes, where both approximations have generally been considered valid. Studies with the Kirchhoff approximation show that shadowing corrections based on geometric optics lead to inaccurate predictions. This work indicates the need for tractable multiple scattering theory for low grazing angle applications. Comparisons with exact results show that “phase perturbation” theory predictions account for a significant part of the multiple scattering associated with shadowing. In addition to better understanding theory with numerical techniques, the accuracy of approximate numerical methods can also be examined. Attempts are now being made to include rough surface scattering in marching solutions of the parabolic wave equation (PE). Methods of verifying the accuracy of marching solutions using exact and PE integral equations will be briefly discussed.
A tutorial review of the role of scattering theory in detection and estimation of sonar signals
Authors: Baggeroer Arthur B. , Ewart T. , McCoy John
Published: October 2005

There are many theories that describe time and Doppler spreads, coherences and intensities, and higher-order probability densities of scattered signals. The sonar signal processor concerned with detection and estimation applications must use parts of these theories to design systems and analyze their performance. This talk will give a tutorial review of how scattering theories are used by the sonar signal processor.
Edge effects on frequency discrimination of tones presented in low- and high-pass noise backgrounds
Authors: Fantini Deborah A. , Emmerich David S.
Published: October 2005

Previous research has indicated that frequency discrimination performance is poorer for tones presented near the sharp spectral edge of a low-pass noise than for tones presented near the edge of a high-pass noise, or for tones in the same low-pass noise with high-pass noise added [Emmerich et al., J. Acoust. Soc. Am. 80, 1668–1672 (1986)]. The present study extends these findings in order to investigate how the steepness of the spectral edges of low- and high-pass maskers influences the discriminability of tones presented near these edges. Frequency discrimination was measured in each of three high- and low-pass noise backgrounds (which differed in the steepness of their filter skirts). The following results were obtained: (1) In the low-pass noise background, frequency discrimination performance improved as the filter skirt became more gradual; (2) in the high-pass noise background, performance first improved and then became poorer as the filter skirt became shallower; and (3) performance in low-pass noise was poorer than that in high-pass noise for the two steepest slopes employed (96 and 72 dB/oct) but not for the shallower slope (36 dB/oct). Results are discussed in the context of lateral suppression and edge pitch effects, and of a trade-off between possible edge effects and masking.
Signal detection analyses of delays in neonates’ vocalizations
Authors: Gray Lincoln
Published: October 2005

Signal detection analyses were applied to momentary delays in the regular peeping of newborn chicks that occur in response to acoustic stimuli. Pulsing 1000-Hz tones at various intensities were repeatedly presented to chicks at 0 and 4 days posthatch. Durations of delays on both stimulus and control (mock) trials were collected in histograms. These histograms were then used to draw receiver operating characteristics (ROC curves) given variable definitions of what constitutes a ‘‘yes’’ response. Areas under these ROC curves were used to evaluate various ways of measuring the delay, as well as the effects of habituation, intensity, and age. Time to the second poststimulus peep was identified as a sensitive indicator of responsiveness. Habituation decreased responsiveness by about 5% per trial over the first three trials. Each dB of intensity increased responsiveness by about 1%. Maturation increased responsiveness by about 21 dB over 4 days. These ROC curves show that momentary delays in the vocalizations of newborn chickens are appropriate measures of auditory signal detection. Similar analyses could be useful in other psychophysical studies that depend on the changing rate of repetitive responses.
Comodulation masking release in a forward-masking paradigm
Authors: McFadden Dennis , Wright Beverly A.
Published: October 2005

Waveforms that yield comodulation masking release (CMR) when they are presented simultaneously with a signal were used in a standard forward-masking procedure. The signal was a 25-ms sample of a 2500-Hz tone. The masker was a band of noise centered at 2500 Hz, 100 Hz in width, and 200 ms in duration. Presented with the masker were two or four cue bands, each 100 Hz wide and centered at various distances from the masker band. These cue bands either all had the same temporal envelope as the masker band (correlated condition) or their common envelope was different from that of the masker band (uncorrelated condition). In the initial experiments, (1) detectability of the tonal signal was 7–18 dB better when the masker band was accompanied by cue bands than when it was not—an effect that would be expected from past research on lateral suppression—but further, (2) the signal was about 3 dB more detectable in the correlated conditions than in the uncorrelated conditions. In follow-up experiments, these CMR-like differences between the correlated and uncorrelated conditions were substantially reduced (although not eliminated) by presenting a contralateral, wideband noise that was gated synchronously with the masker and/or cue bands. The implications are that the initial results were attributable in part to the ‘‘confusion effects’’ known to exist in certain temporal-masking situations, and that listeners are able to obtain greater information about the temporal extent of a masker band from correlated cue bands than from uncorrelated bands. It is suggested that the small CMR-like difference that did remain in the face of controls for confusion may be attributable to a form of dynamic lateral suppression, where the magnitude of suppression covaries perfectly with the magnitude of the envelope of the narrow-band masker. It appears, then, that no explanations beyond confusion and lateral suppression are necessary to account for the reported CMR-like effects in forward masking.
Electrokinetic model of cochlear hair cell motility
Authors: Jen David H. , Steele Charles R.
Published: October 2005

