bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of moments and couple-generating forces near discontinuities in structural-acoustic systems
Authors: Shepard W. Steve
Published: July 2002

In modeling vibration isolators in structural-acoustic systems, the isolator’s dynamic properties are often treated as acting only in the axial direction as moments are often neglected. Furthermore, the size, or scale, of the isolator is often neglected and the isolator is assumed to act at single points on the connected structures. Previous work has shown that concentrated moments can be particularly important when located near a fixed support or a structural discontinuity. This research extends that work to examine the importance of moment scale effects for a system containing a distributed structural discontinuity with its own scale. Moment scale effects are examined by determining the difference in radiated acoustic power for a simple system that is excited by a couple-generating distributed force and a concentrated moment. The distributed force produces a couple that is equivalent to the concentrated moment. As a result, only the scale is being examined. Particular interest occurs when the excitation is located near the structural discontinuity. Based on the cases studied here, moment scale is shown to be important at lower frequencies when the excitation is located near the edges of the discontinuity. At higher frequencies, any overlap of the excitation and discontinuity may warrant the need to consider moment scales.
Synthesis of a robust broadband duct ANC system using convex programming approach
Authors: Bai Mingsian R. , Zeung Pingshun
Published: July 2002

A robust active controller using spatially feedforward structure is proposed for broadband attenuation of noise in ducts. To meet the requirements of performance and robust stability in the presence of plant uncertainties, an H2 cost function and an H∞ constrain are employed in the synthesis of the controller. The design is then converted into a convex programming problem using Q-parametrization and frequency discretization. An optimal controller that satisfies the quadratic cost functions and linear inequality constraints can be found by sequential quadratic programming. The optimal controller was implemented via a digital signal processor (DSP) and verified by experiments. Experiment results showed that the system attained 16.5 dB maximal attenuation and 5.9 dB total attenuation in the frequency band 200–600 Hz.
Matched-field processing gain degradation caused by tidal flow over continental shelf bathymetry
Authors: Orr Marshall H. , Mignerey Peter C.
Published: July 2002

Temporally variable, range dependent sound-speed profiles measured during ebb flow and estimated for slack flow are used to quantify the variability of matched-field signal-processing gain degradation in shallow water propagation channels controlled by tidally driven stratified flow over variable bathymetry. Calculations along a 9.3 km range establish phase changes in the acoustic signal as the primary cause of a 3–9 dB degradation in the coherent matched-field processing output of a full water column vertical array. The work indicates that over a tidal cycle acoustic signal properties and matched-field processing gain can be expected to change continuously in a shallow water stratified channel that has bathymetry variability. Acoustic signals propagating in such tidal flow-controlled environments may be expected to display repeatable (over successive tidal cycles) and predictable changes in their phase coherent properties. These results suggest that matched-field processor replica fields used in the shelf/slope propagation environment will have to be updated regularly during a tidal cycle to maintain maximum processor gain.
Acoustic coupling between oral tract and diatonic harmonica: Recent observations
Authors: Antaki James , Bahnson Henry , Burgreen Greg
Published: July 2002

The diatonic harmonica is arguably one of the most ‘‘vocal’’ of all reed instruments. Due to the relatively short distance, thus tight coupling, between the player’s oral cavity and the instrument, relatively subtle changes in the oral tract may effect dramatic modulations of both frequency and spectral content of the sound produced. Over the past several years we have endeavored to improve the understanding of this interaction, as well as the coupling between reeds of a given cell. This presentation will discuss our most recent observations. Benchtop experiments were conducted by laser vibrometer to measure the simultaneous motion of the reeds. Studies on human subjects were based on x-ray, ultrasonographic, and laryngoscopic imaging of players while sounding notes on the harmonica. Evidence of torsional instability has been observed, and analyzed by subsequent computational fluid dynamics simulation.
Time-domain analysis and synthesis of active noise control systems in ducts
Authors: Wu Zhen , Varadan Vijay K. , Varadan Vasundara V.
Published: July 2002

This paper presents time-domain analysis and synthesis of active low-frequency noise control systems in rigid-walled ducts. In contrast to frequency-domain analysis, time-domain modeling provides a direct physical insight of the noise cancellation mechanism, where noise signals are assumed to be arbitrary real functions of time instead of harmonics. The time-domain analysis is based on a state-space model which is derived from the governing wave equation using combined numerical (finite difference) and analytical techniques. Optimal feedback control laws are synthesized for a variety of active noise control systems with different sensor and source arrangements. The responses of closed-loop systems are simulated, and the results are compatible with those of transfer function synthesis. In addition, the active control systems so designed have the potential of providing global, broadband, and optimal noise reductions without running into the annoying feedback problems in most feedforward control systems.
Characterization of the natural ambient sound environment: Measurements in open agricultural grassland
Authors: Boersma Hielke Freerk
Published: July 2002

