bluuebunny/crossref_metadata_2025 huggingface dataset:
Recognition of speech spectrograms
Authors: Greene Beth G. , Pisoni David B. , Carrell Thomas D.
Published: October 2005

The performance of eight naive observers in learning to identify speech spectrograms was studied over a 2-month period. Single tokens from a 50-word phonetically balanced (PB) list were recorded by several talkers and displayed on a Spectraphonics Speech Spectrographic Display system. Identification testing occurred immediately after daily training sessions. After approximately 20 h of training, naive subjects correctly identified the 50 PB words from a single talker over 95% of the time. Generalization tests with the same words were then carried out with different tokens from the original talker, new tokens from another male talker, a female talker, and finally, a synthetic talker. The generalization results for these talkers showed recognition performance at 91%, 76%, 76%, and 48%, respectively. Finally, generalization tests with a novel set of PB words produced by the original talker were also carried out to examine in detail the perceptual strategies and visual features that subjects abstracted from the training set. Our results demonstrate that even without formal training in phonetics or acoustics naive observers can learn to identify visual displays of speech at very high levels of accuracy. Analysis of subjects’ performance in a verbal protocol task demonstrated that they rely on salient visual correlates of many phonetic features in speech.
Underwater sound from lightning strikes to water in the Gulf of Mexico
Authors: Arnold Roy T. , Bass Henry E. , Atchley Anthony A.
Published: October 2005

Underwater sounds we have measured are interpreted to have been produced by lightning strikes to water in the Gulf of Mexico. The range to the storm cells was approximately 30–40 km. Measurements with a hydrophone tethered to the research vessel Tommy Munro allows us to estimate the total acoustic energy in the sound field. Our estimates are compatible with what one might expect on the basis of the total electrostatic energy dissipated by a typical flash to the ground.
Pressure effects on the dynamic effective properties of resonating perforated elastomers
Authors: Gaunaurd G. , Callen E. , Barlow J.
Published: October 2005

We quantitatively study the effect that hydrostatic pressures have on the static and dynamic effective material properties of perforated viscoelastic elastomers. A resonance methodology that we had developed earlier is here extended and generalized to account for the distorting effect of added pressures. The distortion essentially consists of a broadening of the spectral response plots and a shifting of the resonance peaks/dips that are present in all the graphs of the effective moduli and/or the effective acoustic/material properties of the pertinent composites. For the lossy, air-filled, rubberlike materials considered here, the pressure effect seems to be quite noticeable, but smaller than the viscous effect or than that of the nonuniformity in the cavity-size distribution functions. The model is implemented by a computer code and its numerical predictions are quantitatively displayed for a few of the effective properties of a given perforated elastomer up to pressures of 400 psi. These are the pressures present down to ocean depths of about 900 ft. These perforated elastomers have uses as underwater sound absorbers.
Uniform asymptotic evaluation of the continuous spectrum contribution for a stratified ocean
Authors: Ammicht E. , Stickler D. C.
Published: October 2005

The determination of the continuous spectral contribution for a stratified ocean acoustic model can be a difficult and expensive numerical task. A uniform asymptotic technique has been used to calculate the pressure field for the Pekeris model. It is uniform in the sense that it is valid as a mode passes through cutoff. The basic idea of the technique is to exploit the effect of the various singular points of the integrand representing the continuous spectrum. This idea has been further exploited to describe the continuous spectrum contribution for a general stratified ocean. Numerical examples show that this technique is both accurate and fast.
Perception of the voiced–voiceless contrast in syllable-final stops
Authors: Hillenbrand James , Ingrisano Dennis R. , Smith Bruce L. , Flege James E.
Published: October 2005

A computer editing technique was used to remove varying amounts of voicing from the syllable-final closure intervals of naturally produced tokens of /pqb, pqd, pqg, pag, pig, pug/. Vowels for all six syllables were approximately the same duration, and the final release bursts were retained. Identification results showed that voiceless responses tended to occur in relatively large numbers when all of the closure voicing and, in most cases, a portion of the preceding vowel-to-consonant (VC) transition had been removed. A second experiment demonstrated that removal of final release bursts had very little effect on the identification functions. Acoustic measurements were made in an attempt to gain information about the acoustic bases of the listeners’ voiced–voiceless judgments. In general, stimuli that subjects tended to identify as voiceless showed higher first-formant offset frequencies and shorter intensity decay times than stimuli that subjects tended to identify as voiced. However, for stops following /i/ and /u/ these acoustic differences were relatively small. We were unable to find a single acoustic measure, or any combination of measures, that clearly explained the listeners’ voiced–voiceless decisions.
Shallow water waveguide characterization using the Hankel transform
Authors: Frisk George V. , Lynch James F.
Published: October 2005

