bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic backscatter from an inhomogeneous volume beneath a planar interface: Model and experiment
Authors: Hines Paul C.
Published: October 2005

Mathematical models of acoustic scattering from the ocean bottom currently available, generally fail to predict backscatter levels of sufficient magnitude, for two limiting cases; as the bottom becomes increasingly smooth and as the grazing angle becomes small. A mathematical model of acoustic backscattering is derived herein which attempts to address these shortcomings for the case of a sediment bottom. In the model, scattering results from fluctuations in concentration, where concentration is roughly defined as the water to particle ratio within the sediment. The model allows for penetration of the incident wave into the bottom at subcritical grazing, and retransmission of scattered spherical waves through the (planar) interface. The frequency and grazing angle dependence of the acoustic backscatter are determined primarily by the correlation function of the concentration fluctuations, while the magnitude is controlled by the mean-square value of these fluctuations. To complement the modeling, laboratory experiments were performed to measure volume backscatter from a smooth, water-saturated sand bottom at grazing angles from 10°–50° for frequencies of 25–200 kHz. Agreement between model and data is good. [Work was performed during post-graduate degree at the University of Bath, Bath, U.K.]
Sound scattering by deformed cylinders of finite length
Authors: Stanton T. K.
Published: October 2005

An approximate solution is derived for the scattering of sound by circular cylinders of finite length with a deformed axis and composition profile and (cross-sectional) radius that vary arbitrarily along the axis. This solution is a generalization of previous work [T. K. Stanton, J. Acoust. Soc. Am. 83, 55–63 (1988) and T. K. Stanton, J. Acoust. SOc. Am. 83, 64–67 (1988)] where the scattering by straight finite cylinders of uniform fluid and elastic material, respectively, were described. The new formulation is used to calculate the scattering of sound at all frequencies from a prolate spheroid with a high aspect ratio (ratio of major axis to minor axis) and a uniformly bent finite cylinder of constant cross-sectional radius. There is excellent agreement between the calculations involving the prolate spheroid and the exact spheroidal wave function solution. Furthermore, numerical integration of the deformed cylinder formula required far less computer time than calculating the exact solution. The calculations involving the bent cylinder are compared with backscatter data from preserved euphausiids (shrimplike marine organisms) and suggest that the radius of curvature of the animals plays a major role in the acoustic scatter characteristics of the marine organisms. For example, at 200 kHz, the backscattering cross section of a 23-mm-long euphausiid will decrease by 6 dB if the animal bends by as little as 1.4 mm at the ends. [Work supported by the ONR.]
Canadian “National Guidelines for Environmental Noise Control—Procedures and Concepts for the Drafting of Environmental Noise Regulations/By-laws in Canada.”
Authors: Morison Deirdre A.
Published: October 2005

These National Guidelines have been prepared for legislators at all levels of government, provincial planners, municipalities, consultants, industries, and designers. The intent is to provide a common basis across Canada for the assessment, measurement, and legislative control of environmental noise while, at the same time, providing options to allow flexibility of choice to fit specific needs. The National Guidelines may be adopted or modified, in entirety and in part, into provincial or municipal legislation or into codes of practice. The National Guidelines are divided into two major parts. Part I, Concepts and Procedures, details the various options available in developing a noise control program and includes a section on Land Use Planning and Model Noise Control Legislation presenting sound level objectives and more general bylaws. The second part of the document contains technical reference material, including a section on instrument specification, measurement, and prediction, and another covering noise reduction techniques. Terms and interpretations, references, and technical support documents are included also. The texts of the technical support documents are briefly summarized in the document and are reproduced on microfiche at the end of the National Guidelines. The National Guidelines were prepared by the Working Group on Environmental Noise on the Federal/Provincial Advisory Committee on Environmental and Occupational Health, which intends to provide periodic revisions.
Optimizing impedances in the traveling wave heat engine
Authors: Ceperley Peter H.
Published: October 2005

Thermal coupling between solid surfaces and an acoustic working fluid in a regenerator is essential to the operation of a thermoacoustic engine, while the associated viscous coupling, also between the surfaces and the working fluid, is detrimental to the engine's performance and efficiency. The Prandlt number (roughly 0.7 for most gases over a considerable range of temperatures and pressures) fixes the ratio of these two types of coupling for a thermoacoustic engine with a continuous regenerator. This ratio of couplings can be improved in several ways in traveling wave heat engines with short regenerators [P. H. Ceperley, J. Acoust. Soc. Am. 66, 1508–1513 (1979) and P. H. Ceperley, J. Acoust. Soc. Am. 77, 1239–1244 (1985)]. This paper will discuss the optimization of the flow resistance and length of a short regenerator and also resonant impedance enhancement using split mode excitation [P. H. Ceperley, U.S. Patent 4,686,407 (1987)] to significantly reduce the viscous losses while maintaining good thermal coupling.
Radiation and scattering from laminated spherical shells
Authors: Schmidt Henrik
Published: October 2005

