bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo study of multiple scattering of waves in two-dimensional random media
Authors: Romack George M. , Weaver Richard L.
Published: October 2005

Numerical experiments were conducted to determine the validity of the quasicrystalline approximation and coherent potential approximation methods for theoretically predicting the ensemble average response of a two-dimensional random medium. The medium was composed of a tensioned mesh to which springs of both positive and negative stiffness, acting transversely to the plane of the mesh, were randomly attached at the mesh intersection sites. Various combinations of scatterer density (the number of attached springs divided by the number of sites) and scatterer strength (the spring stiffness) were evaluated at two steady-state forcing frequencies. The theories yielded similar results unless the Waterman and Truell criterion became excessive; however, at that point, both theories failed. Hence, in terms of accuracy, neither theory was found to possess a distinct advantage over the other.
Scattering of plane compressional waves by spherical inclusions in a poroelastic medium
Authors: Zimmerman Chris , Stern M.
Published: October 2005

This study treats the scatter of a plane compression wave by a spherical inclusion embedded in an infinite poroelastic medium. The pressure-solid displacement form of the harmonic equations of motion for a poroelastic solid is developed from the form of the equations originally presented by Biot. Then these equations are solved for the case of a plane wave impinging on a spherical inclusion. Solutions are obtained for the cases when the inclusion is composed of elastic solid or fluid, and when the sphere is fixed and rigid. The incident wave may be composed of any linear combination of Biot ‘‘fast’’ and ‘‘slow’’ waves.
A study of wave propagation on a cylindrical shell using fiber optic laser Doppler velocimetry
Authors: Lee Dowon , Jarzynski Jacek , Berthelot Yves H.
Published: October 2005

A differential laser Doppler velocimeter (LDV) has been used to measure in-plane motion associated with waves propagating on a thin cylindrical shell excited radially at a single frequency by a shaker. It has been established that (1) the laser probe can be used to detect shear waves even in the presence of flexural waves; and (2) that wave-vector analysis of the recorded in-plane motion of the shell allows one to separate very clearly the types of waves propagating on the shell. The fiber optic technology used in the LDV system allows the optical probe head, located at a distance of about 30 cm from the shell, to be scanned over the entire surface of the shell. Data were recorded along an array of 32 points circumferentially and 16 points axially, enough to sample spatially both extensional (fast waves, low wave numbers) and flexural waves (slow waves, high wave numbers). The data were analyzed with both a two-dimensional spatial Fourier transform and a Prony spectral method. The analysis clearly reveals both type of waves separately. Experimentally measured mode shape and dispersion curves are in good agreement with theoretical predictions based on Donnell’s thin shell equations.
Experimental and theoretical study of Lamb wave dispersion in aluminum/polymer bilayers
Authors: Laperre J. , Thys W.
Published: October 2005

This paper deals with the dispersion of Lamb waves in solid bilayers obtained by coating a 0.61-mm-thick aluminum plate with a polymer of thickness between 180 and 500 μm. The theoretical dispersion curves of the bilayers in air are analyzed in terms of the dispersion in the decoupled layers, the aluminum substratum, and the polymer coating, respectively. Because of the smaller acoustic impedance of the polymer coating, it behaves in the bilayer as if it were rigidly held by the aluminum substratum. The side of the polymer facing air is considered to be stress-free. The decoupled aluminum plate is modeled as if it were stress-free on both sides. The approximate boundary conditions for the coating are verified by a separate experiment. The experimental data obtained by means of a double transmission immersion technique, confirm the numerical analysis. Not all theoretically predicted modes are observed. The results show how coupling between the Lamb modes of the aluminum substratum, and those of the polymer coating, makes the bilayer switch between modes. Displacement and stress profiles are used to further elucidate the analysis. In the last paragraph a simple mechanical model composed of two masses and three springs, is analyzed. It exhibits mode coupling and mode switching in a way which is very similar to that found for these solid bilayers.
Parabolic approximation predictions of underwater acoustic effects due to source and receiver motions
Authors: Howell K. J. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

The effects of uniform horizontal source and receiver motion on the intensity of an underwater-acoustic pressure field are investigated. For simplicity, the surface and bottom of a stationary ocean are taken to be horizontal, the sound speed may be range-and-depth dependent, and the source emits a continuous-wave (cw) signal. A Galilean transformation is used to convert the source-receiver motion problem into a fixed receiver-moving source problem in an ocean with a horizontal current. The effects of the transformation on the course, position, and speed of the source are discussed. A parabolic equation incorporating an apparent current due to receiver motion and an approximate Doppler frequency shift due to source and receiver motion is derived from the wave equation. All motion effects are seen to manifest themselves in a single parameter, the ‘‘effective’’ sound speed, once an appropriate time-interval limit is found. Several numerical examples illustrate that the effects of different source and receiver speeds and courses on received intensity can be significant.
Localization using nonindividualized head-related transfer functions
Authors: Wenzel Elizabeth M. , Arruda Marianne , Kistler Doris J. , Wightman Frederic L.
Published: October 2005

