bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection of sound from a randomly layered ocean bottom
Authors: Gilbert Kenneth E.
Published: October 2005

This paper investigates the sensitivity of the plane-wave reflection coefficient to the small-scale random layering in turbidite sediment. A Monte Carlo algorithm is used to generate many numerical realizations of a finely layered stochastic turbidite model. The complex reflection coefficient R is computed for each realization so that a distribution of R values is produced at each frequency and grazing angle. The scatter in the R values is a measure of the sensitivity of R to small-scale turbidite layering. Below 100–200 Hz, R is relatively insensitive to the details of the layering; at higher frequencies the detailed layering is important. To a rough approximation, the sensitivity to layering is independent of the grazing angle. The lack of sensitivity to small-scale layering for f<100–200 Hz indicates that long wavelengths ’’average out’’ the fine structure and suggests that R can be calculated at low frequencies from a ’’smooth’’ geoacoustic model (i.e., a model with no small-scale layering). For f≳100–200 Hz, the reflection coefficient is sensitive to small-scale turbidite layering and hence cannot be accurately calculated from a smooth model.
Scattering from a random surface
Authors: Abarbanel Henry D. I.
Published: October 2005

We give a formulation of the problem of propagation of scalar waves over a random surface. By a judicious choice of variables we are able to show that this situation is equivalent to propagation of these waves through a medium of random fluctuations with fluctuating source and receiver. The wave equation in the new coordinates has an additional term, the fluctuation operator, which depends on derivatives of the surface in space and time. An expansion in the fluctuation operator is given which guarantees the desired boundary conditions at every order. We treat both the cases where the surface is time dependent, such as the sea or surface, or fixed in time. Also discussed is the situation where the source and receiver lie between the random surface and another, possibly also random, surface. In detail we consider acoustic waves for which the surfaces are pressure release. The method is directly applicable to electromagnetic waves and other boundary conditions.
Vertical directionality and depth dependence of averaged acoustic signals and noise
Authors: Cavanagh Raymond C. , Renner William W.
Published: October 2005

The vertical directionality of an averaged acoustic field is shown in theory to depend on the depth at which it is observed in a special way. The result is based on a simple angle transformation, and is limited by the assumption that the field is a superposition of independent plane-wave components which obey Snell’s law for a stratified medium near the receiver location. The approach applies to both transmission loss and ambient noise, and is used to derive a relationship between the directionality at a single depth and the depth dependence of the total (omnidirectional) intensity. Examples show the influence of the local sound–speed profile and illustrate sensitivities in the relationship for special cases. Implications for measurement strategies, data interpretation, and predictive modeling are discussed.
Dichotic CV recognition at various interaural temporal onset asynchronies: Effect of age
Authors: Gelfand Stanley A. , Hoffman Sidney , Waltzman Susan B. , Piper Neil
Published: October 2005

Dichotic CV recognition at interaural temporal onset asynchronies (lag times) of 0, 30, 60, and 90 ms was investigated in normal hearing young and elderly subjects. The results for the young group were consistent with those reported in previous studies (Studdert-Kennedy et al., 1970; Berlin et al., 1973a). The older group demonstrated a mean right ear advantage (REA) at simultaneity of 12.7%, which was not significantly different from that of the young group (12.4%). This suggests that the processes subserving the REA are not affected by age. However, there was a significant reduction in the total (right ear plus left ear) dichotic scores of the elderly group compared to the young; suggesting an age-associated reduction in the channel capacity of the aging auditory system. Further, there were striking aberrations of the dichotic lag effect in the elderly group compared to the young subjects, consistent with age-related changes in auditory temporal processing. The findings are discussed with respect to the aging auditory system and the nature of dichotic speech processing.
Multidimensional analysis of male and female voices
Authors: Murry Thomas , Singh Sadanand
Published: October 2005

This paper is a sequel to a study which showed that the dominant dimension for perceptual discrimination among normal voices was the male–female categorization and which also suggested that discrimination within the male–female categories utilized distinct dimensions. The present study eliminates the male–female axis by treating the gender groups separately and making the within-category dimensions available for more sensitive analysis. The purpose was to determine the number and nature of perceptual parameters needed to explain judgments of voice similarity depending on talker sex and whether the stimulus sample was a sustained vowel or a short phrase. The similarity judgments were submitted to multidimensional analysis via INDSCAL and the resulting dimensions were interpreted in terms of available acoustic measures and unidimensional voice-quality ratings of pitch, breathiness, hoarseness, nasality, and effort. The decisions of the listeners appeared to be influenced by both the sex of the speaker and the stimulus sample, although fundamental frequency (f0), was important for all judgments. Aside from the f0 dimensions, judgments concerning male voices were related to vocal tract parameters, while similarity judgments of female voices were related to perceived glottal/vocal tract differences. Formant structure was apparently important in judging the similarity of vowels for both sexes while perceptual glottal/temporal attributes may have been used as cues in the judgments of phrases.
Formulation and development of a generalized solution for equations governing elastic wave propagation in an arbitrary, inhomogeneous, lossy medium
Authors: Akers Geoffrey Roy
Published: October 2005

