bluuebunny/crossref_metadata_2025 huggingface dataset:
Higher harmonics in the far field due to dynamic crack-face contacting
Authors: Hirose S. , Achenbach J. D.
Published: October 2005

The dynamic problem of contacting crack faces due to incident wave motion is numerically solved by using the boundary element method. The crack is a penny-shaped crack in a stressed elastic solid of infinite extent. The crack is subjected to normal incidence of a longitudinal wave. The contact-boundary conditions with no overlap and no friction on the crack faces give rise to a boundary-type nonlinear problem. A time-domain boundary integral equation is numerically solved by a step-by-step time marching scheme. Crack face solutions are calculated as well as scattered far fields. Fourier amplitudes of higher harmonics of the scattered far fields are obtained as functions of the state of pre-stress.
Sound propagation in a refracting fluid above a layered fluid-saturated porous elastic material
Authors: Tooms Stephen , Taherzadeh Shahram , Attenborough Keith
Published: October 2005

A fast Fourier method of solution of wave equations is applied to sound propagation in a system composed of a horizontally stratified fluid overlying a horizontally stratified porous and elastic solid. A Biot model is used for the porous elastic material. Predictions are made of sound-pressure level in the fluid and vertical displacement in the solid. These are validated by comparison to analytic approximations, and results from another numerical model for propagation in a layered, nonporous viscoelastic material system. The validated code predicts the possibility of significant ground elasticity effects on above-ground propagation.
Measurements of the form function and total scattering cross section for a suspension of spheres
Authors: Thorne Peter D. , Manley Clayton , Brimelow Jason
Published: October 2005

Measurements of the acoustic backscattered amplitude, attenuation, and suspended concentration have been recorded for a number of suspensions consisting of spheres with a known particle size distribution. These data have been employed to obtain the form function and total scattering cross section for suspensions of spheres. Calculations for these parameters are compared with the observations and the effect of having a size distribution is examined.
Elastic scatterer interaction via generalized Born series and far-field approximations
Authors: Schafbuch P. J. , Thompson R. B. , Rizzo F. J.
Published: October 2005

Methods for solving elastic wave scattering problems in three dimensions (3D) with multiple inhomogeneities are discussed. A problem of homogeneous, isotropic elastic defects in an otherwise homogeneous, isotropic elastic full-space is formulated as a boundary integral equation. This equation is solved by discretizing the surface of each scatterer in a fashion known as the boundary element method. The resulting matrix equation may be solved in a fully implicit manner, but an implicit-iterative method is more efficient. With this hybrid method, a portion of the nonsingular integral operator is expanded in a Neumann series. Terms in this series correspond physically to Nth-order Born approximations of the scatterers’ interaction. The relative advantage of this hybrid scheme depends on the number of iterations required. Except for closely situated strong scatterers, terms beyond the first few orders are not significant and thus the method can be quite advantageous. When the separation is large, another approximate method which ignores the evanescent portion of the near scattered field and further neglects the curvature of scattered waves is appropriate. Results from the converged, implicit-iterative approach are compared with this far-field approximation for many situations involving spheroidal voids. The validity of this approximation is explored in the near field.
An approximate analysis for penetration of spaced foils by projectiles at hyper-velocity
Authors: El-Raheb Michael , Chatterjee Amiya
Published: October 2005

An approximate analysis for the hyper-velocity penetration of thin spaced foils is described. Each foil is assumed to deform plastically into a conical shape ending with extensional failure. The cone’s radius grows with time at a rate lower than the speed of propagation of bending waves in the foil’s material. It is found that weight efficiency of the shield rises inversely with foil thickness asymptotically as a result of mass entrained by propagation.
Performance-intensity functions at absolute and masked thresholds
Authors: Studebaker Gerald A. , Gilmore Christine , Sherbecoe Robert L.
Published: October 2005

In most applications of audibility and articulation theories, it is assumed that absolute thresholds and thermal noise maskers affect speech recognition performance-intensity (P-I) functions similarly. The purpose of this study was to evaluate that assumption. Performance-intensity functions for NU-6 monosyllabic words were obtained from eight normal-hearing subjects in quiet and in the presence of two levels of a noise that produced masked pure-tone thresholds parallel to, but higher than, those of each individual in quiet. The results support the practice of treating absolute threshold as a noise-masked threshold in predictions of speech recognition performance.
Temporal asynchrony of less than one-half cycle can be detected in harmonic complexes
Authors: Zera Jan , Green David M.
Published: October 2005

In previous experiments on asynchrony detection in multicomponent complexes [Zera and Green, J. Acoust. Soc. Am. 93, 1038–1052, 1571–1579 (1993)], stimuli in which each component began or terminated at a zero crossing of the sine waveform were employed. Thus, the measurable range of asynchrony for a given component was limited to values larger than one-half the component period. In this experiment, the zero-crossing restriction is relaxed and the results show that the listeners’ asynchrony thresholds lie between 0.1 and 0.5 of the signal period for the conditions most favorable to the detection of asynchrony, namely, a harmonic complex with the asynchrony occurring at onset.
The underwater sound generated by heavy rainfall
Authors: Nystuen Jeffrey A. , McGlothin Charles C. , Cook Michael S.
Published: October 2005