The audibility of manmade sound in a natural environment is affected because of masking by ambient sound. In this report results are presented of measurements of the level and spectral composition of natural ambient sound. The statistical L95 level was determined, i.e., the sound pressure level which is exceeded for 95% of the time, at various wind velocities in open agricultural grassland. The total L95 is described by L95=37.9 log(v)+42.5, where v is the wind velocity. The standard deviation with respect to the data points is 2.4 dB. For the A-weighted L95 we found a similar relation [LA95=22.6 log(v)+22.7]. The relation between wind speed and natural ambient sound level for each 13-oct band was also determined with nominal midband frequencies ranging from 6.3 Hz to 20 kHz separately. The frequency spectrum of ambient sound shows at low frequencies a behavior typical for turbulent processes. The 13-oct band intensity of sound at these frequencies is found to be proportional to f−2. Dimensionless spectra obtained for low frequencies at wind speeds exceeding 2 m/s collapse into a line almost identical to results of low-turbulence measurements performed by Strasberg.
A statistical analysis for an inverse acoustic problem in estimating spatially varying sound velocity
Authors: Huang Cheng-Hung , Wang Duen-Min
Published: July 2002

A simple inverse acoustic algorithm using the Levenberg–Marquardt method is developed to estimate the sound velocity field as a function of depth from the transient measurements of the wave displacement at some suitable locations. The inverse calculations are performed based on the simulated exact and inexact measurement data to show the validity of the present study. Moreover, statistical analysis will also be considered here to determine both the best measurement position and the 99% confidence bounds. Results show that the accuracy of the estimated sound velocity and its sensitivity to the measurement errors depend on the number of measurement data, as well as the measured positions. The reliable inverse solutions can be obtained only when these two factors are chosen properly.
The generation of a Stoneley wave at the end of a fluid loaded plate by an incident bounded beam
Authors: Briers R. , Leroy O. , Shkerdin G. N.
Published: July 2002

This study shows, on the basis of a mode theory, that as a Gaussian ultrasonic beam strikes the edge of a thick plate immersed in a liquid, a Stoneley wave is generated along the liquid/solid interface. As expected, the largest amplitude for the excited Stoneley wave is obtained for normal incidence at the edge but a secondary maximum appears at Rayleigh angle incidence. In this way, it is proved theoretically that the conversion phenomenon of a Stoneley wave into a generalized Rayleigh wave at the extremity of a fluid loaded thick plate is reversible, as was observed experimentally by Tinel [Ph.D. thesis, Université Le Havre, France (1991)].
Acoustic SH phonons in a superlattice with (111) interfaces
Authors: Kato Hatsuyoshi
Published: July 2002

Transmission rates and dispersion relations of SH phonons in a (111) superlattice are calculated. Unlike the case of a (100) superlattice, phonon stop bands appear inside the folded Brillouin zone in general rather than at the center and edges. A superlattice structure factor is introduced appropriately for phonon reflection or Bragg conditions in the superlattice. More importantly, the transfer matrix contains information not only about the dispersion relation, but also about the condition for frequency bands or stop bands in the dispersion relation, and the extinction rule for the Bragg reflection. The locations of the stop bands inside of the folded zone are defined as a function of frequency and incidence angle of the phonons.
Analysis and model/data comparison of broadband acoustic propagation at the Atlantic Generating Station (AGS) site
Authors: Badiey M. , Bongiovanni K. P. , Siegmann W. L.
Published: July 2002

An investigation of broadband acoustic propagation in a shallow-water environment is performed by comparing experimental acoustic data [Badiey et al., J. Acoust. Soc. Am. 96, 3593–3604 (1994)] with results from a frequency-domain, high-order parabolic equation technique. The principal quantity examined, transmission loss versus frequency, is determined for fixed source/receiver positions over short ranges (≈0.5 km) corresponding to experimental configurations. High-resolution geoacoustic data from extensive coring of the site, along with CTD and detailed bathymetric data, are used to construct accurate range-dependent input for PE simulations and range-varying wave number spectra calculations. Generally very good agreement between the PE results and data are observed. Range-dependent mechanisms are seen to have a strong azimuthal dependence in both TL and wave number results for this site. Shear losses are considered by exploiting equivalent fluid relationships. The effects of sediment dispersion through frequency dependent sound speed are also examined.
Elastic characterization of isotropic materials by a single test based on the experimental determination of natural frequencies using laser interferometry
Authors: Bayón A. , Varadé A. , Gascón F.
Published: July 2002

An experimental method is proposed for the elastic characterization of an isotropic material based upon the vibration natural frequencies recorded by means of a single assembly and experiment. Speckle heterodyne optic interferometry is applied to detect the tangential component of the vibration at a point. The sample is a slender rod excited through a broad-spectrum percussion, where the vibration recorded is a superposition of the transverse and torsional natural modes. Spectral analysis of the vibration allows the identification of the transverse and torsional natural frequencies. This is followed by calculation of the elastic moduli.
Analytic investigation of chaos in a class of parabolic ray systems
Authors: Jiang Zhong-Yue , Pitts Todd A. , Greenleaf James F.
Published: July 2002