Wave propagation is actually the transport of energy in a medium that also acts as a sink for the energy. In order to describe this process more accurately than is done in the classical approximation, it is necessary to modify the lossless equations of motion to account for losses in an inhomogeneous, arbitrary medium. This can be accomplished by the introduction of a generalized loss term (loss function) in the wave equation of motion. The inclusion of this term introduces into the force balance equation an effective dissipative force field that is the equivalent of the losses. The development of a general series solution in powers of the parameter (kx) for the complex wave vector k and the displacement x yields a description of the wave field that incorporates the nonlinear effects of losses in its form. This approach gives insight into the higher order processes occurring in an arbitrary, inhomogeneous, lossy medium and shows how a frequency shift occurs in the wave as a result of travel through the medium.
Long-wavelength propagation in composite elastic media I. Spherical inclusions
Authors: Berryman James G.
Published: October 2005

A self-consistent method of estimating effective macroscopic elastic constants for inhomogeneous materials with spherical inclusions is formulated based on elastic-wave scattering theory. The method for general ellipsoidal inclusions will be presented in the second part of this series. The case of spherical inclusions is particularly simple and therefore provides an elementary introduction to the general method. The self-consistent effective medium is determined by requiring the scattered, long-wavelength displacement field to vanish on the average. The resulting formulas are simpler to apply than previous self-consistent scattering theories due to the reduction from tensor to vector equations. In the limit of long wavelengths, our results for spherical inclusions agree with statically derived self-consistent moduli of Hill and Budiansky. Our self-consistent formulas are also compared both to the estimates of Kuster and Toksöz and to the rigorous Hashin–Shtrikman bounds. (For spherical inclusions and long wavelengths, the Kuster–Toksöz effective moduli are known to be identical to the Haskin–Shtrikman bounds.) A result of Hill for two-phase composites is generalized by proving that the self-consistent effective moduli always lie between the Haskin–Shtrikman bounds for n-phase composites. Numerical examples for a two-phase medium with viscous fluid and solid constituents show that the real part of our self-consistent moduli always lie between the rigorous bounds, in agreement with the analytical results. Some of the practical details in the numerical solution of the coupled, nonlinear self-consistency equations are discussed. Examples of velocities and attenuation coefficients estimated when the solid constituent possesses intrinsic absorption are also presented.
A note about Terhardt’s pitch learning hypothesis: A reply to Houtsma
Authors: Divenyi Pierre L.
Published: October 2005

Houtsma’s [J. Acoust. Soc. Am. 68, 1889–1890 (1980)] conclusions do not follow from arguments put forward by Divenyi [J. Acoust. Soc. Am. 66, 1210–1213 (1979)].
Spectral structure of pressure measurements made in a combustion duct
Authors: Miles J. H. , Raftopoulos D. D.
Published: October 2005

The spectral structure of pressure measurements made in a ducted combustion test facility are studied. Dispersion and attenuation of acoustic plane waves may occur in the duct at low frequencies due to combustor emissions and affect the spectral structure. A model that considers the propagation of plane waves through a cloud of particles in a flowing gas, and which includes heat transfer between soot particles and the gas, is discussed. Experimental results are compared with theory.
Bispectral passive velocimeter of a moving noisy machine
Authors: Sato Takuso , Sasaki Kimio , Taketani Mitsuhiro
Published: October 2005

A new method of determination of the velocity of a moving noisy machine by the analysis of a signal detected at a fixed point is proposed. In this system, it is assumed that the trajectory of the object is known beforehand and the special characteristics of a machine noise in the bispectral region are used so that a measuring system which does not suffer from any surrounding Gaussian noise is realized. The nonstationary change of the bispectral characteristics, along with the movement of the object, is detected from a set of short-time bispectra in segmented intervals and the method of minimum mean-square-error fitting is applied to get reliable velocity. The principle, concrete construction, and experimental results are shown. The results show the superiority of the new method over conventional methods.
Pressure developed within a cavity backing a finite panel when subjected to external transient excitation
Authors: Guy R. W.
Published: October 2005

An analysis concerning the response of a cavity-backed panel when subjected to external excitation having arbitrary time and spatial variables is extended here to derive expressions for the pressure developed within the backing cavity. Two cases of practical interest are then considered as examples of application; a normally incident harmonic, and a normally incident ’N’ wave.
Modes of vibration and sound radiation from tuned handbells
Authors: Rossing Thomas D. , Sathoff H. John
Published: October 2005