The solution in terms of spherical harmonics to acoustic and elastic wave propagation problems in spherically stratified media is well established. However, except for very low ka values, a direct numerical implementation is unstable. Propagator matrix approaches have been applied for moderate ka values, whereas environment transformations have been developed to represent the spherical stratification by a plane stratification at higher ka values, in particular in relation to long-range seismic propagation in the solid earth. Here, it is demonstrated that, by introducing a proper normalization of the spherical Bessel functions, unconditional stability can be obtained by using the Global Matrix approach [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813–825 (1985)]. This SAFARI code has therefore been modified to treat propagation in spherically stratified elastic media. The algorithm is stable at least up to ka = 103, allowing modeling of stratifications alternating between high- and low-speed layers, traditionally problematic for propagator approaches. Examples will be given for high-frequency scattering from coated shells as well as simulations of array signal processing performance in relation to structural acoustics experiments. [Work supported by ONR.]
Three-dimensional Green's function for fluid-loaded thin elastic cylindrical shell: Formulation and solution
Authors: Felsen L. B. , He J. M. , Lu I. T.
Published: October 2005

This paper treats sound radiation from a time-harmonic point pressure source located either inside or outside a thin, homogeneous, infinitely long circular cylindrical elastic shell, which is immersed in different interior and exterior fluid media. This Green's function problem is attacked by a combination of the method of separation of variables and the method of images applied to an infinitely extended azimuthal (φ) domain. The reduced one-dimensional problems in the cylindrical (r, φ, z) coordinates are solved by general spectral techniques in terms of one-dimensional characteristic Green's functions gr, gφ, gz, which depend on one or both of the two complex spectral separation parameters (spatial wavenumbers) λ1 and λ2. While the one-dimensional problems in the φ and z domains are straightforward, the presence of the shell in the radial domain introduces substantial complexity. The solution is obtained by defining the discontinuities in the pressure and normal displacement across the shell via recourse to the dynamical equations of motion inside the shell. The synthesis problem is made unique through a complete analysis of the spectral singularities gr,φ,z in their respective complex planes, which permits selection of appropriate integration contours. A host of alternative representations, whose choice (concerning utility) is motivated by the parameter range of interest, can be derived from the fundamental spectral form, and asymptotic reductions lead to a variety of wave processes that have a cogent ray acoustic interpretation. [Work supported by ONR.]
Correlating fan performance parameters and noise
Authors: Dunens Egons K.
Published: October 2005

Computer cabinet designers choose fans based on their air flow characteristics but noise concerns often have a significant impact on the final cabinet design. Many physical and operating parameters can impact the fan noise. The noise emissions from a large number of fans have been measured using ANSI S12.11-1987. Regression analysis is used to evaluate the correlation of the various parameters to the fan noise level in order to understand trade-offs at the initial design stage.
Nonlinear behavior leading to real rarefaction shocks and related phenomena
Authors: Thompson P. A.
Published: October 2005

Early calculations by Bethe, Zel'dovich, and others have suggested the possibility of rarefaction shocks in fluids and solids. Recent experiments have demonstrated the existence of rarefaction shocks in rubber (Kolsky and Rader), quartz (Barker and Hollenbach), iron (Erkman, Ivanov, and Novikov), fluids at near-critical states (Borisov et al.), and in evaporating mixtures (Chaves, Thompson et al.). Analogous discontinuities are found in second sound in superfluid helium. The assertion that all rarefaction shocks violate the second law is untrue, both in theory and practice! Physical experiments in fluids leading to a single-phase rarefaction shock, or to a complete rarefaction-evaporation shock have, until now not been realized. Key ingredients for real rarefaction shocks include a negative nonlinearity parameter Γ, usually some degree of metastability, Chapman-Jouguet conditions, and in the case of fluids, a large molar heat capacity (many molecular degrees of freedom). Examples and related phenomena are discussed.
Random linear projector arrays with reduced acoustic interaction
Authors: Joseph P. M. , Pillai P. R. Saseendran , Sridhar C. S.
Published: October 2005

Acoustic interaction effects among the elements of closely packed sonar projector arrays should be minimized considerably, as it reduces the acoustic power output and deteriorates the beam characteristics, at higher drive levels. This effect can be minimized by restructuring the array format with appropriately chosen interelement spacing [P. M. Joseph and P. R. Saseendran Pillai, in Proceedings of the IEEE International Conference on Acoustics, Speech, and Signal Processing (IEEE, New York, 1988), pp. 2697–2700] and further reduction in interaction effect can be achieved by incorporating the nonuniform array concept. The appropriate interelement spacing for this nonuniform array can be determined by using total enumeration method. But this method cannot be recommended for arrays comprised of large number of elements, as it is a time consuming and tedious process. In the approach presented in this paper, the suitable interelement spacings that reduce the interaction are determined by using Gaussian distributed random numbers with the element spacing of the restructured array as mean and by retaining the array dimension same as that of the restructured array. Beam pattern and array gain are found to be little affected in the randomly distributed element configuration.
Transmission and reflection of a real sound beam at a two-fluid interface
Authors: Tjøtta Jacqueline Naze , Salvesen Hans-Christen , Tjøtta Sigve
Published: October 2005