It has been shown that acoustic ray paths in range-dependent ocean models exhibit chaotic behavior. Most of the investigations into the ray chaos phenomenon have been primarily numerical in nature. Analytical derivation of sufficient conditions for chaos in acoustic systems has been restricted to inherently discrete problems. This article reports a theoretical study of the existence of ray chaos in a class of continuous parabolic ray systems. This class of ray systems is indexed by a family of analytically prescribed double-channel sound-speed profiles perturbed by periodic range-dependent disturbances. The perturbed Hamiltonian ray systems are studied analytically via the Melnikov method. It is shown that, under certain conditions, ray trajectories of the systems are equivalent to trajectories of a classic chaotic system known as the horseshoe map when the perturbation is periodic and small. These conditions are sufficient for ray chaos and easily satisfied, thus explaining why double-channel propagation is very likely to exhibit chaotic behavior.
A psychoacoustic model for the noise masking of plosive bursts
Authors: Hant James J. , Strope Brian P. , Alwan Abeer A.
Published: July 2002

A model for predicting the masked thresholds of the voiceless plosive bursts /k,t,p/ in background noise is proposed. Because plosive bursts are brief, are generated by a noise source, and have different spectral characteristics, the modeling approach accounts for duration, center frequency, and signal bandwidth. Noise-in-noise masking experiments are conducted using a broadband masker and bandpass noise signals of varying bandwidth (100–5483 Hz), duration (10–300 ms), and center frequency (0.4–4 kHz). Data from these experiments are used to parametrize an auditory filter model in which the effective bandwidth and the signal-to-noise ratio at threshold for each filter are duration dependent. The duration-dependent filter model is then used to predict the thresholds of synthetic and naturally spoken plosive bursts in background noise. Finally, results from pilot notched-noise experiments are presented which support duration-dependent frequency selectivity.
Discrimination of changes in the spectral shape of noise bands
Authors: Versfeld Niek J.
Published: July 2002

Discrimination experiments were performed for a change in the spectral shape of noise bands. The subject’s task was to discriminate noise bands with a positive spectral slope from those with a negative spectral slope. Thresholds were measured at several bandwidths and center frequencies, as well as for several noise samples. Experiments were performed while roving the overall intensity. At a fixed center frequency of 1 kHz, sensitivity was best for bandwidths of 3–6 semitones (ST). At larger bandwidths, thresholds increased only slowly. At a fixed bandwidth of 1 ST, threshold hardly changed as a function of the center frequency. At a fixed bandwidth of 58 Hz, threshold was lowest near 500–1000 Hz. Model calculations show that the EWAIF model [Feth, Percept. Psychophys. 15, 375–378 (1974)] can account for the present results if the signal’s bandwidth does not exceed 1 ST. The IWAIF model [Anantharaman et al., J. Acoust. Soc. Am. 94, 723–729 1993] can account for the present results only if the signal’s bandwidth is smaller than 1 ST but larger than about 25 Hz. Results obtained with broadband signals could be described only qualitatively with the multichannel model [Durlach et al., J. Acoust. Soc. Am. 80, 63–72 (1986)]. Then, the model needs the assumption that either the output of the different frequency bands cannot be optimally combined, or that only two bands are used in the discrimination process. The present results are compared with those obtained with two-tone complexes measured under identical conditions [Versfeld and Houtsma, J. Acoust. Soc. Am. 98, 807–816 (1995)].
The calculation of the transient near and far field of a baffled piston using low sampling frequencies
Authors: D’hooge Jan , Nuyts Johan , Bijnens Bart , De Man Bruno , Suetens Paul , Thoen Jan , Herregods Marie-Christine , Van de Werf Frans
Published: July 2002

A method is presented to calculate the near- and far-field transient radiation of acoustical transducers using low sampling frequencies. The method is based on the classical impulse response approach and on the fact that in practical use the spectrum of the excitation function of a transducer is band limited. This makes it possible to use a smoothed version of the impulse response function. A simple expression to calculate this smoothed function, for a rectangular or circular transducer, is derived. The proposed solution allows accurate computation of pressure fields and backscatter signals, while avoiding high sampling frequencies in the far field of the transducers. Several examples illustrate the accuracy of this new solution and its use for spectral analysis of simulated reflected signals.
Dynamic response and power flow in three-dimensional coupled beam structures. I. Analytical modeling
Authors: Farag N. H. , Pan J.
Published: July 2002

