bluuebunny/crossref_metadata_2025 huggingface dataset:
Backscatter spectrum of a randomly perturbed regular array of discrete scatterers
Authors: Cheung Alex T. M. , Buchen Peter W. , Macaskill Charles , Robinson David E.
Published: October 2005

This paper investigates the backscatter spectrum of acoustic beams and plane waves from a particular distribution of discrete scatterers. The distribution is a random spatial perturbation from some underlying regular structure. Models of this type are considered as crude representations of biological tissue, such as the liver. It is shown that, for plane waves, the random perturbations of the scatterers act as a linear filter of the backscatter response. The analytic form of the filter function is directly related to the probability distribution of the spatial perturbations. It is further demonstrated that a similar result holds for acoustic beams, if the lateral scale of the beam variations is large compared with the mean scatterer separations. The impact of this result on ultrasonic tissue characterization studies using attenuation measurements is discussed.
Realistic mechanical tuning in a micromechanical cochlear model
Authors: Kolston Paul J. , Viergever Max A. , de Boer Egbert , Diependaal Rob J.
Published: October 2005

Two assumptions were made in the formulation of a recent cochlear model [P. J. Kolston, J. Acoust. Soc. Am. 83, 1481–1487 (1988)]: (1) The basilar membrane has two radial modes of vibration, corresponding to division into its arcuate and pectinate zones; and (2) the impedance of the outer hair cells (OHCs) greatly modifies the mechanics of the arcuate zone. Both of these assumptions are strongly supported by cochlear anatomy. This paper presents a revised version of the outer hair cell, arcuate–pectinate (OHCAP) model, which is an improvement over the original model in two important ways: First, a model for the OHCs is included so that the OHC impedance is no longer prescribed functionally; and, second, the presence of the OHCs enhances the basilar membrane motion, so that the model is now consistent with observed response changes resulting from trauma. The OHCAP model utilizes the unusual spatial arrangement of the OHCs, the Deiters cells, their phalangeal processes, and the pillars of Corti. The OHCs do not add energy to the cochlear partition and hence the OHCAP model is passive. In spite of the absence of active processes, the model exhibits mechanical tuning very similar to those measured by Sellick et al. [Hear. Res. 10, 93–100 (1983)] in the guinea pig cochlea and by Robles et al. [J. Acoust. Soc. Am. 80, 1364–1374 (1986)] in the chinchilla cochlea. Therefore, it appears that mechanical response tuning and response changes resulting from trauma should not be used as justifications for the hypothesis of active processes in the real cochlea.
The insertion loss of finite length barriers on the ground
Authors: L’Espérance André
Published: October 2005

This paper presents a method for estimating the insertion loss (IL) of a finite length barrier on the ground. This method is an extension of the solution suggested by Jonasson [H. G. Jonasson, J. Sound. Vib. 22 (1), 113–126 (1972)] for estimating the sound reduction by an infinite length barrier on the ground. It uses diffraction theory, combined with a model for sound propagation over the ground, to calculate the diffracted field created by the diffracted path associated with each edge of the barrier. The diffracted paths are identified by simple geometrical considerations. The results obtained using this new method are compared with other theoretical methods and with the results of experimental measurements. It is shown that the new solution is as accurate as other more complex solutions.
An exact ray theoretical formulation of the Helmholtz equation
Authors: Foreman Terry L.
Published: October 2005

Practical computational procedures for obtaining ray theoretical solutions to the inhomogeneous Helmhotz equation ∇2Ψ+k2Ψ=S(r,ω) resort to a well-known approximation. A computational method is presented that enables one to trace rays without resorting to the ray theory approximation, provided a solution to the Helmholtz equation is available by independent means. In other words, given a solution to the Helmholtz equation, the exact rays for that case can be computed. This ray theory therefore serves, not as a computational method, but as a new method of displaying solutions to the Helmholtz equation. Exact ray diagrams are constructed for several cases using this technique. The resulting ray diagrams usually bear little resemblance to the corresponding classical ray diagrams. It is shown that the discrepancy is attributable to the nature of the classical ray theory approximation, which proves in most cases not to be a small perturbation. Some of the properties of the exact rays that distinguish them from their classical counterparts are: (1) The ray trajectories depend on the source frequency and configuration and on the boundaries; (2) the exact rays intrude into shadow zones impenetrable by classical rays; (3) the field is finite at caustics; and (4) the exact rays never exhibit multipathing, which is the hallmark of classical ray diagrams. The contrasts between classical and exact ray theory are demonstrated and explained.
Notes on infrasonic ambient ocean noise: Temporal autocorrelation and diurnal variation
Authors: Nichols Rudolph H.
Published: October 2005

