bluuebunny/crossref_metadata_2025 huggingface dataset:
A system to monitor the noise exposure of persons wearing headsets
Authors: Van Moorhem W. K. , Woo K. S.
Published: October 2005

Although legislation limiting noise exposure in the work place applies to individuals who wear headsets as part of their employment, no method for measuring the noise exposure of these individuals has previously existed. A system for carrying out this measurement has been developed. This system is indirect, in that the electrical signal to the headset is measured, the transfer function of the headset, ear, and dosimeter microphone is applied to the measured signal, and the resulting electrical signal input to a dosimeter. This approach requires the transfer function of the headset be measured for each brand and model that is used, but eliminates the need for in-ear microphones of the more direct approach. The transfer function of the headset is measured using an acoustic manikin head. A limited number of headsets brands and models have been used with this system to investigate both the variations between models and within a model. [Work supported by Department of Labor.]
Reverberation and noise propagation measurements in a power plant
Authors: Brittain Frank H. , Passage Ralph W.
Published: October 2005

The acoustical characteristics of empty spaces are relatively well known. An understanding of room acoustics is important both for designing spaces and for controlling noise from equipment in enclosed spaces. Power plants and similar industrial plants pose a challenge because their spaces are not only very large, but also “full” of equipment. These spaces contain a high concentration of rotating equipment, piping, structural steel, cable trays, gratings, and tanks. Measurements of reverberation time and noise propagation were made in a power plant. The equipment in these spaces changes the acoustical characteristics of the spaces. These measurements show that sound absorption properties of the spaces are greater than are expected from published sound absorption data and theories of room acoustics. Implications of the results for noise control of power and other industrial plants are discussed.
Excitation of surface mode activity of bubbles in ultrasonic fields
Authors: Gould Robert K.
Published: October 2005

When a gaseous bubble finds itself in a liquid in which an ultrasonic field exists, the bubble may undergo radial, orderly surface mode or chaotic surface oscillations depending on the size of the bubble, strength of the sound field, and other parameters such as viscosity of the liquid and frequency of the sound. In the event of purely radial oscillations there is little acoustic streaming in the vicinity of the bubble. However, when bubble surface activity is present, vigorous streaming will occur near the bubble. Experimental studies of a bubble levitated in a 20-kHz standing-wave sound field in a chamber of water have included the obtaining of stroboscopic movies of bubbles undergoing orderly surface modal vibrations of orders 2, 3, and 4, there being no existence of mode 1. The frequency of the surface oscillations is half that of the sound field. Movies of modal oscillations 2, 3, and 4 will be shown. Movies of mode 4 were obtained for the first time this year by George E. Lawrence, while carrying out his senior thesis research.
The threshold of thermally significant cavitation in muscle in vivo
Authors: Hynynen Kullervo
Published: October 2005

The transient cavitation threshold was measured by dogs' thigh muscles in vivo during a 1-s exposure to continuous or pulsed ultrasound at frequencies between 0.25 and 1.68 MHz. The temperature elevation at the focal zone at the depth of 5 cm in the tissues was measured during the sound pulse using a twisted pair thermocouple (wire diameter 50 μm). A focused hydrophone was also used to sense the subharmonic emission from the focal zone. At each thermocouple location the pulses were repeated with increasing applied acoustic power until the temperature elevation became irregular with sudden temperature peaks during the 1-s Pulse and with an appearance of subharmonic emission of noise. Similar events were also observed at higher intensities during low-duty cycle pulses, although not with pulses including only 1 or 2 cycles. These results indicate that transient cavitation can appear at intensities that could be reached during clinical scanned focused ultrasound hyperthermia (400–500 Wcn−2 at 1 MHz) and thus can significantly modify the temperature distribution and the biological effects of the treatment. [Work supported by NCI Grant No. CA 46627.]
Estimation of mean scatterer size from sparse, random distributions of polystyrene spheres in solution via Mie scattering and cepstral signal processing: Theory and experimental results
Authors: Meyer C. R. , Fowlkes J. B. , Carson P. L. , Wang H. , Chan H.
Published: October 2005

Four solutions of narrowly distributed polystyrene spheres of one diameter, either 41, 136, 271, or 381 μm, sparsely suspended in degassed water, were imaged using multiple 5- and 7.5-MHz medical ultrasonic transducers. Radio-frequency backscattering data from the 136-, 271-, and 381-μm solutions were processed using the data from the 41-μm solution as a volumetric reference to correct for transducer diffraction effects and acquisition system gain vibrations. The power cepstrum of the mean log difference spectra averaged over all overlapping data segments was computed and corrected for the effects of attenuation and Rayleigh scattering in the reference. Abcissas of the cepstral peaks were plotted versus scatterer diameter. The zero-intercept, linear regression line for the longer-lag peaks yielded a slope of 3.4 μs/mm, r2 = 0.997, corresponding to a Mie-region periodicity in backscattered cross section of ka = 0.6. This value is in excellent agreement with calculations based on the scattering theory of Faran, which includes shear waves and yields a periodicity of ka = 0.66.
Thresholds for surface wave generation on acoustically levitated gas bubbles
Authors: Horsburgh Steve , Holt R. Glynn , Crum Lawrence A.
Published: October 2005