A recent development in human–computer interfaces is the virtual acoustic display, a device that synthesizes three-dimensional, spatial auditory information over headphones using digital filters constructed from head-related transfer functions (HRTFs). The utility of such a display depends on the accuracy with which listeners can localize virtual sound sources. A previous study [F. L. Wightman and D. J. Kistler, J. Acoust. Soc. Am. 85, 868–878 (1989)] observed accurate localization by listeners for free-field sources and for virtual sources generated from the subjects’ own HRTFs. In practice, measurement of the HRTFs of each potential user of a spatial auditory display may not be feasible. Thus, a critical research question is whether listeners can obtain adequate localization cues from stimuli based on nonindividualized transforms. Here, inexperienced listeners judged the apparent direction (azimuth and elevation) of wideband noisebursts presented in the free-field or over headphones; headphone stimuli were synthesized using HRTFs from a representative subject of Wightman and Kistler. When confusions were resolved, localization of virtual sources was quite accurate and comparable to the free-field sources for 12 of the 16 subjects. Of the remaining subjects, 2 showed poor elevation accuracy in both stimulus conditions, and 2 showed degraded elevation accuracy with virtual sources. Many of the listeners also showed high rates of front-back and up-down confusions that increased significantly for virtual sources compared to the free-field stimuli. These data suggest that while the interaural cues to horizontal location are robust, the spectral cues considered important for resolving location along a particular cone-of-confusion are distorted by a synthesis process that uses nonindividualized HRTFs.
High rate otoacoustic emissions
Authors: Thornton A. R. D.
Published: October 2005

One of the practical problems of testing young children using evoked otoacoustic emissions (EOAEs) is that there is a need for the child to be quiet for a period of a minute or so. To achieve this can mean test periods of 10 min or longer. A new application of maximum length sequences (MLSs) to EOAEs is described that enables the test to be performed in a few seconds or less. Data from adults and neonates obtained at stimulation rates up to 840 clicks/s are presented and compared with conventionally derived emissions and the implications and applications of this new method are assessed.
Detection of weak stochastic signals in double-sided exponential noise using generalized energy detector
Authors: Godara Lal C. , Schultheiss Peter M.
Published: October 2005

Many locally optimum, suboptimum, and ad hoc detectors exploit knowledge of the noise probability density function (pdf) to obtain their test statistic for the detection of stochastic signals in non-Gaussian noise. These detectors appear to offer potential for highly improved performance for very small signal to noise ratios (asymptotically approaching zero). This paper studies a locally optimum detector namely the generalized energy detector, by deriving analytical expressions for a performance measure using a double-sided exponential noise pdf. The paper concludes that the apparently large gains predicted by the asymptotic theory may not be reachable within the practical range of signal-to-noise ratios.
Broadband source signature extraction using a vertical array
Authors: Finette Steven , Mignerey Peter C. , Smith James F. , Richmond Christ D.
Published: October 2005

Source signatures have been extracted from acoustic data received on a large vertical array. Multichannel deconvolution methods were used in conjunction with broadband coherent and incoherent matched-field processors for source signature reconstruction. The signatures were generated by broadband (25–110 Hz) sources located near the first and second convergence zones, approximately 48 and 97 km from the array. Cross-correlation coefficients between known source signatures and deconvolved estimates indicate that faithful reconstructions of both magnitude and phase can be obtained. Use of incoherent noise components from the main diagonals of cross-spectral density matrices produced correlation coefficients ranging from 0.77 to 0.93. Degradation primarily appeared as increased noise in the reconstructed signature. Attempts to include the full spatial coherence of the ambient noise by using off-diagonal matrix components, resulted in correlation coefficients approximately 10% lower. This effect is caused by nonstationarities in the noise field which preclude using an ergodic hypothesis to obtain statistically reliable temporal averages for the cross-spectral density matrices.
Study of Lamb waves based upon the frequency and angular derivatives of the phase of the reflection coefficient
Authors: Lenoir O. , Duclos J. , Conoir J. M. , Izbicki J. L.
Published: October 2005

This article deals with the introduction of a new method which allows the complete characterization of an elastic plate, on the one hand, in terms of resonances and, on the other hand, in terms of Lamb wave propagation. It is based upon the study of the derivatives of the reflection coefficient phase, considered either as a function of a frequency variable or as a function of an angular variable. When the Breit–Wigner approximation is valid, i.e., when the poles of the reflection coefficient are close to the real axis, the comparison with the resonant scattering theory (RST) leads to the characterization of frequency or angular resonances in terms of positions and widths, by means of the location and of the magnitude of the phase derivative peaks. Moreover, this method allows one to establish the important link between this resonant theory derived from the RST and the normal mode theory of propagation. So, the width of a resonance is explicitly related to the imaginary part of the wave vector of the associated Lamb wave.
Low-frequency dispersion and attenuation in partially saturated rocks
Authors: Norris Andrew N.
Published: October 2005

