bluuebunny/crossref_metadata_2025 huggingface dataset:
The auditory periphery of the ferret. II: The spectral transformations of the external ear and their implications for sound localization
Authors: Carlile Simon
Published: October 2005

In the previous paper the directional response characteristics of the ferret auditory periphery were examined. In this study further measurements of the spectral transfer functions (STFs) of the auditory periphery were obtained at locations close to the tympanic membrane. There was considerable variation in the STFs recorded from different animals and between recordings made at each end of the auditory canal in the same animal. However, calculation of the so called ‘‘location dependency function’’ demonstrated that changes in the location of the stimulus produced the same pattern of changes in the STFs in all recordings. Changes in the spectral transformation for azimuth locations in the ipsilateral auditory field were examined by calculating the horizon STF. The gain transformations of frequencies below 20 kHz were found to be asymmetrical about the interaural axis so that maximum gain was obtained for anterior stimulus locations. In contrast, the maximum gain for frequencies above 20 kHz was obtained for stimulus locations about the interaural axis, and movement of the stimulus location into either the anterior or posterior fields produced symmetrical reductions in gain. These changes were related to the directional properties of the periphery examined in the previous paper (Carlile, 1990).The spatial resolution of the monaural information provided by the peripheral STFs is dependent on the rate of change of the transformations as a function of azimuthal displacement of the stimulus location. This was examined by calculating the unsigned first spatial derivative for each frequency in the horizon STF. The spatial derivative of frequency was found to be high for locations about the posterior and anterior median planes. This is discussed in terms of the results of behavioral experiments examining the resolution of sound localization in the ferret and other mammals.
Formant frequencies of Dutch vowels in a text, read at normal and fast rate
Authors: van Son R. J. J. H. , Pols Louis C. W.
Published: October 2005

Speaking rate is thought to affect the spectral features of vowels. Target-undershoot models of vowel production predict more spectral reduction and coarticulation of vowels in fast-rate speech than in normal-rate speech. To test this prediction, a meaningful Dutch text of about 850 words was read twice by an experienced newscaster, once at a normal speaking rate and once as fast as possible. All realizations of seven different vowels and some realizations of the schwa (/E/) were isolated. The first and second formant frequency values of all realizations were measured at five different points, each time by making cross sections at different points in the vowel realization. The different selections of these points are based on procedures used in literature, such as maximal F1 or mean formant value. No spectral vowel reduction was found that could be attributed to a faster speaking rate, neither was a change in coarticulation found. The only systematic effect was a higher F1 value in fast-rate speech irrespective of vowel identity. This possibly suggests a generally more open articulation of vowels, speaking louder, or some other general change in speaking style by our speaker when he speaks fast.
Binaural masking experiments using noise maskers with frequency-dependent interaural phase differences. II: Influence of frequency and interaural-phase uncertainty
Authors: Kohlrausch Armin
Published: October 2005

This study investigates whether binaural signal detection is improved by the listener’s previous knowledge about the interaural phase relations of masker and test signal. Binaural masked thresholds were measured for a 500-ms dichotic noise masker that had an interaural phase difference of 0 below 500 Hz and of π above 500 Hz. The thresholds for two different 20-ms test signals were determined within the same measurement using an interleaved adaptive 3-interval forced-choice (3IFC) procedure. In each 3IFC trial, both signals could occur with equal probability (uncertainty). The two signals differed in frequency and interaural phase in such a way that one signal always had a frequency above the masker edge frequency (500 Hz) and no interaural phase difference (So), whereas the other signal frequency was below 500 Hz and the interaural phase difference was π (Sπ). The frequencies of a signal pair remained fixed during the whole 3IFC track. These two signals thus lead to two different binaural conditions, i.e., NoSπ for the low-frequency signal and NπSo for the high-frequency signal. For comparison, binaural masked thresholds were measured with the same masker for fixed signal frequency and phase. The binaural masking level differences (BMLDs) resulting from the two experimental conditions show no significant difference. This indicates that the binaural system is able to apply different internal transformations or processing strategies simultaneously in different critical bands and even within the same critical band.
The effect of modulation coherence on signal threshold in frequency-modulated noise bands
Authors: Grose John H. , Hall Joseph W.
Published: October 2005