Although handbells can vibrate in many different modes, only the two modes of lowest frequency are normally tuned by the bellcrafters. The frequency of the second mode is generally tuned to be three times that of the first. Each of these modes also radiates sound at twice the modal frequency, however, so that the radiated sound spectrum includes the second and sixth harmonics as well as the first and third. The amplitude of the second harmonic partial is proportional to the amplitude of the fundamental, and a similar relationship relates the sixth harmonic to the third. The first and third harmonics are radiated most strongly at right angles to the bell axis; the second and sixth harmonics are maximum along the axis. Small asymmetries in the bell often create warble due to beats between the two components of a split modal doublet. The tonal quality of a handbell depends upon the clapper strike point, the hardness of the clapper, and the force of the blow in addition to the design and construction of the bell itself.
Room acoustics for the aged
Authors: Plomp R. , Duquesnoy A. J.
Published: October 2005

This article deals with the combined effects of noise and reverberation on the speech-reception threshold for sentences. It is based on a series of current investigations on: (1) the modulation-transfer function as a measure of speech intelligibility in rooms, (2) the applicability of this concept to hearing-impaired persons, and (3) hearing loss for speech in quiet and in noise as a function of age. It is shown that, generally, in auditoria, classrooms, etc. the reverberation time T, acceptable for normal-hearing listeners, has to be reduced to (0.75)DT in order to be acceptable for elderly subjects with a hearing loss of D dB for speech in noise; for listening conditions as in lounges, restaurants, etc. the corresponding value is (0.82)DT.
Sound channel propagation through eddies southeast of the Gulf Stream
Authors: Beckerle J. C. , Baxter L. , Porter R. P. , Spindel R. C.
Published: October 2005

Acoustical signals at 270 Hz from SOFAR floats drifting in the region southeast of the Gulf Stream were recorded during most of 1975 from a near axis sound channel hydrophone near Bermuda. The amplitude levels received exhibit a large increase (12–18 dB) commencing about 24 July, following a long period (March to July) of relatively lower peak level amplitudes. A major part of the increase can be attributed to the influence of a large cyclonic eddy (Gulf Stream ring) that passed slowly between the SOFAR floats and Bermuda. Such an eddy produces a large sound speed anomaly that extends to depths below the axis of the sound channel. On 24 July, two SOFAR floats were known to have approximately the same sound transmission path through the edge of the large eddy. The sound transmission peaks occur when no ocean eddy is between the SOFAR floats and the receiver. Their spacing shows they occur at regular refraction caustics in the sound channel. When the sound transmission path passes through an eddy, these transmission focal distances are shifted to greater range and the signal level may be greatly enhanced. The decrease of caustic peak intensities with range is 5 dB per double distance, and this agrees with theory. Several different levels of peak acoustic intensity occur and these result from two float depths and oceanic thermocline oscillations.
Frequency spectra of acoustic fluctuations caused by oceanic internal waves and other finestructure
Authors: Flatté Stanley M. , Leung R. , Lee S. Y.
Published: October 2005

The frequency spectrum of log-amplitude fluctuations is substantially modified (flattened) by a previously neglected effect: the vertical advection of short internal waves by the more energetic internal waves with large vertical wavelength. The log-amplitude spectrum is sensitive to this vertical advection and to curvature of the equilibrium sound ray, whereas the phase spectrum is not. Noninternal-wave ’’frozen’’ finestructure contributes to the log-amplitude frequency spectrum through vertical advection, but not to the phase spectrum. The Cobb Seamount experiment is treated as an example; the spectrum of the modified theory agrees well with observations except at high frequency ( near the buoyancy frequency ).
Oblique reflection of inhomogeneous acoustic waves
Authors: Weston D. E.
Published: October 2005

An inhomogeneous plane wave, i.e., one having an exponential decay across the wavefront, may be used to model the sound incident on any reflecting boundary. If the decay is away from the boundary there is normally an element of reflection gain associated with the process, corresponding to a release of previously stored energy. This gain is in addition to the loss expected for an equivalent homogeneous wave. It is shown that the gain element is equal to the exponential decay in the inhomogeneous wave resolved across the horizontal beam displacement. This result holds very generally for transmission as well as reflection, for change of wave type, and for the gain element occurring when the incidence medium is lossy. In application to guided waves these results automatically ensure that the attenuation rate is the same, whether modeled by inhomogeneous waves with an element of gain, or by waves with a beam displacement. The incident inhomogeneous wave may be decomposed into a spectrum of homogeneous plane waves having a spread in angle. Similarly an attenuating mode may be regarded as propagating with a spread in equivalent ray angles.
Identification of deleted plosives: The effect of adding noise or applying a time window (A reply to Ohde and Sharf)
Authors: Pols L. C. W. , Schouten M. E. H.
Published: October 2005

A Letter in this Journal [Ohde, R. N. and Sharf, D. J., J. Acoust. Soc. Am. 69, 297–300 (1981)] deals with the identification of voiced and voiceless stops from vocalic transition+vowel stimuli edited from CV and VC syllables. The segmentation points were smoothed by applying a time window. With respect to an earlier study, in which straightforward segmentation without time window was applied, final plosives were still identified better than initial plosives. The present Letter shows that there is, however, one major difference between the with-window and the no-window condition, namely a substantial improvement in identification for initial voiced plosives. This improvement is similar to that found by the present authors in identification experiments with a noise burst adjacent to the segmentation point versus no-noise listening conditions. Instead of a controversy reported by Ohde and Sharf, this Letter suggests a unifying interpretation.
One-dimensional velocity inversion for acoustic waves: Numerical results II
Authors: Gray Samuel H.
Published: October 2005