A theory is developed for the attenuation and dispersion of compressional waves in inhomogeneous fluid-saturated materials. These effects are caused by material inhomogeneity on length scales of the order of centimeters and may be most significant at seismic wave frequencies, i.e., on the order of 100 Hz. The micromechanism involves diffusion of pore fluid between different regions, and is most effective in a partially saturated medium in which liquid can diffuse into regions occupied by gas. The local fluid flow effects can be replaced on the macroscopic scale by an effective viscoelastic medium, and the form of the viscoelastic creep function is illustrated for a compressional wave propagating normal to a layered medium. The wave speeds in the low- and high-frequency limits are associated with conditions of uniform pressure and of uniform ‘‘no-flow,’’ respectively. These correspond to the isothermal and isentropic wave speeds in a disordered thermoelastic medium.
Observations of nonlinear elastic wave behavior in sandstone
Authors: Meegan G. Douglas , Johnson Paul A. , Guyer Robert A. , McCall Katherine R.
Published: October 2005

An experimental investigation of nonlinear elastic wave behavior was conducted using a 2-m-long cylindrical rod of Berea sandstone in order to study the strong elastic nonlinearity that is characteristic of microcracked materials. Measurements of the displacement field at distance x from the source show rich harmonic content with harmonic amplitudes depending on x, source frequency, and source amplitude. The amplitude of the 2ω harmonic is found to grow linearly with x and as the square of both the source frequency ω and the source amplitude U. This behavior is in agreement with the predictions of nonlinear elasticity theory for a system with cubic anharmonicity. From the measured amplitude of the 2ω harmonic the parameter ‖β‖, a measure of the strength of the cubic anharmonicity, is found to be of order 104 (7.0×103±25%). This value is orders of magnitude greater than that found in ordinary uncracked materials. These results suggest that wave distortion effects due to nonlinear elasticity can be large in seismic wave propagation and significantly influence the relationship of seismic signal to seismic source.
Representation of the absorption of nonlinear waves by fractional derivatives
Authors: Ochmann Martin , Makarov Sergey
Published: October 2005

Fractional derivatives of arbitrary order are incorporated into a model nonlinear equation in order to simulate the absorption mechanism in a finite frequency domain. That makes it possible to take into account a power dependence of the absorption coefficient on the frequency at any real degree. The model gives a mathematical description of a large set of well-known absorption mechanisms. The method is applied to calculate weakly nonlinear oscillations in a nonrigid tube. As a result, the value of the absorption coefficient and its dependence on the frequency are found based on experimental data.
Average echoes from randomly oriented random-length finite cylinders: Zooplankton models
Authors: Stanton Timothy K. , Chu Dezhang , Wiebe Peter H. , Clay Clarence S.
Published: October 2005

By heuristically extending the previously developed ray solution [Stanton et al. J. Acoust. Soc. Am. 94, 3454–3462 (1993)] to predict the scattering by cylinders over all angles of incidence, approximate expressions are derived which describe the echo energy due to sound scattered by finite cylinders averaged over orientation and length. Both straight and bent finite length cylinders of high aspect ratio are considered over the full range of frequencies (Rayleigh through geometric scattering). The results show that for a sufficiently broad range of orientation, the average echo is largely independent of the degree of bend—that is, the results are essentially the same for both the straight and bent cylinders of various radii of curvature (provided the bend is not too great). Also, in the limit of high frequency (i.e., the acoustic wavelength is much smaller than the cross-sectional radius of the object), the averages are independent of frequency. The resultant formulas derived herein are useful in describing the scattering by elongated zooplankton whose shape may not necessarily be known in the natural ocean environment. The average echo is shown to depend directly upon standard deviation (s.d.) of the angle of orientation as well as size. If independent measurements of size are made (such as from trawling samples), then the properties of the angle distribution and hence behavior may be inferred from the data. Averages over both angle and a narrow distribution of size are shown to only partially smooth out deep nulls in the scatter versus frequency curves. The formulas compare favorably with laboratory data involving aggregations of animals and a broad range of frequencies (38 kHz to 1.2 MHz).
Psychophysical and speech perception studies: A case report on a binaural cochlear implant subject
Authors: van Hoesel R. J. M. , Tong Y. C. , Hollow R. D. , Clark G. M.
Published: October 2005

Further improvements in speech perception for cochlear implant patients in quiet and in noise should be possible with speech processing strategies using binaural implants. For this reason, presented here is a series of initial psychophysical and speech perception studies on the authors’ first binaural cochlear implant patient. For an approximate matching of the places of stimulation on the two sides, the patient usually reported a single percept when the two sides were simultaneously stimulated. Lateralization was strongly influenced by amplitude differences between the electrical stimuli on the two sides, but only weakly by interaural time delays. Speech testing, comparing monaural with binaural electrical stimulation, showed a binaural advantage particularly in noise.
Measures of auditory brain-stem responses, distortion product otoacoustic emissions, hair cell loss, and forward masked tuning curves in the waltzing guinea pig
Authors: Canlon Barbara , Marklund Kasper , Borg Erik
Published: October 2005

