bluuebunny/crossref_metadata_2025 huggingface dataset:
Predictions of the acoustic scattering response of free-methane bubbles in muddy sediments
Authors: Lyons Anthony P. , Duncan Michael E. , Anderson Aubrey L. , Hawkins James A.
Published: October 2005

The response of the sediments of Eckernfoerde Bay, Germany to acoustic remote sensing previously has been attributed qualitatively to gas features which were postulated to exist in situ within the sediment. The existence of features as small as 0.5-mm equivalent spherical radius has now been confirmed by x-ray computed tomography of cores taken and scanned at in situ pressures. The interaction of an acoustic pulse from the acoustic sediment classification system (ASCS) with this type of gassy sediment was modeled and the results are presented here. The bubble scattering response model includes both the effects of nonspherical bubbles and of sediment resistance to shear deformation (as expressed by the dynamic shear modulus). Model predictions made using the observed gas bubble distribution agree with normal incidence ASCS data, exhibiting extended returns (i.e., greater than the source pulse length) from the seafloor bubble layers as well as high attenuation within the bubble layers. Spectrograms of ASCS and modeled return pulses were also similar. These results suggest that the acoustic return characteristics of the near surface sediments of Eckernfoerde Bay are dominated by scattering from a distribution of gas bubbles with depth.
Ray chaos and eigenrays
Authors: Tappert F. D. , Tang Xin
Published: October 2005

In a realistic range-dependent deep ocean environment that gives rise to ray chaos, a complete set of eigenrays at long ranges is computed using a numerical technique based on the shooting method. The numerical results support and illustrate the known connection between ray chaos and eigenrays, namely, that the number of eigenrays grows exponentially, on average, with increasing range. It is further found that groups of chaotic eigenrays tend to form ‘‘clusters’’ having stable envelopes.
A low-frequency acoustic scattering model for small schools of fish
Authors: Feuillade C. , Nero R. W. , Love R. H.
Published: October 2005

A new low-frequency scattering model for small to moderately sized fish schools has been developed. The model, which uses a mathematical formalism based upon the harmonic solution of sets of coupled differential equations, allows a verified swimbladder scattering ‘‘kernel’’ for the individual fish to be incorporated. It includes all orders of multiple scattering interactions between fish, and calculates the aggregate scattering field by coherent summation. Application to simulated ensembles of closely spaced fish indicates significant deviations from incoherent scattering returns. Peak target strength reductions, and shifts in the resonance frequency, appear due to multiple scattering. The target strength also varies strongly with frequency as a result of interference effects. When applied to widely dispersed ensembles, the model reproduces the results of incoherent scattering. For larger ensembles, at greater depth, the model predicts sharply reduced target strength values around the main resonance. The ensemble effects of a school on the scattering of any single individual show more fluctuations as the school size increases. By reducing the viscous damping in the scattering kernel, the model can also describe scattering from small bubble clouds. The model has been applied successfully to fit experimental broadband low-frequency scattering data from schooling fish.
Acoustic lance: New in situ seafloor velocity profiles
Authors: Fu S. S. , Wilkens R. H. , Frazer L. N.
Published: October 2005

The acoustic lance is an instrument developed to obtain in situ compressional wave velocity and attenuation (Q−1) profiles for a sedimentary layer of several meters thickness at the sediment–seawater interface. The self-contained instrument consists of ten independent recording channels with a linear array of receivers embedded in the seafloor below a broadband acoustic source. It provides in situ recording of full waveforms to determine interval velocity and attenuation. The system can be attached to a gravity corer or to a specially designed probe. A comprehensive experiment was carried out in Mid-Atlantic Ridge sediment ponds where the lance made in situ measurements, and core samples were recovered. Core data agree well with in situ data in one location, but disagree in other locations. Lance data indicate that the sediment ponds have similar in situ velocity distributions, with an acoustic channel much thinner than that predicted by earlier investigators.
Born-type schemes for the acoustic probing of 1-D fluid media from time-harmonic planar reflection coefficients at two incidences
Authors: Lambert Marc , de Oliveira Bohbot Rodrigo , Lesselier Dominique
Published: October 2005