The analytical solution of many problems of acoustics is expressed in terms of a Fourier integral. In this paper, general asymptotic expressions that appxoximate both the location and the value of the maximum amplitude of a one- or two-dimensional Fourier integral are presented. These expressions are generally easier to compute than evaluations using a fast Fourier transform algorithm. The method is used to study the reflection and transmission of a real sound beam at the interface between two homogeneous and dissipative fluid layers. Simplified analytical formulas that explain the beam displacement and other behavior near the interface are obtained. Numerical results are compared with those of an earlier work [see Sagen, Naze Tjøtta, and Tjøtta, J. Acoust. Soc. Am. 85, 24–38 (1989)]. The influence of various parameters on the direction and shape of the reflected and transmitted sound beams is investigated. [Work supported by the IR&D program of ARL:UT, The Royal Norwegian Council for Scientific and Industrial Research (NTNF), and VISTA/STATOIL, Norway.]
Total scattering cross section of an elastic spherical shell: Comparison of exact computations with a GTD model that includes Lamb wave resonances
Authors: Kargl Steven G. , Marston Philip L.
Published: October 2005

The optical theorem, relating the total scattering cross section σt(ka) to the forward scattering function f(θ = 0,ka), is used to study the rich structure contained in σt(ka) for an elastic spherical shell in the frequency range 7 < ka < 100. The partial-wave series (PWS) for f(0,ka) does not facilitate a direct understanding of the physical mechanisms causing this structure. Hence, a model for f(0,ka) is developed from an elastic generalization of the geometrical theory of diffraction (GTD) [P. L. Marston, J. Acoust. Soc. Am. 83, 25–37 (1988)]. The generalized GTD is based on the Watson transformation of the PWS. The GTD model includes explicit contributions from ordinary forward diffraction and from individual Lamb waves excited on the shell. Calculations of σt(ka) with fPWS(0,ka) and fGTD(0,ka) show good agreement between the exact PWS result and the GTD model for the ka range investigated. The agreement confirms the GTD model and demonstrates the relevance of Lamb waves guided by the shell and forward glory scattering. Finally, these calculations verify the correctness of the numerical methods by which the Lamb wave parameters were obtained [S. G. Kargl and P. L. Marston, J. Acoust. Soc. Am. 85, 1014–1028 (1989)]. The numerical computations presented are for a stainless steel shell with an inner-to-outer radius ratio b/a = 0.838. [Work supported by ONR.]
Effects of cognitive workload on speech production
Authors: Van Summers W. , Pisoni David B. , Stokes Michael A.
Published: October 2005

Previous research on the acoustic properties of speech has generally focused on “normal” speech produced under benign conditions. Typically, subjects produce utterances in a quiet laboratory setting with no competing or distracting stimuli present. Almost no basic research has examined speech in more demanding environments. For example, pilots may often be required to produce speech while simultaneously performing several other attention-demanding tasks. The information-processing requirements of these simultaneous tasks may affect the acoustic properties of speech in a wide variety of ways. The present research examined speech produced under benign conditions and while simultaneously performing an attention-demanding perceptual-motor task. Speech produced while carrying out the perceptual-motor task showed reliable increases in amplitude and fundamental frequency and reductions in segmental durations and spectral tilt. The results have implications for automatic speech recognition in demanding environments. [Work supported by Armstrong Aerospace Research Laboratory, Wright-Patterson AFB, Contract No. AF-F-33625-86-C-0549.]
Initial prominence and accent in Seoul Korean prosody
Authors: de Jong Kenneth
Published: October 2005

This paper investigates two questions about the prosodic system of Seoul Korean—whether there is a word-initial prominence, and whether a concurrent F0 peak is best seen as an optional pitch accent or as a boundary tone associated with some prosodic level. It analyzes the utterances of two speakers of the Seoul dialect. The durations of syllables and vowels placed in various positions within a sentence are compared. The two intonational analyses are tested by noting the position of the F0 peak, determining how consistently the peak appears, and noting the effects of pitch range variation. Results suggest: (1) that initial syllables of a word are consistently longer than medial syllables; (2) the position of the initial F0 peak is closely bound to the initial syllable of the utterance, but not of the word; and (3) the initial F0 peak appears in all tokens, except relatively short or fast tokens. This lack is shown to be due to tonal undershoot of a following low tone, as is apparent from strong and continuous relationships between height of pitch fall and rise and the temporal distance between the F0 peaks. These results suggest there is a word initial prominence in Seoul prosody, distinct from initial tones. The tones are best analyzed as boundary markers for some larger prosodic level, which become associated with initial syllables.
Phonetic implementation rules for tones in Yorùbá
Authors: Laniran Yetunde
Published: October 2005

This paper reports on some aspects of the phonetic implementation rules for tones in Yorùbá declarative sentences. Some of the current literature on intonation suggests that declination is not sensitive to the phonological composition of the tones of an utterance. In Yorùbá, tonal composition is relevant, since the rate at which pitch drops in identical tone sequences depends on the tone type. H and M sequences both begin at the same pitch level and are only distinguished subsequently by the degree of declination in the M sequence. The rate of declination in a sequence of L tones is fastest of all. The largest drop in pitch of L sequences is between the final and penultimate L tone for two of the three speakers we have considered so far. Another feature of the F0 contour in Yorùbá is the phenomenon of high-raising by which a H tone is raised by a following and/or a preceding L tone. High-raising seems to be a cumulative effect of surrounding L tones, the pitch value of the H tones decreases in the following representation: LHL > LHM ∼ MHL > MHM.
The intelligibility of speech directed to children and adults
Authors: Goodman Judith C. , Nusbaum Howard C. , Lee Lisa , Broihier Kevin
Published: October 2005