Measurements of ambient ocean noise spectrum levels were made every 6 h at frequencies of 2.5–20 Hz at three deep-bottomed sites in the northeast Pacific over a 40-day period. Autocorrelation times to 1/e at these frequencies were found to range from 8.9–19.9 h over the frequency range and the three sites. Autocorrelation times to the first zero-axis crossing ranged from 25.2–118 h. Forty-day average noise spectrum levels at each of the four daily sampling times were compared with one another; maximum diurnal differences among them at a given frequency and site ranged from 0.2–1.9 dB. Standard deviations of the noise spectrum levels peaked at 10 Hz. Autocorrelation times were much longer than those reported by Perrone and King [J. Acoust. Soc. Am. 58, 1186–1189 (1975)] which, in turn, were longer than those reported by Cotaras et al. [J. Acoust. Soc. Am. 83, 1345–1359 (1988)].
Surface waves on a solid half-space
Authors: Caviglia Giacomo , Morro Angelo , Pagani Enrico
Published: October 2005

Inhomogeneous waves in viscoelastic solids are considered with the aim of a thorough characterization of surface waves in a solid half-space. To ascertain the existence of surface waves and to investigate their properties, a general scheme is established that is appropriate for numerical developments. Viscoelastic and elastic solids are examined in detail and previous results on admissible surface waves are generalized.
Directional spectra observations of seafloor microseisms from an ocean-bottom seismometer array
Authors: Goodman Dean , Yamamoto Tokuo , Trevorrow Mark , Abbott Chuck , Turgut Altan , Badiey Mohsen , Ando Koichi
Published: October 2005

Observations of the directional spectra of seabed motion in shallow water were conducted off the New Jersey coast during the summer of 1987. Using a six-point ocean-bottom seismometer array, each instrument supporting a pressure transducer, and two horizontal and vertical accelerometers, measurements of gravity and seismic waves across the ULF/VLF band were collected in 12.5 m of water. Array dimensions were tuned particularly for directional spectra observations of short-period seafloor microseisms. Directional spectra analysis indicates that in the short-period microseismic band, 1.5–2.5 s, motion of the seafloor is primarily a result of slow seismic waves traveling at apparent velocities near 200 m/s. These propagation velocities for the microseismic band in shallow water are an order of magnitude less than microseismic velocities from similar studies on land. Contemporaneous measurements of the directional spectra of long-period ocean gravity waves, 15–85 s, show an eastern direction of origin; short-period ocean gravity waves, 5–9 s, measured using particle motion analysis, are from the south. The direction of propagation of the microseisms, found from the maximum response of the array, is shown to be approximately N150E—a direction midway between long- and short-period ocean-wave propagation directions. Correlation of particle motion and directional spectra analysis indicates that microseisms have retrograde motion. These results suggest that the microseisms are most likely Scholte interface waves.
Test results using a prototype synthetic aperture sonar
Authors: Gough Peter T. , Hayes Michael P.
Published: October 2005

In this paper, the operation is described of a prototype coherent synthetic aperture sonar (SAS) based on continuous transmission frequency modulation that covers a 1-octave bandwidth. Images calculated from real data (collected from a sonar range in Loch Linnhe, Scotland) show that it is now possible to produce high-quality images of the seafloor at realistic mapping rates. An air-filled steel buoy was used as a test target, and several images are shown of this target using a variety of reconstruction algorithms.
Finite-amplitude effects on ultrasound beam patterns in attenuating media
Authors: Reilly Clarence R. , Parker Kevin J.
Published: October 2005

Some problems relevant to medical ultrasonics are addressed through experimental measurements of focused, pure-tone beam patterns under quasilinear conditions where significant nonlinearities are manifested. First, measurements in water provide a comparison of the beam patterns of the fundamental and nonlinearly generated harmonics against recent theoretical predictions of others. The radial beamwidths, presence and spacing of sidelobes, axial distances to peak pressures, focal shock parameter, time-domain waveform asymmetry, and post-focal falloff of the fundamental through fifth harmonics are discussed relative to various models under preshock conditions (σ<1). Second, the focused sources are placed in a more attenuating fluid to mimic the behavior of these fields in tissue. The changes in beam characteristics are examined relative to measurements at the same intensities in water, and relative to theoretical predictions. The results suggest that, given a known linear(low-intensity) focused beam pattern in water, guidelines can be followed to predict the beam pattern of the fundamental and higher harmonics at higher intensities in water, and then in attenuating media such as tissue.
Sound scattering of a plane wave obliquely incident on a cylinder
Authors: Li Tai-bao , Ueda Mitsuhiro
Published: October 2005

The solution of sound scattering of a plane wave obliquely incident on an isotropic elastic cylinder of infinite length is obtained and verified by experiment. The solution is expressed in terms of phase angles associated with partial scattered waves. It is found that, when the angle of incidence is small, supplementary resonances, which are not present in the case of normal incidence, are excited. The peaks and dips resulting from the resonances appear in the farfield form function ‖f∞‖. Experimental results for several different metals show good agreement with the calculated ones.
Nonlinearity, chaos, and the sound of shallow gongs
Authors: Legge K. A. , Fletcher N. H.
Published: October 2005