A series of four experiments was undertaken to ascertain whether signal threshold in frequency-modulated noise bands is dependent upon the coherence of modulation. The specific goal was to determine whether a masking release could be obtained with frequency modulation (FM), analogous to the comodulation masking release (CMR) phenomenon observed with amplitude modulation (AM). It was hypothesized that an across-frequency grouping process might give rise to such an effect. In experiments 1–3, maskers were composed of three noise bands centered on 1600, 2000, and 2400 Hz; these were either comodulated or noncomodulated with respect to both FM and AM. In experiment 1, the modulation was sinusoidal, and the signal was a 2000-Hz pure tone; in experiment 2, the modulation was random, and the signal was an FM noise band centered on 2000 Hz. The results obtained showed that, given sufficient width of modulation, thresholds were lower in a coherent FM masker than in an incoherent FM masker, regardless of the pattern of AM or signal type. However, thresholds in multiband maskers were usually elevated relative to that in a single-band masker centered on the signal. Experiment 3 demonstrated that coherent FM could be discriminated from incoherent FM. Experiment 4 gave similar patterns of results to the respective conditions of experiments 2 and 3, but for an inharmonic masker with bands centered on 1580, 2000, and 2532 Hz. While within-channel processes could not be entirely excluded from contributing to the present results, the experimental conditions were designed to be minimally conducive to such processes.
Resonant acoustic determination of elastic moduli
Authors: Garrett Steven L.
Published: October 2005

A long rod of circular or elliptical cross section can be selectively excited in the torsional, longitudinal, and flexural resonant modes using a single pair of electrodynamic transducers consisting of coils glued to each end of the bar and placed in the field of a magnet. The elastic moduli of the material can be simply determined to high accuracy by measuring the resonance frequencies of these modes and the mass and physical dimensions of the rod. Since the longitudinal and flexural modes both yield values for the Young’s modulus, the system has a built-in redundancy that makes the interpretation of the data more robust. The large signal amplitudes make automated measurement of the temperature dependence of the moduli simple through the use of a phase-locked loop to track the change in the resonance frequency with temperature.
Calculation of the impulse response of a rigid sphere using the physical optic method and modal method jointly
Authors: Sun Zhigang , Gimenez Gérard , Vray Didier , Denis Florence
Published: October 2005

In this paper a practical method is proposed to calculate the acoustical response of a rigid sphere. This method combines the physical optic method, which gives good results at high frequencies, with the modal method, which is suitable at low frequencies. This gets around the problems that arise when only one of these methods is used, namely the failure of the physical optic method at low frequencies and the convergence difficulties of the modal method at high frequencies. Here, the impulse response (response to a Dirac pressure transmission) of a rigid sphere for a backscattering situation is calculated.
Envelope expansion methods for speech enhancement
Authors: Clarkson Peter M. , Bahgat Sayed F.
Published: October 2005

The last decade has seen increasing interest in techniques for the enhancement of digital speech signals. Significant gains have been made in terms of signal-to-noise ratio (SNR) and quality, but few techniques have produced improvements in intelligibility. A method for speech enhancement based on nonlinear expansion of the spectral envelope is presented. The expansion is consistent with both the long-term spectrum of the speech and with the probability that speech is present in a given sample. Objective SNR measures are used to compare this algorithm with the well-known spectral subtraction method, with an alternative expansion scheme, and with limiting SNRs resulting from perfect recovery of the amplitude spectrum. For the purpose of intelligibility assessments, a simplified version of the algorithm has been implemented on a Texas Instruments TMS320-C25 system. Listening trials with this real-time system, conducted using a modified rhyme test, have produced small, but consistent, improvements in articulation scores.
Reflection of retrograde waves within the cochlea and at the stapes
Authors: Shera Christopher A. , Zweig George
Published: October 2005

A number of authors [de Boer and Viergever, Hear. Res. 13, 101–112 (1984); de Boer et al., in Peripheral Auditory Mechanisms (Springer-Verlag, Berlin, 1986); Hear. Res. 23, 1–7 (1986); Viergever, in Auditory Frequency Selectivity (Plenum, New York, 1986), pp. 31–38; Kaernbach et al., J. Acoust. Soc. Am. 81, 408–411 (1987)] have argued that backward-traveling waves, in striking contrast to waves traveling forward towards the helicotrema, suffer appreciable reflection as they move through the basal turns of the cochlea. Such reflection, if present, would have important consequences for understanding the nature and strength of otoacoustic emissions. The apparent asymmetry in reflection of cochlear waves is shown, however, to be an artifact of the boundary condition those authors impose at the stapes: conventional cochlear models are found not to generate reflections of waves traveling in either direction even when the wavelength changes rapidly and the WKB approximation breaks down. Although backward-traveling waves are not reflected by the secular variation of the geometrical and mechanical characteristics of the cochlea, they are reflected when they reach the stapes. The magnitude of that boundary reflection is computed for the cat and shown to be a large, rapidly varying function of frequency.
Comment on spectral statistics in elastodynamics
Authors: Bohigas O. , Legrand O. , Schmit C. , Sornette D.
Published: October 2005