The probing of a 1-D (depth-) inhomogeneous fluid half-space is carried out from a limited knowledge of plane-wave reflection coefficients with respect to frequency at two precritical incidences. Born-type inversion algorithms are investigated. First, index profiles as a function of a density-dependent pseudodepth are retrieved at two incidences; then density and speed-of-sound profiles versus depth are extracted. A Born-iterative scheme builds up the solution as the limit of a sequence of solutions of approximate, constrained linear problems. A Born-extended scheme directly yields a linearized solution. Two variants of the Born-iterative scheme are developed, the first one when data are known in both amplitude and phase, the second one with amplitude-only data. Possible—but not limiting—applications are in underwater acoustics, once the planar reflection coefficient of a seabed has been found, e.g., from the depth-dependent Green’s function in the spectral domain. Numerical simulations illustrate the schemes. Good index profiles are obtained with reasonable behavior versus noise or other causes of limitations. As is expected, separate probing of speed and density profiles remains difficult. The computationally costly exact scheme is not better than the cheaper approximate one when good data are available, but handles more complicated situations.
Olivocochlear reflex assays: Effects of contralateral sound on compound action potentials versus ear-canal distortion products
Authors: Puria Sunil , Guinan J. J. , Liberman M. C.
Published: October 2005

The strength of the olivocochlear reflex has been assayed by comparing ipsilateral cochlear responses with and without contralateral sound. In humans, ipsilateral cochlear responses have usually been inferred by measuring otoacoustic emissions (OAEs), whereas, in animal work, they have been assessed by measuring compound action potentials (CAPs). Thus reports that the reflex strength is smaller in humans than in animals cannot be interpreted until the differences between the two tests are better understood. The present study directly compares reflex assays using distortion-product (DP) OAE and CAP measures in the same animals. For ipsilateral frequencies of 2–8 kHz and levels from 25 to 80 dB SPL, efferent reflex strength was computed from the CAP or DPOAE amplitude-versus-level curves measured with and without contralateral noise. The ‘‘effective attenuation’’ produced by efferent activation was, with few exceptions, greater when measured with the CAP than with the DPOAE assay. Differences between the two measures increased as frequency increased, with differences as large as 10 dB observed. These results, coupled with previous measurements on humans and animals, suggest that the efferent reflex is at least as strong in humans as has been shown in animal experiments.
The probe-signal method and auditory-filter shape: Results from normal- and hearing-impaired subjects
Authors: Moore Brian C. J. , Hafter Ervin R. , Glasberg Brian R.
Published: October 2005

In the probe-signal method, subjects are required to detect a signal in noise that is presented on the majority of trials at an ‘‘expected’’ (target) frequency but on a minority of trials at an ‘‘unexpected’’ probe frequency. Detection of the probes worsens with increasing separation between the target and probe frequencies. This result has often been interpreted as indicating that subjects monitor the output of a single auditory filter centered at the target frequency. To test this idea, a two-stage experiment was conducted. In the first stage, auditory-filter shapes were estimated using the notched-noise method at center frequencies of 1000, 1259, 1585, and 2000 Hz. These were the frequencies that were used for the targets in the second stage of the experiment. In the second stage, low-pass filtered white noise was presented continuously. On each trial, a cue tone was presented at one of the four possible target frequencies. The specific frequency was selected randomly on each trial. This was followed by two observation intervals during one of which a further sinusoidal tone was presented. This tone was either a target (the same as the cue frequency) (on 60% of trials), or had one of four possible probe frequencies corresponding to that target. The four probe frequencies were chosen to correspond to specific points on the estimated response curve of the auditory filter centered at the target frequency. The percentage of correct detections of a given probe was compared with that obtained in a separate condition where the frequency of the tone was fixed throughout, the cue frequency always equaled the target frequency, and the target was attenuated by an amount corresponding to the attenuation of the auditory filter at the probe frequency. Two subjects with normal hearing and two subjects with unilateral cochlear hearing loss were used. Comparison of the results for the normal and impaired ears suggests that the detectability of the probes is governed more by the selectivity of the auditory filters than by the ratios of the expected and probe frequencies. However, detection of the probes was generally better than would occur if subjects monitored the output of a single auditory filter centered at the target frequency.
Performance bounds on acoustic thermometry of ocean climate in the presence of mesoscale sound-speed variability
Authors: Krolik Jeffrey L. , Narasimhan Sunil
Published: October 2005