The underwater acoustic signature of heavy rainfall is very different from that of light rainfall. During heavy rainfall sound levels are observed to rise with increasing rainfall rate at all frequencies monitored (4–21 kHz) and the 15-kHz spectral peak observed during light rainfall is absent. The sound levels are most highly correlated (r≊0.8) with heavy rainfall rate for frequencies less than 10 kHz. Lower correlations between sound levels and heavy rainfall rate were observed for frequencies above 10 kHz under several different conditions. When wind speed exceeds 10 m/s, wave breaking mixes bubbles downward and creates a layer of bubbles. This bubble layer attenuates subsequent surface-generated sound (from the raindrop splashes) for frequencies above 10 kHz. Extremely heavy rainfall (total rainfall above 150 mm/h) also generates a subsurface bubble layer. This rainfall-generated bubble layer is evidence of rainfall-induced turbulent mixing of the ocean surface layer and has implications for air/sea exchange processes (momentum, heat, and gas exchange). Finally, previous studies have shown that light rain generates acoustic energy above 10 kHz and that this sound is poorly correlated with total rainfall rate. A simple empirical acoustic rainfall rate algorithm for heavy rain is offered. This algorithm may be site specific. Furthermore, it overestimates rainfall rate early in the rain events examined here (convective rain events), and then underestimates rainfall rate later in the same events. This observation is shown to be consistent with likely changes in the drop size distribution during the lifetime of the rain event. The sound produced by large drops within heavy rain (drop diameter greater than 2.2 mm) is shown to dominate the underwater sound field. The empirical acoustic rainfall rate algorithm is therefore more correctly a measure of the rainfall rate from large raindrops. Fortunately, the rainfall rate from large raindrops is highly correlated with the total rainfall rate, making acoustic monitoring of underwater sound an effective measure of rainfall rate in oceanic regions.
Measurement of the sound produced by a tipping trough with fresh and salt water
Authors: Carey William M. , Fitzgerald James W. , Monahan Edward C. , Wang Qin
Published: October 2005

Recent experiments confirm the production of sound by breaking waves at lower frequencies (30 to 500 Hz) with a dipole characteristic. The noise produced has a broadband characteristic associated with the impact and subsequent sounds that have discrete spectral characteristics. Breaking waves are known to produce bubble plumes and bubble clouds; the dynamic evolution of which provides a mechanism for sound production. Since the initial plume and cloud have appreaciable void fractions, compressible resonant oscillations of these structures as a whole or in parts are possible. These bubble plumes would act as compact acoustic monopole sources of sound and due to the pressure release surface would have an effective dipole characteristic. Sufficient energy exists in the initial breaking vorticity and turbulence to excite these regions and to explain measured source levels. These effects have been simulated with a tipping trough experiment that demonstrates the production of low-frequency sound from salt and fresh water tipping trough events. These experimental results are shown to be consistent with the theory of sound radiation from the collective oscillations of bubble plumes.
Analysis of axisymmetric waves propagating along a hollow cylindrical ultrasonic transmission line
Authors: Kanbe Nobuhiro , Tomikawa Yoshiro , Adachi Kazunari , Takano Takehiro
Published: October 2005

A new ultrasonic device for feeding powder with the use of a hollow acrylic cylinder, on which an axisymmetric progressive elastic wave is excited, has previously been proposed. Its characteristics have also been reported. To find vibrational behaviors of the hollow cylinder for feeding powder, the elliptic particle movement on the inside surface was analyzed. The authors have found many forms of elliptic motion. Some of them can move objects inside the cylinder toward the vibration source, as expected, but, on the contrary, the others move in the wave propagation direction.
An experimental study implementing model reference active structural acoustic control
Authors: Clark Robert L. , Gibbs Gary P. , Fuller Chris R.
Published: October 2005

Model reference active structural acoustic control is experimentally investigated in this study for physical systems characterized by stationary, narrow-band disturbances in which the acoustic field remains relatively unchanged. The filtered-x version of the multichannel adaptive least-mean-square (LMS) algorithm was implemented on a TMS320C25 digital signal processing board to achieve the desired control approach, and control inputs were generated with piezoelectric actuators. Model reference control provides the designer with a method of replacing acoustic error sensors such as microphones located in the far-field with error sensors such as accelerometers located on the surface of the structure. As opposed to driving the response of the structure to zero at the coordinates of the accelerometers, the response is driven to some predetermined ‘‘reference’’ value corresponding to the desired far-field acoustic directivity pattern. In essence, the uncontrolled structure is adaptively modified to behave like the reference structure under acoustic control conditions. Results from this study indicate that the same acoustic directivity pattern can be achieved with model reference control, and the only requirement is that the number of structural sensors used in the control approach is at least equal to the number of control actuators required to achieve the desired acoustic directivity pattern.
The effect of aspirin on cochlear mechanical tuning
Authors: Brown Ann M. , Williams Deirdre M. , Gaskill Sally A.
Published: October 2005