Experimental studies on several orchestral gongs of the tamtam and cymbal families suggest that two separate nonlinear mechanisms contribute to the evolution of the sound. The first mechanism is an upward cascade of energy from the low-frequency modes initially excited into high-frequency modes, caused by coupling between tension and shear stresses at regions of sharp change in shape of the gong. The second is a transition from simple periodic nonlinear modal motion to multiple fractional subharmonics, or even chaotic motion, which fills out the radiated spectrum at frequencies between those of the normal linear modes. Each of these mechanisms has considerable hysteresis, so that the spectrum of the radiated sound evolves over a period of several seconds. Measurements using high-level sinusoidal excitation have elucidated some of the features of this behavior.
Range-dependent extensions to Munk’s canonical sound-speed profile
Authors: Robertson J. S.
Published: October 2005

Range-dependent extensions to Munk’s canonical deep water sound-speed profile are discussed. A formalism is presented which ensures that the main properties of the profile are preserved even as the profile changes from place to place in the ocean. These extensions permit one straightforward way to formulate relatively simple analytical expressions for these profiles useful as inputs to propagation models.
Statistical and receiver operating characteristic analysis of empirical spike-count distributions: Quantifying the ability of cochlear nucleus units to signal intensity changes
Authors: Shofner William P. , Dye Raymond H.
Published: October 2005

Analytical methods from signal detection theory were applied in an effort to quantify the ability of cochlear nucleus (CN) units to signal changes in intensity. Of particular interest was the relation between this ability and the different patterns of discharge that characterize auditory neurons. Single-unit responses to best-frequency (BF) tone bursts were recorded from neurons in the gerbil cochlear nucleus, and empirical spike-count distributions were generated. The mean-to-variance ratios for regular units were generally larger than those of irregular units. Receiver operating characteristic (ROC) curves were generated from empirical spike-count distributions. The area under the ROC curve [P(A)] was computed and used to define the performance of an observer detecting whether or not a change in firing rate has occurred, thus signaling a change in intensity. For a given change in mean spike count, units characterized by regular interspike-interval (ISI) histograms typically gave larger P(A) values than did units characterized by irregular ISI histograms. In addition, onset units gave larger values of P(A) than did irregular units for a given change in mean spike count. These results suggest that regular and onset units are better able to signal intensity changes than are irregular units.
The influence of duration on the perception of pitch in single and simultaneous complex tones
Authors: Beerends John G.
Published: October 2005

The influence of duration on the virtual pitch of complex tones was measured using an absolute identification paradigm. If performance with two-tone complexes is expressed in terms of a single central frequency–coding noise function, this function is found to depend on duration in about the same way as the pure-tone difference limen function. The function is further found to be a reasonably good predictor of pitch identification performance with multitone complexes. Another experimental finding was that subjects tend to switch to the analytic mode of pitch perception when complex tones are shortened (i.e., they tend to hear the spectral pitches instead of the virtual ones). A third finding was that with simultaneous complex tones the degradation of each pitch percept depends not only on duration and harmonic order of the tone but also on the harmonic order of the other tone.
Analysis of natural vibrations of a spherical shell with variable thickness
Authors: Hirai Tsukasa , Kuroda Michio
Published: October 2005

This paper is concerned with the natural vibrations of a spherical shell with variable thickness in the meridional direction. The governing equations of motion are based upon the classical small deflection theory of thin shells postulated by Love for the case of shell vibrations. In this paper, it is shown that the eight solutions of these equations for the asymmetrical vibrations can be obtained analytically by the method of series solution. As a practical example, four solutions required in the case of a hemispherical shell with a free edge are derived. Last, to demonstrate the utility of the present method, the numerical results are compared with the experimental data.
Waveguide propagation of ambient sound in the ocean-surface bubble layer
Authors: Farmer David M. , Vagle Svein
Published: October 2005

Measurements of the ambient sound generated by breaking waves over the range 40–20 000 Hz reveal well-defined spectral peaks, the frequency of which may remain generally consistent from one breaking event to the next, but which can change significantly over the course of a storm, or from one storm to another. A theory is proposed, based on the concept of trapping of a portion of the sound in the waveguide formed by the ocean-surface bubble layer. Simultaneous measurements of the bubble population and size distribution as a function of depth and time were obtained with a multifrequency inverted echo sounder, allowing calculation of the resulting (dispersive) sound-speed anomaly profile. Theoretical predictions of the spectral peaks, which are associated with modal cutoff frequencies, are in good agreement with the observations. It is suggested that this result might have application to the remote determination of ocean-surface bubble fields relevant to the study of wave breaking, turbulence, and the air–sea gas flux.
Methods for predicting the sensitivity of matched-field processors to mismatch
Authors: Gingras Donald F.
Published: October 2005