The ability to measure climatic changes in ocean temperature is fundamentally limited by the presence of mesoscale variability. Because ocean acoustic propagation can be used to measure the range-averaged temperature profile, long-range acoustic transmissions have been proposed as a means of filtering out mesoscale variability in order to measure a global warming related trend in mean temperature. In this paper, the Cramer–Rao lower bound (CRLB) on the estimation of the mean depth-dependent temperature profile given a single acoustic transmission is evaluated to provide an indication of the highest accuracy which could be achieved by this experiment. The CRLB derived here applies to broadband vertical arrays of arbitrary length and thus extends previous work. Evaluation of the bound is performed using models of sound-speed variability derived from real Pacific environmental data. Results indicate that the performance of an acoustic thermometry system is limited by mesoscale variability above a threshold value of observation–time–signal-to-noise ratio product and is acoustic noise limited below this threshold. Further, comparisons of the CRLB above this threshold suggest that for a 5000-km source–receiver separation, ATOC accuracy may vary from between 0.01 and 0.1 °C depending on the shape and uncertainty of the change in mean temperature profile.
Matched-field source localization in a range-dependent environment
Authors: Fawcett John A. , Yeremy M. L. , Chapman N. R.
Published: October 2005

In this paper source localization results obtained by matched-field (MF) processing of vertical line array (VLA) data from the PACIFIC ECHO III sea trial are presented. The experimental site was located in a region of significant bathymetric variation. An harmonic source was towed on a series of arcs, providing data for a sequence of different ranges and azimuths. In spite of the significant bathymetric variation, good MF localization results were obtained for a large fraction of the trial time. In the first part of this analysis it is assumed that the azimuth of the source is known. Substantial improvements in MF localization were obtained by using an adiabatic normal mode model to calculate replica acoustic fields for the range-dependent bathymetry. The improvement over the results obtained with flat-bottom waveguide replicas is demonstrated for data from the longer range arcs. In the second part of the analysis, the concept of environmental signal processing, an enhancement to MF processing that is obtained by making use of the complexity of the oceanic waveguide environment, is investigated. The azimuthal variation of bathymetry for the source tracks along the arcs was used to obtain estimates of the source bearing from the VLA data. In many instances, the bearing estimates were in reasonable agreement with the known source bearings.
Experimental results on bulk waves and Rayleigh waves in slate
Authors: Varadé A. , Bayón A. , Rasolofosaon P. N. J. , Gascón F.
Published: October 2005

This paper describes experimental results on velocity measurements of bulk and Rayleigh waves in a highly anisotropic natural medium (slate). Bulk waves velocities are measured using a standard ultrasonic pulse transmission setup. The Rayleigh waves are excited using the wedge technique and recorded by an interferometer which detects both the in-plane and out-of-plane components of the displacement they produce in a point of a sample surface. The experiments constitute part of a study of the propagation of surface seismic waves in anisotropic geological structures using scaled-down models. The elastic behavior of a block of slate whose faces are traversed by these surface waves is studied, and it is verified that this rock shows a good fit to a physical model of a solid with an axis of symmetry of revolution.
Examples of using structural intensity and the force distribution to study vibrating plates
Authors: Zhang Yong , Mann J. Adin
Published: October 2005

The influence of attachments and substructure on the vibration of a plate is a very important problem in noise and vibration control. This paper presents several examples of using an energy viewpoint with experimental data. The normal velocity of each plate, measured with a laser vibrometer or in some cases obtained from analytic calculation, is then used to calculate the structural intensity and force distribution. The structural intensity and force distribution are then used to locate single and double forces applied to a plate with some limitations. In addition, a rib attached to a plate and a constrained layer damping patch attached to a plate is studied. The energy absorbed by the rib and the force exerted by the rib in response to the waves incident on the rib are discussed. Results also show that a constrained layer damping patch is more effective in absorbing shear and bending vibrational energy than in absorbing twisting energy and that the damping patch does not apply a normal reaction force to the plate.
Modeling the vibration of a variable thickness ellipsoidal dish with central point clamp or concentric surface clamp
Authors: Lim C. W. , Kitipornchai S. , Liew K. M.
Published: October 2005

The vibration of shallow spherical and ellipsoidal dishes with variable thickness along the gradient from the apex is studied. The dishes are point-clamped at the apex or surface-clamped over concentric central regions which are modeled as singly and doubly connected domains, respectively. This model simulates domes, tank covers, radar dishes, or the antennas of certain communication satellites which are clamped over a finite region at the apex. The Ritz method is used to develop an efficient numerical procedure incorporating the boundary support characteristics intrinsically. Comparison with finite element and experimental results shows good consistency. Sets of useful vibration frequencies with additional mode shapes are presented to illustrate the capability of the method.
Flexural vibration in a finite piezoelectric hollow cylinder of class 6mm
Authors: Paul H. S. , Natarajan K.
Published: October 2005