The level of cubic distortion measured in the human ear canal reaches a peak when the distortion frequency falls approximately half-an-octave below that of the higher of two stimulus tones. The peak is thought to be indicative of a bandpass filter in the cochlea. The properties of the distortion peak have been measured during the administration of aspirin (3.84 g/day for 2 days) in eight human volunteers. In three of the subjects there was a downward shift of the center frequency of the distortion peak by as much as 200 Hz during aspirin consumption, but no significant change in Q3 dB of the peak. In two of these subjects, the shift in distortion peak was not associated with a change in psychophysical threshold. The mean group delay of the emitted distortion was reduced by approximately 0.5 ms in four of the eight subjects. The measurement of stimulus frequency emission (SFE) did not reveal any downward shift of features in the spectrum corresponding to those seen for the distortion peak. It is concluded (1) that aspirin affects the resonance frequency of the bandpass filter revealed by distortion measurement, but not its tuning; and (2) that the bandpass filter is dissociated from the mechanism responsible for the ‘‘fine structure’’ in the SFE spectrum.
Analysis of scattering from structures containing a variety of length scales using a source-model technique
Authors: Erez Eitan , Leviatan Yehuda
Published: October 2005

Fictitious source models have been applied extensively in recent years to a variety of electromagnetic and acoustic wave scattering problems. This paper is introducing an extension of the source-model technique that facilitates the solution to problems subsuming scatterers that contain a variety of length scales. This extension is in tune with the source-model technique philosophy of using simple sources the fields of which are analytically derivable. It amounts to letting the coordinates of some of the source centers assume complex values. Positioned in complex space, the simple sources radiate beam-type fields, which are more localized and are better approximations of the scattering from the smooth expanses of the structure. The coordinates of the other source centers retain their conventional real values. These latter sources are used, of course, to approximate the fields in the vicinity of the more rapidly varying expanses of the structure. The new approach is applied to analyze acoustic scattering from a structure comprising two adjacent pressure-release spheres of different size. It is found to render the solution computationally more effective at the expense of only a slight increase in its complexity.
Large membrane array scattering
Authors: Kriegsmann G. A. , Scandrett C. L.
Published: October 2005

The scattering of a time harmonic acoustic wave by an array of N identical baffled membranes is considered in the limit as N→∞. The method of matched asymptotic expansions is used to construct an inner and outer expansion; the inner expansion contains the physics of the local periodic structure and the outer expansion has the proper behavior in the far field. The matching process is used to determine a set of unknown coefficients in the analysis and the result is a far-field pattern for the structure that blends the physics of both expansions. In particular, the far-field pattern is highly localized about the Bragg or mode angles of the inner representation. The maximum value of this function is directly proportional to the reflection coefficient determined numerically from the inner problem. Several numerical examples are presented illustrating these features. Moreover, it is observed that the asymptotic theory agrees quite well with the exact answer (obtained by using a finite difference scheme) when N=3.
Directional attenuation of S
H waves in anisotropic poroelastic inhomogeneous media
Authors: Ben-Menahem Ari , Gibson Richard L.
Published: October 2005

The equations of motion for anisotropic poroelastic inhomogeneous media admit separable SH wave motion for the case of azimuthal isotropy coupled with coaxial inhomogeneity and poroelasticity with a diagonal permeability tensor. In homogeneous examples of such media, the low-frequency waves exhibit differential attenuation that is more pronounced along the symmetry axis. If this differential attenuation can be observed, it may be used to determine the permeability of the medium. Media with a vertical gradient of both elastic and permeability properties show different effects. For low-frequency waves, the attenuation acts so as to reverse the effects of elastic parameter gradients on SH wave amplitudes.
A new technique for measuring Rayleigh and Lamb wave speeds
Authors: Kundu Tribikram , Maxfield Bruce
Published: October 2005

A new technique is proposed in this paper to measure Rayleigh and Lamb wave speeds in solid half-spaces and plates. In this technique two transducers are positioned above the specimen in a pitch-catch orientation. The time of flight of the signal from the transmitter to the receiver is recorded. Then the rate of change of this time as the distance between the reflector and the transducer varies is experimentally determined. This rate remains constant when leaky Rayleigh of Lamb waves are generated but it varies when these waves are not generated. Thus surface waves are detected in an indirect manner. An expression is derived to relate the surface wave speed to the signal flight time change rate with the transducer specimen distance. Using this expression Rayleigh and Lamb wave speeds have been accurately determined in isotropic metals and anisotropic composites.
An isohazard function for impulse noise
Authors: Patterson James H. , Hamernik Roger P. , Hargett C. E. , Ahroon William A.
Published: October 2005