A technique for acoustically characterizing shallow water waveguides is presented. For a horizontally stratified ocean and bottom, the method consists of measuring the magnitude and phase versus range of the pressure field due to a cw point source and numerically Hankel transforming these data to obtain the depth-dependent Green’s function versus horizontal wavenumber. It is shown that, in the context of normal mode theory, the Green’s function contains information about the nature of the discrete and continuous modal spectra as well as the plane-wave reflection coefficients of the waveguide boundaries. Inversions are performed using pressure field data generated synthetically over reasonable experimental apertures (1–5 km) to obtain Green’s functions for the cases of an isovelocity water column overlying both hard and fast isovelocity bottoms (Pekeris waveguide). The Green’s function results show excellent agreement with theory, while the subsequently calculated reflection coefficients of the bottom are of somewhat lower quality. It is shown that features of the Green’s function itself can be used to extract modal properties and characteristics of the bottom. The effects of sediment attenuation and shear in the Pekeris case are discussed, and a comparison of this method with conventional phased array mode resolution techniques is made.
Extending the finite difference treatment of interfaces when using the parabolic wave equation
Authors: Gribble Jules deG.
Published: October 2005

In underwater acoustics, the parabolic wave equation is often solved by employing techniques based on finite difference techniques. A major drawback of the finite difference treatment of interfaces to date is that mesh points have been required to lie exactly on the interface. With regularly spaced, predetermined meshes this can be a serious computational restriction. Previous treatments of the parabolic wave equation using finite differences have assumed an equispaced mesh and that at interfaces a mesh point will lie precisely on the interface. In this paper we remove both of these restrictions. This approach also makes it apparent that mesh points can be added or deleted during the solution process, and so presents a more general model to work with.
A hybrid numerical/analytic technique for the computation of wave fields in stratified media based on the Hankel transform
Authors: Mook Douglas R. , Frisk George V. , Oppenheim Alan V.
Published: October 2005

A hybrid numerical/analytic technique is presented for computing the field due to a monochromatic point source in a horizontally stratified medium. It is based on the exact Hankel transform relationship between the field in the range domain and the associated depth-dependent Green’s function in the horizontal wavenumber domain. The method uses a numerical evaluation of the Hankel transform. It is shown that a major source of error in such an evaluation arises from undersampling of the Green’s function at points where it becomes infinite. This error is described in terms of aliasing, analogous to the aliasing that has been well-described for the discrete Fourier transform. It is shown that the error can be substantially reduced by removing the infinities, calculating the Hankel transform of the remaining portion of the Green’s function numerically, and adding to it the analytically computed Hankel transform of the infinities. The sum of the analytic terms and the remaining Hankel transform always exactly equals the true field with no errors introduced other than those associated with the numerical evaluation of the Hankel transform, and the method is accurate in both the near- and farfield regions. The technique is developed in detail for the acoustics problem of a monochromatic point source and receiver in an isovelocity fluid half-space overlying a horizontally stratified fluid medium. It is found that under circumstances of interest in ocean bottom acoustics, where the Green’s function has only a few singularities along the real horizontal wavenumber axis, the technique is efficient and extremely accurate.
A method for measuring the frequency dispersion for broadband pulses propagated to long ranges
Authors: Yang T. C.
Published: October 2005

The time-frequency structure of broadband pulses propagating to long ranges is analyzed with the stationary phase approximation. A method based on this analysis is proposed for measuring the fine structure of the frequency dispersion. The new method determines the mode frequencies to a precision of 0.5 Hz whereas the precision of the sonogram method is typically several Hz. Implications of this improved frequency dispersion measurement are discussed.
Speech processing studies using an acoustic model of a multiple-channel cochlear implant
Authors: Blamey P. J. , Dowell R. C. , Tong Y. C. , Brown A. M. , Luscombe S. M. , Clark G. M.
Published: October 2005

The speech perception of two multiple-channel cochlear implant patients was compared with that of three normally hearing listeners using an acoustic model of the implant for 22 different speech tests. The tests used included a minimal auditory capabilities battery, both closed-set and open-set word and sentence tests, speech tracking and a 12-consonant confusion study using nonsense syllables. The acoustic model represented electrical current pulses by bursts of noise and the effects of different electrodes were represented by using bandpass filters with different center frequencies. All subjects used a speech processor that coded the fundamental voicing frequency of speech as a pulse rate and the second formant frequency of speech as the electrode position in the cochlea, or the center frequency of the bandpass filter. Very good agreement was found for the two groups of subjects, indicating that the acoustic model is a useful tool for the development and evaluation of alternative cochlear implant speech processing strategies.
Comparison of the responses of auditory nerve fibers to consonant–vowel syllables with predictions from linear models
Authors: Sinex Donal G. , Geisler C. Daniel
Published: October 2005

