bluuebunny/crossref_metadata_2025 huggingface dataset:
Applications of the proposed new method for computing attenuation of fractional octave bands of a wideband noise by atmospheric absorption
Authors: Joppa Paul D. , Sutherland Louis C. , Zuckerwar Allan J.
Published: October 2005

A simple method for computing the attenuation due to atmospheric absorption for fractional octave bands of noise, outlined in a previous paper [P. D. Joppa, L. C. Sutherland, and A. J. Zuckerwar, J. Acoust. Soc. Am. Suppl. 1 88, S73 (1990)], is briefly reviewed and example applications to aircraft noise and room acoustics presented. The method uses an analytical approximation of a ‘‘representative’’ frequency for which the pure-tone attenuation loss due to atmospheric absorption is equal to the actual loss for the band of noise. The resulting total band attenuation, δLb for propagation over a distance s, for a band with an exact midband frequency fm, is equal to a nonlinear function of the total pure-tone attenuation a(fm)⋅s over this path where a(fm) is the pure-tone attenuation coefficient at the exact midband frequency fm. The method provides better estimates than in SAE ARP 866A for the true band attenuation when the total true band attenuation is less than about 50 dB. For application to room acoustics, it is shown that the ‘‘distance’’ s involved is simply equal to the reverberation time, T times the speed of sound in the room.
Sound scattering by a single and by a cloud of air bubbles near the sea surface
Authors: Gaunaurd G. C. , Huang H.
Published: October 2005

Sound scattering by an air bubble in a boundless fluid is an old classical problem [i.e., R. Y. Nishi, Acustica 33, 65–74 (1975)]. If the air bubble is near, and strongly interacting with the surface of a liquid half-space, then the scattering cross section (SCS) of the bubble is quite different from its value far away from the boundary. The exact solution for this scattering problem is given that is valid for any incidence direction of the (plane) sound waves, and for any bubble depth, obtained by the method of images. This benchmark solution is found by means of the addition theorems for the spherical wave functions. The resulting SCS contains contributions from the interface, the bubble, and from its image, and it is expressible in terms of coupling coefficients containing products of Wigner 3-j symbols. The formulation is illustrated with many computed plots and it is finally extended to the case of a round, low-concentration cloud of equal size bubbles, just beneath the sea surface. This generalization is possible by replacing the individual bubble properties by those of an ‘‘effective medium’’ describing the bubble cloud just as was found earlier [i.e., J. Acoust. Soc. Am. 85, 541–554 (1989)]. [Work supported by NSWC’s IR Program.]
Temporal response comparisons between model results and measurements of forward-scattered waves from the sea surface
Authors: Yoerger E. J. , McDaniel Suzanne T.
Published: October 2005

The underwater acoustic propagation path for the forward scattering of energy from the sea surface is treated as a linear, time-varying random communications channel in the application of the Helmholtz–Kirchhoff integral formulation of this problem. The model used for data comparisons utilizes the bifrequency system function Γ(ω,ω’) developed by McDaniel [IEEE J. Ocean. Eng. 17, 216–221 (1992)] for the temporal response from a rough surface. The data analyzed for this work were obtained from a shallow-water high-frequency acoustic experiment conducted on the Baltic Sea during May 1993. Acoustic data included measurements of surface forward-scattering, surface reverberation, and direct-path intensities. These were made utilizing two large stationary towers resting on the seafloor. Each tower was equipped with horizontal and vertical receiving arrays anchored 7.6 m above the flat bottom depth of 30 m. Concurrent environmental measurements including wave heights, sound velocity profiles, and sample cores were made. The results presented here are for the surface forward-scattered measurements made at 20, 40, 60, and 90 kHz. [Work supported by the Office of Naval Research, Program Element 61153N, with technical management provided by the Naval Research Laboratory, Stennis Space Center, MS.]
A study on intensity fluctuations in forward scattering from the sea surface
Authors: Dahl Peter H. , Percival Donald B.
Published: October 2005

Fluctuations in the intensity of sound forward scattered from the sea surface are discussed. The data originate from an experiment off the southern California coastline using the research platform FLIP. Measurements were made using omnidirectional sources suspended from a spar buoy (tethered to FLIP) and receivers mounted on FLIP’s hull, with range varying between 500 and 1000 m. The frequency was 20–50 kHz and the roughness parameter χ=2kh sin θ was ≫1 (where k is acoustic wave number, h rms wave height, and θ grazing angle); thus the measurements represent high-frequency, incoherent scattering in a single surface bounce channel. An often used statistical model for intensity fluctuations in such conditions is the exponential PDF, or its equivalent Rayleigh PDF for amplitude. Examples are presented wherein the exponential model fails a Lilliefors statistical goodness-of-fit test. The Lilliefors test is used for this purpose because parameters of the distribution are not known apriori. An alternative to the single-parameter exponential PDF is the two-parameter gamma PDF. Candidate variables, based on sea state and acquisition geometry that are covariates to the nature of intensity fluctuations, are discussed. [Work supported by ONR Code 321.]
Influence of statistical surface models on dynamic scattering of high-frequency signals from the ocean surface
Authors: Bjerrum-Niese Christian , Bjo/rno/ Leif
Published: October 2005