Existing criteria for safe exposure to impulse noise do not consider the frequency spectrum of an impulse as a variable in the evaluation of the hazards to the auditory system. This study was designed to determine the relative potential that impulsive energy concentrated at different frequencies has in causing auditory system trauma. One hundred and thirty (130) chinchillas, divided into 22 groups of 5 to 7 animals, were used. Pre- and postexposure audiograms were measured on each animal using avoidance conditioning procedures. Quantitative histology was used to determine the extent and pattern of the sensory cell damage (cochleograms). Noise exposure employed seven different computer-generated narrow-band impulses (approximately 400-Hz bandwidth) having center frequencies located at 0.260, 0.775, 1.025, 1.350, 2.075, 2.450, and 3.550 kHz, presented at two to four different intensities. An isohazard weighting function derived from the audiometric and histological data demonstrates that equivalent amounts of impulsive energy concentrated at different frequencies are not equally hazardous to the auditory system. Comparison of the derived weighting function with the A-weighting curve indicates that low-frequency impulses are less hazardous than predicted by A-weighted sound exposure level.
Effects of onset asynchrony on pitch perception: Adaptation or grouping?
Authors: Ciocca V. , Darwin C. J.
Published: October 2005

A previous paper by Darwin and Ciocca [J. Acoust. Soc. Am. 91, 3381–3390 (1992)] showed that a slightly mistuned frequency component of a (target) harmonic complex produced smaller pitch shifts in the target if it started 160 ms or more before the other components than if all the components were simultaneous. Three experiments investigated whether this effect of onset asynchrony is due to peripheral adaptation to the leading portion of the mistuned component or to perceptual grouping. The first two experiments showed that the effect of asynchrony could be influenced by grouping mechanisms without changing the amount of adaptation produced by the leading portion of the mistuned component. In the first experiment, the effect of asynchrony was reduced by the presence of an additional (captor) complex which was harmonically related to the mistuned component and synchronous with just its leading portion. In experiment 2, the effect of asynchrony was increased by presenting a captor that was synchronous with the entire mistuned component. This capturing effect was independent of the harmonic relation between the captor and the mistuned component at 40-ms asynchrony; at 160 ms the effect of asynchrony increased further only if the captor and the mistuned component were harmonically related. In the third experiment, the expected amount of adaptation was increased (relative to that produced by a single sine precursor) by presenting several components that were close in frequency to the mistuned component and synchronous with its leading portion. This manipulation produced a larger reduction in pitch shift at short onset-time differences, but a smaller reduction at long onset time differences compared with the less intense sine precursor. The results of the three experiments are consistent with the original results being due mainly to perceptual grouping. Adaptation appears to be the dominant mechanism only at short onset asynchronies and when the leading portion of the mistuned component has been increased in intensity.
Effects of forward masking on intensity discrimination, frequency discrimination, and the detection of tones in noise
Authors: Carlyon Robert P. , Beveridge Hazel A.
Published: October 2005

A series of experiments investigated the deterioration in intensity discrimination at intermediate levels caused by preceding the brief sinusoidal stimuli by an intense narrow-band noise [Zeng et al., Hear. Res. 55, 223–230 (1991)]. Experiment 1 showed that this deterioration acted in a roughly additive manner with the previously reported midlevel deterioration for the intensity discrimination of brief 6500-Hz tones in quiet. The experiment also showed that a smaller, although still substantial, deterioration occurred for the detection of brief tones in bursts of synchronous noise. In experiment 2, the masker could occur either before the signal (louder tone) or standard (softer tone), the choice being selected at random on a trial-by-trial basis, and with the Weber fraction tracked for each condition separately using two interleaved, adaptive procedures. Weber fractions were lower when the masker preceded the signal than when it preceded the standard, arguing against a major role for adaptation in causing the midlevel deterioration. Instead, it is suggested that the deterioration shared a common mechanism with the phenomenon of ‘‘loudness enhancement’’ [R. J. Irwin and J. J. Zwislocki, Percept. Psychophys. 10, 189–192 (1971); Galambos et al., J. Acoust. Soc. Am. 52, 1127–1130 (1972)].

The third experiment showed that Weber fractions did not depend greatly on whether the forward masker occurred only in interval one or only in interval two of a two-interval trial. A fourth experiment investigated the effect of a forward masker on frequency difference limens (DLs). When the masker was presented in both intervals of each trial, there was only a moderate increase in frequency DLs which, in contrast to the elevation in Weber fractions for intensity discrimination, was independent of signal level. Presenting the masker before only the lower frequency tone of a pair to be discriminated usually yielded lower DLs than presenting it only before the higher frequency tone, but this effect was less consistent than for intensity discrimination. The results of all experiments are discussed with respect to the various ways in which an intense narrow-band masker can affect the perception of subsequent brief sounds.
Auditory filter shapes in normal-hearing, noise-masked normal, and elderly listenersa)
Authors: Sommers Mitchell S. , Humes Larry E.
Published: October 2005