The responses of cat auditory-nerve fibers to synthesized consonant–vowel syllables were compared with predictions from linear models based on individual fibers’ threshold tuning curves. Comparisons with the linear predictions provided information about the specific effects of peripheral nonlinearities on the representation of speech sounds. Spectral peaks, such as the formants of vowels, were more prominently represented in synchronized discharge patterns than in the linear predictions. Suppression of responses to other spectral peaks and to stimulus components between spectral peaks accounted for the differences. While profiles of fibers’ synchronized responses were usually dominated by a single formant, predicted linear responses often included broad responses having two or more formants as well as components near the fibers’ characteristic frequencies. In contrast, when no stimulus peak fell within a fiber’s response area, the agreement between the neural response and the linear prediction was quite good. The results suggest that one role for peripheral nonlinearities in the auditory system may be to enhance the neural representation of spectral features such as formants.
A precise noise probability estimation from roughly observed data with quantized levels
Authors: Ohta Mitsuo , Yamaguchi Shizuma , Mitani Yasuo
Published: October 2005

A unified expression for the probability distribution function with quantized state variables for a stochastic noise environmental system is derived in the form of a statistical orthogonal expansion. Next, a new statistical procedure for estimating the precise noise level probability distribution form on the basis of the roughly observed data with a quantized level of a large-difference interval is proposed as an application of the above unified theory. The validity of the method has been experimentally confirmed by applying it to actual indoor noise data observed in a reverberant room of our university, and to outdoor noise data observed in Hiroshima City itself.
The estimation of the frequency-wavenumber spectrum using random acoustic arrays—Part I. Performance of beampower pattern estimators
Authors: Masry Elias
Published: October 2005

The estimation of the frequency-wavenumber spectrum of the ambient noise field from data collected by a totally random array is considered. The standard estimator [J. Acoust. Soc. Am. 71, 97–99 (1982)], which is a normalized beampower pattern, is shown to be biased for sparse arrays. A modified estimator which removes this bias is introduced and its performance is studied. In particular, precise asymptotic expressions for the bias, variance, and covariance of the estimator are established. The density of the number of sensors per unit volume is allowed to be arbitrary and thus the results hold for sparse arrays as well. An application to a representative planar array is given.
Insertion loss tests for fiberglass pipe insulation
Authors: Loney Wayne
Published: October 2005

Insertion loss tests were conducted for three different thicknesses of fiberglass pipe insulation and five different jacketings using a proposed test standard. Results indicate that the procedure is a feasible method for testing pipe lagging. The insertion loss increased with increasing thickness of insulation. A significant increase resulted at all test frequencies for the insulation without jacketing and with the aluminum jacketing. The increases at the higher frequencies due to increased insulation thickness diminished with the use of heavier jacketing. When the insulation thickness was held constant at 2 in., each doubling of the weight of the jacketing resulted in increases in insertion loss at all frequencies. For each thicker insulation, these increases due to heavier jacketings were restricted to fewer test frequencies. There was good agreement between the 100-Hz and 1/3-oct test data for the 2- and 3-in. pipe insulation with a slight preference for the 100-Hz data measured at the lower end of each 1/3 oct.
Acoustic diffraction analysis by the impulse response method: A line impulse response approach
Authors: Lasota H. , Salamon R. , Delannoy B.
Published: October 2005

Acoustic diffraction of plane impulsive waves is considered for free-field, baffled, and pressure release boundary conditions, in the case of an arbitrary spatial distribution of combined, amplitude-time delay modulation in an aperture. The method is based on the impulse response analysis of parallel aperture lines, the line impulse responses being then integrated to give an aperture impulse response. A closed-form, analytical expression is derived for lines having an arbitrary amplitude modulation. In the case of nonmodulated apertures of an arbitrary shape, the aperture impulse response is also of an analytical form, directly involving the aperture contour line. The analysis is performed with emphasis on maintaining clear physical sense of successive evaluation steps.
Perceptual integration of the murmur and formant transitions for place of articulation in nasal consonants
Authors: Kurowski Kathleen , Blumstein Sheila E.
Published: October 2005

This study reassessed the role of the nasal murmur and formant transitions as perceptual cues for place of articulation in nasal consonants across a number of vowel environments. Five types of computer-edited stimuli were generated from natural utterances consisting of [m n] followed by [i e a o u]: (1) full murmurs; (2) transitions plus vowel segments; (3) the last six pulses of the murmur; (4) the six pulses starting from the beginning of the formant transitions; and (5) the six pulses surrounding the nasal release (three pulses before and three pulses after). Results showed that the murmur provided as much information for the perception of place of articulation as did the transitions. Moreover, the highest performance scores for place of articulation were obtained in the six-pulse condition containing both murmur and transition information. The data support the view that it is the combination of nasal murmur plus formant transitions which forms an integrated property for the perception of place of articulation.
Scattering of acoustic waves by a layered elastic obstacle in a fluid—An improved null field approach
Authors: Boström Anders
Published: October 2005