Recently, a set of high eigenfrequencies of small aluminum blocks have been measured and analyzed quantitatively by using methods initially developed in nuclear physics on the basis of an analogy with random matrix theory [R. L. Weaver, J. Acoust. Soc. Am. 85, 1001 (1989)]. At the foundation of the application of random matrix theory is the (classical motion) ⇔ (finite frequency vibration) correspondence according to which the nature of classical geometrical acoustic trajectories determine the correspondence with random matrix theory and thereby the structure of the spectrum (classical chaos→GOE spectrum; regular motion→Poissonian spectrum). Although the classical geometrical acoustics trajectories are not chaotic in the system studied by Weaver, he finds a good agreement with the GOE prediction, in contradiction to the usual wisdom concerning the classical-vibration correspondence. It is suggested that this paradox stems from finite wavelength effects that introduce a coarse graining in the relevant classical dynamics. Interpreted in this way, Weaver’s results seem to confirm that the GOE spectrum initially studied for simple scalar Helmholtz equation may also be valid in the more complicated case of elastodynamics.
Modeling compressional wave velocity and attenuation in carbonate sediments
Authors: Hurley Michael T. , Manghnani Murli H.
Published: October 2005

The Biot poroelastic theory is used to model ultrasonic (1 MHz) compressional wave velocity (Vp) and specific attenuation (Qp−1) for carbonate sediment sequences from three Deep Sea Drilling Project (DSDP) sites 288, 289, and 316 on the Ontong–Java Plateau in the western Pacific ocean. The sediments are assumed to be represented by a granular frame containing tortuous capillary tubes of a constant radius. Experimental data for the variation of shear velocity Vs and bulk density ρ with depth are used as input parameters for the model. Assumptions of the frame Poisson’s ratio σb, grain bulk modulus Kg, and tortuosity α are necessary. The low-frequency asymptote of the Biot theory is adequate in modeling the variation of Vp with depth for sites 288 and 289. Modeled velocities agree to within 8% of experimental. The sensitivity of the modeled velocities to the uncertainty in the input parameters is investigated. The equations of motion are partially differentiated with respect to each parameter and the resulting equations are used in conjunction with each parameter’s uncertainty or error. The uncertainty in the modeled velocities is on average 11% and is mostly dependent upon the uncertainties in Kg and σb. The assumption of constant σb for the chalk-limestone sequences from sites 288 and 289 is then tested. It is found to remain constant at a value of 0.2 for the chalk, and decreases to approximately 0.1 for the transition to limestone. Modeled values for Qp−1 are found to be sensitive to σb and ρ, in addition to the pore space parameters, and are considerably smaller than the experimental observations from sites 288, 289, and 316.
Comment on “Sound scattering of a spherical wave incident on a cylinder” [J. Acoust. Soc. Am. 87, 1871–1879 (1990)] by T. Li and M. Ueda
Authors: Piquette Jean C.
Published: October 2005

Some clarifying remarks regarding earlier work cited in the subject paper are given.
Finestructure in NAPOLI 85, an ocean/acoustic experiment
Authors: Potter J. R.
Published: October 2005

NAPOLI 85 was an ocean/acoustic experiment carried out in the Tyrrhenian Sea to investigate acoustic propagation variability due to inhomogeneities in the ocean medium. The variability in the pulse arrival times has already been presented. This article presents the analysis of the environmental conditions. Data are available from various instruments, including a towed oscillating body (TOB), which was equipped with sensors that provide sound speed. The TOB allows oceanic features to be mapped in the vertical–horizontal plane. These maps show significant finestructure features (typically 4 km long by 40 m deep) that can be tracked through 10-TOB casts over a 3-day period. In contrast to an oceanographer’s viewpoint, the analysis of these features is carried out in terms of their impact on acoustic propagation. A procedure for separating finestructure into internal-wave and non-wave components is extended from previous work and applied. This procedure provides a means to identify the mechanism generating the variability, without the uncertainty inherent in the analysis of one-dimensional data. The ocean variability is found to have been almost entirely caused by advective intrusions, with very little internal-wave activity. An internal-wave model is applied to the separated wave field and is shown to agree moderately well. The model cannot be made to match the non-wave field, which has a β−5/2 horizontal wave-number spectrum. Characteristic length-scale definitions are developed and evaluated for the horizontal and vertical directions. The horizontal length scale is 2 km and is depth invariant. Vertical scales vary from 7–25 m over the depth range 50–250 m, respectively.
Effect of orientation of the viscoelastic behavior of polymers.
Authors: Wetton R. E. , Duncan J. C. , Connolly J. M. , Foster G. M.
Published: October 2005

The dominant relaxation process exhibited by polymers is the αa process giving rise to the glass transition. This process gives high damping (tan δ typically between 1.0 and 2.0) but an accompanying large modulus change (typically three decades). A major problem in utilizing polymers in damping applications is the scale of this modulus variation. It has recently been demonstrated that large changes in the Tg location of many polymers can be achieved by orientation of the chains, provided this orientation is not allowed to relax during the measurement. In the present work, relaxation spectra of natural rubber, SBR rubber, and block copolymer rubbers have been measured at various temperatures in the region above their Tg’s. The relaxation process for most systems is shifted to higher frequencies by several decades. The effect is reported with stress applied both along the orientation direction in tensile experiments and transverse to it in torsional experiments. The results are analyzed within the ‘‘mechanical’’ Cole–Cole complex plane formulations and using time temperature super position. Comparisons are made with the unoriented samples. Consideration is given to the feasibility of using multilayer rubber elements of differing orientations in order to broaden the frequency range of high damping.
Acoustic radiation from finite structures
Authors: Sarkissian Angie
Published: October 2005