To dissociate the effects of age and hearing impairment on changes in frequency selectivity, auditory filter shapes were measured at 2 kHz in four groups of subjects: (1) normal-hearing young subjects; (2) normal-hearing elderly subjects; (3) elderly hearing-impaired listeners; and (4) young normal-hearing listeners with simulated hearing losses. Filter shapes were derived using a modified version of the notched-noise procedure [Glasberg and Moore, Hear, Res. 47, 103–138 (1990)]. Equivalent rectangular bandwidths (ERBs) of auditory filters were not significantly different in young and elderly subjects with normal 2-kHz hearing. Furthermore, filter widths for young subjects with 20- and 40-dB simulated hearing losses overlapped with those obtained from elderly subjects with corresponding degrees of actual hearing loss. One measure that did show significant differences between actual and simulated hearing losses was the degree of filter asymmetry; auditory filters in hearing-impaired listeners were more asymmetrical than those obtained from noise-masked normal-hearing subjects. The dynamic range of auditory filters, however, was comparable for hearing-impaired and noise-masked listeners. Lastly, post-filter detection efficiency was also similar for young and elderly subjects with equivalent hearing levels. These findings suggest that the reduced frequency selectivity often reported for older listeners can be attributed, primarily, to hearing loss rather than increased age. Implications of the results for speech perception in the elderly and models of hearing impairment are discussed.
Trading relations between tongue-body raising and lip rounding in production of the vowel /u/: A pilot ‘‘motor equivalence’’ study
Authors: Perkell Joseph S. , Matthies Melanie L. , Svirsky Mario A. , Jordan Michael I.
Published: October 2005

Articulatory and acoustic data were used to explore the following hypothesis for the vowel /u/: The objective of articulatory movements is an acoustic goal; varying and reciprocal contributions of different articulators may help to constrain acoustic variation in achieving the goal. Previous articulatory studies of similar hypotheses, expressed entirely in articulatory terms, have been confounded by interdependencies of the variables being studied (e.g., lip and mandible displacements). One case in which this problem may be minimized is that of lip rounding and tongue-body raising (formation of a velo-palatal constriction) for the vowel /u/. Lip rounding and tongue-body raising should have similar acoustic effects for /u/, mainly to lower F2. In multiple repetitions, reciprocal contributions of lip rounding and tongue-body raising could help limit F2 variability for /u/; thus this experiment looked for complementary covariation (negative correlations) in measures of these two parameters. An electro-magnetic midsagittal articulometer (EMMA) was used to track movements of midsagittal points on the tongue body, upper and lower lips, and mandible for large numbers of repetitions of utterances containing /u/. (Interpretation of the data was aided by results from area-function-to-formant modeling.) Three of four subjects showed weak negative correlations, tentatively supporting the hypothesis; a fourth showed the opposite pattern: positive correlations of lip rounding and tongue raising. The results are discussed with respect to ideas about motor equivalence, the nature of speech motor programming, and potential improvements to the paradigm.
Effects of cognitive workload on speech production: Acoustic analyses and perceptual consequences
Authors: Lively Scott E. , Pisoni David B. , Van Summers W. , Bernacki Robert H.
Published: October 2005

The present investigation examined the effects of cognitive workload on speech production. Workload was manipulated by having talkers perform a compensatory visual tracking task while speaking test sentences of the form ‘‘Say hVd again.’’ Acoustic measurements were made to compare utterances produced under workload with the same utterances produced in a control condition. In the workload condition, some talkers produced utterances with increased amplitude and amplitude variability, decreased spectral tilt and F0 variability and increased speaking rate. No changes in F1, F2, or F3 were observed across conditions for any of the talkers. These findings indicate both laryngeal and sublaryngeal adjustments in articulation, as well as modifications in the absolute timing of articulatory gestures. The results of a perceptual identification experiment paralleled the acoustic measurements. Small but significant advantages in intelligibility were observed for utterances produced under workload for talkers who showed robust changes in speech production. Changes in amplitude and amplitude variability for utterances produced under workload appeared to be the major factor controlling intelligibility. The results of the present investigation support the assumptions of Lindblom’s [‘‘Explaining phonetic variation: A sketch of the H&H theory,’’ in Speech Production and Speech Modeling (Klewer Academic, The Netherlands, 1990)] H&H model: Talkers adapt their speech to suit the demands of the environment and these modifications are designed to maximize intelligibility.
Acoustic isolation vessel for measurement of the background noise in microphones
Authors: Ngo Kim Chi Thi , Zuckerwar Allan J.
Published: October 2005

An acoustic isolation vessel has been developed to measure the background noise in microphones. The test microphone is installed in an inner vessel, which is suspended within an outer vessel, and the intervening air space is evacuated to a high vacuum. An analytical expression for the transmission coefficient is derived, based on a five-media model, and compared to experiment. At an isolation vacuum of 5×10−6 Torr the experimental transmission coefficient was found to be lower than −155 dB at frequencies ranging from 40 to 1200 Hz. Measurements of the A-weighted noise levels of commercial condenser microphones of four different sizes show good agreement with published values.
Comments on ‘‘On the invention of active noise control by Paul Lueg’’ [J. Acoust. Soc. Am. 87, 2251–2254 (1990)]
Authors: de Heering Philippe
Published: October 2005