Scattering by a layered elastic obstacle submerged in a fluid is considered. The null field approach (T-matrix method) is used, but the method is modified so that all surface fields can be expanded in spherical harmonics. The resulting method is then compared with the conventional null field approach (which uses expansions in regular wavefunctions), and it is concluded that the present method is the better one in general. It is, however, doubtful if the null field approach is applicable to cases where there is no sphere that circumscribes the core and inscribes the outer surface. Some numerical results are given for a layered spheroid and superspheroid.
The effects of stimulus duration on ABR and behavioral thresholds
Authors: Gorga Michael P. , Beauchaine Kathryn A. , Reiland Jan K. , Worthington Don W. , Javel Eric
Published: October 2005

ABR and behavioral thresholds were estimated as a function of stimulus duration for three normal and two hearing-impaired subjects. Stimuli were 2000-Hz tone bursts with 0.5-ms rise/fall times and durations ranging from 1 to 256 or 512 ms. For both groups of subjects, ABR thresholds were independent of stimulus duration. Normal subjects showed greater improvement in behavioral thresholds as a function of duration than did subjects with hearing losses. Thus, it appeared that ABR and behavioral thresholds were affected differently by changes in stimulus duration and that the magnitude of these differences could depend upon the presence of hearing loss. These data indicate that temporal integration may be one factor which makes comparisons between ABR and behavioral thresholds complicated. In the present study, the magnitude of hearing loss, measured by the ABR, would have been underestimated if normal behavioral thresholds for short-duration stimuli were used as the reference.
Role of backward waves in backscattering of ultrasonic beams at a liquid–solid interface
Authors: Stamnes Jakob J.
Published: October 2005

Experimental observations indicate that when a bounded beam of ultrasound is incident upon a plane liquid–solid interface at the Rayleigh angle there is a significant amount of radiation backscattered in the direction of the incident wave. Recently this phenomenon was explained in terms of a backward propagating leaky Rayleigh wave. We show here that in a pulse-echo mode of operation the foward propagating leaky Rayleigh wave is likely to a give a much larger contribution to the signal received at the transducer than the corresponding backward wave.
Natural frequencies of a point-supported circular cylindrical panel
Authors: Irie Toshihiro , Yamada Gen , Kudoh Yasunori
Published: October 2005

An analysis is presented for the free vibration of a point-supported circular cylindrical panel, and the natural frequencies and the mode shapes of vibration are calculated numerically for practical use.
Dynamic characteristics of cylindrical shells at the neighborhood of the ring frequency
Authors: Harari Azriel
Published: October 2005

This analysis presents some of the unique characteristics of a cylindrical shell at the neighborhood of the ring frequency, the frequency at which a wave traveling at the longitudinal propagation speed of an infinite slab will make a complete circle around the circumference in one period.
Speechreading supplemented with frequency-selective sound-pressure information
Authors: Breeuwer M. , Plomp R.
Published: October 2005

The benefit of supplementing speechreading with frequency-selective sound-pressure information was studied by auditorily presenting this information to normal-hearing listeners. The sound-pressure levels in one or two frequency bands of the speech signal with center frequencies of 500, 1600, and 3160 Hz, respectively, and with 1- or 1/3- oct bandwidth were used to amplitude-modulate pure-tone carriers with frequencies equal to the center frequencies of the filter bands. Short sentences were presented to 18 normal-hearing listeners under the conditions of speechreading-only and speechreading combined with the sound-pressure information. The mean number of correctly perceived syllables increased from 22.8% for speechreading-only to 65.7% when sound-pressure information was supplied in a single 1-oct band at 500 Hz and to 86.7% with two 1-oct bands at 500 and 3160 Hz, respectively. The latter signal scored only 26.7% correct syllables without accompanying visual information.
Limits on phonetic accuracy in foreign language speech production
Authors: Flege James Emil , Hillenbrand James
Published: October 2005

This study examined the French syllables /tu/ (‘‘tous’’) and /ty/ (‘‘tu’’) produced in three speaking tasks by native speakers of American English and French talkers living in the U. S. In a paired-comparison task listeners correctly identified more of the vowels produced by French than American talkers, and more vowels produced by experienced than inexperienced American speakers of French. An acoustic analysis revealed that the American talkers produced /u/ with significantly higher F2 values than the French talkers, but produced /y/ with F2 values equal to those of the French talkers. A labeling task revealed that the /y/ vowels produced by the experienced and inexperienced Americans were identified equally well, but that the experienced Americans produced a more identifiable /u/ than the inexperienced Americans. It is hypothesized that English speakers learn French /y/ rapidly because this vowel is not—like French /u/—judged to be equivalent to a vowel of English. The French and American talkers produced /t/ with equal VOT values of about 55 ms, which is intermediate to values commonly observed for monolingual speakers of French and English. It is hypothesized that the bilingual talkers judged the /t/ of French and English to be equivalent, which affected their perceptual target for French /t/ and ultimately their production of this stop.
Intensity perception. XIII. Perceptual anchor model of context-coding
Authors: Braida L. D. , Lim J. S. , Berliner J. E. , Durlach N. I. , Rabinowitz W. M. , Purks S. R.
Published: October 2005