When a gas bubble is acoustically levitated in a standing wave, the spherically symmetric volume oscillations can readily couple into surface waves [M. Strasberg and T. B. Benjamin, J. Acoust. Soc. Am. 30, 697 (1958)]. Using a light scattering technique, the threshold for inception of individual surface waves was examined and the results were compared with both analytical and numerical calculations of this threshold. The observed and calculated values are generally in agreement although the identity of the surface wave mode is difficult to determine. [Work supported in part by the Office of Naval Research.]
The application of Hamilton's principle to a bubbly liquid
Authors: Hawkins J. A. , Bedford A.
Published: October 2005

Naturally occurring bubble populations have a distribution of bubble sizes. Well-established continuum theories exist for the propagation of acoustic waves through a bubbly liquid with a single bubble size. The application of these theories to bubbly liquids with several sizes is necessarily limited. Here two approaches are described based on Hamilton's principle for analyzing the acoustics of bubbly liquids containing a distribution of bubble sizes. First, the mixture is treated as a liquid containing a bubble “continua” of several discrete sizes. The analysis leads to N + 2 (N is the number of different bubble sizes) simultaneous equations in the motion, density, and volume fraction, which must be solved numerically. The system was solved for one, two, three, and five different bubble sizes. The second approach is to assume that a continuous distribution of bubble sizes exists in the liquid. Surprisingly, the second approach leads to a relatively simple expression for the wavenumber. It was shown that the phase velocity and the attenuation of acoustic waves can be determined for an arbitrary distribution of bubble sizes. The two approaches are shown to agree in the limiting case of discrete bubble sizes and to agree with the result obtained by Commander and Prosperetti [K. W. Commander and A. Prosperetti, J. Acoust. Soc. Am. 85, 732–746 (1989)]. [Work supported by ONR, IR&D Program of ARL:UT.]
On the passive power absorption potential of the eardrum
Authors: Rabbitt R. D.
Published: October 2005

Experimental evidence reported by Khanna [Int. Cong. Acoust. B6-4, Toronto (1986)] and Allen [Peripheral Auditory Mechanisms (Springer, New York, 1985), pp. 46–51] suggests that a very large fraction of the incident acoustic power in the cat ear canal is absorbed at the eardrum. In some animals, the high efficiency extends over a very wide frequency range from 300 Hz–30 kHz. These findings are sensitive to the condition of the animal and are subject to relatively large interanimal variations, particularly at high frequencies. Theoretical models describing the function of the middle ear differ significantly in predicting the power absorption and in predicting the fraction of the energy flux dissipated within the eardrum itself. Some insight into the behavior of the eardrum can be gained by studying the power absorption properties when the ossicular chain is immobilized or removed. In doing so, the dynamics of the ossicular chain, and to a large extent the dynamics of the cochlea, is removed from the system, leaving the eardrum coupled to the acoustics in the ear canal and in the tympanic cavity. The power absorption potential of the eardrum for several internal dissipation mechanisms is investigated using three-dimensional representations of the eardrum, ear-canal acoustics, and middle-ear acoustics. Results imply that the acoustic behavior of the middle-ear air chamber(s) has a profound influence on energy transmission and absorption potential of the eardrum.
Impedance measurements in the ear canal
Authors: Puria Sunil , Allen Jont B.
Published: October 2005

The objective of the present work is to make accurate impedance estimates at the eardrum Ztm (ω). This is done by measuring the thevenin parameters of an earphone using a four-cavity calibration method [J. B. Allen, “Measurement of eardrum acoustic impedance,” in Peripheral Auditory Mechanisms, edited by J. B. Allen et al. (1985)] for frequencies up to 15 kHz. The calibrated earphone is then used to measure the ear canal impedance Ze (ω) near the ear canal entrance. To transform Ze to Ztm, the ear canal cavity has been modeled. The following effects were accounted for by the model: (a) the jump in area from the earphone calibration cavity to that of the ear canal, (b) the distance to the eardrum, (c) variations in cross-sectional ear canal area, and (d) effects due to ear canal wall impedances. It is desirable that parameters of the ear canal be derivable from Ze. Preliminary results isolating each of these effects first in tubes and then in real ear canals are presented.
Influence of insertion depth of an insert earphone on hearing threshold levels and on real ear attenuation values
Authors: Lindgren Fredrik , Berger Elliott H.
Published: October 2005