This paper deals with the prediction of the dynamic response and vibrational power flow in general three-dimensional coupled beam structures. An arbitrary loading condition is assumed and flexural waves in two perpendicular planes and longitudinal and torsional waves, may be excited simultaneously in each beam. The interaction of different wave types at the coupling boundaries is therefore expected. Suitable for the low- and medium-frequency range, the modal receptance method used here allows the prediction of the detailed structural response and power flow components carried by the different wave types through joint boundaries and at any cross section of the beam structure. The mathematical description of the three-dimensional beam structure and the manipulation of receptance matrices are presented in such a form that the vibration of any complex beam structure may be described systematically and with clear physical interpretations. The prediction of the input and output power for each component beam quantifies the energy dissipation in the beam, which may be taken as a measure of the spatial average response level of the beam. Computational examples of the power flow components at the joint boundaries of the component beams in coupled three-dimensional structures are used to illustrate the significance of the theoretical results.
Modification of Skudrzyk’s mean-value theory parameters to predict fluid-loaded plate vibration
Authors: Torres Rendell R. , Sparrow Victor W. , Stuart Alan D.
Published: July 2002

The geometric-mean drive-point admittance (or “mobility”) of a complex structure is given by the admittance of the corresponding infinite structure (i.e., the “characteristic admittance,” Yc). The frequency response of an infinite plate, for example, coincides with the geometric-mean response of a finite one. Eugen Skudrzyk’s “mean-value theorem” was derived and experimentally verified without consideration of fluid loading. This paper shows that Skudrzyk’s method can be applied to fluid-loaded plates well below the coincidence frequency. Skudrzyk’s general mathematical expression allows simplified modifications that account for fluid loading and result in an approximate fluid-loaded characteristic admittance that differs only by a small multiplicative factor (<2 dB) from a correct analytical expression derived by Crighton.
Further consideration of the waveguide propagation of ambient sound in the ocean-surface bubble layer
Authors: Ye Zhen
Published: July 2002

Measurements of the ambient sound generated by breaking waves over the range 40–20 000 Hz reveal well-defined spectral peaks [D. M. Farmer and S. Vagle, J. Acoust. Soc. Am. 86, 1897–1908 (1989)], suggesting the modulation of the ambient sound by the waveguide formed by the ocean-surface bubbles. The measurements show that the sound-speed profile in such a waveguide may be modeled by an exponential form. The theory of the waveguide propagation of the ambient sound is considered. It is shown that the sound propagation in the ocean-surface waveguides bears analogy with that in the optical waveguides formed by diffusion and can be solved analytically in a simple form. The cutoff frequencies of such waveguides are determined by a simple equation that incorporates only the waveguide parameters. Theoretical predictions of the spectral peaks, which seem to be associated with the modal cutoff frequencies, are compared favorably to the observations. Moreover, the present results are compared to the previous theory base on the model of inverse square sound-speed profiles in great details. It is shown that, although the two profiles are almost the same shape in the cases considered here, the sound propagation in the two waveguides is rather different. It is shown that the normal-mode propagation in the inverse square model is very sensitive to both source and receiver positions in addition to the waveguide parameters, and different modes can overlap, thereby making data fitting difficult. On the other hand, in the exponential model, the sound spectral function depends mainly on the waveguide parameters, e.g., sound-speed anomaly at the surface and the e-folding depth. Therefore the distinct spectral peaks observed are a stable prediction from the exponential waveguide model. The simplicity and the stability of the results can help solve the inverse problem, that is, “given an observed distribution of spectral peaks, can the bubble distribution be inferred?”
Doubly asymptotic approximations for transient poroelastodynamics
Authors: Qi Quan , Geers Thomas L.
Published: July 2002

A doubly asymptotic approximation (DAA) is an approximate temporal impedance relation at the boundary of a continuous medium. Here, first- and second-order DAAs are formulated for an infinite external poroelastic medium described by Biot’s equations. As with their acoustic, elastodynamic, and electromagnetic predecessors, the poroelastodynamic DAAs approach exactness in both the early-time (high-frequency) and late-time (low-frequency) limits, effecting a smooth transition between. They also lend themselves to straightforward boundary-element discretization, producing matrix ordinary differential equations in time that are readily solved by numerical integration. An initial examination of poroelastodynamic DAA accuracy is presented for two problems with spherical symmetry.
Study of woodwind-like systems through nonlinear differential equations. Part I. Simple geometry
Authors: Barjau Ana , Gibiat Vincent , Grand Noël
Published: July 2002

Idealized woodwind models assume a well-localized nonlinearity coupled to a linear bore whose mathematical description is usually expressed through a convolution product. For the case of the simplest bore geometries, cylindrical and conical, the convolution can be transformed into a delayed differential equation. When including in it the nonlinearity, the usual concepts of nonlinear dynamical systems allow a better understanding of the system’s evolution. In this paper they are applied to the cylindrical and conical geometries and some characteristics of their behaviors are analyzed at the threshold of oscillation through an analytical study. It is shown that their dynamics cannot be reduced to a finite number of degrees of freedom (effective dynamics). Finally numerical simulations reveal peculiar characteristics of the direct and inverse bifurcations involved in such simple systems for quadratic and cubic nonlinearities respectively.
Does nonlinear capacitance of the outer hair cell really improve its high-frequency response?
Authors: Iwasa K. H. , Chadwick R. S.
Published: July 2002