In our preliminary theory of intensity resolution [e.g., see N. I. Durlach and L. D. Braida, J. Acoust. Soc. Am. 46, 372–383 (1969)], two modes of memory operation are postulated: the trace mode and the context-coding mode. In this paper, we present a revised model of the context-coding mode which describes explicitly a process by which sensations are coded relative to the context and which predicts a resolution edge effect [L. D. Braida and N. I. Durlach, J. Acoust. Soc. Am. 51, 483–502 (1972); J. E. Berliner, L. D. Braida, and N. I. Durlach, J. Acoust. Soc. Am. 61, 1256–1267 (1977)]. The sensation arising from a given stimulus presentation is coded by determining its distance from internal references or perceptual anchors. The noise in this process, combined with the sensation noise, constitutes the limitation on resolution in the model. In the revised model the probability density functions of the decision variable are not precisely Gaussian (and cannot be expressed analytically in closed form). This paper outlines the predictions of the model for one-interval paradigms and for fixed-level two-interval paradigms and derives estimates of the values of model parameters.
Integration of spectral and temporal cues separated in time and frequency
Authors: Espinoza-Varas Blas , Jamieson Donald G.
Published: October 2005

Subjects discriminated a ‘‘standard’’ pair of tone bursts (T1, T2) from a ‘‘comparison’’ pair (T1+Δt, T2+Δf), containing increments in the duration Δt of the first burst and/or the frequency Δf of the second burst. The threshold (d′=2.0) for Δt was measured as a function of Δf, and the threshold for Δf as a function of Δt. The integration of increments in duration and frequency was studied as a function of the spectral and temporal separation between T1 and T2. A trade-off between the values of Δt and Δf required for d′=2.0 performance was observed. This integration takes place when Δt, Δf occur simultaneously in the same spectral region, and when they occur separated by up to 120 ms, or by up to a full octave. The efficiency of integration was similar for all conditions of temporal and spectral separation studied, because the discriminability of Δt and of Δf is also nearly uniform across experimental conditions. The results from all experimental conditions are adequately described by a vector summation model derived from TSD. In a subsidiary experiment, subjects categorized pure tones varying in duration and frequency as ‘‘high’’ or ‘‘low’’ in pitch and ‘‘long’’ or ‘‘short’’ in duration. It was found that combined variations in duration and frequency result in essentially independent perceptual processes, although pitch has a small effect upon the perceived duration. It is concluded that spectral–temporal integration is a general ability operating in a variety of stimulus conditions. Listeners integrate independent evidence provided by the temporal and spectral cues in favor of, or against, particular stimulus states.
The effects of multichannel compression/expansion amplification on the intelligibility of nonsense syllables in noise
Authors: Walker Gary , Byrne Denis , Dillon Harvey
Published: October 2005

The effects of six-channel compression and expansion amplification on the intelligibility of nonsense syllables embedded in speech spectrum noise were examined for four hearing-impaired subjects. For one condition (linear) the stimulus was given six-channel amplification with frequency shaping to suit the subject’s hearing loss. The other condition (nonlinear) was the same except that low level inputs, to any given channel, received expansion amplification and high level inputs received compression. For each condition, each subject received the nonsense syllables at three different input levels, representing low, average, and high intensity speech. The results of this study, like those of most other studies of multichannel compression, are mainly negative. Nonlinear processing (mainly expansion) of low intensity speech resulted in a significant degradation of speech intelligibility for two subjects and in no improvement for the others. One subject showed a significant improvement in intelligibility for the nonlinearly processed average intensity speech and another subject showed significant improvement for the high intensity input (mainly compression). Clearly, nonlinear processing is beneficial for some subjects, under some listening conditions, but further research is needed to identify the relevent characteristics of such subjects. An acoustic analysis of selected items revealed that the failure of expansion to improve intelligibility was primarily due to the very low intensity consonants /O/ and /k/, in final position, being presented at an even lower intensity in the expansion condition than in the linear condition. Expansion may be worth further investigation with different parameters. Several other problems caused by the multichannel processing were also revealed. These included alteration of spectral shapes and band interaction effects. Ways of overcoming these problems, and of capitalizing on the likely advantages of multichannel amplification, are currently being investigated.
Ultrasonic investigation of the nonlinearity parameter B/A in biological media
Authors: Xiu-fen Gong , Ruo Feng , Cheng-ya Zhu , Tao Shi
Published: October 2005

The nonlinearity parameter B/A was determined for several biological samples by using comparative, insert-substitution methods. The values of B/A for solutions of dextrose, sucrose, and polyethylene glycol were found to increase linearly with solution concentration and exhibit independency upon the solute molecular weight.
Divergence of the hydrodynamic limit in the doubly asymptotic approximations for cylindrical shells
Authors: Hains F. D.
Published: October 2005