Temporal variations of scattering of high-frequency, monochromatic signals from the ocean surface has been studied numerically. In the high-frequency domain the dynamic scattering can be modeled by a coherence function of the scattered pressure field, which is based on the Kirchhoff integral; the surface roughness is described by a spatial surface spectrum and the surface motion is described by the gravity-wave dispersion relation [D. Dowling and D. Jackson, J. Acoust. Soc. Am. 93, 3149–3157 (1993)]. Applying some modifications to this approach, the temporal coherence function is found by numerical evaluation of a double integral. The time-varying scattering can be examined in the frequency domain by the power spectrum (the Fourier transform of the coherence function). It is examined how a monochromatic signal is shifted and smeared in the frequency domain by comparing computations for the Pierson–Moskowitz spectrum (for a fully developed sea) with computations for the JONSWAP spectrum (for fetch-limited seas). The following results, among other issues, have been obtained: As the fetch decreases, the surface waves become shorter, leading to increasing frequency shifting of the scattered signal. [Work sponsored by the Danish Technical Research Council and the EU/MAST programme.]
Modeling the azimuthal dependence of sea surface backscatter during CST-7
Authors: Dubberley John , Keiffer Richard S. , Novarini Jorge
Published: October 2005

The operator expansion method is applied to realizations of 2-D roughness measured during CST-7 in order to probe the azimuthal dependence of the backscatter from time-evolving, non-fully developed seas which contain swell from distant surface wave sources. To use wave buoy measured data without extrapolation in frequency beyond the measured surface wave spectra, the measured frequencies examined will be limited to 75 and 150 Hz. The modeling goal will be to determine that if surface scatter was alone responsible for acoustic backscatter from the surface, could there be a measurable azimuthal dependence in the scattering during this experiment? Comparisons to some available measured azimuthal dependence will be shown.
Stability of signal plus noise in performance evaluation of processing schemes
Authors: George Jacob , Wagstaff Ronald A.
Published: October 2005

The stability of signal plus noise and the mechanisms governing the combination of signal and noise at the receiver are reported. These questions become important in performance evaluation of processing schemes which are designed to enhance the S/N ratio. Of special interest is the case of a weak signal combining with a relatively stronger noise. Even though the nonlinear interaction of sound by sound continues to be a hot topic [see, for example, P. J. Westervelt, ‘‘Answer to criticism of experiment on scattering of sound by sound,’’ J. Acoust. Soc. Am. 95, 2865 (1994)], the largely linear effects governed by the superposition principle are of primary importance in the present application. Simple rules governing the combination of signal and noise, obtained through analysis of experimental data and model calculations, will be discussed. [Work supported by ONR, with technical management provided by NRL/SSC.]
Noise assessment and prediction system (n
a
p
s) evaluation
Authors: Noble John M. , Olsen Robert O. , Okrasinski Richard
Published: October 2005

A system has been designed to provide an assessment of noise levels that result from testing activities at Aberdeen Proving Ground, MD. The system receives meteorological data from surface stations and an upper air sounding system. The meteorological data are used as input into an acoustic ray trace model which projects sound level contours onto a two-dimensional display of the surrounding area. This information is also provided to the range control office where a decision can be made to proceed or delay the test activity depending upon acoustic propagation conditions. To evaluate the noise level predictions, a series of microphones is located off the reservation to monitor sound-pressure levels. Any events of significant level are transmitted back to the central display unit, allowing for comparison between prediction and data. The computer models are modular, allowing for a variety of models to be utilized and tested to achieve the best agreement with data. This technique of prediction and model validation will be used to improve the noise assessment system.
Matching pursuits with differential operator dictionaries
Authors: Trappe Wade , Lakey Joseph D.
Published: October 2005

This paper will examine in brevity the matching pursuit algorithm proposed by Mallat and Zhang, which yields an adaptive signal decomposition that may be used to derive a phase plane representation of a signal. Based on these ideas, and motivated by the application of wavelets to linear differential operators, a new numerical method for solving differential equations is proposed which is based on performing a matching pursuit algorithm in an operated dictionary. Using this new algorithm the nonhomogeneous Helmholtz differential operator with zero and nonzero boundary conditions shall be examined. A classical differential equation arising from acoustics shall be presented and solved using this new method. Results are presented for the one-dimensional case, and the extension to higher dimensions is examined using the concept of tensor products to construct a dictionary for higher dimensional Hilbert spaces.
Calculation of the transient acoustic wave field emitted by a focused transducer with an arbitrary rim
Authors: de Hoop Adrianus T. , Zeroug Smaine , Kostek Sergio
Published: October 2005