Speech directed to very young children differs markedly from speech directed to adults in vocabulary, syntax, and intonation. Are there differences in segmental intelligibility as well? Speech was recorded from six mothers addressing their 2 year olds, and, in another session, addressing an adult, under comparable conditions. Open and closed-class words were excised from both types of speech and were presented, in isolation, to adult listeners for identification. Children may not understand closed-class words, so mothers may not articulate them clearly. Excised open-class words expressed either new or previously given information. Whereas repeated information is articulated less clearly in speech to adults, repeated information in speech to children may be intended to aid comprehension. Thus the given/new distinction may affect the intelligibility of speech to adults and to children differently. Preliminary results indicate that child-directed speech may be less intelligible than adult-directed speech, particulary for closed-class words: Expectations about children's linguistic knowledge apparently affect articulation of different word classes. [Work supported by NIH and a Biomedical Research Support Grant.]
Comprehension of natural and synthetic speech
Authors: Ralston James V. , Mullennix John W. , Lively Scott E. , Greene Beth G. , Pisoni David B.
Published: October 2005

Previous studies comparing the comprehension of natural and synthetic speech passages have produced conflicting results. All of these studies used successive measurement techniques in which subjects' comprehension was assessed after the presentation of a passage. However, comparative studies have found that successive methods are less sensitive than simultaneous “on-line” measures. Successive measures are also known to be influenced by memory factors. Subjects in the present experiment monitored for word targets while they listened to short passages and then verified statements after each passage. Both monitoring and verification performance for passages of synthetic speech were depressed relative to passages of natural speech. There was a significant interaction between voice and text difficulty in the monitoring latency data, suggesting that both factors affect mechanisms drawing from the same limited processing resources. Finally, there was a significant interaction between voice and sentence type in the verification task. Subjects listening to passages of synthetic speech had relatively poor memory for propositional information compared to surface (word) information. Taken together, the results indicate that comprehension of synthetic speech is poorer and slower than natural speech. Memory for propositional information extracted from passages of synthetic speech is particularly poor. [Work supported by NSF.]
Perception of Hindi retroflex versus dental stops by monolingual speakers of American English
Authors: Polka Linda
Published: October 2005

Cross-language studies have shown that foreign consonant contrasts vary in the degree of perceptual difficulty that they present adult non-native listeners. Phonemic, phonetic, and acoustic factors have been considered important in accounting for this variability. These factors were examined by comparing English listeners' perception of the Hindi retroflex versus dental place-of-articulation contrast in four different voicing contexts: prevoiced, voiceless aspirated, voiceless unaspirated, and breathy voiced. Differences in the perceptual difficulty of the four Hindi contrasts were predicted based on: (1) phonemic status (the functional status of the contrast in listeners' native phonology), (2) phonetic familiarity (as allophones or free variants), (3) differences in acoustic salience related to voicing, and (4) assimilation strategies. Differences in performance in a categorial AX discrimination task were ordered from most to least errors: prevoiced, voiceless aspirated, breathy-voiced, and voiceless unaspirated. Perceptual differences were correlated with both acoustic salience of place cues and subjects' descriptions of their assimilation strategies. [Work supported by NICHD and NINCDS.]
Effects of auditory and phonetic training on Americans' discrimination of Hindi retroflex-dental contrasts
Authors: Strange Winifred , Polka Linda , Aguilar Manuela C.
Published: October 2005

Previous research has shown that the Hindi retroflex-dental contrast among stop consonants is not easily differentiated by English speakers even after some training. In the present study, subjects were given 4 days of training (768 trials) in a categorial AX discrimination task on full (unmodified) or truncated tokens of naturally produced breathy-voiced [dha] vs [d̪ha]. Interstimulus intervals (ISI) were either short (550 ms) or long (1500 ms). Conditions favoring auditory-processing strategies (short ISI and truncated syllables) yielded the most improvement during training. However, pre-test to post-test improvement in “phonetic-level” discrimination of the full syllables was not significantly different across the four training conditions, and there was no transfer to discrimination of the contrast in voiceless aspirated [tha] - [t̪ha] or prevoiced [da]-[d̪a] stops. Large individual differences Pound in each training condition suggest that subjects' strategies may be more important than stimulus and task variables in predicting success in perceptual differentiation of non-native contrasts. [Supported by NINCDS.]
Experimental measurements of normal incidence reflection/scattering from undeformed natural sea ice
Authors: Francois R. , Williams K. , Wen T. , Mourad P.
Published: October 2005