Recently, the application of singular value decomposition has been discussed in identifying source modes of a radiating structure by providing a representation to the Neumann Green’s function for the far field of the structure. The source modes, identified as such, will form eigenstates of radiated power. The determination of such states is of significant interest in acoustics, having applications in radiation filtering and beaming. A different algorithm is introduced for the computation of the modes which does not require the application of singular value decomposition. Since eigenstates of radiated power are also eigenstates of the surface acoustic resistance, these modes may be computed by simply diagonalizing this operator which is real and symmetric. The eigenvalues computed will be proportional to the radiated power from each mode.
Fresnel zone effects in the scattering of sound by cylinders of various lengths
Authors: DiPerna Daniel T. , Stanton Timothy K.
Published: October 2005

The backscattering behavior of straight cylinders is examined whose lengths range from much less than the diameter of the first Fresnel zone of the source/receiver pair to much greater than the first Fresnel zone, with special emphasis on the complicated ‘‘transitional region,’’ where the cylinders occupy a finite number of Fresnel zones (≊1–5). In general, the scattering characteristics of cylinders in this region can only be described numerically. The scattering is described by first adapting the deformed cylinder formulation [T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989)] to the point-source/point-receiver combination. Numerically evaluating this expression showed the scattering characteristics to be dominated by Fresnel zone effects—oscillations in the backscatter versus length curve caused by constructive and destructive wave interferences due to phase shifts from contributions along the cylinder axis. An experiment was performed that involved measurement of backscatter versus cylinder length in the transitional region, and there is reasonable agreement between the results and the trend as predicted by the approximate theory.
Scattering of sound by atmospheric turbulence: A numerical simulation above a complex impedance boundary
Authors: McBride Walton E. , Bass Henry E. , Raspet Richard , Gilbert Kenneth E.
Published: October 2005

A computer simulation of the effect of small-scale turbulence on atmospheric sound propagation over a complex impedance boundary is developed. The atmospheric turbulence is modeled as an ensemble of spherically symmetric eddies with Gaussian refractive profiles. Single scatter is assumed and a closed form of the first Born approximation for scattering is obtained, giving each eddy’s contribution to the total fluctuation of the sound pressure at a receiver downrange. The numerical simulation is accomplished by repeated calculations for many ‘‘realizations,’’ or snapshots of the turbulent medium. Each eddy’s scatter contribution is added up coherently for a particular configuration of eddies, yielding that realization’s total sound pressure. The eddies are then given a random change in their coordinates. The total sound pressure is calculated for this realization, and the process repeated. Better agreement with the analytical results of Karavainikov [Akust. Zh. 3, 175–186 (1957)] for an unbounded medium is obtained at the higher frequencies with the use of the first Rytov approximation to scattering. A complex impedance boundary is added and the predictions of the standard deviations of the amplitude fluctuations, amplitude probability distributions, and structure functions are then tested against experimental data. Good agreement is found whenever the average sound pressure level was well above the background noise level.
Further studies of a model for azimuthal encoding: Lateral superior olive neuron response curves and developmental processes
Authors: Blum Jacob J. , Reed Michael C.
Published: October 2005

A number of investigators have published measurements of the outputs of single neurons from the lateral superior olive (LSO) of the cat for a variety of auditory signals. The response curves show a very wide range of shapes and thresholds. In this paper, the single neuron response curves predicted by a previously published model for the encoding of azimuthal location by the LSO to the experimental curves are compared. The predicted curves are in good qualitative agreement with the experiments and, in addition, the model provides an explanation of the seemingly paradoxical drop in output as interaural intensity difference (IID) is held fixed and absolute intensities are raised. The particular shape of the response curve depends on the location of the LSO neuron examined. In the model, two possible developmental programs to form the adult pattern of connections from the anteroventral cochlear nucleus and the medial nucleus of the trapezoid body onto the LSO are also examined. In the first, connections are made by a forward stochastic process in which there is a limit on the numbers of synapses formed on each LSO cell. In the second, there is no such limit, but in later developmental stages pruning of synapses occurs which reduces their number to the limit. Both schemes give similar adult connectional patterns. The LSO response curves generated by the model are similar to those observed in LSO neurons of the developing gerbil by Sanes and Rubel [J. Neurosci. 8, 682–700 (1988)]. Thus the model mechanism not only encodes azimuthal location by activity across the population of neurons, but is also consistent with single unit neurophysiological measurements of LSO output in both developing and adult animals.
Single-phase drive of a circular ultrasonic motor
Authors: Kurosawa Minoru , Ueha Sadayuki
Published: October 2005