Closed-form analytic expressions are derived for the transient acoustic wave field emitted by a focused transducer with an arbitrary rim. The radiating part of the transducer is a spherical surface bounded by a simply connected closed curve of arbitrary shape. Starting from the Kirchhoff–Huygens representation of the emitted acoustic wave field, the expression for the acoustic pressure is transformed into a line integral along the rim of the transducer by employing the Maggi–Rubinowicz transformation in the Kirchhoff theory of diffraction by a black screen. The resulting line integral for the transient acoustic pressure is evaluated numerically to study the shape of the beam emitted by the transducer in its dependence on the shape of the rim and to analyze the resolving power of the transducer in ultrasonic applications. For a focused transducer with a circular rim, a closed-form analytic expression is derived for the transient acoustic pressure on its axis. These results serve as a check on the numerical results obtained for the more general cases. For all cases, the acoustic pressure at the focus admits a closed-form analytic representation. [Adrianus T. de Hoop performed this research as a Visiting Scientist with Schlumberger-Doll Research, Ridgefield, CT.]
Transient axial solution for the reflection of a spherical wave from a paraboloidal mirror
Authors: Hamilton Mark F.
Published: October 2005

A method used previously [J. Acoust. Soc. Am. 93, 1256 (1993)] to derive a transient axial solution for a spherical wave reflected from an ellipsoidal mirror is applied to the case of a paraboloidal mirror. The incident spherical wave is radiated from the focus of the mirror. A solution for the impulse response of the reflected axial pressure is obtained in the form h(z,t)= δ(t−z/c0)−he(z)δ[t−te(z)]−(c0/zF)hw(z,t), where δ is the Dirac delta function, c0 is sound speed, z is axial distance from the base of the mirror, zF is distance to the focus, he is the relative amplitude of the edge wave, te its relative time of arrival, and hw is the wake. Simple expressions are obtained for he and hw. Beyond the focus, the geometrical acoustics result he∼(1+d/zF)−1 is recovered for the edge wave, where d is the mirror depth. In the far field, hw becomes a delta function, the impulse response reduces to h(z, t)∼(2z2F/c0z)ln(1+d/zF)δ’(t−z/c0), and the derivative of the source waveform is thus obtained. Calculations for various source waveforms are presented. Related measurements are discussed in the following presentation by Gelin etal. (Paper 1pPA5). [Work supported by ONR.]
Experimental study of reflection of airborne, spark-produced N waves by a paraboloidal dish
Authors: Gelin Lawrence J. , Shorey Jamie M. , Hester Daniel M. , Blackstock David T.
Published: October 2005

An experimental investigation of the transient response of a paraboloidal reflector is reported. An inhomogeneous plane N wave was produced by locating an electrical spark at the focus of a machined aluminum paraboloidal reflector (focal length zF=5.08 cm, radius a=10.80 cm). A second reflector (zF=5.17 cm, a=10.05 cm) was constructed by spinning a container of epoxy at constant speed and allowing it to cure. Peak pressure P and arrival time were measured across the beam (fixed axial distance z measured from the reflector surface, variable radial distance r) and along the axis. The range of measurements was r≤80 mm and 20.74 mm≤z≤95.74 mm. Small-signal N waves (P=400 Pa, duration T=9 μs) were measured as well as stronger ones (P=1000 Pa, T=12 μs). For small-signal N waves the axial measurements generally confirm Hamilton’s theoretical prediction (previous paper, 1pPA4) although the edge waves are weaker than forecast. Transverse measurements agree with ray-theory predictions off axis but are up to 10% low in the axial region. For stronger N waves, transverse measurements of arrival time and peak pressure show evidence of self-refraction (ray bending due solely to finite-amplitude effects). [Work supported by ONR, ARL:UT IR&D program, and NASA.]
Transient acoustic wave fields in continuously layered fluids with attenuation
Authors: Verweij Martin D.
Published: October 2005

The space-time domain acoustic wave field in an isotropic, lossy, continuously layered fluid is analyzed using a method that employs a combination of higher-order WKBJ asymptotics and the Cagniard–De Hoop method of inversion. The loss behavior of the fluid is described with the aid of general temporal compliance and inertia memory functions. The continuous layering of the medium manifests itself in the acoustic wave speed, the density of mass, and both memory functions, which are independent, continuous functions of the vertical coordinate. After the application of forward transformations, higher-order WKBJ asymptotic representations of the transform domain solution are derived. The coefficients that occur in these representations satisfy a recurrence scheme, which is well suited for implementation in a symbolic manipulation program. The transform domain WKBJ asymptotic representations are analytically transformed back to the space-time domain with the aid of the Cagniard–De Hoop method. Numerical results for several configurations with an intricate loss behavior are presented.
Observation of individual bond breaking events in precursors, cascades, etc. in the onset and progression of fracture
Authors: Zhang Tianming , Savitski S. R. , Maynard J. D.
Published: October 2005

Experimental measurements of fracture have been made using a wide bandwidth (10 MHz) transducer and a system with a relatively large bond size, with the result that one is able to observe individual bond breaking events. The data provide a direct test of ‘‘fuse’’ models [L. de Arcangelis, S. Redner, and H. J. Herrmann, J. Phys. Lett. (Paris) 46, L585 (1985)] and scaling theories of brittle fracture. Measurements have been made with uniform tensile stress and bending stress, with the latter corresponding to a phase transition in the presence of an external field. For samples of the same width, the observations are quite consistent, showing the effects of precursors, onset, progression, stress waves, crack arrest, and other interesting phenomena. A significant difference in precursors for the uniform and bending stress fields is observed, perhaps a result of the dimensionality of the maximum stress field. [Work supported by NSF Grant No. DMR-9306791 and by ONR.]
Landmark detection for distinctive feature-based speech recognition
Authors: Liu Sharlene A.
Published: October 2005