In a recent paper Guicking [J. Acoust. Soc. Am. 87, 2251–2254 (1990)], gives a historical report on the invention of active noise control by Paul Lueg. Guicking states, inter alia, that Lueg was the first to describe and patent the principle of the compensation of a noise signal by another in antiphase. Lueg’s patent application was, however, predated, if only by a few weeks, by Henry Coanda’s application for a patent on, essentially, the same invention. This letter gives some details and comments on the latter application.
Simulating transfer functions in a reverberant room including source directivity and head-shadow effects
Authors: Kompis Martin , Dillier Norbert
Published: October 2005

A new procedure for simulating the acoustical response of a receiver to a source in a reverberant room is proposed. Convolving such an impulse response with an input signal, e.g., speech, is useful in applications where an acoustical environment must be highly reproducible, easily controllable, or is unavailable for an actual recording. The proposed procedure is an extension of the image method by Allen and Berkley [J. Acoust. Soc. Am. 65, 943–950 (1979)]. The new features include the possibility to simulate simple source and microphone directivity, as well as head-shadow effects, which can be considerable for subjects with microphones mounted close to the head. A rigid sphere diffracting a plane wave provides a good approximation for the effects of speaker as well as listener head shadow and allows simple yet realistic simulations of many relevant situations. Implementational issues are discussed and the method is verified by comparing simulation results with recordings in actual rooms. It was found that by including source directivity and head shadow, transfer functions become significantly more realistic.
High-frequency bistatic reverberation from a smooth ocean bottom
Authors: Stanic S. , Kennedy E. , Ray R. I.
Published: October 2005

High-frequency bistatic reverberation was measured from a smooth, sandy, featureless bottom located 19 miles south of Panama City, FL. Bistatic scattering variability is presented as a function of frequency (20–180 kHz), grazing angles (9.5°–30°), and small horizontal and vertical bistatic scattering angles. Results show that bistatic variabilities tend to decrease with decreasing grazing angles and decreasing source beamwidths. Possible explanations for these decreasing variations are also presented.
Analysis of ultrasonic velocities in hydrocarbon mixtures
Authors: Berryman James G.
Published: October 2005

Ultrasonic velocity data on hydrocarbon mixtures were shown by Wang and Nur [J. Acoust. Soc. Am. 89, 2725 (1991)] to agree quite well with the predictions of a simple mixing rule (volume average of velocity). The same data are reanalyzed using Wood’s formula and the time-average approximation. Wood’s formula for acoustic velocity is shown to be always less than the time-average formula, which is itself always less than the simple mixing rule result. Although the volume average rule agrees best with the data on binary mixtures of 1-decene and 1-octadecene, all these formulas agree with the data to within 1% and, therefore, it is not possible to distinguish among the formulas using this data set. Similar results are also found for six multicomponent hydrocarbon mixtures.
On the influence of frequency and width of an ultrasonic bounded beam in the investigation of materials: Study in terms of heterogeneous plane waves
Authors: Van Den Abeele K. , Leroy O.
Published: October 2005

Theoretically obtained three-dimensional plots showing the behavior of the reflection coefficient for heterogeneous plane waves upon arbitrary layered media as function of incidence angle and heterogeneity, supply valuable information for the investigation of the reflector when using bounded ultrasonic beams. The presence of leaky interface modes and their angular positions for a specific sample are determined by the fd products (frequency times thickness) of the constituent layers. Deformations of the reflected and transmitted bounded beam profiles and the contribution of surface wave radiation (leaking energy) at vibrational mode angles are governed by the fW product (frequency times beamwidth). For a given layered medium, optimum conditions for observing particular mode vibrations and large deformations of reflected ultrasonic profiles can be predicted theoretically.
Active control of sound power using acoustic basis functions as surface velocity filters
Authors: Naghshineh Koorosh , Koopmann Gary H.
Published: October 2005

An improved method of active structural acoustics control is presented that is based on the minimization of the total power radiated from any structure expressed in terms of a truncated series sum. Each term of this sum is related to the coupling between the orthogonal eigenvectors of the radiation impedance matrix (referred to as ‘‘basis functions’’ in this paper) and the structural surface velocity vector. The basis functions act as surface velocity filters. These acoustic basis functions are found to be weak functions of frequency but their corresponding weighting coefficients increase monotonically with frequency. The minimization of the radiated power is shown to result in a structural surface velocity vector that couples poorly to those acoustic basis functions that account for high-efficiency sound radiation. This strategy is demonstrated numerically for a clamped–clamped baffled beam in air. Point force primary and control actuators (shakers) are used to explore the control mechanisms. As expected, the minimization of the radiated power results in a controlled beam response that contains much lower supersonic wave-number content than that of the uncontrolled beam response. Finally, an unexpected benefit of the control strategy described is that it provides a rational procedure for selecting the number and placement of actuators and sensors on a structure for effective control. This development is significant since this procedure does not require a priori knowledge of the dynamics of the structure.
Sound-pressure level calculations using the RRA algorithm for depth-dependent speeds of sound valid at turning points and focal points
Authors: Ziomek Lawrence J.
Published: October 2005