A method of single-phase drive of an ultrasonic rotary motor is proposed where the vibration mode of a circular stator is rotated by a single-phase source. If a small mass is attached to the circular ring vibrator, the degenerate doublets of the vibration mode are perturbed and separated into two orthogonal vibration modes with different resonance frequencies. The two modes can be excited with a phase difference of 90° by a single-phase source if the amount of the mass is appropriate. This causes the rotation of the vibration mode. The proposed method is successfully studied theoretically and compared well experimentally.
Some effects of auditory grouping factors on modulation detection interference (MDI)
Authors: Hall Joseph W. , Grose John H.
Published: October 2005

The ability to detect the existence of amplitude modulation at a target frequency is reduced when amplitude modulation exists at a flanking frequency. This effect has been termed modulation detection interference (MDI) [Yost and Sheft, J. Acoust. Soc. Am. 85, 848–857 (1989)]. One explanation for MDI holds that the masking and target frequencies are grouped together by the auditory system such that it is difficult to analyze the modulation at each frequency separately. The present study investigated conditions where the asynchrony of temporal gating of the target and flanking frequencies was manipulated in order to make the frequencies more or less likely to be grouped together by the auditory system and perceived as originating from a single putative source. A second experimental manipulation attempted to perceptually segregate the masking and target frequencies on the basis of harmonicity or spectral proximity. The results of the experiments indicated that manipulations that were intended to enhance the segregation of the masking and target frequencies reduced the magnitude of MDI effects. This generally supported an interpretation that MDI is related in some way to auditory grouping. A final experiment was performed in which the subject had to detect the presence of amplitude modulation, but also had to identify which of two frequency components carried the modulation. Subjects were often poor in discriminating which of two frequencies was amplitude modulated, even when the modulation itself was clearly audible. It was concluded that part of the MDI effect might be due to the poor ability of the auditory system to associate modulation with the carrier of the modulation. The results of the present study are in agreement with past models of MDI proposed by Yost and his colleagues, but do not necessarily directly support the idea that MDI reflects auditory grouping by common modulation.
The relationship between the impulse response and angular spectrum methods to evaluate acoustic transient fields
Authors: Stepanishen P. , Forbes M. , Letcher S.
Published: October 2005

Impulse response time domain and angular spectrum or wave vector time-domain methods can be used to investigate the spatial temporal characteristics of acoustic fields from planar ultrasonic transducers which are subjected to pulsed wideband excitations. Both methods are developed here from the time-dependent Green’s function solution of the initial-boundary value problem. The close relationship of the methods is made apparent by the use of spatial-temporal Fourier transform techniques of analysis. Axisymmetric fields are then addressed as a special case via the use of Hankel and Fourier transform techniques. Finally, classical solutions to the associated harmonic boundary value problems are then shown to result from temporal Fourier transforms of the time-dependent field solutions.
Analytical investigation of the flattening effect: The reactive power balance rule
Authors: Boutillon Xavier
Published: October 2005

McIntyre et al. [J. Acoust. Soc. Am. 74, 1325–1345 (1983)], through comprehensive time-domain analyses of the bowed string mechanisms and various numerical simulations, have first pointed out that the hysteretical character of the sticking–slipping process necessarily induces, under certain end conditions, a flattening effect (the note plays flat as the bow pressure exceeds a given level). Taking advantage of a frequency-domain analysis, it is demonstrated that the area of the hysteresis cycle has an analytical relation to various physical parameters of the bowed string, leading to the concept of reactive power. The flattening effect appears as a consequence of this relation. Another possible consequence is the observed dependence of the spectrum and intensity of the string vibration on the bow pressing force. Based on realistic assumptions, an algorithm is proposed to connect the flattening effect or the intensity variations to the physical characteristics of the string. Finally, the variations of the flattening effect with playing parameters such as bow position or bow velocity are evaluated.
Radiation from a submerged thermoacoustic source
Authors: Gabrielson Thomas B.
Published: October 2005

Radiation of sound from a submerged and freely flooded tube, closed at one end and open at the other, follows well-known relationships if the exit dimension is much smaller than a wavelength. If the tube is instead filled with a gas and submerged in water, the radiated power is higher than that of the flooded tube for the same internal acoustic pressure. If the density-sound-speed product, ρc, is much higher in the liquid than in the gas, as would normally be the case, then the radiated power is greater by the factor 1/0.36(ka)2, where k is the wave number in the water and a is the tube radius. This provides an ideal setting for construction of an underwater acoustic source using a standing-wave thermoacoustic driver since this driver is force limited rather than displacement limited. The performance is ultimately limited by the hydrostatic pressure and the dimensions of the tube.
Speaker normalization of static and dynamic vowel spectral features
Authors: Zahorian Stephen A. , Jagharghi Amir J.
Published: October 2005