This work is a component of a proposed knowledge-based speech recognition system, which uses landmarks to guide the search for distinctivefeatures. In an utterance, landmarks identify localized regions where the acoustic manifestations of the linguistically motivated distinctive features are most salient. An algorithm for automatically detecting landmarks implemented by abrupt articulatory movements is described. The algorithm is a hierarchically structured algorithm rooted in linguistic and production theory. It looks for abrupt energy changes in six frequency bands and at two levels of temporal resolution. Landmarks are found based on information about which bands contain the abrupt change, the steady-state quality in the vicinity of the proposed landmark, segmental duration constraints, and an articulatory continuity requirement. Tested on a database of continuous speech recorded in a silent room by male and female speakers, the landmark detector is shown to perform well, with a 94% true detection rate and a 10% false detection rate. Most of the missed landmarks were adjacent to reduced vowels. These promising results indicate that landmarks are robustly identifiable points in the speech waveform and that a landmark detector as a front end in a speech recognition system is feasible. [Work supported by NSF.]
Acoustical monitoring of sediment transport in the bottom boundary layer at the inner continental shelf LEO-15 site
Authors: Traykovski Peter , Lynch James , Irish James , Newhall Arthur
Published: October 2005

The bottom boundary layer (BBL) is of great importance in oceanography as it determines the amount of frictional stress a flow encounters from the ocean bottom, and it plays a major role in controlling sediment transport processes. The backscatter of acoustical energy from suspended sediments has proven to be a valuable tool in studying the BBL. Preliminary results from acoustical monitoring of sediment transport at the ‘‘Long-Term Ecosystem Observatory’’ (LEO-15) site located in 15 m of water off of the southern New Jersey coast are presented. The acoustical backscatter system that was deployed at this site during the winter and spring of 1994 is capable of profiling the entire water column by using a downward looking 5-, 2.5-, and 1-mHz sonars and a 1-mHz upward looking sonar. The fine resolution images produced from this system resolved several sediment suspension events and bottom feature movement was observed. [Work supported by NOAA.]
New frontiers in molecular acoustics of liquids
Authors: Sarvazyan Armen
Published: October 2005

The major accomplishments in molecular acoustics of liquid systems are summarized. The most promising direction in this field is acoustical thermodynamics. The possibility of acoustical evaluation of thermodynamic parameters of liquids comes from the fact that compressibility of the fluid is the second derivative of Gibbs free energy on pressure. Changes of enthalpy, entropy, free energy, and their pressure and temperature derivatives (heat capacity, volume, expansibility, compressibility, etc.) can be calculated from the pressure and temperature dependencies of sound velocity in the fluid by using additionally the data on the temperature dependencies of density and heat capacity of the fluid at 1 atm. Another new area is related to the studies of the acoustic nonlinearity parameter B/A which is a simple function of the pressure derivative of the bulk modulus and provides unique information on the character of intermolecular forces in the liquid. In aqueous solutions B/A is significantly determined by the structure of water in the hydration shell of the solute. The state of the art in the instrumentation for molecular acoustic studies is presented. New types of acoustical resonators based on the use of cylindrical standing waves enabling one to make measurements in microliter volume samples will be described. a)Permanent address: Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences.
A locus equation study of syllable-final stop place of articulation
Authors: Sussman Harvey M. , Shore Jadine , Fruchter David
Published: October 2005

Syllable-final stops have different coarticulatory and perceptual properties compared to syllable-initial stops. Locus equations have previously been used to acoustically characterize place of articulation for initial stop consonants [H. Sussman, H. McCaffrey, and S. Matthews, J. Acoust. Soc. Am. 90, 1309–1325 (1991) and H. Sussman, K. Hoemeke, and F. Ahmed, J. Acoust. Soc. Am. 94, 1256–1268 (1993)]. Since locus equations also encode degree of coarticulation, they might also provide an adequate phonetic description of VC events for final /b/, /d/, and /g/ following varied vowel contexts. Each of ten speakers, five male and five female, produced three repetitions of 90 CVC tokens. For each final stop (/b,d,g/) there were ten medial vowels and three initial consonants—bVb, dVb, gVb, bVd, dVd, gVd, bVg, dVg, gVg. Three points along the second formant were measured—F2 onset (Hz), F2 midvowel (Hz), and F2 offset (Hz). Offset locus equations (VC) were generated for each syllable-final stop place, both across initial consonantal contexts and as a function of each initial stop. In addition, 3-D plots were generated to determine how F2 onset (x), midpoint (y), and offset (z) could acoustically capture and differentiate lexical contrasts. [Work supported by NIDCD.]
Speakers nasalize /edh/ if it is preceded by /n/, but listeners don’t care—They still hear /edh/
Authors: Manuel Sharon Y.
Published: October 2005