Sound-pressure level (SPL) calculations are made along individual ray paths for one-dimensional, depth-dependent, speeds of sound using an enhanced version of the recursive ray acoustics (RRA) algorithm. The SPL calculations are valid (i.e., finite) at turning points and focal points and do not require the use of Airy functions. The SPL calculations include the effects of frequency-dependent volume attenuation and frequency-dependent attenuation due to surface and bottom reflections. The ocean surface and bottom are treated as boundaries between viscous fluid media. Although the ocean surface is modeled as a planar boundary, the bathymetry is an arbitrary function of horizontal range. Sound speed versus depth and bathymetric data are represented by orthogonal function expansions. Computer simulation results from preliminary test cases are presented. [Work supported by NAVSEA.]
Prufer transforms and numerical solutions to the Helmholtz equation
Authors: Baggeroer Arthur B.
Published: October 2005

The Prufer transformation maps the second-order, linear Helmholtz differential equation to two first-order, nonlinear differential equations. The coupling between the two separates such that the equation for the eigenvalue is a single nonlinear first-order equation. This transformation has long been useful in theoretical studies of Strum–Liouville where many properties of the eigenvalues have been derived using it. It turns out also to have some useful numerical properties especially for problems involving waveguides where the coupling between the boundaries is poorly conditioned. It also identifies explicitly the both stability points in the evanescent sections of the modes and the local oscillation frequency in the ducted section. The numerical aspects of using the Prufer transform and some examples are discussed in the presentation.
Multipath structures of pulse signals in shallow water with a thermocline
Authors: Zhang Renhe , Zhu Ye
Published: October 2005

It was observed that the pulse signals in shallow water with a thermocline have regular multipath structures, which are strongly dependent on the depths of source and receiver. When both the source and receiver are located above the thermocline, the received signal consists of a train of almost equispaced wave packets and the time interval T between packets is related to the speed-profile parameters. When the source is below the thermocline and the receiver is above, the received signal consists of a train of wave packets with time intervals τ and (T−τ), where τ is dependent on the distance from the source to the bottom. The formulas of intervals T and τ were deduced by the ray theory, and the calculated values of T and τ are consistent with measured ones. The normal-mode theory was used to model the waveforms of pulse signals, and the effects of speed-profile, geoacoustic parameters, signal parameters, and source and receiver depths on waveform structure were studied.
PE modal decomposition of VLA data
Authors: Thomson David J. , Ebbeson Gordon R.
Published: October 2005

The first step in any matched-mode processing application is the decomposition of the measured acoustic field into its horizontal wave-number (modal) components. Previously, a PE-based method was described for carrying out the modal decomposition of the pressure field received on a vertical line array (VLA) [D. J. Thomson etal., J. Acoust. Soc. Am. 89, 2000 (1991)]. For that method, the VLA field was first interpolated between hydrophones and then extrapolated into the ocean bottom. This interpolation/extrapolation stage was needed to construct a suitable starting field on the fine computational grid used by the PE algorithm. In this paper, a modified PE model is presented that eliminates the computational grid in the bottom by applying an exact, nonlocal boundary condition along the ocean-bottom interface. Consequently, it is no longer necessary to extrapolate the VLA field prior to propagating it with PE. To demonstrate the effectiveness of the boundary condition, PE-based modal decomposition is carried out using simulated VLA data generated for a shallow-water environment.
VLF cw signal analysis
Authors: Levinson Scott J. , Bedford Nancy R. , Mitchell Stephen K. , Lange Joan C.
Published: October 2005

Very-low-frequency (VLF) sound waves transmitted at 7 and 10 Hz from a source towed at a depth of 122 m were sampled over the bottom half of the water column by an 18-element vertical hydrophone array anchored on the bottom (3170 m deep). Analysis included the comparison of measured beam levels with corresponding eigenray and adiabatic normal mode models at short (0.7–20 km) and long (35–60 km) ranges. At short ranges, the VLF measurements and both models were consistent in indicating easily distinguishable direct, bottom, bottom–surface, and bottom–surface–bottom interacting arrivals. At longer range, the arrivals typically consisted of three from the surface and three from the bottom, corresponding to two, three, and four bottom interactions. The continuous range over which a particular arrival order dominated was 5 km or less. An anomalous bottom loss observed at 30°–34° at 7 Hz appears to be the result of a slow hydrate layer in the sediment. Except for these angles, VLF bottom loss was low compared to typical values at higher frequency, and it is consistent with conventional modeled loss calculations for the pre-assessed geoacoustic parameters of the sediment. [Work supported by the ASW Environmental Acoustic Support (AEAS) Program of the Office of Naval Research.]
Characteristic dimensions and prediction at high frequencies of the surface impedance of porous layers
Authors: Lafarge Denis , Allard Jean F. , Brouard Bruno , Verhaegen Christine , Lauriks Walter
Published: October 2005