Two different approximate methods for solving the problem of one-dimensional velocity inversion are compared numerically. The comparisons reflect basic differences, both in the approach to the problem and in the form of its solution. Although the methods differ in accuracy and applicability, their similarities lead to the conjecture that a relatively straightforward exact inversion method can be obtained.
Side lobe interference suppression with an adaptive null processor
Authors: Anderson V. C.
Published: October 2005

Experimental data illustrates the suppression of side lobe interference levels achieved with an adaptive beamformer DICANNE (Digital Interference Canceling Adaptive Null Network Equipment). The experimental DICANNE is a 32-channel system operating broadband over a 2-octave audio bandwidth. Although the experimental nulls formed were not perfect, a 5-dB improvement in detection threshold was observed at an element interference-to-noise ratio of 0 dB.
Noise correlation functions for anisotropic noise fields
Authors: Talham R. J.
Published: October 2005

When attempting to predict array signal-to-noise gain in terms of correlation functions, a first approximation is obtained by assuming ideal propagation, zero time delay, and two-dimensional or three-dimensional isotropic background noise. These assumptions lead to the familiar noise correlation functions J0(X) and sin X/X. In this paper, noise correlation functions are given for anisotropic background noise fields and isotropic fields are treated as special cases. It is shown that only for a special orientation of elements does the noise correlation function reduce to J0(X) in a two-dimensional isotropic field. For a noise field whose power in a given direction is proportional to the radius vector of an oblate spheroid it is shown that when the elements are horizontal the noise correlation function departs from sin X/X toward J0(X) as the noise field changes from three-dimensional isotropic to two-dimensional isotropic. However, when the elements are vertical, the noise correlation function is shown to depart from sin X/X toward unity. Quantitative results are given for noise fields of different anistropy.
Linguistic timing factors in combination
Authors: Port Robert F.
Published: October 2005

This study attempts to determine the ways in which linguistic timing factors combine with each other in the production of English and specifically, to test and explore aspects of the timing model of Klatt [J. Acoust. Soc. Am. 59, 1208–1221 (1976)]. In two experiments the tensity feature of a sentence stressed vowel and the voicing of the following stop were changed along with a variable that alters the length of the VC syllable. The duration of both the vowel, V, and the following stop closure, C, were measured. In the first experiment either one or two unstressed syllables are added to the word and in the second speaking tempo is changed. The significant results of both experiments are accounted for with a formal timing model that separately specifies (1) the Vm+C duration (where Vm= mean duration across the two vowels /i/ and /i/) depending on tempo or word length, (2) the ratio Vm/C depending on the voicing of the stop (/b/ or /p/), and (3) as a final ordered step, a rule that adjusts the vowel length by a constant ratio depending on the identity of the vowel. This integrated model provides for (1) the ’’incompressibility’’ effects, (2) prosodic properties, and (3) the constant V/C ratios for values of the voicing feature found in perception experiments.
A synthesizer of random signals with bispectral characteristics—A machine noise simulator
Authors: Sasaki Kimio , Sato Takuso , Kano Masatoshi
Published: October 2005

Machine noises, both the power spectral and bispectral characteristics are taken into account, have been synthesized by randomly modulating the relative phases of multiple sinusoidal oscillators which are harmonically related with one another. Each of the random signals for phase modulation consists of a common random signal and a mutually independent one. The power spectrum has shapes which consist of line spectral peaks with the corresponding surrounding spread hills. The spread of each hill and the relative height to that of the line peak are controlled by the power of the corresponding phase-modulating random signal, while the bispectral characteristics are controlled by changing the ratio of mixing powers of the common random signal and independent ones. The principle and a concrete construction of a machine-noise synthesizer based on this principle are presented. The details of the statistical properties of the generated random signals are also examined from both theoretical and experimental viewpoints. As an application of the system acoustical noises from a gear train are synthesized. The results show the effectiveness of the method as a simulator of rotating-machine noises.
Brillouin scattering in molten NaNO3: The Landau–Placzek ratio
Authors: Knape Gunilla
Published: October 2005

An experimental study of the ratio of intensities of the central line, in the molecular scattering of light, to the Brillouin components has been made in molten NaNO3 over a temperature range from 310° to 450°C. The measurements were performed at frequencies just below any relaxation frequency. The relative intensities of the fine structure components are compared to the Landau–Placzek ratio and also to the generalized Landau–Placzek ratio, applicable to relaxing liquids.
Nonlinear distortion of 4th sound in superfluid 3He-B
Authors: Garrett Steven
Published: October 2005