There is a conceptual error in the paper, “A theoretical basis for the high-frequency performance of the outer hair cell’s receptor potential” by El S. Hassan [J. Acoust. Soc. Am. 101, 2129–2134 (1997)]. Correcting the error reverses the conclusion, and reveals that the nonlinear capacitance in the outer hair cell is a factor that degrades, rather than improves, the high-frequency response of the receptor potential of the outer hair cell.
Oblique coherent waves inside and outside a randomly cracked elastic solid
Authors: Angel Y. C. , Bolshakov A.
Published: July 2002

Propagation of antiplane waves in an elastic solid that contains a cracked slab region is investigated. The cracks have a uniform probability density in the slab region, are parallel to the boundaries of the slab, and the solid is uncracked on either side of the slab. When an antiplane wave is obliquely incident on the cracks, it is shown that the average (coherent) motion in the solid is governed by a pair of integral equations. This result is obtained by taking an average of the exact system of equations for N nonintersecting cracks and by letting N tend to infinity keeping the crack density constant. Then, it is assumed that the average exciting stress near a fixed crack is equal to the average coherent stress, and it is shown that the pair of integral equations yields simple analytical formulas for the complex-valued wave number and the refracted waves inside the slab as well as for the wave amplitudes outside the slab. These quantities depend on incident angle, crack density, frequency, and slab thickness. Numerical results, which are valid for small values of the crack density, are presented as functions of frequency and incident angle.
Analysis of ceramic thickness shear piezoelectric gyroscopes
Authors: Yang J. S.
Published: July 2002

Equations for linear piezoelectricity are formulated in a reference frame rotating at a constant angular velocity and are simplified by a perturbation procedure when the angular velocity of the reference frame is small. The equations thus obtained are then employed in the analysis of a rectangular ceramic plate piezoelectric gyroscope operating with thickness shear modes. Approximate analytical solutions to the equations resulted from the perturbation procedure are obtained based on Mindlin’s two-dimensional equations for a piezoelectric plate which are simplified by the thickness shear long wave approximation. Free-vibration frequencies and mode shapes, as well as the condition for double resonance, are obtained. Forced vibration is also studied which leads to a simple expression for the voltage sensitivity of the gyroscope. The analysis is approximate and qualitative mainly with the purpose of exhibiting some most basic characteristics of the gyroscope. Some of the results are compared with finite element numerical method.
Waves in elastic and anelastic stratified microstructure: A numerical comparison
Authors: Le Lawrence H. , Burridge Robert
Published: July 2002

Burridge et al. [J. Acoust. Soc. Am. 94, 2884–2894 (1993)] presented a fast algorithm to compute wave propagation through a stack of finely layered elastic or anelastic microstructure. The method goes beyond previous work in two aspects: (a) the sample autocorrelation is used so that the coda of the computed response is preserved; and (b) the anelastic effect due to intrinsic attenuation is incorporated and by order-of-magnitude argument, the terms governing the scattering and anelastic effects enter separately but in a similar way. The present work is a numerical justification of the perturbation theory. Using a standard linear solid model with a single Debye relaxation mechanism, a finely layered microstructure was made anelastic. Using the SH case as an example, impulse responses were computed using two methods: the approximate method and an exact method for both elastic and anelastic media at normal and oblique angles of incidence. The impulse responses obtained by the two methods agree well for both elastic and anelastic cases. The results of the investigation can be summarized in several points: (a) accuracy is best for the head of the pulse; (b) the presence of anelasticity increases the time delay and dispersion of the broad pulse; and (c) the perturbation code is 30–54 times faster than the exact code.
All-optical investigation of the lowest-order antisymmetrical acoustic modes in liquid-loaded membranes
Authors: Desmet C. , Gusev V. , Glorieux C. , Lauriks W. , Thoen J.
Published: July 2002

The antisymmetrical Scholte–Stoneley wave in liquid-loaded metal and polymer membranes were excited via the laser-induced thermoelastic effect and were detected with a laser beam deflection technique. The experimentally determined dispersion relation for this wave is in accordance with theory in a wide frequency range. However, no evidence of the propagating subsonic lowest-order anitsymmetrical pseudo-Lamb wave was found.
Inhomogeneous absorption and geometric acoustics
Authors: Tappert F. D.
Published: July 2002

The conventional formulation of geometric acoustics in the presence of inhomogeneous (spatially varying) absorption is examined. This formulation is found to fail under conditions of multipath propagation, because interference between ray paths is not taken into account when the absorptive losses are calculated. The example of high-frequency attenuation due to a surface bubble layer is studied, and Weston’s correction term is discussed.
Sensor systems for global vibration and noise control
Authors: Sun J. Q. , Hirsch S. M. , Jayachandran V.
Published: July 2002