In this study, the flexural vibration in a finite piezoelectric circular hollow cylinder belonging to crystal class 6mm is considered. Both the inner and outer curved surfaces and the end plane surfaces are free from traction and electric potential. Solutions for the mechanical displacements and the electric potential are derived in a series form. Boundary conditions on shear stress are satisfied exactly term by term in the series and the remaining boundary conditions are satisfied by an orthogonalization procedure. Numerical analysis is carried out for the piezoelectric ceramic PZT4. The natural frequencies are calculated for the circular modes one and two and presented graphically.
A genetic algorithm-based method for synthesis of low peak amplitude signals
Authors: Horner Andrew , Beauchamp James
Published: October 2005

The maximum amplitude of a waveform corresponding to a particular harmonic spectrum depends on the phases of its harmonic components. A waveform with a low peak-to-rms ratio is desirable in situations requiring a maximum signal-to-noise ratio. This paper introduces a genetic algorithm-based method for selecting the phases that produces better results than previously described methods. Results for four different amplitude spectra are given. For the case of a flat spectrum with up to 40 harmonics, the genetic algorithm finds peak factors (peak/√2 rms) ranging from 0.98 to 1.24.
Acoustic time-domain reflectometry for irregular surface recognition
Authors: Veysoglu M. E. , Cooke C. M.
Published: October 2005

The theoretical scattering of acoustic wave pulses from irregular surfaces is studied by using time-domain analysis. The purpose has been to examine the application of acoustic time-domain reflectometry (ATDR) to the nondestructive testing of surface geometry characteristics. A finite-difference time-domain (FDTD) simulation method is used to obtain the reflected wave response from irregular surfaces to an incident short pulse by calculating the scattered field and determining the net pressure at an acoustic sensing transducer. Various configurations pertinent to nondestructive testing of irregular surfaces are considered and the relationships between the transducer output waveform and the surface features are investigated. A strong correlation between the pulse width of the reflected pulse and the surface roughness is established for important configurations of interest. Results are determined for a range of surface conditions extending from the Kirchhoff limit where single scattering approximation is accurate to cases where complex multiple scattering effects become important. Conditions for departure from the single scattering limit are identified from simulations.
Travel-time perturbations due to internal waves: Equivalence of modal and ray solutions
Authors: Traykovski Peter
Published: October 2005

In a recent paper, Lynch et al. used modal and ray based perturbation techniques to compare predicted variances of acoustic travel times due to internal waves to measured variances in the Barents Sea Polar Front experiment [Lynch et al., J. Acoust. Soc. Am. 99, 803–821 (1996)]. One of the interesting results of this work is that the modal and ray travel-time variances are substantially different for rays and modes with the same grazing angle. Specifically, the maximum modal travel-time variance shows a resonant effect in which the variance increases with increasing frequency. Unlike the modal solution, the ray travel-time variance has a geometrically constrained maximum, independent of frequency. In this paper, the linear first-order solutions for the ray and modal variances due to the internal waves are reviewed, and in an Appendix the effects of the linearizing assumptions are examined. The ray and mode solutions are then shown to be consistent by considering a truncated sum of modes that constructively interfere along a geometric ray path. By defining the travel-time perturbation due to a truncated sum of modes, the travel-time variance of the modal sum is derived. With increasing frequency the maximum value of this variance converges to a frequency-independent result with a similar magnitude to the ray maximum variance.
Left–right asymmetry in the buildup of echo suppression in normal-hearing adults
Authors: Grantham D. Wesley
Published: October 2005

Echo threshold is that critical delay of a lagging signal (the echo) at which the echo is ‘‘suppressed’’—i.e., at which one rather than two events is perceived. It has recently been shown that echo threshold increases in most subjects when they are exposed to a train of redundant information prior to the test stimulus presentation—that is, there is buildup of echo suppression in the presence of the preceding train [Clifton et al., J. Acoust. Soc. Am. 95, 1525–1533 (1994)]. The present investigation measured echo threshold in 25 normal-hearing adult subjects, both for isolated (baseline) test stimuli and for test stimuli preceded by a redundant train of stimuli (buildup conditions). The test stimulus was a 4-ms wideband noise burst pair, in which the lead burst was presented from either the left or right side (from near −45° or near +45° in different runs), and the lag burst was presented from the opposite side. Echo delay was varied adaptively, and the subject’s task was to indicate on each trial which of two alternative positions (separated by 20°) the lag source was presented from. Average echo threshold in the baseline condition was 11.2 ms (in agreement with previous results) and did not depend on whether the lead burst was on the subject’s left or right side.