Recent experiments have shown that isolated outer hair cells of the cochlea can vibrate under the influence of a transcellular oscillating electric field. Since high voltages have been measured in the cochlea, this result might suggest a basis for electromechanical feedback. A mechanical model of the hair cell has been developed and adapted to test the electrokinetic theory of motility, a postulate of which is that cochlear voltage gradients act on charged proteins embedded in the cell membrane to deform the cell. From the model it was deduced that the amount of charge density required is within the physiologic range. The significant result is that the amplitude of cell elongation for a fixed voltage amplitude is virtually constant for frequency less than a certain cutoff. The value of this frequency depends on the various physical parameters of the system and especially on the spacing between cells. Power transfer to the basilar membrane appears to peak near the cutoff frequency, and the amount is not very dependent on cell length, but is highly dependent on cell spacing.
A new method of directivity synthesis
Authors: Lan Jun
Published: October 2005

A completely new synthesis method, called the successive approximation method, is developed in this article. By introducing a control function and using a step-by-step approach program, various directivity functions can be obtained in which the envelope of the peaks of the sidelobes fits with a specified curve, with equisidelobe directivity functions, and with the directivity functions corresponding to the maximum directivity factor for specified sidelobe levels. This method is applicable for various forms of arrays and can be used with amplitude shading, phase shading, and unequally spaced arrays. Numerical calculations have been made for linear arrays to permit study of the directivity functions with the maximum directivity factor for specified sidelobe levels. Then, these directivity functions are compared with equisidelobe directivity functions. Calculations show that, when specified sidelobe level is low enough, the directivity function with the maximum directivity factor is just the equisidelobe directivity function.
Composite-roughness theory applied to scattering from fetch-limited seas
Authors: McDaniel Suzanne T. , McCammon Diana F.
Published: October 2005

The prediction of surface scattering strength using composite-roughness theory requires a detailed knowledge of the ocean wave spectrum. While extensive research in the past has produced a good empirical representation of the wavenumber spectrum of a fully developed sea, only recently have the spectra of fetch-limited seas been examined. A fetch-limited sea spectrum is similar in most respects to a spectrum at reduced windspeed except that a small region of ‘‘overshoot’’ occurs on the high-frequency side of the swell peak. Scattering strength computations show that the fetch-limited condition has an effect only on the near-specular returns where values can be 2–10 dB higher than those for a fully developed sea. Computations with composite-roughness theory including the Fresnel phase approximation and source beam patterns are also made. Comparisons are shown with surface scattering data in both monostatic backscattering and bistatic forward scattering geometries.
Effects of spectral flattening on vowel identification
Authors: Dubno Judy R. , Dorman Michael F.
Published: October 2005

The identification of front vowels was studied in normal-hearing listeners using stimuli whose spectra had been altered to approximate the spectrum of vowels processed by auditory filters similar to those that might accompany sensorineural hearing loss. In the first experiment, front vowels were identified with greater than 95% accuracy when the first formant was specified in a normal manner and the higher frequency formants were represented by a broad, flat spectral plateau ranging from approximately 1600 to 3500 Hz. In the second experiment, the bandwidth of the first formant was systematically widened for stimuli with already flattened higher frequency formants. Normal vowel identification was preserved until the first formant was widened to six times its normal bandwidth. These results may account for the coexistence of abnormal vowel masking patterns (indicating flattened auditory spectra) and normal vowel recognition.
Temporal factors in the discrimination of tonal sequences
Authors: Sorkin Robert D.
Published: October 2005