An important issue in sensor studies is to define sensor configurations such that the reduction of a performance measure based on the sensor measurements will guarantee a decrease in a global response measure of the system. This paper presents a study of sensors along this line. In the paper, the concept of global sensor systems is introduced. The condition for such a sensor system is derived. This concept is then applied to structural and acoustic control problems. It is shown in the paper that the nodal placement of sensors always leads to a global sensor system, and allows a single sensor gain to scale the sensor based performance measure in such a way that it is identical to the true global performance measure of the system response. Tonal and narrow-band problems are also considered where a global sensor system may be redundant. The rank of a reduced performance matrix is used to determine the number of sensors needed in these applications. The theory of the paper is demonstrated by using simple examples. Further work needs to be done to extend the present study to more complex systems. Nevertheless, the study presented in this paper may have significant implications in designing practical sensor systems for both structural and acoustic control problems.
The mammalian auditory hair cell: A simple electric circuit model
Authors: Rattay F. , Gebeshuber I. C. , Gitter A. H.
Published: July 2002

A model based on the potassium current pathway through the hair cell is used to analyze the electrical behavior of mammalian inner and outer hair cells. Without taking into account the effects of calcium it is possible to simulate experimental results concerning the shape and strength of the receptor potential and the frequency dependent ac (alternating current) and dc (direct current) components of the receptor current. This model and a simplified form of it are utilized to explain: (1) Transduction latencies: that the receptor potential follows a stimulating signal with a very short delay, under the assumption of a constant number of open K+ channels in the lateral part of the cell membrane. (2) Transduction gains: why higher potential changes are measured in inner hair cells than in outer hair cells, although the outer hair cells are expected to be exposed to higher stereociliary motions: in inner hair cells a decrease in the conductance of the basolateral membrane causes higher gain (receptor potential increases) and together with an increase of membrane capacitance slower reaction (a larger time constant). (3) Transduction channel kinetics: that the shortest (0.1 ms) as well as the longest (20 ms) possible open times of the transduction channels in the stereocilia have different frequency related effects on the shape of the receptor potentials.
Diotic and dichotic detection using multiplied-noise maskers
Authors: van de Par Steven , Kohlrausch Armin
Published: July 2002

Detection thresholds were measured with a multiplied-noise masker that was in phase in both ears and a sinusoidal signal which was either in phase or out of phase (NoSo and NoSπ conditions). The masker was generated by multiplying a low-pass noise with a sinusoidal carrier. The signal was a sinusoid with the same frequency as the carrier and a constant phase offset, ϑ, with respect to the carrier. By adjusting the phase offset, the stimulus properties were varied in such a way that only interaural time delays (ϑ=π/2) or interaural intensity differences (ϑ=0) were present within the NoSπ stimulus. Thresholds were measured at a center frequency of 4 kHz as a function of bandwidth for ϑ=π/2 and for ϑ=0. In a second experiment thresholds were measured for a bandwidth of 25 Hz as a function of the center frequency. The results show that narrow-band BMLDs at 4 kHz can amount to 30 dB for the ϑ=0 condition. For this condition, narrow-band BMLDs are also reasonably constant across frequency, in contrast to results obtained with standard Gaussian-noise maskers. For ϑ=π/2, BMLDs are restricted to the frequency region below 2 kHz provided that the masker is narrow band, but BMLDs of up to 15 dB are found at 4 kHz if the masker is 50 Hz or wider. The frequency dependence of the binaural thresholds seems to be best explained by assuming that the stimulus waveforms are compressed before binaural interaction.
Bounds and approximations for elastodynamic wave speeds in tetragonal media
Authors: Zuo Q. H. , Hjelmstad K. D.
Published: July 2002

This paper presents an analytical study of elastodynamic waves propagating along an arbitrary direction in anisotropic materials with tetragonal symmetry. Upper and lower bounds are developed on the wave speeds through an additive decomposition of the acoustic tensor into an associated hexagonal counterpart and a rank-one modification, the eigenproperties of which can be determined analytically. The bounds are obtained by applying the minimax property of eigenvalues. Linear approximations of the wave speeds are obtained from a first-order expansion of the eigenvalues of the acoustic tensor, with respect to a tetragonality index, about the value of that index for which tetragonal symmetry degenerates to hexagonal symmetry. A numerical example shows that the linear approximations agree remarkably well with the exact values of the wave speeds.
Ultrasonic capacitance transducers for flow and temperature tomography in air
Authors: Hutchins David A. , Wright William M. D. , Schindel David W. , Carpenter Peter W.
Published: July 2002

Capacitance transducers have been constructed that can operate at frequencies of up to 2 MHz in air, over a wide bandwidth, and with good efficiency. These have been used to propagate signals in air across regions containing variations in air flow and temperature. A source and receiver pair were scanned along a set of projections under computer control, allowing various ray paths across a chosen cross section to be selected. For each location, the received waveform was digitized and recorded, and the propagation time determined from cross-correlation techniques. The data were then used to form tomographic images, which corresponded to variations in either temperature or flow speed, both of which affect the local acoustic velocity. In one experiment, an air-jet was imaged at various distances from the nozzle. In another, the temperature variations in air above a hot metal tip were determined. Images will be shown for both sets of experiments, and the usefulness of the technique discussed.
Acoustically driven sinuous instability of a planar air jet
Authors: Nolle A. W.
Published: July 2002