Most array processing schemes rely on the use of a signal replica correlated with the sensor observations to detect and localize targets of interest. Matched-field processors make use of signal replicas that are accurately tuned to available environmental knowledge. When knowledge about the array system, such as sensor positions, or environmental parameters, such as sound speed, is imprecise, this causes a ‘‘mismatch’’ between the replica and the observations. The performance of the processor may be seriously degraded by this mismatch. Analytic methods for predicting the sensitivity of the output power level to replica mismatch are developed, and bounds on the reduction in power level are developed. The use of these methods is illustrated through discussion of an example. Matched-field array processing methods can, in many situations, significantly improve target detection and localization performance. This article provides analytical tools which can be used to assess the performance of such processors in the context of real world system limitations.
Environmental and system effects on source localization in shallow water by the matched-field processing of a vertical array
Authors: Hamson Rachel M. , Heitmeyer Richard M.
Published: October 2005

This paper presents simulated and experimental results on source localization in shallow water by the matched-field processing of a vertical array. Range-depth ambiguity surfaces are obtained by the spatial correlation of the incident field (modeled or real) with a modeled replica of that field. All modeled fields are generated by the Centre’s normal-mode program. The simulated results indicate that a high-quality ambiguity surface can be obtained provided that the incident field is formed by a significant number of contributing modes, and that the array spans a large fraction of the water column. Changes in the acoustic environment that reduce the effective number of modes result in a degraded surface. The effect of mismatches between the ‘‘true’’ environmental parameters and those used to compute the replica field is also investigated. Errors in the bottom parameters do not severely effect the results, but small mismatches in sound-speed profile or water depth can degrade the result significantly. Examples of localizations obtained with real data from a Mediterranean site are presented, for source ranges up to 19 km from a vertical array that spanned half the water depth. Successful localizations were obtainable, though high sidelobes were also present.
Formant estimation by linear transformation of the LPC cepstrum
Authors: Broad David J. , Clermont Frantz
Published: October 2005

A method is described for estimating vowel formant frequencies from linear combinations of cepstral coefficients. The method is robust in that large errors from misidentified peaks are rare. It can be explained in terms of a Fourier cosine series of the desired identity between formant estimates and their true values. This analysis also sheds some light on the high correlations between the formants and dimensions of the log spectrum reported by Pols et al. [J. Acoust. Soc. Am. 53, 1093–1101 (1973)].
Comments on ‘‘The growth of and recovery from TTS in human subjects exposed to impact noise’’ [J. Acoust. Soc. Am. 8
5, 1681–1690 (1989)]
Authors: Ward W. Dixon
Published: October 2005

This letter disputes the contention that the growth of temporary threshold shift (TTS) with time can be adequately described by Gompertz functions. The similarity between TTS growth functions in high levels of impact and of continuous noise is stressed, a similarity that leads to the proposition that some sort of peak-limiting action that occurs at the stapes serves to protect the cochlea in the 120-dBA region.
Low-frequency characteristics of vehicle interior sound fields
Authors: Yanagawa Hirofumi
Published: October 2005

Good-quality sound reproduction requires a flat frequency response at the listening position. In a very small listening space, such as a vehicle interior, reflected waves introduce significant variation in the frequency response. Experimental results and a simple model are presented.
Estimating velocity ratio in marine sediment
Authors: Bachman Richard T.
Published: October 2005

Presented in this letter are least-squares regression relationships between velocity ratio (R; the ratio between surficial sediment sound speed and bottom water sound speed) and sediment mean grain size (Mz, phi units), porosity (η, %), and density (ρ, kg/m3). The relationships are: R=1.296−6.01×10−2 Mz +2.83×10−3 Mz2; R=1.675−1.639×10−2 η +9.762×10−5 η2; and R=1.513−8.24×10−4 ρ+3.2249×10−7 ρ2. These equations, respectively, explain 91.6%, 88.0%, and 86.4% of the variation observed in velocity ratio. Velocity ratio relationships are more convenient than those previously available because they do not require temperature and pressure correction to in situ conditions.
A mass transfer probe for measurements of cavitation activity in ultrasonic fields
Authors: Perusich Stephen A. , Alkire Richard C.
Published: October 2005

A new type of probe was developed to evaluate the distribution of kinetic, thermal, and acoustic energy in an ultrasonically induced cavitation field. The probe is based on an electrochemical mass transfer technique for direct measurement of the flux of reactants to a surface. Cavitation was generated in a focused ultrasonic field at 1.58 MHz over a large range of focal intensities. Electrochemical measurements of the reduction of ferricyanide to ferrocyanide in a NaOH solution show that the focal area dimensions (as characterized by the cavitation activity) increased almost an order of magnitude in the presence of intense cavitation. The cavitation activity is attributed to fluid motion generated by cavitation-induced jets and microstreaming. A mathematical model is proposed to predict the mass transfer rate at the surface under cavitation conditions and to relate the mass transfer coefficient to the acoustic focal intensity. The concept of the mass transfer probe resulted from the author’s previous work in the study of the electrochemistry of metals in the presence of ultrasound [S. Perusich, Ph.D. thesis, University of Illinois at Urbana, Urbana, IL (1985)].
A study of timing in an Estonian runic song
Authors: Ross Jaan
Published: October 2005