The surface acoustic impedance of a glass wool and a reticulated foam is measured in a free field up to 20 000 Hz. The characteristic dimensions Λ and Λ′ can be calculated for the glass wool, and the surface impedance can be predicted with no adjustable parameters. The motion of the frame is not taken into account. The agreement between measurement and prediction is good. For the foam, the characteristic dimensions cannot be calculated, because the geometry of the frame is not simple. A correct choice of Λ and Λ′ allows a precise prediction of the surface impedance for a large range of frequencies and different thicknesses.
An acoustic and perceptual comparison of English and Spanish vowels
Authors: Bradlow Ann R.
Published: October 2005

This paper addresses three issues. First, the effect of inventory size on the acoustic realization of vowels in English and Spanish is examined. Results indicate that the English vowel space differs from the Spanish vowel space in range, but not in tightness of within-category clustering. The second experiment tests the hypothesis that the perceptual categories coincide with the produced categories within a given language. Indeed, the data suggest that the perceptual and acoustic vowel spaces within English and Spanish correspond closely to each other. Finally, this study explores cross-language differences in vowel perception. These data suggest that there are universal, perhaps psychophysical, boundaries which are independent of inventory size: in both languages, the boundaries between /i/ and /e/, and between /u/ and /o/ are primarily in the F1 dimension, and are in the 400- to 500-mels region. This suggests that the observed regularities in vowel inventories across languages may stem, in part, from universal, auditory-perceptual mechanisms. Results of experiments in which English listeners responded to Spanish-based stimuli, and vice-versa, will also be discussed.
Vowel normalization by articulatory normalization: Preliminary results
Authors: Payan Yohan , Perrier Pascal
Published: October 2005

This paper presents an approach to vowel normalization based on the exloitation of the concept of formant to cavity affiliation as described in the vocalic theory of speech production [G. Fant, AcousticTheoryofSpeechProduction (Mouton, La Hague, 1960)]. For closed vowels, this concept allows an estimation of the ratio of the respective back and front cavities lengths of two speakers, by the ratio of the associated formants. In order to propose a normalization of the vocalic space of different speakers, a ‘‘reference speaker’’ was used whose articulatory and acoustic properties are well defined: the articulatory model as proposed by Maeda [J. Acoust. Soc. Am. Suppl. 1 81, S146 (1988)]. Vowel normalization consists then in the projection of the vocalic space of one given speaker in the vocalic space of this model. Geometrical relations between the studied speaker and the ‘‘reference speaker’’ are extracted from [i] and [u] for front and velopalatal vowels, and from [a] and [u] for back and velopharyngeal vowels. Here, [y] and [u] give some indications about the lip shapes. This method is here tested by her ability to predict the vowels of the studied speaker starting from the vowels of this model.
Integrality of nasalization and F1 in vowels in isolation and before oral and nasal consonants
Authors: Kingston John , Macmillan Neil A.
Published: October 2005

Vowels vary multidimensionally, and the perceptual effects of the dimensions may combine independently or may interact. The dimensions examined in these experiments were the acoustic correlates of soft palate height and tongue height, which covary directly in natural speech. A modified Garner paradigm was used in which accuracy replaced speed as the dependent measure; a detection-theory analysis permitted inferences about perceptual representation. For isolated vowels, nasalization and F1 were integral, in the sense that corresponding perceptual dimensions were correlated, replicating Kingston [Phonetica 47, 149–179 (1991)]. The degree of integrality was yet stronger for vowels before consonants, whether the consonant was nasal or oral. These results suggest that soft palate height and tongue height are covaried by speakers so that their acoustic correlates contribute to a single perceptual property, the distribution of energy at the low end of the vowel’s spectrum. The lack of a context effect is unexpected given the finding of Krakow etal. [J. Acoust. Soc. Am. 83, 1146–1158 (1988)] that nasalization in a vowel does not affect judgment of its height if there is a neighboring nasal to which that nasalization can be attributed. This discrepancy may occur because listeners in this experiment made judgments of nasalization as well as vowel quality.
Finding eigenrays by optimization with application to tomography and overcoming chaos
Authors: Kuperman W. A. , Collins Michael D.
Published: October 2005

Eigenrays may be determined with the initial-value approach of shooting. The eikonal equation is solved repeatedly, with the initial conditions being the position and direction of the ray at one of the end points, until the correct initial conditions are found (i.e., until the ray nearly intersects the other end point). It has been demonstrated that this approach is relatively inefficient [B. R. Julian and D. Gubbins, J. Geophys. 43, 95–113 (1977)] and prone to chaos [Smith etal., J. Acoust. Soc. Am. 91, 1939–1949 (1992)]. When formulated in terms of Fermat’s principle, finding eigenrays is a boundary-value problem that should be free of the ill effects of chaos. If the index of refraction is perturbed, the perturbed eigenrays may be determined efficiently from the unperturbed eigenrays. This fact is exploited to perform tomography efficiently with an optimization procedure that alternates between attempting to satisfy Fermat’s principle and attempting to match travel time. After a sequence of iterations, both the index of refraction and the eigenrays are obtained.