Measures of the auditory brain-stem response (ABR), distortion product otoacoustic emission (2f1−f2), hair cell loss, and forward masked tuning curves were obtained from waltzing guinea pigs and their age-matched controls at postnatal day 2, 9, 15, and 30. A mild ABR threshold shift (10–15 dB) is seen by 2 days postnatal and gradually increases to a more severe threshold shift (40–50 dB) by postnatal day 15. Already by 30 days the auditory brain-stem response, being beyond the output of the instrumentation, could not be elicited. The mean distortion product otoacoustic emission (DPOE) amplitude as a function of f1 amplitude for the postnatal day 2, 9, and 15 waltzing guinea pigs were only between 3 and 8 dB below the control values for stimulus levels below 65 dB SPL. The DPOE audiogram constructed for the waltzing guinea pigs shows no more than an 8-dB mean difference from the control values when the intensity of f1 was 50 dB SPL, and no more than 10 dB when f1 was 60 dB SPL. Analysis of the individual cases revealed that the DPOE amplitude could be greater than control values. On the contrary, when f1 stimulus levels were below 65 dB SPL, DPOEs could not be detected for the postnatal day 30 waltzing guinea pigs. At stimulus levels above 65 dB SPL, DPOEs could be recorded yet these responses were depressed from control values by 10 to 25 dB. Analysis of surface preparations of the organ of Corti from the day 15 waltzing guinea pig reveals that the prominent alteration occurs on the third row outer hair cells.

To a lesser extent, the second row outer hair cells, and then the first row outer hair cells are affected while the inner hair cells appear normal. In contrast, the organ of Corti from the postnatal day 30 waltzing guinea pig showed a more extensive outer hair cell loss among all three rows as well as a considerable degree of inner hair cell loss. Forward masked auditory brain-stem response tuning curves were generated at 8, 4, and 1 kHz for control and waltzing guinea pigs between 2 and 12 days of age. All tuning curves obtained from waltzing guinea pigs showed progressive decreases in sensitivity with increasing age. The Q 10 dB values of the 1- and 4-kHz tuning curves were not different between the controls and the waltzing guinea pigs at any age. However, compared to the controls, the Q 10-dB values of the 8-kHz tuning curves were reduced by 50% for the waltzing guinea pigs.
Binaural simulation of concert halls: A new approach for the binaural reverberation process
Authors: Martin J. , Van Maercke D. , Vian J-P.
Published: October 2005

A geometrical cone-tracing method associated with the signal processing technique is used to calculate the binaural impulse response of a concert hall. Some inaccuracy and the computation time of the geometrical algorithm tend to limit the method for the high-reflection orders which are necessary to provide a good listening effect. In order to extend the response, a new approach is presented based on different statistical processes that depend on both the acoustical and geometrical characteristics of the hall. After a theoretical presentation (new statistical results are proposed to describe the sound field behavior in a concert hall), some simulations are given in order to illustrate the different statistical processes. This simulation technique seems to be a very convenient tool both for the design of a new concert hall and for the study of the important parameters in auditory spaciousness.
Broadband determination of ultrasonic attenuation and phase velocity in insulating materials
Authors: Ditchi Thierry , Alquié Claude , Lewiner Jacques
Published: October 2005

Ultrasonic attenuation and phase velocity in a solid insulating material are determined in a broad frequency band by studying the propagation of a pressure pulse in a sample of this material submitted to an electric field of known value. During the propagation of the pulse in the sample, which is placed between short-circuited electrodes, a current is generated in the external circuit. This signal gives directly the time dependence of the pressure pulses entering and exiting the sample, from which the frequency-dependent attenuation and phase velocity are deduced by Fourier analysis. The pressure pulse is generated by the impact of a laser pulse on an absorbing surface adjacent to one face of the sample. New results obtained in polyethylene and silicone samples are presented. The proposed method presents the following advantages: It avoids the use of a transducer, reduces the impedance matching requirements, and provides information in a broad frequency band by a single measurement.
Effect of a soft layer on the normal modes in a fluid-filled borehole
Authors: Renlie Lasse
Published: October 2005

The effect of a thin concentric layer, with a low S-wave velocity, located between the fluid and a fast formation on the acoustic response in a fluid-filled borehole is studied. It is shown that the layer significantly influences the modal behavior in the borehole. In addition to the Stoneley and pseudo-Rayleigh modes, there exists another set of modes associated with the layer. The interaction between the two set of modes has several prominent features. Dispersion relations and excitation functions are calculated and compared with the case where the layer is replaced by the borehole fluid. These calculations show that the Stoneley wave velocity is significantly lowered at low frequencies and the dispersion of the Stoneley mode is altered at higher frequencies. The excitation functions show that there exist narrow frequency regions where no modes exist. The consequences of these effects for acoustic logging is shown by calculating full waveforms for the case with and without the layer.
Electromechanical coupling coefficients and far-field radiation patterns of lithium niobate bars (Y-cut) used in high-frequency acoustical imaging and nondestructive testing
Authors: Assaad Jamal , Bruneel Christian , Decarpigny Jean-Noël , Nongaillard Bertrand
Published: October 2005