Presumably as a result of coarticulation, /edh/ often assimilates to a preceding /n/ in phrases like ‘‘win those,’’ but this assimilation is not complete for all features. With respect to the feature [nasal], the assimilation is often radical. The entire consonant region in the middle of the two-word sequence is nasalized. However, acoustic evidence suggests that contextually nasalized /edh/ retains its dental place of articulation. Specifically, F2 is considerably lower at the release of a contextually nasalized /edh/ than at the release of a true /n/, as would be expected for a dental consonant. Perception tests show that listeners can generally tell the difference between natural tokens of pairs like ‘‘win nos’’ and ‘‘win those,’’ even when the /edh/ is completely nasalized. In addition, a synthetic stimulus continuum was constructed in which items differed only with respect to F2 frequency in the vicinity of the nasal consonant regions of phrases like ‘‘win nos.’’ Listeners systematically reported hearing ‘‘those’’ more often when F2 was low at the release of the nasal consonant. These results are consistent with the claim of Krakow, Fowler, and others, that listeners can at least sometimes factor out coarticulatory effects. [Work supported by NSF.]
Effect of fundamental frequency perturbations on medial stop-consonant [voice] judgments
Authors: Molis Michelle R. , Diehl Randy L.
Published: October 2005

Previous research has suggested that the direction of short-duration fundamental frequency (F0) perturbations following consonants provides a cue to consonant [voice] status. More recently, Silverman [Phonetica 43, 76–91 (1986)] proposed that the [voice] cue is provided by the direction and extent of F0 perturbations relative to the underlying intonational contour. A competing view, the low-frequency hypothesis, suggests that F0 participates in a more general way whereby any low-frequency energy in the region of the consonant will contribute to the perception of a [+ voice] consonant. In this study, 15 speech stimulus series, each ranging perceptually from /aga/ to /aka/, were synthesized by varying VOT from 10 to 45 ms in 5 ms steps. Fifteen different pitch contours were generated by designating F0 targets at three points in the stimulus: initial vowel, onset of voicing energy after closure, and 100 ms after the onset of voicing. Three F0 values were used, arranged into two pairs: 100 and 120 Hz and 120 and 140 Hz. The results indicated that the value of F0 at vowel onset, rather than the relative movement of F0, is the best predictor of subjects’ judgments of consonant [voice] status. [Work supported by NIDCD.]
Devoicing a /z/ does not make an /s/
Authors: Smith Caroline L.
Published: October 2005

It is well known that voiced stops in English tend not to be fully voiced. For many American speakers, voiced fricatives may also have little or no voicing. In what phonological contexts do speakers devoice underlying /z/? Previous research [T. Veatch, Ling. Soc. Am. mtg., 69 (1989)] emphasized the influence of the following segment. The present study confirms this, and investigates the likelihood of devoicing in different positions in syllable, word, and sentence. Five speakers of American English recorded multiple repetitions of sentences in which /s/ and /z/ occurred in matched environments. Measures of acoustic durations, airflow, and vocal fold vibration as evidenced by EGG were used to compare the production of /z/ and /s/. Preliminary data from one speaker show a variety of /z/’s, with the duration of vocal fold vibrations as a percentage of fricative duration ranging from 0% to 100%. However, the acoustic vowel length difference preceding /s/ and /z/ is maintained, and even those tokens of /z/ in which there was no vocal fold vibration have reduced airflow compared to matched tokens of /s/, suggesting that devoiced /z/ may differ from underlying /s/ in glottal constriction or level of pulmonic activity. [Work supported by NIH.]
Spectral discontinuities and the vowel-length effect
Authors: Lotto Andrew J. , Kluender Keith R. , Holt Lori L.
Published: October 2005

Perception of the voicing contrast in CV syllables can be affected by the duration of the following vowel such that longer vowels lead to more ‘‘voiced’’ responses. On the basis of several experiments, Green, Stevens, and Kuhl [Percept. Psychophys. 55, 249–260 (1994)] concluded that continuity of pitch, but not continuity of formant structure, determined the effective length of the following vowel. In attempts to replicate these findings, it was found that both effects were highly dependent upon particular choices of pitch and formant values. First, discontinuity in pitch does not preclude the vowel-length effect when fundamental frequency changes from 200 to 100 Hz and 200-Hz partials extend continuously through test syllables. Second, spectral discontinuity does preclude the vowel-length effect when formant changes result in a spectral peak moving to another harmonic. Even when perceived identity of the vowel remained constant, formant changes that resulted in a change in peak harmonic precluded the vowel-length effect. Yet, changes that did not change peak harmonic and did change perceived vowel identity did not preclude the vowel length effect. Taken together, the results indicate that neither phonemic continuity nor talker continuity, perse, is critical to the vowel-length effect. [Work supported by NSF and NIH.]
Perceptual evidence of voicing assimilation in Russian
Authors: Burton Martha W. , Robblee Karen E.
Published: October 2005

Previous research has provided acoustic phonetic evidence of voicing assimilation in obstruent clusters across prepositional boundaries in Russian [Burton etal., J. Acoust. Soc. Am. 95, 2875(A) (1994)]. The current study investigated whether native speakers of Russian perceive the initial consonant in obstruent clusters consistent with the claims of voicing assimilation or whether they show sensitivity to the underlying voicing of the obstruent. Obstruent clusters that were at the boundary between a preposition and a word were excised from sentences produced by three native speakers of Russian. Listeners were presented with four fricative-stop combinations /zd,sd,zt,st/ and four stop-fricative combinations /dz,tz,ds,ts/ preceded by 30 ms of an unstressed vowel and followed by 70 ms of a stressed vowel. Subjects heard eight repetitions of three tokens of each cluster from each speaker. Results indicated that responses were consistent with the voicing characteristics of the following consonant, not the underlying consonant, supporting voicing assimilation. However, in the /zt/ clusters, there were more voiced responses than in the /st/ clusters, which suggests some evidence of incomplete devoicing of the fricative. Implications of the study for phonetic and phonological theories of speech will be discussed.
Acoustic features differentiating Korean medial tense and lax stops
Authors: Shin Ji-Hye
Published: October 2005