All note durations were measured in an Estonian runic song where one and the same melodic pattern is repeated 32 times in succession. It was found that the durations acoustically tend to form two categories that could be called the short and the long note. This result was confirmed by the multidimensional scaling of the measured durations. Other dimensions that seem to influence the relative duration of a particular note in the performance are related to the metrical position of the note and to whether a vowel or a diphthong corresponds to the note in the sung text. The results of this study suggest also that the opposition of the short and long notes may determine the rhythmic structure of the runic song rather than the properties of the verbal text.
What’s in a whisper?
Authors: Tartter Vivien C.
Published: October 2005

Whispering is a common, natural way of reducing speech perceptibility, but whether and how whispering affects consonant identification and the acoustic features presumed important for it in normal speech perception are unknown. In this experiment, untrained listeners identified 18 different whispered initial consonants significantly better than chance in nonsense syllables. The phonetic features of place and manner of articulation and, to a lesser extent, voicing, were correctly identified. Confusion matrix and acoustic analyses indicated preservation of resonance characteristics for place and manner of articulation and suggested the use of burst, aspiration, or frication duration and intensity, and/or first-formant cutback for voicing decisions.
An addendum to ‘‘Effects of noise on speech production: Acoustic and perceptual analyses’’ [J. Acoust. Soc. Am. 8
4, 917–928 (1988)]
Authors: Summers W. Van , Johnson Keith , Pisoni David B. , Bernacki Robert H.
Published: October 2005

The authors respond to Fitch’s comments [H. Fitch, J. Acoust. Soc. Am. 86, 2017–2019 (1989)] on an earlier paper. New analyses are presented to address the question of whether F1 differences observed in the original report are an artifact of linear predictive coding (LPC) analysis techniques. Contrary to Fitch’s claims, the results suggest that the F1 differences originally reported are, in fact, due to changes in vocal tract resonance characteristics. It is concluded that there are important acoustic-phonetic differences in speech when talkers speak in noise. These differences reflect changes in both glottal and supraglottal events that are designed to maintain speech intelligibility under adverse conditions.
Evaluation of two multichannel tactile aids for the hearing impaired
Authors: Weisenberger Janet M. , Broadstone Susan M. , Saunders Frank A.
Published: October 2005

Two multichannel tactile devices for the hearing impaired were compared in speech perception tasks of varying levels of complexity. Both devices implemented the ‘‘vocoder’’ principle in their stimulus processing: One device had a 16-element linear vibratory array worn on the forearm and displayed activity in 16 overlapping frequency channels; the other device delivered tactile stimulation to a linear array of 16 electrodes worn on the abdomen. Subjects were tested in several phoneme discrimination tasks, ranging from discrimination of pairs of words differing in only one phoneme under tactile aid alone conditions to identification of stimuli in a larger set under tactile aid alone, lipreading alone, and lipreading plus tactile aid conditions. Results showed both devices to be better transmitters of manner and voicing features of articulation than of place features, when tested in single-item tasks. No systematic differences in performance with the two devices were observed. However, in a connected discourse tracking task, the vibrotactile vocoder in conjunction with lipreading yielded much greater improvements over lipreading alone than did the electrotactile vocoder. One possible explanation for this difference in performance, the inclusion of a noise suppression circuit in the electrotactile aid, was evaluated, but did not appear to account for the differences observed. Results are discussed in terms of additional differences between the two devices that may influence performance.
Noise level, inner hair cell damage, audiometric features, and equal-energy hypothesis
Authors: Borg Erik , Engström Berit
Published: October 2005

Rabbits were exposed to 2- to 7-kHz noise either for a short duration at a high sound-pressure level (15 or 30 min at 115 dB SPL), or a long duration at a low level (512 h at 85 dB SPL). The high-level exposure produced a hearing loss in the frequency range 2–6 kHz, whereas the low-level exposure gave maximum hearing loss at 12–20 kHz. The 115-dB exposure caused significantly more damage to inner hair cells than the 85-dB exposure. The implications of the present results for evaluating audiograms, equal-energy hypothesis, risk criteria, and subjective auditory features are pointed out.
Nonlinearities in cochlear receptor potentials and their origins
Authors: Dallos Peter , Cheatham Mary Ann
Published: October 2005

Using intracellular recording methods in vivo [P. Dallos, J. Neurosci. 5, 1591–1608 (1985)], we have examined various nonlinear characteristics of receptor potentials from hair cells located in the low-frequency region of the guinea pig cochlea. Patterns of saturation for ac and dc response components obtained from Fourier analysis and directly from averaged waveforms are studied. Growth patterns of lower harmonic components are investigated and the interesting nonmonotonic properties of even harmonics noted. The latter are seen in both inner and outer hair cell responses, primarily with stimuli near the cells’ best frequency. Fundamental ac and the dc potentials occasionally exhibit nonmonotonic growth. These patterns are studied and their occurrence in inner and outer hair cell responses considered.
Optimum oversampling
Authors: Niland R. A.
Published: October 2005