For high-frequency applications in ultrasonic imaging and nondestructive testing, lithium niobate (LiNbO3) can be used when cut under the shape of long bars with proper orientation and width to thickness ratio W/T. However, due to a strong material anisotropy, the modeling of such elementary bar transducers, for the sake of optimization, is quite difficult. In this paper, the use of the finite element method, with the help of the ATILA code, is proposed to compute resonance frequencies, coupling coefficients, electrical impedances and in-water far-field directivity patterns. (YZw)36° and (YXl)36° cuts with different W/T ratios have been analyzed and numerical results have been carefully and successfully compared with measurements. Main results concern the (YZw)36° cut for which symmetrical directivity patterns are obtained. In this case, a quite constant value is found for the thickness mode coupling coefficient ke in the ranges W/T<0.8 (ke≊50%) and 1.2<W/T<1.7 (ke≊40%). For the (YXl)36° cut, the directivity pattern is nonsymmetrical. In all the cases, a clear physical interpretation of transducer radiation characteristics is provided in terms of vibration modes. This analysis is the first application of new damping finite elements developed together with a specific extrapolation method and presented in a previous, companion paper [Assaad et al., J. Acoust. Soc. Am. 94, 562–573 (1993)].
Radiation pattern of a focused transducer: A numerically convergent solution
Authors: Chen Xucai , Schwarz Karl Q. , Parker Kevin J.
Published: October 2005

The radiation pattern of a focused transducer is reexamined. The radiation field is divided into an illuminated zone and a shadow zone. A numerically convergent solution of the pressure distribution in terms summations of Bessel functions is provided. This solution is computationally more advantageous than earlier results where a double or single integral in the complex plane is required. The pressure amplitude differs from earlier reports slightly for off-axis locations at low frequency. This difference may have significance for backscatter coefficient determination where scatterers are assumed present over a time-gated volume. The solution for a flat disk radiator is obtained as a limiting case.
Reproduction of plane wave sound fields
Authors: Kirkeby Ole , Nelson Philip A.
Published: October 2005

The problem of reproducing a desired sound field in space, not just at a number of discrete points, but over a continuous two-dimensional area, is investigated. In theory, any sound field can be reconstructed perfectly in a given region by using a continuous monopole/dipole layer, but this is obviously not possible in practice. This paper attempts to give some quantitative measures of the extent to which a given sound field can be reproduced by using a number of discrete monopole sources. Some of the physical limitations that apply to any sound reproduction system are illustrated by studying a simple model. The desired sound field is a plane wave, the sources are ideal monopoles in a free field, and the optimal source accelerations are calculated using the traditional least-squares method. All calculations are undertaken in the frequency domain, and three different loudspeaker arrangements are studied. The results clearly demonstrate that the quality of the reproduced sound field is mainly determined by the size of the receiver area and the angles between the sources as seen from the center of the receiver array.
Intelligibility-weighted measures of speech-to-interference ratio and speech system performance
Authors: Greenberg J. E. , Peterson P. M. , Zurek P. M.
Published: October 2005

This Letter describes decibel measures of speech-to-interference ratio and of system gain derived from simple modifications of the articulation and speech transmission indices. The rationale for the use of these measures is presented.
The quasisteady approximation in speech production
Authors: McGowan Richard S.
Published: October 2005

Because boundary-layer separation is important in determining force between flowing air and solid bodies and separation can be sensitive to unsteadiness, the quasisteady approximation needs to be examined for the flow-induced oscillations of speech (e.g., phonation and trills). A review of the literature shows that vibratory phenomena, such as phonation and tongue-tip trills, may need to be modeled without the quasisteady approximation.
Synthetic aperture processing for a towed array and a moving source
Authors: Fawcett John A.
Published: October 2005

In this paper the use of synthetic aperture processing is examined for simultaneously estimating a source’s unknown rest frequency, relative radial speed, and bearing from towed array hydrophone data. By examining this three-dimensional estimation problem, it is concluded that for the situation where the velocity and/or rest frequency of the source are unknown there is no advantage in using coherent synthetic aperture techniques instead of incoherent methods to estimate the source’s bearing. The case of multiple sources is also examined and it is concluded that although long-time coherent processing can improve bearing resolution for two closely spaced targets, the same results can be obtained by taking a long-time Fourier transform and then using conventional beamforming methods.
A study of the reduction of explosive impulses by finite sized barriers
Authors: Saunders David J. , Ford Roy D.
Published: October 2005