Two methods are described for speaker normalizing vowel spectral features: one is a multivariable linear transformation of the features and the other is a polynomial warping of the frequency scale. Both normalization algorithms minimize the mean-square error between the transformed data of each speaker and vowel target values obtained from a ‘‘typical speaker.’’ These normalization techniques were evaluated both for formants and a form of cepstral coefficients (DCTCs) as spectral parameters, for both static and dynamic features, and with and without fundamental frequency (F0) as an additional feature. The normalizations were tested with a series of automatic classification experiments for vowels. For all conditions, automatic vowel classification rates increased for speaker-normalized data compared to rates obtained for nonnormalized parameters. Typical classification rates for vowel test data for nonnormalized and normalized features respectively are as follows: static formants—69%/79%; formant trajectories—76%/84%; static DCTCs 75%/84%; DCTC trajectories—84%/91%. The linear transformation methods increased the classification rates slightly more than the polynomial frequency warping. The addition of F0 improved the automatic recognition results for nonnormalized vowel spectral features as much as 5.8%. However, the addition of F0 to speaker-normalized spectral features resulted in much smaller increases in automatic recognition rates.
Local high-order radiation boundary conditions for the two-dimensional time-dependent structural acoustics problem
Authors: Pinsky Peter M. , Thompson Lonny L. , Abboud Najib N.
Published: October 2005

The time-dependent structural acoustics problem involving solution of the coupled wave equation over an infinite fluid domain is posed as a coupled problem over a finite fluid domain with local time-dependent radiation boundary conditions applied to the fluid truncation boundary. The proposed radiation boundary conditions are based on an asymptotic approximation to the exact solution in the frequency domain expressed in negative powers of a nondimensional wave number. A sequence of differential operators that match the leading terms of the asymptotic expansion provide boundary conditions that are of progressively higher order and increasing accuracy. Time-dependent boundary conditions are obtained through an inverse Fourier transform. The relationship of these approximate local operators to the exact nonlocal Dirichlet-to-Neumann map is examined. To illustrate their effectiveness, the boundary conditions are employed in a finite element formulation for the time-dependent structural acoustics problem. In contrast to nonlocal boundary conditions based on the Dirichlet-to-Neumann map or retarded potential integral formulations, the proposed local boundary conditions preserve the data structure of the standard finite element method and do not require storage of a large pool of historical data during the solution process. Numerical results illustrate the accuracy of the proposed boundary conditions as effected by the operator order, acoustic wave number, radiation directionality, and distance from the acoustic source.
The wall-pressure spectrum in turbulent flow over a randomly inhomogeneous elastic solid
Authors: Howe M. S.
Published: October 2005

The characteristics of the low-wave-number and acoustic domains of the turbulent boundary layer wall-pressure spectrum are critically dependent on the structural properties of the wall. This dependence is examined in this paper in terms of a theoretical model of turbulent flow of water over an elastomeric material containing a random distribution of rigid (but movable) filaments. The interaction of hydrodynamic, convective boundary layer pressure fluctuations with the filaments generates a secondary pressure field by scattering. The intensities of the secondary pressures are negligible compared to the convective pressures responsible for their generation, but may nonetheless be large enough to produce significant changes in the relatively weak, low-wave-number region of the wall pressure. The magnitude of the changes depends on the relative mass density of the material of the filaments, on their diameters relative to the boundary layer thickness, and on their fractional volume density. Numerical results indicate that increases of the order of 10–20 dB (compared to theoretical estimates for the homogeneous elastomer) can be produced by filaments occupying only 1% by volume of the elastomer. Predictions of this kind suggest that experimental data relating to the low-wave-number and acoustic domains are easily contaminated by the presence of relatively small nonuniformities in wall properties.
On the time-domain description of conical bores
Authors: Agulló J. , Barjau A. , Martínez J.
Published: October 2005

Traditionally the description of the acoustical behavior of a bore has been done in the frequency domain through the acoustical impedance or the reflection coefficient. Whenever the time-domain response of it (impulse response, reflection function) has been needed, it has usually been obtained through the Fourier transform (FT) of the corresponding frequency-domain function. However, there are a number of cases in which this approach is unsuitable because the FT leads to noncausal functions which cannot be understood physically as impulse responses or reflection functions. In such cases the time-domain calculation is unavoidable. This calculation leads to exponentially growing functions which obviously do not accept an FT. This article presents the time-domain calculation of the main basic functions (reflection and transmission functions associated with a single discontinuity, impulse responses of anechoic bores) which are needed to obtain the input reflection function and the impulse responses of a bore. The analytical calculation of an application case is also presented.
Informational processing of complex sound. III: Interference
Authors: Lutfi Robert A.
Published: October 2005