Human observers were asked to judge whether or not two sequences of eight or more tones had the same serial pattern of frequencies. The temporal envelopes of the sequences were manipulated by randomly varying the tone durations or intertone gaps. In the correlated condition, the temporal envelopes of the sequences were varied across trials; the two sequences within each trial had the same temporal envelope. In the uncorrelated condition, the temporal envelopes were varied both across and within trials; every sequence had a unique temporal pattern. Performance in the uncorrelated condition decreased with increased variability in the temporal envelope. Performance in the correlated condition was independent of temporal variability, but decreased with increases in the time interval between the onsets of the two sequences. This pattern of results is consistent with an extension of a model of auditory discrimination developed by Durlach and Braida [J. Acoust. Soc. Am. 46, 372–383 (1969)], in which two processing modes are postulated: a trace mode and a context mode. When the tonal sequences had unique temporal patterns, context mode processing was dominant; when the sequences had identical temporal patterns, trace mode processing was preferred. The effect of variables such as the number of tones, the tone duration, the time gap between tones, and the time interval between sequences was consistent with the predictions of the discrimination model.
Principal-component amplitude compression for the hearing impaired
Authors: Bustamante Diane K. , Braida Louis D.
Published: October 2005

Principal-component amplitude compression, a means for matching speech to the reduced dynamic range in sensorineural hearing impairments, is a multiband approach aimed at preserving details of spectral shape while reducing overall level variation. The effect of compression has been studied for the first and second principal components (PC1 an PC2) of the short-term speech spectrum, which are roughly representative of overall level and spectral tilt, respectively. Compression of PC1 roughly equalizes consonant and vowel levels while compression of PC2 provides time-varying high-frequency emphasis. The effect on speech intelligibility of sensorineural hearing-impaired listeners of two principal-component compression system implementations, compression of PC1 and compression of both PC1 and PC2, was compared to that of linear amplification (LA), independent compression of multiple bands (MBC), and wideband compression (WC). Results indicate that compression of overall level as provided by compression of PC1 and WC improved intelligibility relative to LA over a 10- to 15-dB range of input levels. While MBC was beneficial in some cases, it did not provide higher intelligibility than WC. Compression of PC2 did not benefit but rather degraded performance relative to LA. Error analyses and band-level measurements indicate that the highest intelligibility is obtained when audibility is improved and the relative spectral shapes of different speech sounds are preserved.
Inverse acoustic scattering from an elastic sphere
Authors: Ayres V. M. , Gaunaurd G. C.
Published: October 2005

A technique is presented to determine the material properties of elastic spheres using the resonance features present in their backscattering cross sections. The method is based on an asymptotic solution of the elastodynamic equations governing the sphere’s response in the high-frequency (x≡k1a≫1) regime. Our study shows that the modal resonances that an elastic sphere communicates to its echo fall into two distinct families. The set of broader resonances is the dilatational family. The narrower set is the shear family. They are both present in all the modes (n>0) contained within the sonar cross section except for the n=0 mode that contains only broad resonances. Both sets of resonances are separated by spacings that asymptotically (x≫1) tend to uniform values that we have respectively called Δ and Δ′. The dilatational and shear wave speeds in the elastic sphere are shown to be respectively proportional to these spacings, so that the two wave speeds can be immediately determined from them. The sphere’s density is found from the width of any high-order (i.e., l≫1) dilatational overtone of any mode n. The elastic constants of the sphere (i.e., λ2 and μ2) can be determined immediately from the knowledge of cs2, cd2, and ρ2. Hence, determination of the two spacings Δ, Δ′ and of the width Γnl of any single dilatational overtone uniquely determines the complete material composition of the sphere. The method works best for metallic substances. The detailed numerical calculations that are displayed illustrate the simplicity with which the sphere’s complete elastic composition can be extracted from four resonance peaks in its returned acoustic echo.
Classification of resonances in the scattering from submerged spheroidal shells insonified at arbitrary angles of incidence
Authors: Werby M. F. , Gaunaurd G.
Published: October 2005

A numerical study is presented for plane-wave scattering from thin steel spheroidal shells in the frequency region corresponding to the onset of resonances. Arbitrary incidence angles are allowed for, in order to analyze the possible aspect-angle dependence of resonances. Both monostatic angular distributions and backscattered echoes are examined as a function of the nondimensionalized quantity kL/2, where the wavenumber k is 2π/λ and L is the length of the spheroid. Shell thickness is chosen to be very thin so that the physical mechanisms involved in the process can be isolated. In the analysis and in the absence of a resonance, only ‘‘background’’ effects associated with soft-body scattering are observed (due to the very small thickness of the shell), while a characteristic coherent effect is observed in the resonance region. Analysis of the exact theoretical predictions leads to the conclusion that elastic resonances for these objects correspond to modal, vibrational, surface standing waves at discrete frequencies with a relatively fixed phase velocity. Moreover, the surface standing-wave interpretation leads to simple semiphenomenological expressions that can reliably predict the resonance locations. Furthermore, the study leads to the conclusion that only two modes of vibration are allowed, namely those along the axis of symmetry and those perpendicular to it. Thus only two classes (or modes) of resonances exist, corresponding to surface standing waves along and perpendicular to the spheroid’s axis of symmetry. This property can be exploited to elicit geometrical (and to some extent material) characteristics of the object from its echo, in particular, its length-to-diameter or aspect ratio L/D.
Nonlinear and non-Gaussian ocean noise
Authors: Brockett Patrick L. , Hinich Melvin , Wilson Gary R.
Published: October 2005