The influence on pure-tone hearing threshold levels (HTLs) of the insertion depth of the coupling foam eartip of EARTONE™ 3A insert audiometric earphones was investigated in 16 subjects using three distinctly different insertion depths: shallow, intermediate, and full. HTLs were also measured using conventional earphones, model TDH-50P with MX/41-AR cushions. In addition, sound field real ear at threshold (REAT) values re: ANSI S12.6-1984 were recorded in each condition. The results showed that there was a tendency toward poorer HTLs as the eartip was positioned further away from the eardrum, with the difference between the three widely disparate insertion depths amounting to 1.3–5.3 dB in the frequency range 0.5–6 kHz. In contrast, at 8 kHz, significantly less (8.1 dB) energy was required for elicitation of threshold response in the shallow position as compared to the two other. However, no statistically significant differences were found between the most appropriate (full and intermediate) insertion depths at any tested frequency. Although REAT values showed increased attenuation for the frequencies 0.125–1 kHz as the eartip was inserted more deeply in the ear canal, at all three insertion depths over all tested frequencies, values were more than 15 dB greater than the attenuation obtained with the conventional earphone.
Distortion product emissions as predictors of frequency-specific auditory thresholds
Authors: Kimberley Barry P. , Nelson David A.
Published: October 2005

Distortion product emission (DPE) input-output functions were measured at seven frequency regions, covering a range from 700–6000 Hz, for each of 50 ears. Auditory thresholds at each frequency region were determined using adaptive, forced-choice psychophysical techniques. One-half of the subjects had auditory thresholds less than 25 dB HL at every frequency. One-half of the subjects had a variety of patterns of pure sensorineural loss. The stimulus level required to just raise an emission above the noise floor is a feature that can be measured directly from a DPE input-output function. This feature is called “emission threshold.” When frequency-specific auditory thresholds were compared with corresponding emission thresholds, a close correlation was found over a range of auditory thresholds from − 6 to + 55 dB SPL. A linear regression between auditory and emission threshold has a slope of 1.0 and a regression coefficient of 0.86. However because emission threshold does not grow as quickly as auditory threshold at high threshold values, a better correlation of 0.9 is obtained by allowing a cubic nonlinear fit. Emission thresholds correlated with auditory thresholds in a similar way at each frequency region. Thus DPE measurements appear to be well correlated with frequency-specific auditory thresholds. This finding suggests an enhanced clinical value of DPE measurement. DPE measures appear able to predict frequency-specific sensory thresholds with reasonable accuracy over a moderate range sensory thresholds. [Work supported by American Otologic Society.]
Spontaneous otoacoustic emissions: Evidence for a cricadian rhythm of frequency variation
Authors: Haggerty Holly S.
Published: October 2005

An investigation of the hour-by-hour frequency stability of spontaneous otocacoustic emissions was conducted over a 24-h period. Two emissions were recorded from each of two audiometrically normal adults. Time series analysis was used to model the autocorrelation structure of the measurements, to resolve each 24-h series of measurements into cyclical components of various periodicities, and to test the statistical significance of given cycles within the spectrum of each series. Results showed a significant 24-h cycle for all emissions, suggesting a circadian rhythm of frequency fluctuation. [Work supported by the Knowles Research Foundation.]
Parameter estimation for a resonant tectorial membrane cochlear model
Authors: Allen J. B.
Published: October 2005

One of the basic problems of cochlear modeling is in systematically determining the parameters of the model from neural data. Frequency domain models give the response along the basilar membrane for pure-tone inputs, whereas the data that are desirable to match are families of tuning curves as a function of frequency for many positions along the basilar membrane. This computational problem has been sidestepped by transforming the neural tuning curve data to place, forming neural excitation patterns. This allows for a major simplification of the data fitting process. If the neural data are accurately fit in the place domain for several well-separated frequencies, then the frequency tuning data should fit as well. Using this approach, fits to neural tuning curves using passive cochlear models were greatly improved over the entire range of CFs. The model assumptions will be discussed and the results will be compared to measured data.
The effect of induced round window fistula on the SP/AP amplitude ratio
Authors: Campbell Kathleen C. M. , Savage Michael M. , Harker Lee A.
Published: October 2005

The ratio of the summering potential (SP) and action potential (AP) amplitudes was studied in 19 guinea pigs before and after surgical induction of a round window fistula. Stimuli included 2000- and 8000-Hz tone bursts and click stimuli at intensity levels of 100, 90, and 80 dB SPL. The following p values are for the 90-dB SPL level, but results were similar for all three intensity levels. After fistula induction, the SP/AP ratio enlarged in response to the 8000-Hz tone-burst (p < 0.0076) and click stimuli (p < 0.0001), but not for the 2000-Hz tone-burst stimuli (p < 0.5627). Analyzed separately, the SP significantly enlarged after fistula induction for clicks (p < 0.0001) and 8000-Hz tone bursts (p < 0.0006) but not for the 2000-Hz tone bursts (p < 0.5110). The AP enlarged slightly after fistula induction in response to the clicks (p < 0.0052) but not in response to the 8000-Hz (p < 0.1780) or the 2000-Hz (p < 0.1723) tone bursts. These results suggest that the SP/AP amplitude ratio may be sensitive to the presence of perilymphatic fistula with selected stimuli.
Cyclic temporal pattern perception and neuronal adaptation
Authors: Robin Donald A. , Abbas Paul J. , Hug Linda N.
Published: October 2005