Using narrow-band pulses, experimental measurements of normal incidence reflection/scattering from the ice/water interface of naturally growing first year sea ice have been made. The results cover the frequency range from 20–300 kHz. A sufficient number of realizations have been obtained, using different experimental techniques, that generalization of the results can be made. The techniques involve monostatic experiments, ensonifying several different diameters of cylindrical ice surfaces, and undeformed areas of ice, using transducers with a variety of directivities including omnidirectional. The growing, or skeletal, layer of ice results in a graded porous, rough surface that can be treated using Biot theory to obtain acoustic velocities, a continuous velocity profile for reflection, and Kirchhoff theory for scattering. The results indicate that the mean amplitude reflection coefficient follows the approximate equation, RA = 0.40 − 0.157 log (f) (fin kHz), in the transition region from about 2–200 kHz. At lower frequencies, the reflection coefficient is determined by the bulk velocity of the ice (the velocity gradient in the skeletal layer being unimportant); at high frequencies, the surface roughness and ice/water surface impedance mismatch may both contribute to the mean reflection coefficient observed. [Work supported by Office of Navy Technology with technical management by NORDA.]
Measurements of low-frequency ambient noise in the Greenland Sea
Authors: Buckingham Michael J.
Published: October 2005

Sonobuoy measurements of omnidirectional ambient noise spectra have been made at several positions between the Denmark Strait and the Fram Strait off the east coast of Greenland. Results from lines of buoys placed normal to the ice edge indicate that, below 200 Hz, the noise level is essentially uniform across the edge, with no peak observed in the level at the interface between the ice cover and the open water. Noise levels tend to be insensitive to wind speed/sea state, showing a typical level of 83 dB re: 1 μPa2/Hz at 100 Hz. Usually, the buoy nearest the coast shows the highest spectral level, suggesting that coastal processes are perhaps the principal source of low-frequency ambient noise in the Nordic Seas. Several mechanisms could be responsible for the noise, one hypothesis being the movement of glaciers from the Greenland ice cap, at an elevation of ≈ 2000 m, down towards the sea. Each glacier contains on the order of a billion tonnes of ice or more which grinds its way over rough, rocky terrain. This movement generates seismic waves in the ground which could couple into the ocean through the seabed: An interface (Scholte) wave may propagate along the sea bottom and radiate acoustic energy into the water column.
On supercritical incidence of a finite-amplitude plane dilatational wave in an elastic solid
Authors: Shu Kun-Tien , Ginsberg Jerry H.
Published: October 2005

An earlier analysis [K. T. Shu and J. H. Ginsberg, J. Acoust. Soc. Am. Suppl. 1 85, S139 (1989)] described nonlinear reflection and refraction phenomena of a finite-amplitude dilatational wave at subcritical incidence on a plane interface between two bonded solids. The present work extends the earlier description to cases where the angle of incidence exceeds the critical value. The incoming wave is assumed to originate from the slower medium, so two critical angles exist, associated with evanescence of either the transmitted dilatational or shear wave. The finite-amplitude version of Snell's law indicates that the dependence of the phase speed of the incident wave on its instantaneous amplitude induces, in the case of evanescent waves, fluctuations in the phase velocity parallel to the interface and in the decay rate normal to the boundary. This effect mirrors the fluctuations in the transmission and reflection angles of propagative waves. A numerical algorithm is developed to evaluate reflected or transmitted waveforms at a specified field point. In the special case of incidence close to a linear critical angle, the finite amplitude Snell's law indicates that the corresponding wave fluctuates between propagative and evanescent properties within a single period. [Work supported by NSF.]
A new resonant photoacoustic technique for measuring very low optical absorption in glasses and crystals
Authors: Yu Chang , Maynard J. D.
Published: October 2005

One of the most sensitive methods for measuring low optical absorption in glasses involves the photoacoustic effect. Conventional methods use high-power pulse lasers and attached piezoelectric transducers to obtain detectable acoustic signals, but this method is limited by noise and scattered light at the transducer. A new technique has been developed using a cw laser, which, although it has less power, may be modulated at the acoustic resonant frequency of the sample and thus generates an acoustic signal amplified by the quality factor (Q) of the resonance. Since Q's of 105 to 106 are readily obtained, a cw laser with only 0.01% of the energy of a pulse laser may be used to obtain several orders of magnitude improved sensitivity. To increase the Q and thus increase the sensitivity, the measurements are made in vacuum, the sample supports (three saphire spheres) are located at nodal lines with computer-controlled positioners, and the transducers are noncontact interdigital capacitors that sense the motion of a nearby dielectric sample or the fringe field of a nearby piezoelectric sample. The noncontact transducers also eliminate the problem of scattered light. [Work supported by the Office of Naval Research.]
Observation of optoacoustic amplitude in CS 2 at high input energies
Authors: Cheyne Stanley A. , Bass Henry E.
Published: October 2005