A kernel is developed that enables a bandlimited signal to be optimally reconstructed from a finite number N of samples taken at the Nyquist rate or faster. The point reconstruction error, which falls as only N−0.5 at the Nyquist frequency, drops exponentially with N if there is even moderate oversampling.
Origin of the 33-driven ceramic ring-stack transducer
Authors: Miller Harry B.
Published: October 2005

The idea of segmented hollow ceramic cylinders in place of integral hollow cylinders was not an obvious design choice 30 years ago. In fact, it looked like a step backward, as regards simplicity of construction. However, it paid off handsomely in performance gains. The origin of this invention is described.
On the application domain of the Green’s function approximation for mild anisotropic media [Comments to the article ‘‘On Green’s functions for elastic waves in anisotropic media,’’ J. Acoust. Soc. Am. 8
3, 118–121 (1988)]
Authors: Tverdokhlebov Andrey , Rose Joseph L.
Published: October 2005

A Green’s function for anisotropic media was developed for materials having no cusps in the energy velocity profile and exhibiting a mild anisotropy, that is with a relatively small deviation of the quasilongitudinal wave velocity from its averaged value. A scaling transform is introduced that allows severe anisotropy to be considered.
Localization of sound in rooms IV: The Franssen effect
Authors: Hartmann William Morris , Rakerd Brad
Published: October 2005

The Franssen effect is an illusion that causes human listeners to make large errors in localizing a sound source. This paper describes steps taken to convert the illusion into an experiment in order to study the localization precedence effect as it operates in rooms. The results of the experiment suggest that there are two components to the illusion: The first is the inability of listeners to localize a sine tone in a room in the absence of an onset; the second is the obscuring of modulation cues by the irregular transient response of a room. Experiments show that the Franssen effect fails completely in anechoic environment, as expected if the effect depends upon the implausibility of steady-state cues in a room. The Franssen effects also fails when the spectrum of the sound is dense.
Propagation of ground-borne vibrations from surface sources
Authors: Trochidis A.
Published: October 2005

The propagation of ground-borne vibration from surface sources has been investigated theoretically, and a simple method for obtaining the motion on the surface as well as the attenuation of the vertical motion with the distance from the source for various ground models has been presented. Provided that the depth of the layers and the wavenumbers remain small, the analysis used in this paper gives quite acceptable results.
Application of adiabatic mode theory to the calculation of horizontal refraction through a mesoscale ocean eddy
Authors: Hall Marshall V. , Irving Mark A.
Published: October 2005

Adiabatic mode theory is used to calculate the path in the horizontal plane of vertical acoustic normal modes (at a frequency of 25 Hz) that have propagated through an idealized gulf-stream eddy of radius 125 km whose center is 625 km from the source. The arrival directions of the modes (which are calculated using a simple algorithm) and their relative amplitudes are used to calculate the apparent bearing of the source at positions beyond the eddy (the algorithm cannot be applied to positions within the inhomogeneity) on a line at 5° to the source-center axis. For source and receivers at a depth of 600 m, the source bearing deviation decreases from 0.5° at 740 km to 0.4° at 860 km (its asymptote, as range becomes infinite, is zero). The results for a transducer depth of 600 m are compared with a previously published calculation based on a parabolic equation method that used identical eddy parameters and transducer configurations. The two methods are found to predict broadly the same bearing deviation, except that the adiabatic mode-theory predictions are around 0.04° smaller than the average parabolic equation predictions. The effect of coupling from other modes on the amplitude of the important mode is found to be only 2% and hence negligible. For the eddy model considered, the degree of horizontal refraction of normal modes decreases as the mode number is increased. The bearing deviation therefore increases as the depth of the transducers is increased.
A model of the intensity probability distribution for wave propagation in random media
Authors: Ewart Terry E.
Published: October 2005

Ewart and Percival [J. Acoust. Soc. Am. 80, 1745 (1986)] have shown that the generalized gamma distribution effectively models intensity probability distributions of temporal fluctuations observed in a field experiment and transverse spatial fluctuations simulated in numerical experiments. In both cases the fluctuations are due to wave propagation through a medium with a random index of refraction. Here, the transverse spatial intensity fluctuations of a wave propagating through a medium with a power-law autocorrelation function of wave speed are modeled over a regime that spans 108 in scattering strength and 106 in scaled range (range divided by the Fresnel length). This scattering parameter regime transforms to ranges between 100 m and 100 km and to frequencies between 100 Hz and 100 kHz when normalizations typical of observed ocean internal wave fluctuations are used. Contour plots of the variance, skewness, and kurtosis of the intensity distribution are presented for the range/frequency plane. It is shown that the region of saturation, i.e., exponential intensity distribution, cannot be attained except for very large source strengths. Also, the lognormal intensity distribution, which is assumed for scintillation indices near zero, can be applied only in the region of vanishingly small intensity fluctuations. This work, while based on plane-wave propagation and a fourth-order power-law transverse spectrum of the medium, retains the essential character of the intensity fluctuations and provides a prescription for modeling the intensity distribution for any medium where the random index of refraction process can be assumed stationary.
Acoustic microscopy applied to nonlinear characterization of biological media
Authors: Germain L. , Jacques R. , Cheeke J. D. N.
Published: October 2005