Sets of regularly repeating auditory stimuli elicit unique perceptions; listeners are able to identify specific temporal patterns. Some temporal patterns are unambiguous (only one pattern can be perceived), while others are ambiguous (numerous patterns can be detected). While the psychophysical properties of such percepts have been well studied, little is known about the underlying neurological bases of temporal pattern perception. In this experiment, the role of adaptation in temporal pattern perception was examined by studying neural responses in four cats to a temporal pattern that is perceptually unambiguous and one that is perceptually ambiguous. Measurements were made of the whole-nerve action potential, the auditory brain-stem response, and potentials from the surface of the primary auditory cortex. The adaptation patterns corresponded with the perceptual organization of temporal patterns in humans at all levels of the nervous system studied.
Functional organization of normal human auditory central nervous systems observed with multiple noninvasive techniques: Year one of the CNS project
Authors: Lauter Judith L.
Published: October 2005

The coordinated noninvasive studies (CNS) project is designed to bring together a variety of noninvasive methods for studying living brains in order to demonstrate the feasibility of a “human neuroscience” paradigm based On a combination of behavioral testing with noninvasive neuroanatomical and neurophysiological examinations of the same individuals. Initial project focus is on brain asymmetries related to complex-sound processing. Preliminary results on subjects studied to date will be presented, documenting: (1) behavioral asymmetries expressed in terms of relative ear advantages, (2) individual differences in anatomical (MRI) asymmetries, (3) patterns of physiological “resting asymmetries,” and processing asymmetries observed during auditory stimulation (qEEG, PET), (4) the degree of within-subject consistency of asymmetry direction and magnitude observed with several noninvasive methods (MRI, EPs, qEEG, etc.), and (5) the coincidence of auditory-system asymmetry descriptions based on behavioral versus neuroanatomico-physiological measurements. [Work supported by AFOSR.]
Perception of sequenced pitch and duration changes by patients with frontoparietal lesions
Authors: Colson Karen A. , Robin Donald A. , Luschei Erich S.
Published: October 2005

Current evidence suggests that auditory processing of nonlinguistic pitch and timing features may be differentially impaired following focal, unilateral cortical insult. Three experiments were conducted to examine the ability of patients with well-defined, left, frontoparietal lesions and normal, matched controls to perceive relative pitch and/or duration changes in tonal sequences. Performance patterns for two right frontoparietal patients also were examined. Subjects identified whether or not any tone in a three-tone sequence was higher in pitch and/or longer than the other tones. Compared to the controls, the left anterior group typically required a significantly larger difference (e.g., Hz and/or ms) between the standard and comparison tones to accurately identify relative changes in pitch, duration, and pitch and duration combined. The right frontoparietal patients performed the three tasks at a level similar to that of the normal controls. Based on the findings, the perception tasks seem to involve a complex interaction between temporal and spectral features and appear to be sensitive for detecting left, anterior patients' difficulties with these aspects of auditory processing.
Acoustics and synthesis of fricative consonants
Authors: Stevens Kenneth N.
Published: October 2005

This paper attempts to integrate some recent research of Dennis Klatt on the analysis and synthesis of fricative consonants with further experimental and theoretical studies of fricative production. The speech production studies examine data on airflows and pressures during voiced and voiceless fricatives, and estimate from these data the time variation of the areas of the glottal and supraglottal constrictions and the spectra of the sound sources at these constrictions. These calculations are based on theoretical and experimental data on airflow in constricted tubes and on sound generation in turbulent flow. Acoustic spectra in a number of utterances containing fricatives in various vowel environments are measured at critical points within the utterances, and are interpreted in terms of the production studies. Particular attention is paid to events near the consonant-vowel and vowel-consonant boundaries, where the dominant source changes from frication noise to aspiration noise to glottal vibration. Based on this research, new synthesis rules for fricative consonants are proposed. [Research supported in part by NIH Grant No. NS-04332.]
Perceptual evaluation of MITalk and DECtalk
Authors: Pisoni David B.
Published: October 2005

In the spring of 1979, we began the first of what would eventually become many dozens of behavorial studies on the perceptual evaluation of synthetic speech produced automatically by rule. The MITalk text-to-speech system was just nearing completion at MIT. At that time, I spent many hours with Dennis Klatt talking about and planning a variety of perceptual tests to evaluate the MITalk system. In this paper, I will first summarize the initial results obtained with the MITalk system in 1979. Then I will describe the evaluation of DECtalk. I believe that one of the reasons that DECtalk has consistently shown such high levels of segmental intelligibility, levels often approaching those observed with natural speech, was Dennis' intense fascination with the results of our error analyses of the MRT that he used to selectively modify, refine, and improve the quality of the synthetic speech produced by DECtalk. In working with Dennis, it became clear to me that one of his major goals was to develop a system tht would produce the very best quality synthetic speech possible. The data from additional perceptual tests demonstrate clearly that Dennis was successful in achieving his goals for DECtalk. DECtalk remains the standard against which all other text-to-speech systems are compared. [Work supported by NSF.]
Perceptual and acoustic charactertics of distorted /r/
Authors: Ohde Ralph N. , McCarver Michael E. , Sharf Donald J.
Published: October 2005