Bispectral analysis is a statistical tool for detecting and identifying a nonlinear stochastic signal-generating mechanism from data containing its output. Bispectral analysis can also be employed to investigate whether the observed data record is consistent with the hypothesis that the underlying stochastic process has Gaussian distribution. From estimates of bispectra of several records of ambient acoustic ocean noise, a newly developed statistical method for testing whether the noise has a Gaussian distribution, and whether it contains evidence of nonlinearity in the underlying mechanisms generating the observed noise is applied. Seven acoustic records from three environments are examined: the Atlantic south of Bermuda, the northeast Pacific, and the Indian Ocean. The collection of time series represents both ambient acoustic noise (no local shipping) and noise dominated by local shipping. The three ambient records appeared to be both linear and Gaussian processes when examined over a period on the order of a minute, but were found to be nonlinear and non-Gaussian when examined over shorter time periods on the order of a second. In each case the time series dominated by local shipping noise tested to be nonlinear and non-Gaussian over both short and long time periods.
Review of text-to-speech conversion for English
Authors: Klatt Dennis H.
Published: October 2005

The automatic conversion of English text to synthetic speech is presently being performed, remarkably well, by a number of laboratory systems and commercial devices. Progress in this area has been made possible by advances in linguistic theory, acoustic–phonetic characterization of English sound patterns, perceptual psychology, mathematical modeling of speech production, structured programming, and computer hardware design. This review traces the early work on the development of speech synthesizers, discovery of minimal acoustic cues for phonetic contrasts, evolution of phonemic rule programs, incorporation of prosodic rules, and formulation of techniques for text analysis. Examples of rules are used liberally to illustrate the state of the art. Many of the examples are taken from Klattalk, a text-to-speech system developed by the author. A number of scientific problems are identified that prevent current systems from achieving the goal of completely human-sounding speech. While the emphasis is on rule programs that drive a formant synthesizer, alternatives such as articulatory synthesis and waveform concatenation are also reviewed. An extensive bibliography has been assembled to show both the breadth of synthesis activity and the wealth of phenomena covered by rules in the best of these programs. A recording of selected examples of the historical development of synthetic speech, enclosed as a 33  (1)/(3) - rpm record, is described in the Appendix.
Acoustic comparison of soprano solo and choir singing
Authors: Rossing Thomas D. , Sundberg Johan , Ternström Sten
Published: October 2005

Five soprano singers were recorded while singing similar texts in both choir and solo modes of performance. A comparison of long-term-average spectra of similar passages in both modes indicates that subjects used different tactics to achieve somewhat higher concentrations of energy in the 2- to 4-kHz range when singing in the solo mode. It is likely that this effect resulted, at least in part, from a slight change of the voice source from choir to solo singing. The subjects used slightly more vibrato when singing in the solo mode.
Transient sound radiation from a clamped circular plate with viscoelastic layers
Authors: Jeon Jae-Jin , Lee Byung-Ho
Published: October 2005

In this article, the transient sound radiation from a clamped circular plate with a viscoelastic layer excited by impact is studied analytically and experimentally. The composite plate vibrations are obtained by using the normal mode analysis and the eigenvalues are obtained by a Mindlin plate theory, including the rotary inertia and shear deformation. In impact, the contact force developed between the ball and the plate with attached layers is obtained by Hertz contact theory. The radiated sound pressure in the farfield is calculated by the Rayleigh integral. Prediction of the waveforms of sound radiating from the plate with attached layers and a method for reducing noise generation from the plate by impact force are also shown in this article. The analytical results can be applicable to multilayered plate and noncentral impacted cases. Using the results of this article, the thickness of an attached viscoelastic layer to reduce the noise to the desired level can be decided.
Fish target strengths for use in echo integrator surveys
Authors: Foote Kenneth G.
Published: October 2005

I n situ measurements of fish target strength are selected for use in echo integrator surveys at 38 kHz. The results are expressed through equations in which the mean target strength TS is regressed on the mean fish length l in centimeters. For physoclists, TS=20 log l−67.4, and for clupeoids, TS=20 log l−71.9. These equations are supported by independent measurements on tethered, caged, and freely aggregating fish and by theoretical computations based on the swimbladder form. Causes of data variability are attributed to differences in species, behavior, and, possibly, swimbladder state.