The relative density of the superfluid component of 3He is expected to be significantly depressed by flow. For this reason the distortion of a finite amplitude fourth sound wave exhibits an unusual amplitude dependence. For waves of sufficiently large initial amplitude, a fully developed shock wave will contain two discontinuities per wavelength. Calculations which determine the threshold amplitude are presented and comparisons with thermodynamic data suggest that waves of sufficient amplitude should be experimentally accessible. A tabulation of the most recent thermodynamic data for 3He is included.
Triangular ridge acoustic waveguide and coupler
Authors: Oliver W. A. , Dong S. B. , Yeh C.
Published: October 2005

Using a more efficient computational scheme in solving the finite element approach to the problem of triangular ridge acoustic waveguides, we have investigated the higher-order modes in this single-material structure. The coupling characteristics of two neighboring triangular guides were also studied. Specific numerical results and discussions are given.
Study of multichannel amplitude compression and linear amplification for persons with sensorineural hearing loss
Authors: Lippmann R. P. , Braida L. D. , Durlach N. I.
Published: October 2005

Experiments were conducted on five listeners with sensorineural hearing impairments using two 16-channel, computer-controlled, amplitude compression systems, and four linear systems. One of the compression systems was designed to restore normal equal loudness contours, the other employed reduced high-frequency emphasis and reduced compression ratios. The linear systems differed only in their frequency-gain characteristics (orthotelephonic plus three characteristics with high-frequency emphasis that were expected to produce better results than orthotelephonic). In the main experiment, all systems were compared for each listener using nonsense CVC monosyllables and sentence materials spoken by male and female talkers and presented in quiet/anechoic and noisy/reverberant environments at the most comfortable level for each listener. The linear systems with high-frequency emphasis performed substantially better than the orthotelephonic system. Performance with compression was generally slightly worse than with linear amplification. Compression was superior to linear amplification only when speech materials with significant item-to-item level variation were used in quiet with subjects with more severe losses and when reduced input speech levels were used. To the extent that these two conditions represent real-life communication conditions, these results suggest that compression is preferable to linear amplification in a wearable hearing aid.
Lens in the nearfield of a circular transducer: Gaussian–Laguerre formulation
Authors: Cavanagh Eduardo , Cook Bill D.
Published: October 2005

The case of a thin lens located in the nearfield of a circular transducer is analyzed assuming circular symmetry for arbitrary transducer size and lens aperture, with or without absorption in the lens medium. Using the Fresnel approximation, the acoustic field is mathematically expressed as a series expansion of Gaussian–Laguerre functions. This technique is applied to the case of a circular-piston–lens system and an analytical series solution of the field obtained for arbitrary positions of the lens. Numerical results are presented corresponding to several positions of the lens in the nearfield of the circular piston. It is found that the field pattern behind the lens is strongly dependent on the distance between the transducer and the lens, and the ratio of the focal length to the parameter a2/λ. Here a is the radius of the transducer and λ is the acoustic wavelength. It is also shown that the theory presented here can be applied to study the field of finite Gaussian transducers, focused and unfocused, and transducer–iris systems.
Laser-generated ultrasonic pulses at free metal surfaces
Authors: Aindow A. M. , Dewhurst R. J. , Hutchins D. A. , Palmer S. B.
Published: October 2005

Longitudinal, shear, and surface acoustic pulses have been generated by irradiation of free metal surfaces with a Q-switched Nd:YAG laser. Laser energies as low as 3 mJ are sufficient to generate ultrasonic pulses, in various metals, that are readily detected by conventional piezoelectric transducers, without the need for laser focusing. The generation efficiency of longitudinal, shear, and Rayleigh modes has been studied in both the presence and absence of a plasma. Experimental data in graphical form highlight several features of the acoustic source, from which a qualitative model is proposed.
Contaminating effect of probe noise on jet pressure correlations
Authors: Hoglund Leif E. , Siddon Thomas E.
Published: October 2005

When a fast-responding static pressure probe is inserted into a flow, there are several possible mechanisms for the generation of extraneous noise. If the probe signal is cross correlated with the farfield sound, then the ’’probe noise’’ may contribute a dominant portion of the total correlatable noise from the local source region. A theoretical model is developed for predicting the distortion of ’’causality’’ correlation signatures (obtained when in-flow probes are cross correlated with the farfield sound), due to the parasitic probe noise. The predicted correlation functions agree with experiments conducted using probes of various shapes and sizes. In practice, the contaminated portion of the causality correlation signature is expected to be displaced in time from the ’’true’’ jet pressure correlation. An unexpected result of the present experiments is the absence of any legitimate correlation between the turbulent pressure fluctuations and the farfield jet noise. This leads to the conclusion that the extent and strength of the jet pressure fluctuations as noise sources must be very weak. Therefore, any probing device inserted into the flow will generally produce a large and potentially misleading portion of the total correlation.
Display of the underwater sound wavefront using the theory of holographic interference
Authors: Wu Wei-Tsong
Published: October 2005