One type of articulation disorder is a sound distortion that has been defined as an allophonic variation within the perceptual boundary of a target phoneme. An established finding in speech perception is that sounds are more accurately identified across sound categories than within sound categories. In order to determine if distorted /r/ could be accurately and reliably perceived, six speech pathologists identified the productions of prevocalic /r/ and /w/ words of 12 children diagnosed as having an /r/ misarticulation. The results of the identification tests revealed a relatively high average distorted /r/ category of 70% or better for four children. Moreover, intrasubject reliability scores for these distorted /r/ children averaged 80% or better. Preliminary findings of spectrographic analyses of formant transition onsets show that F3 onsets of distorted /r/ are substantially higher than F3 onsets of /r/ for normal and synthetic versions of children's speech. [Work supported by Biomedical Research Support Grant No. RR-05424.]
Perception of some consonant contrasts in noise
Authors: Alwan Abeer
Published: October 2005

The goal of the present study is to examine the acoustic properties that listeners use to distinguish between speech sounds when these sounds are presented in noise. A series of perceptual experiments was conducted using natural stimuli consisting of nonsense CV syllables, where C was either /m/,/n/,/b/, or/d/, and V was either /ɑ/, /iy/, or /ow/. The stimuli were degraded by adding various levels of white noise and were presented to subjects in identification tests. Preliminary results show that when the noise is at a level such that the transition of the second formant frequency of the vowel is masked, confusions between the place of articulation for the stimuli occur. Noise levels for which confusions in manner of articulation occur can also be predicted from masking theory. These results are compared with results reported earlier [e.g., Miller and Nicely (1954)] where the thresholds of idenfication were described in terms of the signal-to-noise ratio. These results will be discussed further in terms of the acoustic theory of speech production and the masking theory of the auditory system. [Work supported in part by an NIH grant.]
Consequences of the acoustic bipolar couplings to large aspect ratio scatterers
Authors: Hackman Roger H.
Published: October 2005

It has been suggested that a plane wave axially incident on a large aspect ratio scatterer couples to both the insonified end of the scatterer and to the end in the geometric shadow, at low kD/2 (Dis either the minor axis of a spheroid or the diameter of a cylinder) [Williams et al., J. Acoust. Soc. Am. 85, 2372–2377 (1989)]. This effect is concretely established, and its experimental consequences are discussed in some detail. A novel closed-form expression is derived for the axisymmetric, elastic response of a large aspect ratio target that directly incorporates the bipolar coupling of the acoustic and elastic fields. The form of the final expression is, in some respects, similar to that obtained from the generalized geometric theory of diffraction in the high-frequency limit for elastic spheres and cylinders, although the physical assumptions are quite different. Simple, approximate estimates of the parameters involved in this expression are obtained and compared with a T-matrix calculation.
Contributions to the form function for elastic spheres based on a product expansion of the S function: Numerical tests
Authors: Marston Philip L.
Published: October 2005

Associated with the scattering phase shift δn, of the nth partial wave for a sphere of radius a is the function Sn (x) = exp[2iδn], where x = ka. A theorem from classical scattering theory leads to a product expansion of Sn, which allows for multiple resonances [P. L. Marston, J. Acoust. Soc. Am. Suppl. 1 84, S185 (1988)]. This Sn remains manifestly unitary even for multiple resonances l and clarifies implicit assumptions of RST. The elastic contributions fne to the form function depend on complex ka pole locations xnl ≡ Xnl − i(Γnl/2) and −xnl*, where Xnl > 0, Γnl > 0, and * denotes complex conjugation. In the case of only two resonances (l = 1,2), it may be shown that fne ≈fn1 + fn2 + fn(int) + fnL. The fnl have a Breit-Wigner form fnl = exp(2iξn)[(2n + 1)/x](−1)nΓnl/[Xnl − x −(i/2)Γnl] and ξn is the phase shift associated with the background factor of Sn. The term fnL is a term associated with the pole at −xnl* in the left half of the complex ka plane while fn(int) is an interaction term. The effect of fnL is small if Γnl ≪ Xnl. This approximation of fne is confirmed by numerical comparison with the fne, based directly on the product expansion. The comparison also shows that omission of the term fn(int) can introduce substantial errors for x between Xn1 and Xn2. [Work supported by ONR.]
Combining statistical and linguistic models for synthesis of prosodic contours
Authors: Ostendorf Mari , Price Patti , Shattuck-Hufnagel Stefanie , Veilleux Nanette , Wightman Colin , Garcia Rudy
Published: October 2005