A virtual mass, hydrodynamic limit is used in the method of doubly asymptotic approximations for the vibration analysis of submerged structures in water. Here, the pressure field induced by the low-frequency breathing mode vibration of an infinite, elastic circular cylinder in an unbounded liquid is shown to be divergent, while the pressure field induced by the transverse vibration of a rigid cylinder is finite. In order to treat a vibrating cylinder whose volume changes with time, the free surface of the water should be considered.
Monaural and binaural auditory brainstem responses in relation to the psychophysical loudness growth function
Authors: Howe Susan W. , Decker T. Newell
Published: October 2005

Electrophysiological measures of the brainstem response to auditory stimuli permit comparisons to be made between latency shifts across intensity increments and psychophysical measures of loudness growth. Monaural comparisons leave much room for uncertainty in the interpretation of the nature of the relationship between the two response modes. A more definitive method for examining this relationship is to compare the monaural and binaural data obtained from psychophysical and electrophysiological measures. It is shown here that, while the brainstem electrophysiological response to intensity changes can be described by a power function, the latency of the neural response does not provide a direct link to the process of loudness summation or to the psychophysical response to loudness growth.
An extension of maximum entropy beamforming to arbitrary planar arrays with statistics
Authors: Hebbert R. S. , Barkakati Leha T.
Published: October 2005

The usual formulation of maximum entropy (ME) beamforming assumes no statistics in the spatial correlation matrix of the received signals. In practice the ME method is restricted to uniform line arrays of half-wavelength spacing. In this paper, an extended maximum entropy (EME) method is presented allowing statistics in the spatial correlation matrix. Also, a method of solution is given for arbitrary arrays. Results are presented for real and simulated underwater acoustic data.
Magnetoacoustic wave propagation in paramagnetic insulators exhibiting induced linear magnetoelastic couplings
Authors: Maugin G. A. , Hakmi A.
Published: October 2005

The propagation of bulk and surface magnetoacoustic waves is studied in paramagnetic materials on the basis of a phenomenological, fully nonlinear, rotationally invariant, thermodynamically admissible theory of the magnetoelasticity of insulators such as rare-earth compounds. The work is self-contained and develops from basic nonlinear equations to solve for propagation modes after linearization of both volume and surface equations about a bias state in accordance with the methods of nonlinear continuum mechanics. The initial nonlinear feature of the theory, associated with rotational invariance, allows one to place in evidence the effects of a bias magnetic field on the dynamical properties of the medium. In particular, among the effects thus exhibited are (1) a symmetry breaking favoring the existence of magnetoelastic couplings (biased piezomagnetism), which would not exist in the absence of bias fields, (2) an alteration in the bulk-wave speeds (direct magnetoacoustic effects), (3) an acoustical linear birefringence, and (4) in addition to the classical Rayleigh mode, creation of an SH magnetoacoustic surface mode akin to the Bleustein–Gulyaev mode of acoustoelectricity, results from adequate symmetry breaking effects of the bias magnetic field. The influence of viscosity and magnetic relaxation is also examined.
The propagation of plane waves in a thermally stratified atmosphere
Authors: Van Moorhem W. K. , Landheim Gregory K.
Published: October 2005

The behavior of a plane wave reflecting from a finite impedance surface with a realistic atmospheric temperature profile is investigated. An approximate solution has been implemented on a digital computer and this solution is presented graphically for a number of cases at low incidence angles.
Damping of bubble oscillations induced by transport of surfactants between the adsorbed film and the bulk solution
Authors: Glazman Roman E.
Published: October 2005

At frequencies well below the resonance, the forced oscillations of a microbubble suspended in a surfactant solution are affected by the dilational elasticity of an adsorbed film and by the adsorbate exchange occurring due to bubble’s surface area oscillations. The model introduced for computation of the exchange rate uses the relaxation time of the adsorption–desorption process, on which the experimental data are available in the literature, as the governing parameter. An important manifestation of the surfactant exchange, as found by solving a linearized problem of the bubble motion coupled with the adsorbate flux, is that it induces a considerable dissipation of acoustic energy. Computations are presented for the driving frequencies (ω) ranging from 102 to 105 s−1 and bubble diameters 10–200 μm. The total damping of a clean bubble is also computed, for comparison. The predicted damping constant for a 20-μm bubble covered with a condensed film of a fatty substance can exceed that for a clean bubble by several orders of magnitude at ω<104 s−1.
Apparatus-independent acoustical-material characteristics obtained from panel-test measurements
Authors: Rudgers Anthony J. , Solvold Christine A.
Published: October 2005