The optoacoustic amplitude as a function of laser pulse energy has been measured. A nitrogen laser emitting UV (337 nm) pulses 800 ps in duration was used to excite liquid carbon disulfide (CS2), which strongly absorbs the UV radiation. Measurements indicate an optical absorption coefficient of 370 cm−1 implying an optical penetration depth of 27 μm. The spatial profile of the pulse was an ellipse at the focal point with dimensions of 330×90 μm. The energy coupled with the short penetration depth resulted in a high energy density (532 J/cm3). This was varied by placing glass microslides in the beampath. The optoacoustic amplitude as a function of energy exhibited changes in slope as the liquid in the focal volume underwent vaporization. The experimental observations were explained in terms of an energy-dependent coefficient of thermal expansion and optical absorption. [Work supported by the Office of Naval Research.]
Spectral fusion based on coherence of amplitude modulation
Authors: Sheft Stanley , Yost William A.
Published: October 2005

The ability of listeners to attend to a subset of components (the target) of a tonal complex was investigated using a forced-choice procedure. The stimulus was an eight-component tonal complex. The components of the target subset (n = 1, 2, or 3 components) were distinguished from the complex by coherent amplitude modulation (AM). Each trial of the cued 2IFC task was preceded by a presentation of the coherently modulated target components in isolation. For each interval of a trial, either the target or an equal number of nontarget components shared the coherent AM. Subjects were required to detect the interval in which the target components were coherently modulated. The remaining components of the complex were all either modulated at different rates, modulated with a random shift of the target-modulator phase angle, or not modulated. Performance was measured as a function of the number of target components, the harmonic relationship among the target components, and the harmonic relationship between the target and nontarget spectral groups. With coherent AM of harmonic target components, the increment in d′ with increasing n exceeded predictions based on the combination of independent sources of information, suggesting that these stimuli may be processed as an entity by the auditory system. [Work supported by NINCDS.]
Phase transitions in speech production and their perceptual consequences
Authors: Tuller Betty , Kelso J. A. Scott
Published: October 2005

Previous work shows that the relative phasing of articulatory events varies little across two levels of speaking rate and stress. But, one may ask, varies little with respect to what? A methodology is required that differentiates articulatory patterns as they evolve in time. With this aim, subjects were instructed to say /ip/ or /pi/ repetitively, at increasing speaking rates, while monitoring their glottal and lip movements. For /pi/, the observed interarticulatory phase relationships did not depend on speaking rate. For /ip/, relative phasing often changed markedly, suggesting that loss of stability underlies articulatory change (a phase transition). In two follow-up perceptual experiments, listeners appeared to judge the consonant's syllable affiliation on the basis of interarticulator relative phase, and did so in a “categorical” manner. These findings, interpreted in light of a theoretical model based on synergetics [Kelso et al., Physics Scripta 35, 79–87 (1987)], may help resolve controversies concerning whether or not a particular variable is an articulatory “invariant.” [Work supported by NIH and NIMH.]
Inferring the shape of a towed array by processing the data from its acoustic sensors
Authors: Ferguson Brian G.
Published: October 2005

When a horizontal linear array of underwater acoustic sensors is towed through the sea, motions within the water mass and variations in the tow vessel's heading can cause the shape of the array to deviate from a straight line. Distortion of the array's linear configuration can lead to degradation in the detection and localization performance of the array, unless the spatial processing of the acoustic data can compensate for the nonlinear shape of the array. One method for monitoring the shape of the array involves instrumenting the array with compasses and depth sensors. Another technique is presented here whereby the data from the acoustic sensors themselves are used to infer the spatial distribution of the sensors along the array.
Experimental and theoretical wave propagation in solid and hollow cylinders in fluid
Authors: Plona Thomas J. , Kostek Sergio , Chang Shu-Kong
Published: October 2005

A comparison between experiment and theory is made involving axi-symmetric wave propagation along solid and hollow cylinders immersed in a fluid (i.e., water). The theoretical methods to generate waveforms include both integral representation and finite-difference modeling. The dispersive modal characteristics are calculated from the waveforms. The experiments are made on solid and hollow steel cylinders of 0.75 in. and 0.625 in. The source and receiver transducers are made from PZT rings 1.0 in. and 0.5 in. high which freely slide along the cylinders. Data are collected as a function of source-receiver spacing and over a frequency range of 40–240 kHz. A Prony's method is used to obtain the modal characteristics. Discussions will focus on the good agreement between theory and experiment, the differences between the mode structures in the two cases and the asymptotic behaviors at short and long wavelengths. Some interesting comparisons between monopole and dipole modes will also be made.
Measurement of acoustical and microstructural properties of real and model porous materials
Authors: Stinson Michael R. , Champoux Yvan , Daigle Gilles A.
Published: October 2005

Detailed measurements of several parameters describing porous materials are currently being made. The acoustical behavior of the porous materials is determined using an impedance tube technique, modified to provide both characteristic impedance and propagation constant, as a function of frequency. To define the microstructural properties, flow resistivity and porosity are initially being measured. Several real materials are being considered, including samples of reticulated open-pore foam, felt materials, and natural soils. A series of model porous materials, with well-defined microstructure, is also being developed. The first in this series consists, simply, of circular pores of uniform cross section, formed in a rigid host material. The measurements will be interpreted in terms of existing rigid-frame models of the acoustical properties of porous materials.
Sensitivity to envelope coherence
Authors: Richards Virginia M. , Green David M. , Onsan Zekiye A.
Published: October 2005