Two investigations have been carried out on the diffraction of high level (160-dB peak) impulses around barriers of finite size. One of the investigations, carried out with the barrier situated on hard ground, has shown peak sound levels to be reduced by as much as 12 dB by an effective barrier height of 1.8 m and source–receiver separation of 25 m. The results of this investigation have been compared with a number of linear diffraction theories for both thin and thick barriers. The major finding is that while most theories can reasonably predict the peak diffracted sound level and general wave shape they all fail to predict the sharp leading edge of the pulse which is observed in practice. For the second investigation, in which the barrier was situated on an acoustically soft surface, an effective barrier height of about 1.2 m gave a reduction of around 6 dB in the peak sound level for a source–receiver distance of 25 m compared to unobstructed propagation over the same surface. The results show reasonable agreement between prediction and theory for receiver positions well in the shadow zone. However, near the shadow boundary and in the bright zone agreement is not as good.
A comparison of transient-evoked and distortion product otoacoustic emissions in normal-hearing and hearing-impaired subjects
Authors: Gorga Michael P. , Neely Stephen T. , Bergman Brenda M. , Beauchaine Kathryn L. , Kaminski Jan R. , Peters Jo , Schulte Laura , Jesteadt Walt
Published: October 2005

The ability of transient-evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) to distinguish normal hearing from hearing impairment was evaluated in 180 subjects. TEOAEs were analyzed into octave or one-third octave bands for frequencies ranging from 500 to 4000 Hz. Decision theory was used to generate receiver operating characteristic (ROC) curves for each of three measurements (OAE amplitude, OAE/noise, reproducibility) for each OAE measure (octave TEOAEs, 1/3 octave TEOAEs, DPOAEs), for octave frequencies from 500 to 4000 Hz, and for seven audiometric criteria ranging from 10 to 40 dB HL. At 500 Hz, TEOAEs and DPOAEs were unable to separate normal from impaired ears. At 1000 Hz, both TEOAE measures were more accurate in identifying hearing status than DPOAEs. At 2000 Hz, all OAE measures performed equally well. At 4000 Hz, DPOAEs were better able to distinguish normal from impaired ears. Almost without exception, measurements of OAE/noise and reproducibility performed comparably and were superior to measurements of OAE amplitude, although the differences were small. TEOAEs analyzed into octave bands showed better performance than TEOAEs analyzed into 1/3 octaves. Under standard test conditions, OAE test performance appears to be limited by background noise, especially for the low frequencies.
Fine structure of the 2f1-f2 acoustic distortion product: Changes with primary level
Authors: He Ning-ji , Schmiedt Richard A.
Published: October 2005

The fine frequency structure of the 2f1-f2 acoustic distortion product (ADP fine structure) was examined in ten human subjects with normal hearing. Primary frequencies (f1 and f2) were incremented in steps of 1/32 octave with an f2/f1 ratio of 1.2. The primary levels were kept equal to each other and varied from 45 to 65 dB SPL in 2.5-dB steps. The results show that the ADP fine structure is characterized by a series of peaks and valleys across frequency, with a peak-to-peak frequency spacing of about 3/32 octave and a peak-to-valley amplitude ratio of up to 20 dB. At frequencies below 4000 Hz, as primary level increases, the sharpness of the ADP fine structure is not significantly reduced and the pattern gradually shifts to lower frequencies. At frequencies above 4000 Hz, a flattening of the pattern is sometimes observed at high levels. A consequence of the underlying process responsible for the fine structure is that ADP input/output (I/O) functions can be highly variable in shape. Dramatic shape changes can occur for ADP I/O functions obtained with primary frequency changes of as little as 1/32nd of an octave. The outward cause of I/O function variability is the behavior of the ADP fine structure with level; i.e., it remains robust at high levels and systematically shifts to lower frequencies with level. As a result, ADP peaks can shift to valleys with increasing level and vice versa. Thus, small shifts in primary frequency can result in significant changes in the shape of the ADP I/O function in humans.
The effects of aging on otoacoustic emissions
Authors: Stover Lisa , Norton Susan J.
Published: October 2005

Otoacoustic emissions were measured in 42 normal hearing subjects ranging from 20 to 80 years old. For each subject spontaneous, click-evoked, tone-burst-evoked, stimulus frequency and distortion product emissions were measured across a wide intensity range for frequencies between 1 and 3 kHz. Although there are significant differences between age groups, the results indicate no age effect independent of hearing sensitivity on any type or parameter of otoacoustic emissions (OAE). The effect of increasing age is confounded with the effect of decreasing sensitivity such that post hoc analyses are inadequate to separate the effects of sensitivity and age on otoacoustic emissions. Even within the range of audiometrically normal hearing, OAE characteristics vary with threshold for all age groups. The conclusion is that hearing sensitivity must be included as a controlled variable in order to accurately assess intrinsic aging effects.
A coherent ray model of plane-wave reflection from a thin sediment layer
Authors: Chapman N. Ross , Chapman David M. F.
Published: October 2005