Using the theory of holographic interference and the variable properties of the refractive index of water that has been disturbed by wave motion, a method has been developed where two holograms of the underwater acoustic field are photographed successively on one film plate, before and after the introduction of a wave, which could range in frequency from subsonic to supersonic. A He–Ne laser beam is used to illuminate the film plate, and the image of the wavefront is reconstructed. This new method helps to remove the difficulty underwater acoustic engineers have frequently encountered when observing the scene of an underwater wave.
Acoustical inverse problem for the cochlea
Authors: Sondhi Man Mohan
Published: October 2005

In this article, we will show how the stiffness K(x) of the basilar membrane may be estimated from a measurement of the impulse response at the stapes (i.e., from a measurement of the pressure developed just inside the stapes in response to an impulse of stapes velocity).
Spontaneous narrowband acoustic signals emitted by human ears
Authors: Zurek P. M.
Published: October 2005

In the ears of many persons, a spontaneous and continuous narrowband acoustic signal can be measured with a probe microphone in the ear canal. In a sample of 32 persons with normal hearing who were tested bilaterally, an oto-acoustic emission (OAE) was detected in 22 ears of 16 persons. These signals were most often found between 1.0 and 2.0 kHz and in all cases, the sound pressure in the occluded ear canal was less than 200 μPa. The behavior of these emissions was investigated in a number of experiments on the author’s own OAE at 1910 Hz. In one of these studies, the suppression of an OAE by an external tone was examined. It was found that a contour of constant suppression (amplitude versus frequency of external tones that produce a criterion reduction in the amplitude of the OAE) exhibits frequency selectivity like that commonly associated with cochlear frequency analysis. The existence of OAE’s of cochlear origin demonstrates that the ingredients for active biomechanical processes are present in the inner ear and supports the notion that such processes increase the sensitivity and selectivity of mechanical frequency analysis in the cochlea.
Acoustic pressure amplitude thresholds for rectified diffusion in gaseous microbubbles in biological tissue
Authors: Lewin Peter A. , Bjo/rno/ Leif
Published: October 2005

One of the mechanisms often suggested for the biological action of ultrasonic beams irradiating human tissues is concerned with the presence in the tissues of minute gaseous bubbles which may, under the influence of the ultrasonic field be stimulated to grow to a size at which resonance or collapse occurs with severe associated shear stresses. The evidence for the existence of microbubbles in tissues is reviewed. The results of calculations, using two existing theoretical models, of the peak pressure threshold as a function of frequency are presented. The frequency is normalized with the resonant frequency of the bubble, and results are presented for three bubble radii (1, 2, and 3.5 μm) and for different values of the gas concentration in the tissue between 0.1 and 1. The results from two models differ suggesting that an improved model and better experimental data for the threshold calculations would be appropriate for further calculations. The thresholds calculated range below the peak pressure amplitudes used in continuous wave diagnostic instruments, indicating the need for a more careful investigation both of this damage mechanism and of the exposures used in routine diagnosis. The results of calculations for typical (transient) exposure conditions from pulse-echo equipment are presented, indicating that rectified diffusion and stable cavitation are improbable phenomena in these circumstances.
Measurement of sound velocity with the scanning laser acoustic microscope
Authors: Grant D. R. , Bernardin J. E.
Published: October 2005

A method of calculating sound velocity in homogeneous liquids is described using a Sonoscan acoustic microscope. The operating procedure was modified by attaching a spacer to one end of the coverslip which caused the interference line spacing to depend upon the wavelength of sound in the sample. Data are reported for solutions of bovine serum albumin and the wheat flour protein, A gliadin.
Temporal sampling requirements for estimation of long-term average sound levels in the vicinity of airports
Authors: Schomer P. D. , DeVor R. E.
Published: October 2005

Community noise temporal sampling requirements in general, and in the vicinity of airports or other large noise producers in particular, are not well understood. Frequently, the purpose is to sample and estimate the true yearly Day/Night Average Sound Level (DNL) or Community Noise Equivalent Level (CNEL). This being the case, it is important to note that day-to-day samples are not independent, but, in fact, the time series formed by these day-to-day samples exhibits an autocorrelated structure. For this reason, sampling requirements are 4 to 8 times larger than are calculated by assuming purely random day-to-day data. Moreover, the data may exhibit weekly and yearly deterministic trends. As a result of those factors, the analysis herein shows that sampling requirements sufficient to achieve a precision of +2 to −3 dB of the true yearly CNEL or DNL value with a 95% confidence level can be summarized as 14 days of totally random sampling throughout the year, or 3–4 weeks of quasi-random sampling taken one week at a time, or at least 30 days of totally continuous sampling.
Reflection coefficient identification by means of correlation: Application to a layered medium
Authors: Gazanhes C. , Herault J. P. , Stephanakis K.
Published: October 2005