In a 2IFC paradigm, listeners indicated whether two, simultaneously presented, sinusoidally amplitude-modulated tones had envelopes that were in-phase rather than out-of-phase. The depth of modulation, m, necessary for 70% correct decisions was determined. Thresholds were obtained for carrier frequency separations of 2/3 and 4/3 of an octave, for geometric means of the two carriers ranging from 500–8000 Hz, and for modulation rates varying from 4 to 320 Hz. Increasing the frequency separation of the two carriers from 2/3 to 4/3 of an octave had little effect, reducing sensitivity by at most 5 dB. Similarly, thresholds were nearly independent of the geometric mean of the tonal carriers. Plotting detection threshold as a function of modulation rate yielded curves that were roughly low pass in character: For modulation rates less than 100 Hz, performance levels were approximately constant, and, for modulation rates less than 100 Hz, sensitivity to envelope phase deteriorated with increased modulation rate. [Work supported by the Air Force Office of Scientific Research and the National Institutes of Health.]
Phase effects in masking of one modulation frequency by another
Authors: Strickland Elizabeth A. , Viemeister Neal F.
Published: October 2005

Masking of one modulation frequency by another was measured in a 3IFC task. The carrier was broadband noise at a spectrum level of 30 dB SPL. This was amplitude modulated by a sinusoidal masker or a sinusoidal signal plus a sinusoidal masker. Masker modulation depth was fixed at 25% or 50%, and masker frequencies ranged from 2–800 Hz. Threshold signal modulation depth was measured for signals of 4, 16, 100, and 400 Hz. The masking functions showed broad tuning for modulation frequency consistent with that seen by Bacon and Grantham [J. Acoust. Soc. Am. 85, 2575–2580 (1989)]. For example, for a signal modulation frequency of 100 Hz, the amount of masking only varied over 5 dB for masker modulation frequencies from 40 to 140 Hz. Thresholds were phase dependent for masker frequencies of half, equal to, or twice the signal frequency. For equal signal and masker frequency, thresholds were consistent with detection of differences in envelope power, independent of signal/masker phase. Results are discussed in terms of models of modulation detection. [Work supported by grants from NINCDS (NS12125) and NICHHD (HD-07151).]
The slow compressional wave in a porous medium by the finite element method
Authors: Teng Yu-chiung
Published: October 2005

The finite element results for a fluid/porous-solid/fluid system are presented by using the double-nodel-layer technique. The pressure-type fluid elements are used to model the fluid fields: The porous solid is modeled by Biot's medium [J. Acoust. Soc. Am. 28, 168 (1956)]. The Biot's theory predicts that for propagation of acoustic waves in fluid-saturated elastic porous media, a second compressional wave exists. Geertsma and Smit [Geophysics 41, 169 (1961)], using Biot's theory, predicted the generation of this second type of compressional wave at an open interface between a liquid and a porous solid. Plona [Appl. Phys. Lett. 36, 259 (1980)] observed the second type of compressional wave in his liquid/porous-solid/liquid experiment at ultrasonic frequencies. Given suitable physical parameters in the finite element calculations, excellent agreement with the Plona's measurement has been obtained. The finite element results for a sealed interface, showing a diminishing of the second type compressional wave, also agree with the experimental work performed by Rasolofosaon [Appl. Phys. Lett. 52, 780 (1988)].
Experimental studies of low-frequency propagation over flat terrain
Authors: Wilson D. Keith , Thomson Dennis W.
Published: October 2005

Experimental studies of atmospheric acoustic propagation have included monitoring the level of a 27.7-Hz source at a distance of 770 m. Two of the extended duration experiments consisted of recording SPL at 1-min intervals for 75 h over dry ground (Oct. 1988), and for 144 h over frozen, snow-covered ground (March 1989). Comprehensive surface layer micrometeorological measurements, including monitoring the turbulent momentum, heat, and moisture fluxes adjacent to the path, as well as continuous Doppler sodar measurements of the boundary layer wind profiles, were made. These measurements are used to reconstruct the time-dependent “along path” sound speed profiles. Interpretation of the acoustic data includes comparisons with theoretical predictions from a fast field program (FFP).
Detection of relative-frequency changes in tonal sequences
Authors: Kidd Gary R. , Watson Charles S.
Published: October 2005

It was previously reported that listeners' abilities to detect frequency changes in randomly generated sequences of tones were substantially worse when the changed sequence was transposed in frequency [G. R. Kidd and G. S. Watson, J. Acoust. Soc. Am. Suppl. 1 84, S141 (1988)]. Listeners apparently rely on absolute frequency whenever they can and are relatively poor at using relative-frequency information even when they must do so to perform a discrimination task (i.e., when the changed pattern is transposed). The ability to detect changes in relative frequency was examined further in new experiments that included both high- and low-uncertainty conditions with five-tone and two-tone sequences. Under high-uncertainty conditions, performance with both five- and two-tone sequences was again relatively poor when the patterns were transposed, although somewhat better with the two-tone sequences. Under low-uncertainty conditions, performance with transposed patterns at both sequence lengths was often as good or better than with untransposed patterns, suggesting a strong role of pattern familiarity in the identification of patterns by the sequences of relative frequencies. [Work supported by AFOSR and NIH.]
Temporal DLs in isochronic loudness and pitch patterns
Authors: Monahan Caroline B. , Hirsh Ira J.
Published: October 2005