A panel-test evaluation of an acoustical material is generally made with the material, in the form of a slab, attached to a stiff support plate. However, measured acoustic transmission and reflection characteristics of the panel comprising the material and the support plate are not the intrinsic acoustic characteristics of the acoustical material. Rather, these characteristics are indicative only of the acoustic behavior of the material when it is attached to a particular support plate and immersed in the particular fluid medium in which the panel test is conducted. An analytic method is described that can be used to obtain, from the results of a panel test in which an acoustical material is evaluated while attached to a support plate, the intrinsic acoustic properties of the material. This is done by analyzing an equivalent-circuit analog network that describes the panel. A general one-dimensionally nonhomogeneous acoustical material is considered in this analysis. The acoustic properties of such a material may vary in an arbitrary way in the direction perpendicular to the faces of the slab of material that is being evaluated, but in any plane parallel to the slab faces, these properties are considered to be the same everywhere. The analysis shows that the intrinsic properties that determine the acoustic behavior of such a nonhomogeneous material can be specified in terms of three impedances. These impedances can be determined from the two complex pressure reflection coefficients and the complex pressure transmission coefficient measured in a panel test made with the material attached to the support plate. The values of these impedances are, however, independent of the nature of the support plate and of the fluid surrounding the panel when the acoustical material is evaluated. That is, by using the method presented, one can analytically remove the effects of the support plate and the surrounding fluid from the panel-test results. Consequently, once the impedance values specifying the acoustical material are obtained, the analysis shows that it is possible, in principle, to predict the acoustic performance of the material in a wide variety of different circumstances. Some implications of the analysis in the case of effectively homogeneous acoustical materials are also examined. In particular, it is shown how the complex sound speed characterizing such a material can be obtained by panel-test measurements.
Heat generated by ultrasound in an absorbing medium
Authors: Cavicchi T. J. , O’Brien W. D.
Published: October 2005

Nyborg’s [J. Acoust. Soc. Am. 70, 310–312 (1981)] derivation of heat generation density has been examined. An alternative approach has been developed to yield the same expression by assuming a complex wavenumber with the linear acoustic equations.
Membrane damping by a constrained layer
Authors: Cole John E.
Published: October 2005

An analysis of the effectiveness of a constrained layer damping treatment for in-plane vibrations of a plate is presented. The loss factor is shown to be that of an unconstrained layer treatment for frequencies below a cutoff frequency and to be substantially larger above this frequency.
Rayleigh waves on a convex cylindrical poroelastic surface.Part II
Authors: Tajuddin M. , Moiz A. A.
Published: October 2005

The propagation of Rayleigh waves on a convex cylindrical poroelastic surface is studied for pervious and impervious surfaces. A plot relating the nondimensional phase velocity with the angular wavenumber is presented. The results for a plane surface and a purely elastic solid are studied as particular cases.
A canonical ocean bottom sound velocity profile
Authors: Kawahara Hiroshi , Frisk George V.
Published: October 2005

A new canonical sound velocity profile is presented in which the velocity cubed varies linearly with depth and is characterized by two parameters. The ray acoustic equations have exact analytic solutions for this profile, and the expressions for horizontal range, travel time, and intensity are derived. It is shown that the canonical profile can be derived approximately from Hamilton’s profile for bottom sediments obtained from sonobuoy data. The agreement between the two is shown to be excellent for both the velocity and the velocity gradient even for sediment thicknesses of 1 km.
Comments on ‘‘Distortion of finite amplitude ultrasound in lossy media,’’ by M. E. Haran and B. D. Cook [J. Acoust. Soc. Am. 7
3, 774–779 (1983)]
Authors: Trivett D. H. , Van Buren A. L.
Published: October 2005

Readers of the subject paper might conclude that Haran and Cook are the first to derive an alogorithm based on Burgers’ equation which calculates the nonlinear propagation of a plane wave in a lossy medium with nonquadratic frequency-dependent absorption coefficients. In fact, we presented such an algorithm in an earlier paper [D. H. Trivett and A. L. Van Buren, ‘‘Propagation of plane, cylindrical, and spherical finite amplitude waves,’’ J. Acoust. Soc. Am. 69, 943–949 (1981)] and we feel that the Haran and Cook’s reference to our work was insufficient. Although the derivation given by Haran and Cook is correct, it contains an inconsistency in notation. Also, their numerical results for propagation in fresh water correspond to different initial conditions than stated in the paper.
Incoherent ultrasonic wave attenuation in inhomogeneous media
Authors: Gazalet Marc , Frohly Jacques , Perdigao Joao , Bruneel Christian
Published: October 2005

A simplified theoretical model based upon phonon diffusion is proposed in this paper for the evaluation of the intensity level of ultrasonic waves in inhomogeneous media. This model shows large similarities with well-known energy transfer theories and leads to particularly simple analytical results applicable to the case where the incoherent wave level predominates over the coherent one. A characteristic length beyond which acoustic image reconstruction is no longer feasible is defined here and a very simple analytical formula for this important parameter is derived. This model is then applied to the acoustic wave propagation in concrete. A reasonable fit is found between theory and experiments in this case.
Time-variant filtering for nonstationary random processes
Authors: Tsao Y. H.
Published: October 2005