We apply signal processing techniques to determine the reflection coefficients of a layered medium. A frequency modulated signal propagating through the medium is reflected back by the different layers giving rise to several echoes. The cross-correlation function between the echoes and the transmitted signal exhibits peaks at lag corresponding to the time delays associated with the various layers; the amplitude of the peaks are related to the reflection coefficients. In order to compute these reflection coefficients automatically on a digital computer, a theoretical model is derived from the wave equation. This work can be extended to problems in biomedical echography, seismic data processing, and nondestructive testing.
Statistical approach to passive target tracking
Authors: Hinich Melvin J. , Bloom Michael C.
Published: October 2005

The paper presents a method for passively tracking a moving target using a sequence of bearings from a surveillance platform. The key assumption for the method is that the target is moving at a constant speed on a fixed heading during the data acquisition period. This is the same assumption that is made for Ekelund ranging. Parameter estimates are computed after bearings are taken as the tracking platforms maneuvers. No specific maneuver by the tracking platform is required. The estimators presented in this paper are approximately maximum likelihood when the target is distant from the platform.
Laser–Doppler velocity meter applied to tympanic membrane vibrations in cat
Authors: Buunen T. J. F. , Vlaming M. S. M. G.
Published: October 2005

This paper describes a simple interferometer that can be used for the measurement of extremely small vibrations (down to 0.01 nm) in biological preparations. Instead of amplitudes it measures velocities by detecting the Doppler–shift in the frequency of light diffusely scattered by a vibrating object. It has been applied to the measurement of malleus vibrations in cat. The malleus itself scatters sufficient light for the interferometer to operate so that no mirror is needed that might load the malleus. Since the instrument measures velocities it is very well suited for this application because the velocity of the malleus vibrations is much less dependent on the signal frequency than is its amplitude. The method is very insensitive to background noises or vibrations so that no special precautions for isolation need to be taken. The vibrations of the malleus measured with this instrument turn out to be in excellent agreement with data by previous workers. The effect of underpressure in middle ear cavities on the transfer function was measured and appears to be rather severe (11 dB sensitivity decrease) for frequencies below 1500 Hz only. The linearity of the malleus vibration was checked for sound pressures of 30 dB SPL up to 110 dB SPL.
Study of the transient motion in the cochlea
Authors: Holmes Mark H.
Published: October 2005

The transient problem obtained from a three-dimensional hydroelastic model of the cochlea is studied. In the model, the fluid motion is described by the linearized Navier–Stokes equations, and the basilar membrane is modeled as an elastic plate. The resulting problem is first reduced through the use of a slender body approximation which is, in turn, simplified by introducing expansions in terms of the reciprocal of the Reynolds number. With this, the wave-like nature of the solution is analyzed, comparing it with the long-time solution, as well as with experiment.
Effects of rise/decay time on the lateralization of interaurally delayed 1-kHz tones
Authors: Kunov Hans , Abel Sharon M.
Published: October 2005

Experiments in lateralization were performed to evaluate the relative contribution of onset and phase cues in binaural hearing. A 1-kHz signal was presented with interaural stimulus delays ranging from 0 to 1000 μs, corresponding to phase shifts of 0 ° to 360 °. For a given value of delay, the leading signal was presented randomly to the right or left ear over a block of 100 trials, and the laterality of the resultant image was judged. The percentage of correct judgments was plotted as a function of delay with rise/decay time as a parameter. Values of rise/decay time ranged from 0 to 500 ms. The results indicated that rise/decay times of at least 200 ms are necessary to avoid contributions from the onset cue to the formation of lateralization judgments. For rise/decay times shorter than 200 ms, a conflict occurs between phase and onset cues in the region of phase shifts from 180 ° to 360 °. At the limit with very short rise/decay times, the onset cue completely overrides the phase cue.
Velocity inversion in a stratified medium with separated source and receiver II
Authors: Gray Samuel H.
Published: October 2005

An earlier reference [J. Acoust. Soc. Am. 68, 234–240 (1980)] describes an inverse method for determining the velocity in a stratified medium. The inversion is performed by processing data (reflected sound waves) which have passed through the medium and been observed at one point. The location of the observation point need not be the same as that of the source, but their separation must be small in an appropriate sense. The results of that reference are greatly strengthened here, by recasting the problem in terms of the traveltime of the waves from the source. In particular, processing the exact same data using a different algorithm leads to a more accurate mapping of both size and location of the velocity variations.
Improved performance of receiving arrays in the presence of localized nearfield noise sources
Authors: Van Buren A. L.
Published: October 2005

This paper describes an element shading technique for improving the performance of a receiving array in the presence of localized nearfield noise sources. The shading reduces the array response over a prescribed frequency range to sound sources located within a prescribed nearfield volume while retaining desirable farfield characteristics. A numerical technique is presented for computing the optimum (in the least-squares sense) shading coefficients for a given array, frequency range, nearfield volume, and desired farfield characteristics. The technique was used to obtain shading coefficients for a line array of 20 elements. The theoretical results were confirmed experimentally by measurements made using a specially constructed line. An improvement of more than 30 dB in the signal-to-noise ratio of the line array (relative to when the array is uniformly shaded) was obtained, even when the nearfield noise sources were located directly between the center of the array and the desired farfield signal source.
Attenuation of acoustic waves in lithium niobate
Authors: Bajak I. L. , McNab A. , Richter J. , Wilkinson C. D. W.
Published: October 2005