“It is very important to get the timing, intonation, and allophonic detail correct in order that a sentence sound intelligible and moderately natural.” [D. Klatt, J. Acoust. Soc. Am. 82, 737–793 (1987)]. This important review article included prosody as a research issue for improving text-to-speech synthesis. Klan's suggestions for improving prosody are addressed here: Development of new systems for control of F0 and duration, and mechanisms for adding variety. The proposed synthesis system is a statistical model trained on text, parts of speech, pronunciation, lexical stress, prosodic labels (major and minor boundaries, accents, etc.), and acoustic parameters (relative F0 and duration). The synthesis problem is to predict the prosodic labels and acoustic parameters given the text and the statistical model. Several hours of speech have been collected from professional FM newscasters, a labeling scheme has been converged on, and a portion of the data has been labeled. The components of the system so far implemented will be discussed: (1) statistical modeling of sequences of parts of speech to predict major prosodic breaks, (2) the role of breath noise in naturalness, and (3) the implementation of a sinusoidal model for duration and pitch modification of waveforms. [Work supported by NSF.]
Measurement of polymer complex modulus properties using several techniques
Authors: Lewis Thomas M. , Legros Dominique
Published: October 2005

Various techniques for measurement of the dynamic mechanical properties of polymers are discussed. Special emphasis is given to the vibrating beam, SDOF resonance, SDOF impedance, creep, relaxation, forced oscillation (Metravib viscoanalyzer), and forced torsional oscillation (Metravib micromechanalyzer) techniques. Material property data, generated over wide ranges of temperature and frequency (using the above techniques), are presented in terms of reduced frequency upon application of an Arrhenius temperature-frequency shift function. Comparison of these properties in the reduced frequency format indicates good correlation between techniques. Specific examples are included consisting of data generated from commercially available materials in both shear and tension-compression states of stress from which estimates of Poisson's ratio may be determined.
Frequency-temperature superposition in polymer damping behavior
Authors: Jones David I. G.
Published: October 2005

The problem of determining optimum shift factors for frequency-temperature dependence of polymeric material complex modulus properties has not been fully resolved even half a century after the pioneering work of Williams, Landel, and Ferry. The question of what form, such as the WLF (Williams, Landel, Ferry) equation or the Arrhenius equation, best depends on both the material and th& quality of the test data. In most cases, the data scatter is sufficient to prevent a definitive choice. These issues will be discussed with reference to available test data for several polymeric materials, obtained by various measurement techniques. It will be shown that the least ambiguous shift factor estimates are obtained when data scatter is as low as possible, and the frequency range of data at each temperature is as wide as possible, as would be expected. It will also be shown that differences arising from the use of different shift factor equations are not sufficient for most engineering applications.
Internal friction in polymer systems
Authors: Bicerano Jozef , Rieke James K.
Published: October 2005

Internal friction is an effective mechanism for dissipating energy in polymer systems. Of particular interest is the ability to dampen and absorb unwanted acoustic and mechanical vibrations. The use of internal friction will become more effective when detailed geometric, thermodynamic, and kinetic models are developed for the physical phenomena producing the vibration damping. A model that relates the viscoelastic properties of polymeric systems to their molecular level structures has been developed. This model considers the nature of the temperature and frequency dependences of the storage and loss components of the complex moduli of polymers. It provides correct and internally consistent correlations. Therefore, it constitutes a first step in an attempt to bridge the gap between the results of application of an external stress (such as acoustic or mechanical vibration) and the molecular level properties of the polymers.
Inversion using simulated annealing
Authors: Basu Atanu , Frazer L. Neil
Published: October 2005

The problem here is finding the profile m̄ that minimizes E(m̄) = ‖d̄ − ḡ(m̄)‖ − ε‖m̄ − m̄0‖ in which d̄ is a data set, m̄0 is the bias, and ḡ is a Green's function. If ḡ is nonlinear and the dimension of m̄ is large, then finding Emin is difficult. Simulated annealing (SA) seeks Emin by sampling from the probability distribution p(m̄) = exp[− E(m̄)/T]/Z in which T is so small that p spikes at Emin. This would be silly if one had to generate Z numerically, but SA does not need to know Z. The physical analogy for SA is that each component of m̄ is an atom in a melt having temperature T and free energy E. Rapid cooling of the melt gives a glass (high E) but slow cooling gives a single crystal (low E). Problems with SA are that slow cooling consumes the computer budget faster than it finds Emin and that the freezing temperature Tc is difficult to determine. Accordingly, much research on SA concerns cooling schedules that do not require Tc. In wave field inversion problems, it was found that known cooling schedules gave poor results and that knowledge of Tc was essential. A rapid method to find Tc was discovered. Also, SA was no longer thought of as a process that terminates; rather Tc is determined accurately keeping the melt at Tc and letting SA find many good m̄. A measure of resolution in m̄ space is the “order parameter” η = ‖m̄ − m̂‖, where m̂ is the unknown true profile. Expected values of η(E) can be obtained from synthetic data.
Adaptive array processing of full-wave acoustic fields
Authors: Wengrovitz Michael S. , Schmidt Henrik
Published: October 2005