The sinuous instability wave of a planar air jet is excited by localized acoustic flow across the nozzle. Phase velocity and the growth exponent are found from synchronous hot-wire measurements made beyond the excited region, where the profile is approximately sech squared. In the observed range of scaled radian frequency, 0.02–1.33 (the stability limit), results agree with real-frequency (spatially growing) analysis but not with complex-frequency (temporally growing) analysis, which predicts smaller phase velocity at low frequencies. In further tests, the acoustic driving signal is independent of downstream distance, as in an organ pipe. The jet deflection is then the sum of acoustic convection and of the instability wave, summing to zero at the nozzle, as proposed by Fletcher, Elder, and others. The instability-wave theory applies to linear behavior in the inviscid limit and therefore to a hypothetical nonspreading jet. The local velocity profile width must be considered in relating to a physical jet. In a flue organ pipe oscillating at equilibrium amplitude the jet deflection at the lip exceeds the range of validity. Direct sound generation by the jet is investigated briefly.
Effects of context on time-compressed speech intelligibility in older adults
Authors: Vaughan Nancy , Kasper Ronda
Published: July 2002

The purpose of this study was to assess the effects of context on sentence intelligibility at high compression rates in older adults. A group of older participants listened to time-compressed low-predictability sentences from the SPIN-R test and high-context sentences from the Connected Speech Test (CST). Many studies have shown that speech intelligibility declines significantly at a 60% compression rate especially for older adults. An algorithm called the Synchronized Overlap Add (SOLA) has been shown to produce intelligibility scores above 80% on the CST for adults aged 65–75 years at 60% compression. This method uses an autocorrelation function to combine common elements in overlapping sequential frames of the speech signal, producing highly intelligible speech at high rates of compression. An apparently similar algorithm used in another study of older adults produced intelligibility scores around 50% for the low-predictability sentences of the SPIN-R test at a 60% compression rate. The question of whether the varying results of time-compressed speech intelligibility was due to differences in algorithms or to differences in context of the speech materials remains unanswered. The results of the current study are discussed in terms of speaker gender, context, and methods of time-compression.
Effects of stimulation mode on speech recognition by cochlear implant users
Authors: Fu Qian-Jie , Shannon Robert V.
Published: July 2002

This study investigated the effects of both mode of stimulation and frequency allocation on speech recognition in three subjects implanted with Nucleus-22 multichannel cochlear implant. A four-channel processor with continuous interleaved sampling speech processing strategy was implemented through a custom interface. The temporal envelopes from four broadbands were used to modulate 500 pps, 100 ms/phase pulse trains and then delivered to four electrodes 16, 11, 6, 1 with three stimulation modes: BP+1, BP+3, BP+5. Ten different frequency allocations were used and each frequency allocation mapped different insertion depths of these four electrodes based on Greenwood’s place-to-frequency function. Results showed that the recognition score was highly dependent on the frequency allocation in all stimulation modes, indicating that it may be indispensable to match the frequency allocation to the tonotopic location of activated electrodes. Results also showed that a speech processor with BP+5 stimulation mode was more robust to the mismatching between the frequency allocation and tonotopic location of electrodes, indicating that a speech processor with more broad stimulation, such as a monopolar stimulation mode, may be advantageous for most cochlear implant users, especially for those who have either shallower insertion depth or uneven nerve survival patterns. [Work supported by NIDCD.]
Stochastic word models for articulatorily constrained speech recognition and synthesis
Authors: Hogden John , Nix David , Gracco Vincent , Rubin Philip
Published: July 2002

Stochastic word models based on hidden Markov modeling (HMM) techniques are commonly used for speech recognition and are increasingly being used for speech synthesis. An alternate technique for generating stochastic word models using Maximum Likelihood Continuity Mapping (MALCOM) will be presented. MALCOM generates a stochastic model of speech assuming (1) that speech sounds are periodically emitted as a point moves smoothly through a low-dimensional space called a continuity map (CM), and (2) that the sound emitted at time t is a probabilistic function of the position of the point at time t. The assumptions underlying MALCOM are intended to mimic speech production in that (1) speech sounds are produced as the articulators move slowly through a low-dimensional articulator space, and (2) the speech sound produced at time t is a function of the articulator positions at time t. A method for finding CM trajectories (analogous to articulator trajectories) corresponding to a known sequence of phonemes will be shown, and how to use these trajectories as word models for speech recognition and synthesis will be shown. A preliminary test of the theory will be presented in which articulator trajectories estimate given phoneme sequences and phoneme temporal positions are compared to measured articulator trajectories.
Interactive Korean speech recognition for a mobile robot
Authors: Lee Jae-Young , Yoon Seok-Hyun , Chung Kwang-Woo , Hong Kwang-Seok
Published: July 2002