The attenuation of acoustic waves in the bulk of LiNbO3 at room temperature has been measured in the frequency range 500 MHz to 10 GHz. The measurement technique involved optical detection at the lower half of the frequency range and high resolution pulse echo method at 9.45 GHz. The attenuation is found to depend on the square of the frequency, so the attenuation coefficient may be given in terms of an effective viscosity value, according to a treatment based on the theory of perturbation. The attenuation coefficient has been determined for various modes and propagation directions allowing the complete determination of the viscosity tensor, from which the attenuation coefficient can be calculated for any desired type of acoustic wave in LiNbO3.
Theoretical study of the penetration of highly directional acoustic beams into sediments
Authors: Tjo/tta Jacqueline Naze , Tjo/tta Sigve
Published: October 2005

Recently Muir et al. [J. Sound Vib. 64, 539–551 (1979)] presented results of an experimental study of the penetration of directional acoustic beams into bottom sediments. We consider here the linearized theory of the refracted sound field produced by a highly directional beam in a bottom sediment. Simplified equations, valid for ka large (k, k′, wavenumbers in sediment and water, respectively; a, width of the incident beam at the interface; qi, angle of the acoustic axis with the normal to the interface) are derived and solved analytically, subject to the nondissipative boundary condition at the interface. The radiation field is found to be similar to that of a phase shaded and infinitely compliant piston source. The solution is valid whenever the characteristic length of the diffraction effects is small compared to the attenuation length in the sediment; this is the case in the experiment referred to. Results are in good agreement with the Muir et al. experiment. The reflected sound field is also considered.
Evaluation of four-pole parameters for a straight pipe with a mean flow and a linear temperature gradient
Authors: Prasad M. G. , Crocker Malcolm J.
Published: October 2005

Four-pole parameters for a straight pipe system in the presence of a uniform mean flow and a linear temperature gradient are presented. The system was analyzed using first-order perturbation theory and a Green’s function approach. The general four-pole matrix derived reduces exactly to several other simpler cases already in the literature. The use of the matrix in engine exhaust system predictions is also given.
Effects of ground cover on the propagation of sound through the atmosphere
Authors: Bolen L. N. , Bass H. E.
Published: October 2005

Bands of noise were propagated over various ground surfaces and sound amplitudes were measured as a function of frequency of the sound source (40 Hz–2kHz), distance of propagation (5–300 m), and surface conditions. By treating the surface impedance as an adjustable parameter, the impedance as a function of frequency was determined from the measured sound amplitudes assuming spherical wave propagation in the vicinity of a locally reacting surface. The surface flow resistance was also experimentally determined in each case. In the frequency range 40 Hz–2 kHz, the results for three distinctly different surfaces suggest that the impedance can be computed from the specific flow resistance [C. I. Chessell, J. Acoust. Soc. Am. 62, 825 (1977)]. Surface vegetation appears to have little effect on the impedance.
Acoustic radiation from an impulsively excited elastic plate
Authors: Mackertich Seroj S. , Hayek Sabih I.
Published: October 2005

The acoustic radiated pressure time signature of a submerged elastic plate which is impulsively loaded is predicted analytically by use of integral transforms on time and space. The first arrival of the acoustic pulse at an observer point in the medium was shown to correspond to the acoustic time of arrival for the normal distance from the observer to the plate. After the first arrival, the time signature oscillates with decreasing amplitude with the passage of time. The period of oscillation was shown to increase with time and the decay rate was shown to decay inversely with elasped time.
Effect of absorber geometry on apparent absorption coefficients as measured in a reverberation chamber
Authors: Bartel Thomas W.
Published: October 2005

Measurements were made in the NBS reverberation chamber to determine the apparent random incidence absorption coefficient as a function of the area, perimeter, and shape of the test specimens for three different materials arrayed as combinations of rectangular pieces. Measurements made with the specimen edges exposed and with the edges covered with reflecting material were compared. The experimental results were compared with a theoretical model [T.D. Northwood, J. Acoust. Soc. Am. 35, 1173–1177 (1963)] using values of the acoustical admittance obtained from impedance tube measurements performed on the same materials. Both the experimental and theoretical results indicate that the random incidence absorption coefficient increases approximately linearly with E, the ratio of the perimeter to the area of the specimen for values of E ranging from 1.3 to 3.3 m−1. The theoretical analysis indicates, however, that a linear extrapolation to the value E = 0 is not necessarily valid. It was also found that if the specimen area and perimeter are kept constant, the values of the random incidence absorption coefficient decrease by a few percent as the specimen shape is changed to increase the number of vertices (inside plus outside right-angle corners) in the configuration.