Much research has been done on the cues differentiating the three Korean stops in word initial position. This paper focused on a more neglected area: the acoustic cues differentiating the medial tense and lax unaspirated stops. Four adult Korean native speakers, two males and two females, pronounced 16 minimal pairs containing these stops. The average duration of vowels before lax stops is 93 ms longer than before their tense counterparts (143 ms for lax versus 50 ms for tense). In addition, the average duration of the stop closure of tense stops is 178 ms longer than that of lax stops (74 ms for lax versus 252 ms for tense). These durational differences are so large that they may be phonologically determined, not phonetically. Moreover, vowel duration may vary with the speaker’s sex. Female speakers have much shorter vowel duration before the lax stops. The quality of voicing, tense or lax, is also a cue to these two stop types, as it is in initial position, but the relative duration of the stops and of the preceding vowel appear to be much more important cues. The consequences of these results for the phonological description of Korean as well as the synthesis and automatic recognition of Korean will be discussed.
Hemispheric differences in the perception of Zulu click consonants
Authors: Avery Robert A. , Best Catherine T.
Published: October 2005

Past research has shown that speech sounds are processed better by the left hemisphere, nonspeech sounds by the right hemisphere, in most right-handed people. To date, however, it is unknown whether phonetic contrasts from an unfamiliar language show this same pattern, and whether they are perceived as speech. It is known that adults’ perception of non-native speech contrasts is strongly influenced by their language experience; thus non-native contrasts may be handled by different processes than are native contrasts. Best etal. [JEP:HPP 14, 345–360 (1988)] suggested that English speakers’ excellent discrimination of Zulu click consonants occurs because they hear the clicks as nonspeech. Right-handed native speakers of English and of Zulu or Xhosa participated in a dichotic listening study on cerebral dominance for perception of clicks in isolation and in /Ca/ syllables. Natural tokens of Zulu click consonants were used (apical, lateral, and palatal places of articulation, and voiceless aspirated, voiceless unaspirated, and voiced categories). Native speakers of Zulu and Xhosa showed a left hemisphere dominance for discrimination of both the isolated clicks and /Ca/ syllables, while native speakers of English demonstrated no such hemispheric dominance. [Work supported by NIH Grant No. HD-01994.]
Combining time averaging and ensemble averaging in analyzing voiceless fricatives in Mandarin
Authors: Xu Yi , Wilde Lorin
Published: October 2005

The random fluctuations and spurious peaks typically seen in fricative spectra can be reduced by time averaging, i.e., averaging spectra obtained with overlapping time windows over an interval of the frication noise. Furthermore, token-to-token as well as individual speaker variations in fricatives can be reduced by ensemble averaging, i.e., averaging over noise spectra of multiple tokens in the same relative time interval. However, for studying coarticulatory variation in the frication noise, neither of these two methods alone is adequate: Time averaging does not handle token-to-token and individual speaker variations; ensemble averaging requires a large number of tokens to produce smooth and consistent spectra. In the present study, time averaging and ensemble averaging were combined in the analysis of coarticulatory variation of fricatives in Mandarin. The size of the time-averaging interval was 20 ms, and the size of the individual FFT windows was 8 ms. The time-averaged spectra were further ensemble-averaged over ten repetitions of the same sentence by the same speaker. Results indicated that the spectra thus obtained were smooth, and they revealed spectral changes over time more clearly than those obtained by either time averaging or ensemble averaging alone. Further ensemble averaging across different speakers was also explored and has produced encouraging data. [Work supported by NIH.]
Ejectives in Babine-Witsuwit’en
Authors: Davis Katharine , Hargus Sharon
Published: October 2005

Acoustic properties of ejectives in an Athabaskan language of British Columbia were examined. Data from ten native speakers were recorded in the field. Following Hogan [Phonetica 33, 275–284 (1976)], prerelease closure, burst duration, voice onset time, and postrelease silent interval were measured. Following Ingram and Rigsby [Proceedings of the XIth International Congress of Phonetic Sciences, Talinn, Estonia 2, 134–137 (1987)], burst amplitude and the fundamental frequency of the following vowel were also measured. Values were compared with those of homorganic nonejectives (voiceless unaspirated and voiceless aspirated). Preliminary results show that the ejective stops may be distinguished from plain aspirated stops by VOT alone. Ejectives and plain unaspirated stops have similar VOTs; the principal differences appear to occur in the vowel onset and in the prerelease closure phase. Strong ejective characteristics such as those of Navajo [Lindau, J. Phonet. 12, 147–155 (1984)] do not appear to be present. The present findings, combined with those of Ingram and Rigsby (1987) for the contiguous but unrelated language Gitksan, imply that relatively weak ejectives may be an areal phenomenon. Results will also be contrasted with published data from the related languages Chipewyan and Navajo.
Acoustic correlates of manner of articulation for Urdu stop consonants
Authors: Hussain Sarmad
Published: October 2005