This paper is concerned with the effects of time-variant (including time-invariant) linear systems (filters) upon the nonstationarity of an acquired random process. The basis approach is the frequency domain description and, therefore, the relationship between the modulation function (MF) and the power spectral density function is emphasized though the both are time-dependent for nonstationary processes. In particular, this paper proposes a general series form of the input–output relationship expressed in terms of the relevant modulation functions of the processes. Based upon this form, the problems of filtering a nonstationary input can be conveniently handled. The system performance is also described by a time-variant differential equation and the technique proposed in this paper is the so-called Modulation Function Equation (MFE) method which is an alternative time-variant differential equation, derived from an ordinary one, yet with the randomness excluded. The principle of deriving a class of MFE is presented and the technique is applied to some practical problems, e.g., trolley wires, in order to describe their responses to a random nonstationary excitation (noise and/or vibration). The solutions of the formed MFE are, however, essentially those of the equivalence of the frequency implementation which is now defined as being the frequency/time two-dimensional function for the time-variant systems (filters). By invoking the MFE technique the implementation can be conducted numerically or analytically. This paper discusses such possibilities and, in particular, develops two approximations: namely the System Iterative Method (SIM) and the Power Series Method (PSM) for a class of time-variant MFEs; they both may be usefully applied to certain nonstationary problems.
Estimating the trajectory of an accelerationless aircraft by means of a stationary acoustic sensor
Authors: Dommermuth F. , Schiller J.
Published: October 2005

The flight parameter of an aircraft moving without acceleration can be estimated by exploiting the target-generated noise received by a directional sensor consisting of three or four microphones. The Cramér–Rao lower bound is calculated to investigate the theoretical accuracy of estimates. Moreover, an algorithm is proposed which computes the maximum-likelihood estimate. Extended simulations prove the algorithm to work reliably and fast, and the estimate to be nearly unbiased and efficient when averaged over a large region of flight parameters. Results obtained with real data are included.
The estimation of the frequency-wavenumber spectrum using random acoustic arrays—Part II. A class of consistent estimators
Authors: Masry Elias
Published: October 2005

A class of consistent frequency-wavenumber spectral estimators of the ambient noise field from the output of a totally random n-dimensional array is introduced. The performance of these spectral estimators is established. In particular, precise asymptotic expressions for the bias, variance, and covariance of the estimators are obtained together with exact rates of quadratic-mean convergence. It is shown that the results hold for any positive value of the density of the number of sensors per unit volume and are thus valid even for sparse arrays. An application to a representative planar array is given.
A frequency-domain beamforming algorithm for wideband, coherent signal processing
Authors: Weber M. E. , Heisler R.
Published: October 2005

Coherent detection processors for sonar (e.g., matched filters for active systems) require continuous time series as input and have conventionally been coupled to delay-and-sum time-domain beamformers. As an alternative, we have extended the FFT beamforming technique to be functionally equivalent to a time-domain beamformer. The procedure utilizes the ‘‘analytic’’ representations of the hydrophone signals as input and produces continuous beam time series as output, thereby allowing for complete flexibility in post-beamformer processing. The method will be applicable when the array elements are uniformly spaced, and when a large fraction of the possible beams are to be computed. In such cases, the algorithm offers the following advantages relative to a conventional time-domain beamformer: (1) elimination of the need for a high input sampling rate to achieve acceptable beam patterns—the frequency-domain approach is insensitive to the sampling rate provided this exceeds the (bandpass) Nyquist rate; (2) reduction of high beam sidelobe levels due to dead or malfunctioning array elements—the response of missing array elements is readily estimated in the frequency domain by interpolating from the spectra of neighboring sensors; and (3) potential reductions in the computational load when the array is large or the center-frequency/bandwidth ratio of the signal is high. Using a general purpose array processor we have demonstrated near real-time evaluation of a complete beam set for a 128-channel linear array. Computer-generated ‘‘acoustic’’ data were used to confirm that the software preserves the envelope, spectrum, and temporal correlation properties of signals while yielding near-theoretical performance in reducing beam sidelobe levels.
Cumulative detection and positive signal excess probabilities for a sonar model with two components
Authors: Wilmut Michael J. , MacKinnon Robert F.
Published: October 2005

The sonar equation is the basis for the prediction of sonar performance. Under certain assumptions concerning the signal-to-noise probability density function, one may calculate the probability of detection for a system with known processor gain. Herein, the detection process is assumed to be applied to a series of nonoverlapping time intervals. The signal-to-noise ratio in dB is assumed to be the sum of two independent Gaussian random variables, one of which is perfectly correlated from interval to interval, the other of which is uncorrelated. Analytic expressions for probability of detection are derived and evaluated numerically for various cases. In addition, the probability of signal excess being greater than zero is calculated and compared to the probability of detection.