In an adaptive procedure, listeners discriminated the delay of a single tone in otherwise isochronic six-tone patterns. The temporal DL was measured at three tempos (isochronic intervals of 50, 100, and 200 ms) and for four delay positions (tones 2–5). In experiment 1, patterns comprised loud (forte) and soft (piano) tones: thus FFPPPF, PFPFPF, etc., where F was 80 dB SPL and P was 70 dB SPL. In experiment 2, frequency patterns were “parallels” of the loudness patterns of the first study: thus HHLLLH, LHLHLH, etc., where H(igh) was 1667 Hz and L(ow) was 1000 Hz. In both studies, the measure of timing accuracy (Weber ratio × 100) was similar to that found in earlier literature for the discrimination of single time intervals, namely, 5%–8% at 200 ms, 9%–15% at 100 ms, and 15%–25% at 50 ms. Accuracy was poorest for early serial positions of the delayed tone. This effect occurred primarily at 50 ms and was significant only in the loudness experiment. In experiment 1, at 50 and 100 ms, accuracy was about 2% better when the delayed tone was loud rather than soft. In experiment 2, accuracy was inversely related to the number of pitch changes per pattern. At 50 ms, accuracy was about 6% better when the delayed tone and the tone following identical rather than different in frequency. [Work supported by AFOSR.]
Sound transmission to the chest wall in the subglottal respiratory system at low frequencies
Authors: Wodicka George R.
Published: October 2005

The amplitude of sound transmission from the mouth to sites overlying the extrathoracic trachea and on the posterior chest wall was measured from 100 to 600 Hz. Bandlimited white noise was input into the mouth of each subject with the glottis open at resting lung volume, and measurements were performed using accelerometers. The ratios of the transfer functions between the tracheal site and the source, and the chest wall site and the source, were estimated. All of the resulting spectra exhibited a peak that occurred for the group at 129 ± 6 Hz with a Q of 2.2 ± 0.4. Also, a trend of decreasing spectral energy as frequency increased from the peak location was observed (− 17, ± 5 dB/oct). The fundamental radial mode of a model thoracic cavity, which is a large rigid cylinder filled uniformly with lossless lung tissue, provides a good estimate of this low-frequency resonance. This agreement suggests that thoracic cavity resonances may have particularly important effects on sound transmission in the subglottal respiratory system at frequencies below roughly 250 Hz.
Minimum audible movement angles for sources varying in both elevation and azimuth
Authors: Perrott David R. , Saberi Kourosh
Published: October 2005

A minimum audible movement angle (MAMA) experiment was performed in a “simulated motion” paradigm which allowed travel along vertical, horizontal, or oblique paths. Velocities of travel ranged from 1.8–230°/s. With motion restricted to the horizontal plane, MAMA thresholds increased from about 1.7° at the lowest velocity (1.8 °/s) to roughly 10° at a simulated velocity of 230°/s. With the sound traveling on an oblique plane (45° rotation above the horizontal) MAMA thresholds generally matched those of the horizontal condition. When the motion was restricted to the vertical plane (the array was rotated 90° from the horizontal) MAMA thresholds were substantially higher at all velocities than thresholds observed in the other array orientations, often exceeding 8° even at low velocities. Post hoc tests conducted at oblique planes 80° and 87° indicated that the slightest deviation from the vertical, had a significant impact on MAMA thresholds. A deviation of 10° from the vertical orientation was sufficient to reduce thresholds to those obtained when the sound moves on the horizontal plane (0° rotation above horizontal). These results suggest: (1) the ability to detect motion is essentially independent of the path traveled with one noted exception; sources traveling on an absolute vertical dimension, and (2) detection of the direction of travel is possible with azimuth changes of only a few tenths of a degree if concurrent changes in elevation are available. Some implications of these results are discussed. [Work supported by NSF and NIH.]
Low pitched notes associated with large bowing forces
Authors: Hanson R. J. , Schneider A. J. , Halgedahl F. W.
Published: October 2005

For bowing forces greater than the Schelling maximum [J. Shelling, J. Acoust. Soc. Am. 53, 26–41 (1973)] there are various periodic motions possible with periods much longer than any natural period of the string [M. E. McIntyre, R. T. Schumacher, and J. Woodhouse, J. Acoust. Soc. Am. 74, 1325–1345 (1983)]. Aperiodic motion with a corresponding raucous sound are, however, much more readily produced with a large bowing force. If care is exercised by the player, a repetitive waveform with a nonraucous sound for very large bowing forces can be maintained for as long as several seconds. The resulting pitch that is heard is in agreement with the fundamental frequency of the harmonic series obtained with a frequency analyzer. This is not the small flattening effect with moderately high bowing force analyzed by McIntyre et al. but is a large effect producing pitches typically ranging from a musical 6th to a musical 12th below the normal pitch. Systematic patterns of the measured frequencies as a function of normal string frequencies have been observed and possible interpretations will be presented.