This paper is a study on the implementation of a speech recognition mobile robot to which the interactive Korean speech recognition techniques are applied. The speech command uttered the sentential connected word and is asserted through the wireless mic system. This speech signal transferred LPC-Cepstrum and short-time energy which are computed from the received signal on the DSP board to a notebook PC. In the notebook PC, the DP matching technique is used for the recognizer and the recognition results are transferred to the motor control unit which outputs pulse signals corresponding to the recognized command and drives the stepping motor. It has been implicitly assumed that, for connected word recognition, each word in the string can be followed by any other word in the string. However, for some connected word recognition tasks, there is an explicit set of rules governing which words can logically follow other words to form valid sentences in the language. In this paper, a grammar network was applied to reduce the recognition speed of the recognizer, so that real time recognition is realized. The misrecognized command is revised by interface revision through conversation with the mobile robot. The recognition system asks the user for help whenever there are two or more recognition candidates whose likelihood scores are all high and it is difficult to resolve small differences in the string. The recognizer asks the user to verify the first choice decision; if it is not verified, the recognizer asks the user to verify the second choice, etc. Alternatively, the recognition system can list the confusing candidates and ask the user to choose the correct string based on the string index number in the list.
Research of finite-amplitude acoustic pulse propagation in a thin capillary filled with a viscous-elastic fluid
Authors: Esipov Igor B. , Mikhalevich Vladislav G.
Published: July 2002

Acoustic wave propagation in a thin capillary filled with a viscous fluid is accompanied by additional attenuation because of sound energy outflow to the capillary wall due to viscous forces. It is known that a whole class of fluids exists, which change their viscous properties (shift modulus) under the applied stress. It is the so-called Bingham fluids. The results of experimental research of wide frequency band sound pulse propagation in the capillary filled with a raw oil are presented. A pulse was generated by laser radiation. The amplitude of the pulse reached up to 1 MPa and its time duration was about 20 ns. Acoustic signal reception was provided by a PVDF gage and registered by a digital oscilloscope in the frequency range of 100 MHz. Experiment shows a kind of induced ‘‘transparency’’ for the high-amplitude sound pulse propagated along a capillary of 0.4-mm radius. This effect of acoustic-induced transparency of viscous fluid shows a rapid growth of high-frequency components of the sound signal passed through the capillary with respect to the growth of laser pulse energy. Meanwhile, for the small-amplitude sound signal propagation the linear relation between laser pulse energy and sound pulse amplitude is valid. [Work is partially supported by the Russian Foundation of Basic Research (project 97-02-17789).]
Investigation of a particle velocity field in nonlinear standing waves
Authors: Ilinskii Yurii A. , Lipkens Bart , Zabolotskaya Evgenia A.
Published: July 2002

A one-dimensional model of nonlinear standing waves in an oscillating closed cavity has been developed at MacroSonix and was presented at the 1997 Acoustical Society meeting in San Diego. The present study focuses on the characteristics of the particle velocity wave field. Measurements of the particle velocity are very difficult to execute, but insight into the velocity field yields important information of the properties of an acoustical resonator. Waveforms and harmonic amplitudes of velocity as well as pressure waves along the resonator axis are calculated. Results are presented for three geometries: a cylinder, a cone, and a bulb-type resonator. The resonators are oscillated at the fundamental resonance frequency. Numerical calculations show that for dissonant resonators, in which harmonics of the fundamental frequency are not coincident with higher modal frequencies, Mach numbers on the order of 0.5 can be achieved, while for a cylindrical resonator Mach numbers are much more limited. For the resonators considered, the velocity waveforms have different characteristics: a shocked waveform for the cylinder, a sawtooth-type wave for the cone, and a disturbed sine wave for the bulb. An interesting result is that the velocity waveform is fundamentally different from the pressure waveform.
Parametric excitation of a Helmholtz resonator
Authors: Prather Wayne E. , Denardo Bruce , Raspet Richard
Published: July 2002

Parametric excitation of an oscillator results from the modulation of a parameter upon which the natural frequency of the oscillator depends. If the drive amplitude exceeds a threshold determined by dissipation, the response amplitude grows exponentially until it is saturated by a nonlinearity of the system. Hence, large amplitudes may be possible. An unsuccessful attempt to parametrically excite the fundamental mode of a Helmholtz resonator is reported. The apparatus consists of two equal-volume cavities connected by a U-shaped neck similar to a trombone slide, where the neck length is modulated at twice the Helmholtz frequency. In model systems, the effective quality factor diverges as the parametric drive amplitude approaches threshold from below. the extent to which a parametric drive amplitude is below threshold can thus be probed by performing a frequency sweep with a small-amplitude direct drive. However, the effective quality factor in our system is found to decrease as the parametric drive amplitude is increased, as a result of turbulence caused by the parametric drive. This indicates that parametric excitation by neck length modulation may not be possible. Current work on a Helmholtz resonator in which the cavity volume is modulated is also reported on. [Work sponsored by ONR.]