The use of an acoustic microscope as a method for nonlinear characterization of biological media is evaluated. The method consists of measuring the second harmonic signal generated in a sample located at the focus of the acoustic lens. Two experimental configurations were compared: The first is the simple case where the sample is a liquid mixture filling the space between the lens cavity and the receiver; in the second case, the liquid mixture is confined to a thin layer at the focal plane, in order to simulate a real tissue layer. Aqueous solutions of ethylene glycol and methanol were used as liquid samples. Simple theoretical models are presented for each configuration and the predictions show good qualitative agreement with experimental measurements. These results confirm our belief that the acoustic microscope is potentially a good tool for nonlinear B/A imaging of biological systems.
Source correlation effects on the sound power radiation from spherical shells
Authors: Peng H. , Banks-Lee P.
Published: October 2005

The sound power radiated from a fluid-loaded thin spherical shell under the action of correlated axisymmetric annular forces is formulated in this study. By assuming that two forces possess identical bandlimited white-noise spectra, uniformly distributed against the equator of the spherical shell, numerical evaluations of the nondimensional sound power are performed for a steel shell immersed in air and water, respectively. The results show that (1) keeping the input power the same, point forces always produce higher sound power levels than distributed forces; (2) when the band of excitation falls into a relatively low frequency region where only very few, if any, shell modes can be excited, the cross spectra between forces generally have important effects on the radiated sound power level; (3) when the band covers a relatively wide frequency range where more shell modes can be excited, the role of source correlations becomes important only if the two forces are located close to one another; (4) when two forces are positively correlated (r=+1), there always exists an optimal separation distance (expressed as angle Θ1) between the two forces that will produce a relatively minimum sound power level. This phenomenon of sound power reduction is discussed by means of sound power spectrum analysis. These conclusions are applicable for spherical shells immersed in air and in water.
Informational processing of complex sound. I: Intensity discrimination
Authors: Lutfi Robert A.
Published: October 2005

This paper reports on some initial experiments using the sample discrimination paradigm to investigate normal-hearing listeners’ ability to process information in complex, nonspeech sounds. An important feature of the sample discrimination experiment is that the value of the difference to be discriminated randomly varies from trial to trial. It is this variation that yields potential information. In the present study, listeners heard a pair of multitone complexes (or sequences) on each trial. The individual levels of the tones were drawn from two normal distributions differing only in mean. The listener’s task was to identify the sound having the higher mean tone level. For an ideal observer in these experiments, performance in d′ grows as the square root n, where n is the number of tones. Obtained d′ grew more nearly as the cube root of n regardless of whether the tones were played sequentially or simultaneously or whether they were increased in number from high frequencies to low or from low frequencies to high. A preliminary model is proposed in which discrimination performance depends predominantly on the information content of the sounds and is largely independent of the physical dimensions along which the sounds vary. Information content is defined in terms of the variance of the underlying stimulus distributions and a stimulus equivocation factor that is derived from the data. Based on this model, transmitted information is estimated to be between 1.0 and 2.6 bits.
Forward masking patterns produced by intracochlear electrical stimulation of one and two electrode pairs in the human cochlea
Authors: Lim H. H. , Tong Y. C. , Clark G. M.
Published: October 2005

Three psychophysical forward masking studies were conducted on a multichannel cochlear implant patient. The first study investigated the masking pattern produced by a bipolar electrode pair at different stimulus currents. It was found that the masking pattern for a single-masker bipolar electrode pair had a maximum located at an electrode position where the masker and probe coincided. The spread of the masking pattern was not symmetrical about the maximum. The amount of masking decreased very rapidly toward the apical direction and less rapidly toward the basal direction from the position of the maximum. As the stimulus current increased, the amount of masking at the maximum increased and the masking pattern broadened toward the base. The second study investigated the masking pattern produced by the activation of single bipolar electrode pairs with different spatial extents. The spatial extent of a bipolar electrode pair is defined as the distance between the apical and basal electrode members of the bipolar pair. With a small spatial extent (1.5 mm), the more basal electrode pairs (higher threshold and smaller dynamic range) produced broader masking patterns than the more apical electrode pairs (lower threshold and wider dynamic range), suggesting that there was more current spread at the basal region. With a larger spatial extent (4.5 mm), an additional secondary masking maximum was observed in the vicinity of the apical electrode member of the masker; this was observed only when the apical electrode member lay within the low-threshold apical region. The third study investigated the masking patterns produced by two loudness balanced bipolar masker electrode pairs activated within a stimulus period (inverse of the pulse repetition rate). The biphasic current pulses delivered to the two electrode pairs were nonoverlapping in time. It was found that, at any probe electrode position, the amount of masking produced by the two combined bipolar electrode pairs approximately followed the greater of the two maskings produced respectively by the two individual bipolar masker electrode pairs.
Finite element modeling of radiating structures using dipolar damping elements
Authors: Bossut Regis , Decarpigny Jean-Noël
Published: October 2005