This study investigates the acoustic correlates for the four manners of stop articulation ([±voice, ±aspirated]) at the four different places of articulation (labial, dental, alveolar, and velar) in Urdu. The study follows up Davis’ work [J. Phonet. 22, 177–193 (1994)] on manner in the homologous velar stops in Hindi. Data from four subjects for the 16 stops (ten different tokens of each stop for each subject) support Davis’ assertion that F2 ‘‘lag’’ time (between stop-released and onset of F2 for the following vowel) is a more conclusive measure for the feature [aspirated] than the traditional voice onset time (VOT) measure. However in Urdu, unlike Hindi, lag time alone does not exhibit a four-way contrast. A measure of ‘‘lead’’ time (pre-stop-release voicing) is also required. Thresholds for lead time and lag time permit all four manners to be distinguished without reference to the place of articulation for all the subjects. Thus the phonological features [voice] and [aspirated] are more phonetically orthogonal in Urdu than Hindi. The results contribute to the ongoing debate on the invariance versus variability of acoustic cues, and to the discussion concerning the representations relating the phonological and phonetic levels of speech.
High-frequency forward scattering from Gaussian spectrum, pressure release, corrugated surfaces: Measurements of twinkling exponents and the dependence of the second moment on distance from surface and pulse length
Authors: Stroud J. S. , Marston P. L. , Williams K. L.
Published: October 2005

A single realization of a Gaussian spectrum surface (rms roughness 1.5 cm, correlation length 10 cm) was manufactured out of Styrofoam. This surface provided a pressure release, corrugated surface for an underwater, forward-scattering investigation. Omnidirectional source and receiver were used in the frequency range of 100–300 kHz. Short pulses were used to allow isolation of individual contributions to the scattered field. These individual contributions were then classified using catastrophe theory [K. L. Williams, J. S. Stroud, and P. L. Marston, J. Acoust. Soc. Am. 96, 1687–1702 (1994)]. The frequency dependence of the mth higher-order intensity moments Im was measured and compared to predictions [M. V. Berry, J. Phys. A 10, 2061–2081 (1977)] that Im is proportional to kνm (for m≳2), where νm is a twinkling exponent. Also, the dependence of I2 on distance from the surface was examined at a single frequency utilizing various pulse lengths. It is known that far from a surface the wave field will obey Gaussian statistics (I2=2). For short pulses, however, the statistics of the wave field are strongly dependent upon individual reflections. For longer pulses this is the case near the surface but as one moves away it is shown that the Gaussian limit is approached. [Work supported by ONR.]
Acoustic backscatter from bubbles confined in sediment pores
Authors: Boyle Frank A. , Chotiros Nicholas P.
Published: October 2005

A model for acoustic backscatter from trapped gas bubbles in sandy sediments was recently presented [F. A. Boyle and N. P. Chotiros, J. Acoust. Soc. Am. 93, 2397(A) (1993)]. One of the assumptions was that trapped bubbles respond to an ambient acoustic field as if they were free bubbles surrounded by an infinite volume of water. A refinement to this model includes the effects of solid particles surrounding and constraining the fluid around the bubbles. A new expression for the sediment backscattering strength accounts for fluid confinement in pores. This confinement affects sediment acoustic impedances, bubble resonances, and scattering cross sections. Biot fast and slow compressional waves are treated separately. [Work supported by Naval Res. Lab., Stennis Space Center.]
Bistatic acoustic scattering from trapped gas bubbles in sandy sediments
Authors: Boyle Frank A. , Chotiros Nicholas P.
Published: October 2005

A technique based on acoustic reciprocity has recently been used to calculate backscattering strengths of marine sediments [F. A. Boyle and N. P. Chotiros, J. Acoust. Soc. Am. 93, 2397(A) (1993)]. The method begins with computation of the pressure induced at an element of scattering volume in the sediment. The pressure returned to a projector is then obtained via a reciprocal relationship between source and scatterer. A similar technique is developed to permit the calculation of bistatic scattering strengths. This technique is combined with a Biot model for acoustic penetration and a scattering model involving trapped bubble resonance scattering, to arrive at a bistatic sandy sediment acoustic scattering model. [Work supported by Naval Res. Lab. Stennis Space Center under the MCM Tactical Environmental Data System (MTEDS) project.]
A dynamic penetrometer for rapid assessment of seafloor parameters
Authors: Akal T. , Stoll R. D.
Published: October 2005