In this study, theoretical results from information theory and detection theory are applied to provide a formal analysis of the interaction of target and context uncertainty on the discrimination of brief multitone sequences. The experiments employ a sample-discrimination task in which the performance of an ideal observer is held constant while the relative variability of the target σT and context σC is varied. Listener performance in these experiments was less than ideal but increased monotonically with σT/σC whether the task was to discriminate the frequency or the intensity of the target. Performance was also constant for a constant σT/σC regardless of the target’s position in the sequence. The results are consistent with a class of models in which the decision variable is a weighted sum of the tone values comprising the sequence. Weighting functions computed from the trial-by-trial data suggest that limits in performance result from trial-by-trial variability in the weights. The decision variable also serves as the basis for an analysis in which performance is linearly related to the information rate of the context independent of target position or task. In this analysis, target and context uncertainty contribute additively to the overall uncertainty associated with the decision variable.
The detectability of a tone added to narrow bands of equal-energy noise
Authors: Richards Virginia M.
Published: October 2005

The ability to detect a 2000-Hz tone added to bands of noise centered at 2000 Hz was measured using a two-interval, forced-choice, pulsed-masker paradigm. The stimuli ranged in duration from 50–200 ms, and the maskers ranged in bandwidth from 5–320 Hz. In one condition, the bands of noise had equal energy across the two intervals of each trial and in a second condition the levels of the stimuli were independently and randomly chosen from a 30-dB range on a presentation-by-presentation basis. The energy model failed to predict the data obtained either in the presence or in the absence of level variation. Control experiments showed that exposure to level variation yielded an overall reduction in sensitivity, suggesting that the presence of level variation leads to changes in the listeners’ detection strategies. Computer simulations indicated that changes in either the fine structure or envelopes of the waveforms were sufficient to account for detection when changes in stimulus energy were not reliable.
Effects of musical training and absolute pitch ability on event-related activity in response to sine tones
Authors: Wayman John W. , Frisina Robert D. , Walton Joseph P. , Hantz Edwin C. , Crummer Garry C.
Published: October 2005

The neural correlates of music perception have received relatively little scientific attention. The neural activity of listeners without musical training (N=11), highly trained musicians (N=14), and musicians possessing ‘‘absolute pitch’’ (AP) ability (N=10) have been measured. Major differences were observed in the P3, an endogenous event-related potential (ERP), which is thought to be a neurophysiological manifestation of working memory processing. The P3 was elicited using the classical ‘‘oddball’’ paradigm with a sine-tone series. Subjects’ musical backgrounds were evaluated with a survey questionnaire. AP ability was verified with an objective pitch identification test. The P3 amplitude, latency and wave shape were evaluated along with each subjects’ performance score and musical background. The AP subjects showed a significantly smaller P3 amplitude than either the musicians or nonmusicians, which were nearly identical. The P3 latency was shortest for the AP subjects, and was longest for the nonmusicians. Performance scores were uniformly high in all three groups. It is concluded that AP subjects do indeed exhibit P3 ERPs, albeit with smaller amplitudes and shorter latencies. The differences in neural activity between the musicians and AP subjects were not due to musical training, as the AP subjects had similar musical backgrounds to the musician group. It is also concluded that persons with the AP ability may have superior auditory sensitivity at cortical levels and/or use unique neuropsychological strategies when processing tones.
The validity of the linear orifice impedance model for predicting the impedance of a tube
Authors: Elger Donald F.
Published: October 2005

The orifice impedance model usually works well for modeling sound transmission through an orifice. However, for a long orifice or for an orifice with a large load impedance, the standard impedance model may be invalid. The goal of this paper is to establish when the orifice impedance model gives a valid estimate of the impedance of a tube in series with a load impedance. The method involved a comparison of the orifice impedance model with a transmission line model. Comparison showed that if both ‖Γkl‖<0.1 and ‖ZL/Zc‖ <0.1, then the orifice impedance model is valid (Γ is the propagation coefficient, k is the wave number, l is the tube length, and ZL/Zc is dimensionless load impedance). If either of these limits is unsatisfied, then the validity of the orifice impedance model depends on six variables. Numerical comparisons of the two models showed the effects of these variables. Computations were restricted to air, and most calculations were in the shear wave-number range of 1≤S≤100 [S=r0(ω/ν)1/2, where r0 is tube radius, ω is frequency, and ν is kinematic viscosity]. Graphical results show the limits of validity of the orifice impedance model.
An equivalent fluid approximation for a low shear speed ocean bottom
Authors: Tindle C. T. , Zhang Z. Y.
Published: October 2005

The acoustic reflection coefficient for a homogeneous fluid over a homogeneous solid with a low shear speed is shown to be well approximated by replacing the solid with a fluid of different parameters. Explicit formulas for the density and attenuation coefficient of the equivalent fluid are given. Since the acoustic field in the upper fluid depends only on the reflection coefficient of the bottom, a uniform solid bottom with low shear speed can be approximated by assuming a fluid bottom with suitably chosen parameters. Shallow water examples are given.
A modified ray theory for predicting the V(x,z) response of a point-focus acoustic microscope in the presence of a crack
Authors: Chizhik Dmitry , Davids Douglas A. , Bertoni Henry L. , Somekh Michael G.
Published: October 2005