Adaptive array processing methods have been developed and applied in a number of areas including radar, communications, and underwater acoustics. Assessing the performance of these methods is more difficult in the underwater acoustics context due to the complex influence of the ocean environment on the signal and noise fields. Arrivals across the array are not plane waves, as typically assumed in radar and communications problems, but are solutions to the wave equation applicable to the particular ocean environment. This paper describes an efficient computational method that interfaces the full-wave solution for horizontally stratified media with adaptive array processing algorithms. The computational method has been used to provide coherent arrival data for full-wave array beam pattern calculation, and noise spatial-correlation matrices for deriving array gain corresponding to various adaptive arrays. The computational method has been used to study a number of important array processing issues for multidimensional arrays with large number of elements in oceanic environments. Example issues discussed in the paper include applicability of partially adaptive beam-forming algorithms, sensitivity of array performance to environmental parameters such as bottom composition, convergence rates of adaptive nulling algorithms in underwater environments, and array calibration.
Modal decomposition of fields in range-varying waveguides
Authors: Thomson David J.
Published: October 2005

Numerical solutions to parabolic equations (PE) provide the total contribution to the field at each point on the computational grid. For some applications, it is instructive to examine the propagation of individual spectral components, particularly in range-dependent waveguides, where mode coupling can be important. This paper presents a novel method for decomposing a numerical PE field into its horizontal wavenumber spectrum. At a given range in a range-dependent waveguide, the PE field versus depth is provided as initial data to a PE model which is used to propagate the field in a range-independent waveguide characterized by the local environmental conditions at the range of the initial data. A Fourier transform of this propagated field yields the PE modal spectrum directly. Moreover, if the standard parabolic equation is used to propagate the field, then the PE modal spectrum can be postprocessed into the correct modal spectrum for the one-way wave equation [D. J. Thomson and D. H. Wood, J. Acoust. Soc. Am. 82, 224–232 (1987)]. A numerical example involving upslope propagation is used to illustrate the proposed spectral decomposition method.
The problem of energy conservation in one-way wave equations
Authors: Porter Michael B. , Ferla Carlo M. , Jensen Finn B.
Published: October 2005

A recent attempt to define and numerically solve range-dependent benchmark problems in ocean acoustics [J. Acoust. Soc. Am. Suppl. 1 81, S39–S40 (1987)] revealed some inherent problems with energy conservation for one-way wave equations when applied to sloping bottom environments. The problem turned out to be associated with the use of a stair-step approximation to a sloping interface, and, in particular, with the rise of the stair steps, where a one-way equation allows only one out of two necessary interface conditions to be fulfiled (continuity of pressure or horizontal particle velocity). The loss of energy increases with increasing slope and density contrast at the water/bottom interface, and it can become quite significant (3–6 dB) for slopes of a few degrees and a density contrast of 2. A simple fix to this problem is to solve for a density-reduced pressure (p/ρ) instead of pressure (p), a trivial modification to existing one-way parabolic equation codes. Numerical results for both up- and downslope propagation show that the modified wave equation performs very well with errors being reduced by 75% for realistic slopes and density contrasts.
A convolution algorithm for standard parabolic-equation modeling
Authors: Joyce Robert F. , Head Martha E. M.
Published: October 2005

The split-step Fourier algorithm for solving the acoustic parabolic equation involves two Fourier transforms, one forward and the other inverse. These may, of course, be replaced by a convolution. For the standard parabolic equation, the particular form of one of the convolved factors allows the convolution integral to be solved using a single Fourier transform. Application of this technique results in a limitation on the allowed range step. When applicable, however, the convolution algorithm reduces computer run times to about 60% of those required by the standard split-step Fourier algorithm. Examples are presented and limitations are discussed.
An acoustic echo canceler implemented with AT&T DSP16A
Authors: Kuo Sen M. , Zhao Huan
Published: October 2005

Acoustic echo control in teleconferencing and hand-free phone systems is not trivial because of its special characteristics. Many acoustic cancellation algorithms have been published in recent years but they are either of theoretical consideration or are computer simulations with complicated computation burdens, which makes real-time implementation impossible. In this paper, a two-band scheme is proposed to realize an acoustic echo canceler with an AT&T WE DSP16A microprocessor. The structure of the algorithm is optimized so it can give an echo return loss enhancement (ERLE) of more than 25 dB. A double talk detector is developed with the subband adaptive algorithm so that it will ensure full duplex communication. Performance of this canceler is evaluated with both computer simulation results and real-time test results.
Adaptive acoustic echo cancellation algorithms in teleconferencing systems
Authors: Kuo Sen M. , Zhao Huan
Published: October 2005