Information on geoacoustic and geotechnical parameters of the seafloor is important in sonar performance evaluation as well as in engineering applications. Since measurement of these parameters using traditional methods usually involves some rather elaborate experimental procedures, there is the need for a simple system that can remotely measure some of these parameters from a moving ship or aircraft. To accomplish this a new technique using a probe similar to the expendable bathythermograph (XBT) has been developed wherein the thermistor used to measure water temperature is replaced by an accelerometer. When the probe first impacts the bottom there is rapid deceleration controlled by the shear strength of the sediment, followed by a period of damped oscillation with frequency dependent on the geoacoustic properties of the sediment. Thus when the impact signature is fully analyzed it is possible to obtain information on both the shearing strength of the bottom as well as the geoacoustic properties. At present a series of laboratory and field tests are being carried out in a cooperative program at Lamont–Doherty Earth Observatory and SACLANT Centre. Preliminary results of this work are presented in this paper. [Work supported by ONR.]
Numerical study of various thermoacoustic refrigerator configurations
Authors: Hofler Thomas J.
Published: October 2005

The results of numerical models and optimizations for various configurations of thermoacoustic refrigerators will be presented. The refrigeration goals are large-scale refrigeration with low temperature span, high efficiency, and reasonably high power density. The physical equations used are the usual plane wave Rott formulation with improved solutions for the heat exchangers and shaped resonator ducts. The primary emphasis will be on solutions having the highest system efficiency, excluding losses associated with electrical drivers and secondary heat exchange.
A nonlinear analysis of a simple thermoacoustic system
Authors: Kumon Ronald E.
Published: October 2005

A simple thermoacoustic system was studied to try to better understand the interaction between the temperature, pressure, and velocity modes of the system. The system considered was a one-dimensional ‘‘tube,’’ closed and isothermal at both ends and filled with a helium gas. Initially, the gas is static but with a sinusoidal temperature distribution. To obtain a simplified model of the system, a Galerkin-type method was applied to the full hydrodynamic equations in one spatial dimension and the ideal gas law equation of state. By substituting highly truncated sine and cosine series in the spatial variable with time-dependent amplitudes into the aforementioned PDEs, the model was reduced to a set of coupled nonlinear ODEs. First, these equations were linearized and examined for series expansions with different number of terms. Next, the nonlinear ODEs were studied. Finally, these results were compared with direct finite-difference calculations using MacCormack’s method to integrate the full hydrodynamic equations.
Experimental study of acoustic turbulence and streaming in a thermoacoustic stack
Authors: Gaitan D. Felipe , Gopinath Ashok , Atchley Anthony A.
Published: October 2005

Recent developments in thermoacoustic devices have generated a renewed interest in finite amplitude standing waves and the nonlinear effects associated with them. In a typical thermoacoustic device, a stack and two heat exchangers are placed inside a resonator approximately midway between the velocity and pressure antinodes. These elements, consisting of closely spaced rigid plates, present both a discontinuity in the fluid flow and a rigid boundary with which the fluid can interact. Under these conditions, at least two well-known effects may occur: acoustic streaming and turbulence. These effects are of particular interest since they could significantly affect the thermoacoustic heat transport inside the stack. In this study, the fluid velocity inside and near a stack was measured qualitatively and quantitatively using a stroboscopic lamp and a laser Doppler velocimeter, respectively. Measurements under different conditions will be presented and discussed. [Work supported by ONR.]
Numerical modeling of unsteady flow in the neighborhood of a thermoacoustic stack
Authors: Worlikar A. S. , Knio O. M.
Published: October 2005

A low-Mach-number compressible flow model for the simulation of acoustically driven flow fields within thermoacoustic couples is constructed. The model is based on the assumption that length of the thermoacoustic stack is much smaller than the wavelength of the driving standing wave. The latter assumption is used to obtain a simplified description of the impact of acoustic waves while retaining all of the essential features of the unsteady flow developing in the neighborhood of solid boundaries. Results of numerical simulations are presented which illustrate the nonlinear response of the flow to different driving amplitudes and frequencies. [Work supported by the Office of Naval Research.]
Thermoacoustic sound source in the Helmholtz limit
Authors: Raspet Richard , Lightfoot Jay A. , Belcher James R. , Bass Henry E.
Published: October 2005

Thermoacoustic engines are placed in resonant cavities for Q amplification. Variations in the cross-sectional area of the resonator serve to reduce device volume and to minimize nonlinear distortion by detuning higher harmonics. In the case of a thermoacoustic sound source, these cross-sectional variations in the resonator area may be carried to an extreme such that the resonator approaches the Helmholtz limit. This limit produces a dimensionally compact, low-frequency thermoacoustic sound source. A thermoacoustic sound source in the Helmholtz limit has been constructed. The measured particle velocity and acoustic pressure in the device will be compared to Helmholtz idealization. [Work supported by ONR.]
Radial versus plane wave thermoacoustic engines: Which is best?
Authors: Arnott W. Patrick , Lightfoot Jay , Raspet Richard , Bass Henry E.
Published: October 2005

Most previous work in thermoacoustics has considered placing the elements in plane wave resonators. The lowest radial or breathing mode of a cylindrical resonator is also potentially useful for producing thermo- acoustic sound sources or refrigerators. An immediate advantage of the radial geometry is the separation of higher modal frequencies from the higher harmonics of the fundamental when the engine is working at large amplitude. Criteria recently developed for deciding which geometry is best will be presented. This will be followed by a comparison of plane and radial wave refrigerators and sound sources. The short stack approximation for both geometries will be used in the comparison. Our derivation of this approximation is not limited by the additional boundary layer approximation. [Work supported by ONR.]