The finite element modeling of a radiating structure can be performed by surrounding this structure with a limited fluid domain, upon the external boundary of which a nonreflexion condition is prescribed for the acoustic field. This condition can be implemented with the help of damping finite elements which are attached to the external boundary and are designed to absorb the successive components of the pressure field multipolar expansion [Bayliss et al., ICASE Rep. No. 80/1, NASA, Langley (1980)]. This paper describes an axisymmetrical finite element which damps the monopolar and dipolar components of the radiated field. Then, it provides an original extrapolation algorithm to compute farfield quantities (sound pressure level or transmitting voltage response, directivity patterns,...) from the previously obtained nearfield. Finally, it demonstrates the accuracy of the method in two test cases and describes its application to the analysis of a free-flooded ring transducer used in sonar devices.
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o ultrasonic heating of fetal bone
Authors: Drewniak J. L. , Carnes K. I. , Dunn F.
Published: October 2005

The temperature increase measured in vitro in human fetal femurs exposed to 1 MHz, continuous wave ultrasound at 37 °C is reported. The temperature is measured with a thermocouple probe and is given for several gestational ages. The initial rate of the temperature increase in the specimens is evaluated and compared to known values of absorption in soft tissue. For example, the initial rate of temperature increase in the 108-day gestational age specimen resulting from exposure to ultrasound is 30 times greater in the fetal bone than that of soft tissue with an absorption coefficient of 0.05 cm−1.
Reverberant overlap- and self-masking in consonant identification
Authors: Nábělek Anna K. , Letowski Tomasz R. , Tucker Frances M.
Published: October 2005

Two effects of reverberation on the identification of consonants were evaluated for ten normal-hearing subjects: (1) the overlap of energy of a preceding consonant on the following consonant, called ‘‘overlap-masking’’; and (2) the internal temporal smearing of energy within each consonant, called ‘‘self-masking.’’ The stimuli were eight consonants /p,t,k,f,m,n,l,w/. The consonants were spoken in /s–at/ context (experiment 1) and generated by a speech synthesizer in /s–at/ and /–at/ contexts (experiment 2). In both experiments, identification of consonants was tested in four conditions: (1) quiet, without degradations; (2) with a babble of voices; (3) with noise that was shaped like either natural or synthetic /s/ for the two experiments, respectively; and (4) with room reverberation. The results for the natural and synthetic syllables indicated that the effect of reverberation on identification of consonants following /s/ was not comparable to masking by either the /s/-spectrum-shaped noise or the babble. In addition, the results for the synthetic syllables indicated that most of the errors in reverberation for the /s–at/ context were similar to a sum of errors in two conditions: (1) with /s/-shaped noise causing overlap masking; and (2) with reverberation causing self-masking within each consonant.
The perceptual effects of child–adult differences in fricative-vowel coarticulation
Authors: Nittrouer Susan , Whalen D. H.
Published: October 2005

Earlier work [Nittrouer et al., J. Speech Hear. Res. 32, 120–132 (1989)] demonstrated greater evidence of coarticulation in the fricative-vowel syllables of children than in those of adults when measured by anticipatory vowel effects on the resonant frequency of the fricative back cavity. In the present study, three experiments showed that this increased coarticulation led to improved vowel recognition from the fricative noise alone: Vowel identification by adult listeners was better overall for children’s productions and was successful earlier in the fricative noise. This enhanced vowel recognition for children’s samples was obtained in spite of the fact that children’s and adults’ samples were randomized together, therefore indicating that listeners were able to normalize the vowel information within a fricative noise where there often was acoustic evidence of only one formant associated primarily with the vowel. Correct vowel judgments were found to be largely independent of fricative identification. However, when another coarticulatory effect, the lowering of the main spectral prominence of the fricative noise for /u/ versus /i/, was taken into account, vowel judgments were found to interact with fricative identification. The results show that listeners are sensitive to the greater coarticulation in children’s fricative-vowel syllables, and that, in some circumstances, they do not need to make a correct identification of the most prominently specified phone in order to make a correct identification of a coarticulated one.
Shadowing by randomly rough surfaces
Authors: McCoy John J.
Published: October 2005

A computational framework for incorporating the effects of shadowing into prediction models for estimating both the coherent component of a surface-scattered field, and the coherence function defined on the total field, is presented. The incorporation is via a number of ‘‘shadowing’’ functions that are identified as precisely described conditional statistics of the surface topography. It is demonstrated that a shadowing function commonly used in the literature follows from one of those identified herein as appropriate for estimating the coherent component of the field, but only upon making a statistical independence assumption that cannot be justified.