In teleconferencing systems, acoustic echoes consist of acoustic coupling between louder speakers and microphones and the room reverberations. The echoes could be very annoying and even cause howling if the echo level is high enough. Among many ways of canceling acoustic echoes in teleconferencing system, the adaptive digital signal processing approach is very promising since adaptive filtering has the capability to trace the change of the echo path and cancel echoes actively. Adaptive algorithms to cancel acoustic echoes in both the time and frequency domains are presented, and the computer simulation results are compared in a proposed paper. The algorithms included are LMS, NLMS, LLMS, SDLMS, SELMS, SSLMS for FIR adaptive filtering and RLMS, SHARF, and Pole-Zero for IIR adaptive filtering. Performance of these adaptation algorithms will be discussed. Subband adaptive filtering algorithm, which has a faster convergence rate, will also be presented.
Timbre and the perceptual organization of musical patterns
Authors: Wessel David
Published: October 2005

Timbre, usually defined as the condition of attributes other than pitch, loudness, and duration, plays a strong role in determining the perceptual organization of musical patterns. Timbre's primary organizational influence appears to be on perceptual grouping, as in auditory stream segregation and rhythmic segmentation. Grouping by timbre can influence the tonal implications of otherwise ambiguous pitch material. Extensions of the author's previous work on the perception of timbral analogies demonstrate that timbre melodies and timbrally based phrasing and articulation can exhibit invariances similar in character to the manner in which pitch patterns exhibit perceptual invariance under transposition. With the strong organizing influence of timbre in mind, it is argued that care should be taken in experiments on melodic and rhythmic organization to control for the influence of timbre. Pure tones and fixed spectra exhibit a strong correlation between fundamental frequency and measures of the location of the spectral envelope, an important timbral determinant and are inappropriate for many experiments on music perception. A simple set of procedures for preparing stimuli with independent control of spectral envelope, temporal envelope, and frequency content is provided and demonstrated.
Pulsed focused fields
Authors: Felsen Leopold B.
Published: October 2005

Highly concentrated clumps of field energy that move through an environment without diffusing are of interest for a variety of applications. The basic problem is the synthesis of source distributions over an initial aperture to achieve this objective. Various analytical approaches have been used to explore how initial transient source field distributions can be tuned up so as to generate compact wavepackets that stay together indefinitely. The meaning of “staying together” and “indefinitely” depends strongly on how the problem is defined and has led to some startling conclusions in the early phases of investigation. At present, there seems to be agreement that no radically new phenomena are operative here but that interesting pulse shapes can be synthezied by clever spectral tuning of input conditions. Various techniques—based on direct time-domain synthesis, real and complex spectral synthesis, and use of transient beam-type basis elements—are reviewed within the context of causality and finite aperture size. Also discussed is a modeling scheme whereby a pulsed focused beam is generated analytically by assigning complex values to the source location and initiation time. This parametrization is useful for converting spherical pulse interaction with a perturbating environment directly into focused pulse interaction with that environment. [Work was supported by the Innovative Science and Technology Office through the U.S. Army Harry Diamond Laboratory.]
Dynamic mechanical properties of neoprene rubber blends
Authors: Madigosky W. M.
Published: October 2005

Blends of neoprene with other elastomers can be used to provide certain properties that are not obtainable with either elastomer alone. Although the effect of blending on the physical properties of neoprene blends has been investigated, the effect of blending on the dynamic mechanical properties has not been investigated to the same extent. Neoprene is compatible with natural rubber, SBR, NBR, polysulfide rubber, and has limited compatibility with butyl rubber. Seventy different blends were prepared and the physical properties measured. The dynamical mechanical properties are being measured on a Polymer Laboratories DMTA and frequency shifted using the WLF equation. This paper presents data and an analysis of the samples measured thus far.
Theoretical and experimental investigation of high-temperature damping treatment using ceramic-fiber interlayer between plates
Authors: Chow L. C. , Pinnington R. J.
Published: October 2005

The damping techniques available for high-temperature applications, such as in power generating plants, are very limited. As part of the investigation of high-temperature damping work being carried out in ISVR, this paper describes the theoretical and experimental assessment of damping of plates using ceramic-fiber material as an interlayer. An experimental rig that is used to measure the ceramic-fiber material dynamic properties at elevated temperature will also be described.
Treatment of an elastic bottom in the parabolic approximation
Authors: Papadakis John S. , Taroudakis Michael I. , Mayfield Betty
Published: October 2005

The use of impedance boundary conditions in the solution of the parabolic equation in underwater acoustics enables the treatment of bottoms of various types provided that appropriate boundary conditions can be expressed. The conditions are incorporated in an implicit finite difference (IFD) scheme for the parabolic equation. The integrals appearing in the computing scheme are evaluated either analytically, if possible, or numerically. For a sea bottom considered as an elastic homogeneous half-space, an impedance boundary condition can be evaluated relating the acoustic field in the sea at the water-bottom interface with that of the elastic bottom. The condition is inserted in the IFD scheme and the pertinent integrals are evaluated numerically by means of a fast Fourier transform algorithm. Results demonstrating the satisfactory behavior of the scheme are presented for range-independent environments. However, the method is also directly applicable to range-dependent environments.