Plane-wave reflection from a thin, elastic-solid sediment layer over a hard basement is modeled by a simple model that coherently combines rays from only two ray families: a family of compressional waves that transit the sediment layer any number of times before returning to the water and a similar family that includes doubly converted compressional waves. (The latter are compressional waves that are converted to shear waves at the basement, make one or more round-trip transits of the sediment layer, and are converted back into compressional waves at the basement.) The theory is applied to homogeneous sediments having low shear speeds, and it provides valuable insight into the physical processes governing reflection from several seabed environments of interest. The coherent sum of all the rays belonging to these families leads to an approximate closed-form expression for the overall reflection coefficient that includes several characteristic features also simulated by full wave-theoretical numerical models, such as bottom-loss resonances related to sediment shear waves and large losses associated with the excitation of interface waves at the sediment/basement boundary. Calculated examples are provided.
Low-frequency underwater sound generation by impacting transient cylindrical water jets
Authors: Kolaini Ali R. , Roy Ronald A. , Crum Lawrence A. , Mao Yi
Published: October 2005

The impact of a jet of water onto a still-water surface results in the entrainment of large amounts of air and the eventual formation of a bubble plume. Results from an experimental study of the noise produced by this process is presented. Preliminary results of this study were reported previously by Kolaini et al. [J. Acoust. Soc. Am. 89, 2452–2455 (1991)]. The densely populated bubble plumes were generated by dropping a fixed volume of water, held in a cylindrical container, onto a still-water surface. High-speed video images reveal the formation of a cylindrical bubble plume with a very high void fraction which grows in size until all the water is injected into the tank. As the leading end of the plume advances, a section of the plume separates near the crater region formed by the jet. After detachment, the separated plume, which is roughly spherical in shape, undergoes volume pulsations, and radiates relatively large-amplitude, low-frequency sound. The nature of the acoustic emissions from bubble plumes depends on the height of the water in the container, the container’s radius, and the velocity of the impacting jet. The natural frequency of oscillation of an individual bubble plume is inversely proportional to the radius of the plume and ranges from a few tens of Hz to over 100 Hz depending upon the void fraction of air contained within the plume. Results obtained with salt water as well as with rough jets are also discussed. The high-speed video observations reveal that immediately following the bubble plume detachment, there is evidence of an axial jet directed downward into the bubble plume and an opposing jet directed upward into the crater formed by the impact. This jet appears to be the physical mechanism that drives the cloud into oscillation. Measurements indicate that the acoustic intensity radiated from bubble plumes correlate with the total potential energy of the water jet.
A fast Green’s function method for one-way sound propagation in the atmosphere
Authors: Gilbert Kenneth E. , Di Xiao
Published: October 2005

A Green’s function method is used to derive a fast, general algorithm for one-way wave propagation. The algorithm is applied to outdoor sound propagation. The general method is not limited to atmospheric sound propagation, however, and can be applied to other problems, such as sound propagation in the ocean and electromagnetic wave propagation. The new algorithm, called ‘‘GF-PE’’ (Green’s function method for the parabolic equation), reduces to the well-known Fourier split-step algorithm for the parabolic equation (PE) when no boundary conditions are imposed (e.g., at a ground surface). With the GF-PE, range steps many wavelengths long are possible, while with a PE algorithm based on a finite-difference range step, such as the Crank–Nicolson method, the range steps are typically limited to a fraction of a wavelength. Because of its longer range step, the new algorithm is 40–450 times faster than PE algorithms that use the Crank–Nicolson method. For outdoor sound propagation over a locally reacting ground surface, the computed GF-PE field is the sum of three terms: a direct wave, a specularly reflected wave, and a surface wave. With the new method, the air–ground impedance condition is treated exactly and results in an analytic expression for the surface wave contribution. Numerical results from the GF-PE model are presented and compared to exact calculations, fast-field program (FFP) calculations, and PE results computed with the Crank–Nicolson method. The GF-PE algorithm is shown to be accurate and approximately two orders of magnitude faster than a PE based on the Crank–Nicolson method. Hence, the new algorithm opens the door to some useful new computational capabilities such as real-time predictions on desktop computers, fast pulse calculations, and practical three-dimensional calculations.
Attenuation of sound waves in drill strings
Authors: Drumheller Douglas S.
Published: October 2005

During drilling of deep wells, digital data are often transmitted from sensors located near the drill bit to the surface. Development of a new communication system with increased data capacity is of paramount importance to the drilling industry. Since steel drill strings are used, transmission of these data by elastic carrier waves traveling within the drill pipe is possible, but the potential communication range is uncertain. The problem is complicated by the presence of heavy-threaded tool joints every 10 m, which form a periodic structure and produce classical patterns of passbands and stop bands in the wave spectra. In this article, field measurements of the attenuation characteristics of a drill string in the Long Valley Scientific Well in Mammoth Lakes, California are presented. Wave propagation distances approach 2 km. A theoretical model is discussed which predicts the location, width, and attenuation of the passbands. Mode conversion between extensional and bending waves, and spurious reflections due to deviations in the periodic spacings of the tool joints are believed to be the sources of this attenuation. It is estimated that attenuation levels can be dramatically reduced by rearranging the individual pipes in the drill string according to length.
Finding the direction of a sound source using a vector sound-intensity probe
Authors: Hickling Robert , Wei Wei , Raspet Richard
Published: October 2005