A modified geometric ray approach is used to predict the V(x,z) or the acoustic material signature of a circular point-focus scanning acoustic microscope for an isotropic surface containing a surface-breaking crack. The microscope response is assumed to consist of a specularly reflected geometric contribution, and the leaky contribution due in part to surface waves scattered from the crack. The long thin straight crack is presumed to be characterized by symmetric reflection and transmission coefficients. This approach is numerically simple and can be used to evaluate the response of acoustic lenses of various geometries. The method is used to predict line scan V(x,z0) response of a microscope in the vicinity of the crack for several defocus distances z0 and the results are compared with measurements.
Acoustic radiation from fluid-loaded, ribbed cylindrical shells excited by different types of concentrated mechanical drives
Authors: Burroughs Courtney B. , Hallander J. Eric
Published: October 2005

Analytic expressions are derived for the far-field acoustic radiation from a fluid-loaded circular cylindrical shell reinforced with two sets of parallel periodic ribs and excited by seven types of mechanical point drives: single radial, in- and out-of-phase double radial, axial moment, circumferential moment, and in- and out-of-phase in-plane double circumferential. The ribs interact with the cylindrical shell only through normal forces. The model includes the effects of fluid loading, internal damping, and interactions between ribs. Measurements of the acoustic radiation from a ribbed cylindrical shell excited by different types of drives are presented. Comparisons between measured and predicted results are made. Predictions of the acoustic radiation from the unsupported and supported shell with different types of drives are compared. The effects of properties of the shell and types of drives on the acoustic radiation are examined by example and some physical interpretation of significant features are offered.
Integration of acoustic cues for consonants across frequency bands.
Authors: Rubin B. A. , Uchanski R. M. , Braida L. D.
Published: October 2005

To what extent can disjoint frequency bands of speech be treated as independent perceptual channels when consonants are identified? To test the independence hypothesis, consonants were filtered into four bands (0.0–0.7, 0.7–1.4, 1.4–2.8, and 2.8–5.0 kHz). Filtered speech bands were presented to listeners with normal hearing monotically. Pairs of these bands (e.g., 0.0–0.7 and 0.7–1.4 kHz) were presented dichotically, and summed (producing a 0.0–1.4 kHz band) for diotic presentation. Consonant identification scores for the combined band conditions were predicted by models of cue integration that have been applied to audiovisual consonant identification [L. D. Braida, Q. J. Exp. Psychol. 43A, 647–677] on the basis of confusions observed in the single band conditions. For most subjects and conditions, diotic and dichotic scores were similar. For a few subjects scores were lower for the diotic 0.0–1.4 kHz band case than for the corresponding dichotic condition. Predicted two-band scores agreed more closely with dichotic than diotic scores. Thus while most listeners appear to integrate cues across bands efficiently, some apparently experience across-band interference of peripheral origin.
A comparative study of the performance of time-frequency representations for the analysis of echo returns.
Authors: Hackman Roger H. , Abatzoglou Theagenis J. , Arnold Hal , Reagan J.
Published: October 2005

In a scattering experiment, the contributions (pulses) associated with different dynamical scattering processes generally arrive at the field point at different times. The structure of these individual pulses is related to the characteristics of the underlying scattering dynamics (the ‘‘dynamical’’ bandwidth of the coupling, underlying wave dispersion, etc.). Thus the time-frequency structure of the echo return is intimately connected not only with the frequency bandwidth and shape of the incident pulse, but also with the target response. Elements of the above have been discussed by previous authors [e.g., N. Yen etal., J. Acoust. Soc. Am. Suppl. 1 84, S185 (1988)]; in this paper, a comparative study is presented of the analysis capabilities of several time-frequency analyses tools, including the Wigner distribution, Choi–Williams distribution, the Gabor transform, and continuous wavelet algorithms. The study is based on echo returns that have been synthesized from a numerical T-matrix solution for a finite steel cylinder. The target echoes in this study may generally be characterized as multicomponent, time-varying signals with a time–bandwidth product that is not large.
Reflection of focused sound beams from curved surfaces.
Authors: Averkiou Michalakis A. , Hamilton Mark F.
Published: October 2005

The reflection of focused sound beams from surfaces with spherical curvature is investigated theoretically and experimentally. Theoretical predictions for the incident and reflected beams are based on the parabolic wave equation. A circular source with a uniform amplitude and quadratic phase distribution is assumed. Solutions for the reflected beam are derived for both pulsed and continuous sources. The experiments were performed in water with a 3.5-MHz source that has a nominal radius of 2.5 cm and focal length of 15 cm. Accurate measurements of the incident beam, particularly very near the source, were used to characterize the effective radius and focal length. Reflection from both convex and concave surfaces was investigated. The targets were made of nickel with radii of curvature that vary from 5 cm up to infinity (planar targets). Measurements of the reflected beam were obtained with a needle hydrophone that passed through a small hole in the center of the source. Agreement between theory and experiment is excellent, and the results suggest novel ways to measure surface curvature. [Work supported by the David and Lucile Packard Foundation, ONR, and NSF.]