Good spatial resolution of a sound source can be achieved with the four closely spaced pressure transducers in a vector sound-intensity probe. In contrast, a receiving array generally requires an extensive distribution of transducer elements. Experimental results are presented that demonstrate the ability of a vector probe to determine the direction of a sound source in water, both without and with noise interference. Measurements of the sound-intensity vector, or sound-power flux, were performed using the cross-spectral method. Spectral subtraction and averaging over the frequency range of a source were found to be effective tools for determining the direction of a source when there is uncorrelated interference and background noise.
Modal analysis of a Korean bell
Authors: Rossing Thomas D. , Perrier Alexis
Published: October 2005

The vibrational modes of a small Korean bell have been studied, by using holographic interferometry and modal analysis with impact excitation. The asymmetry due to the dang jwa and the ornamentation gives rise to mode doublets and a slow beating, which is carefully controlled and considered to be an important characteristic of Korean bell sound. Mode doublet splittings range from 1% to 9%. The fundamental (2,0) mode, which decays much more slowly than the higher modes of vibration, determines the pitch of the bell.
Comments on ‘‘Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). I: Effects of click level, rate and polarity’’ [J. Acoust. Soc. Am. 85, 2514–2525 (1989)]
Authors: Burkard Robert , Boettcher Flint , Voigt Herbert , Mills John
Published: October 2005

The purpose of this comment is to propose a peak-labeling nomenclature for the gerbil brain-stem auditory-evoked response (BAER) which is different than that used by Burkard and Voigt [J. Acoust. Soc. Am. 85, 2514–2525 (1989)]. This proposed nomenclature is a compromise between the use of five primary peaks (i–v) used by Burkard and Voigt (herein called the ‘‘Boston group’’) and the use of three primary peaks (I–III) proposed by Mills and colleagues (herein called the ‘‘Charleston group’’). This proposed standardization recognizes four peaks occurring within 4 to 5 ms of stimulus onset, labeled i through iv. This standardization will allow easier comparisons of gerbil BAER data obtained across laboratories.
Comments on ‘‘Cooperative radiation and scattering of acoustic waves by gas bubbles in liquids’’ [J. Acoust. Soc. Am. 92, 2837–2841 (1992)]
Authors: Wu Junru , Du Gonghuan
Published: October 2005

A brief comparison is given between two theoretical approaches—the radial displacement and the volume displacement—in describing sound emission of a pulsating bubble. The impropriety of the latter is pointed out.
Three-dimensional modeling of narrow-band pulse spreading using normal modes
Authors: Wild Michael , Joyce Robert
Published: October 2005

Energy from a narrow-band pulse, interacting with a time-varying ocean surface, will be spread into upper and lower sidebands. This can be modeled in a range-independent ocean environment, using normal modes and a coupling scheme based on first-order perturbation theory. The structure of the scattered signal from the two-dimensional Pierson–Moskowitz surface wave spectrum is presented. A normal-mode model with environmental inputs from a shallow sea has been used, and a comparison is made with measured data.
A comparison of speech discrimination with cochlear implants and tactile aids
Authors: Carney Arlene Earley , Osberger Mary Joe , Carney Edward , Robbins Amy M. , Renshaw Julia , Miyamoto Richard T.
Published: October 2005

This study investigates patterns of speech discrimination in profoundly hearing-impaired children who have received cochlear implants or tactile aids. The change/no change procedure was used to assess speech discrimination in these children. Three groups of subjects were tested: the first group used 3M/House single-channel cochlear implants; the second group used Nucleus 22-channel cochlear implants; and the third group used two-channel Tactaid II+ vibrotactile aids. Nine contrasts were constructed that assessed discrimination of suprasegmental and segmental speech features. Subjects were presented with stimulus trials in which stimuli changed during the trial or in which stimuli remained the same. Hits, misses, false alarms, and correct rejections were tallied and d′ values were calculated for individual subjects for each contrast. Results indicated that different patterns of speech discrimination are provided by the three sensory prosthetic devices. For all contrasts, mean discrimination performance with the Nucleus device was better than that observed for the other two devices, despite the shorter duration of subject experience with this cochlear implant. In addition, interactions between device and speech contrast were not observed. Examination of individual subject performance revealed that each device group had a distribution of good to poor performers. The results suggest that the change/no change procedure is able to provide information regarding speech perception through sensory prosthetic devices despite existing differences in vocabulary and language skills of subjects.