Average echo threshold in the buildup conditions was significantly elevated. Interestingly, there was a significantly greater buildup effect when the lead stimulus came from the subject’s right side (average echo threshold: 24.4 ms) than when it came from the left side (average: 18.8 ms). This result agrees with informal observations made by Clifton and Freyman [Percept. Psychophys. 46, 139–145 (1989)] and suggests that there is more effective suppression of echo information when the lead stimulus originates from the right side (i.e., the side contralateral to the typically dominant hemisphere) than when it originates from the left side. The distribution of the magnitude of buildup effects across subjects (i.e., echo threshold in the presence of the train minus baseline echo threshold) was unimodal and symmetric, both for lag source on left (mean: 14.1 ms) and for lag source on right (mean: 6.7 ms). These results are discussed in relation to other hearing asymmetries that have been reported.
Decay in the effect of vibrotactile masking
Authors: Makous James C. , Gescheider George A. , Bolanowski Stanley J.
Published: October 2005

Vibrotactile forward masking experiments were conducted on the thenar eminence of the hand to determine the time course of masking in the Pacinian (P) or a non-Pacinian (NP I) channel. Brief masking and test stimuli that contained energy centered either below 27 or at 500 Hz were used to preferentially activate the NP I or P channels, respectively. Test thresholds were measured at different fixed delays (Δt) between the masking and test stimuli that ranged from 5 to 995 ms. Masking stimulus level was also varied from 5 to 25 dB above threshold. The masking effect followed an exponential decay with different time constants for each of the channels, but a similar asymptote (residual masking) for both channels. At the higher masking stimulus levels, the time constant for the P channel was about 40 ms, while the time constant for the NP I channel was about 100 ms. Residual masking in both channels increased about 1 dB for every 5-dB increase of masking stimulus level.
Phonemic restoration and integration during dichotic listening
Authors: Eimas Peter D. , Tajchman Gary , Nygaard Lynne C. , Marcus David J.
Published: October 2005

In a series of experiments, evidence was obtained for phonemic restoration when a word with the segment /s/ excised and replaced by silence and a comparable noise segment were presented dichotically. What has been called phonemic integration was also demonstrated by presenting the excised /s/ and the word with the /s/ removed and replaced by silence dichotically. Phonemic restoration and integration effects tended to be enhanced when barely audible versions of the excised /s/ or noise segment replaced the silence. Finally, phonemic integration was obtained when words with an excised CV syllable or VC rime were presented dichotically together with the remainder of the word.
Frequency discrimination and speech recognition by patients who use the Ineraid and continuous interleaved sampling cochlear-implant signal processors
Authors: Dorman Michael F. , Smith Luther M. , Smith Michael , Parkin James L.
Published: October 2005

Patients who use the Ineraid cochlear implant were tested in four experiments with materials which assessed frequency discrimination and speech understanding. In each experiment both frequency discrimination and speech recognition varied among patients. Correlations between the two measures were significant and ranged from 0.60 to 0.83. Most generally, frequency discrimination was better in the frequency domain of F1 than in the domain of F2. In experiment 5, both the Ineraid signal processing strategy and a continuous interleaved sampling (CIS) strategy were implemented for a single patient. The CIS strategy improved frequency discrimination in the domain of F2 and improved speech understanding.
A stroboscopic study of lip vibrations in a trombone
Authors: Copley David C. , Strong William J.
Published: October 2005

The purpose of the present study was to obtain detailed photographic sequences and lip motion data on which lip models for brass instruments may be more accurately based. The study expands upon an earlier study by Martin [J. Acoust. Soc. Am. 13, 305–307 (1942)] by using advanced fiber-optic stroboscopy, a real instrument mouthpiece, and by studying two dynamic levels. The trombone was selected as representative of the brass family because its relatively large mouthpiece permitted the use of an optic probe. Lip motion was observed from the front and side for six notes (Bflat2, F3, Bflat3, D4, F4, Aflat4) played at loud and soft dynamic levels. The video sequences were used to obtain information on lip opening area, lip motion perpendicular to airflow, and lip motion parallel to airflow. The data are tabulated and represented in graphic form.
Vorticity characteristics of the vibrational intensity field in an actively controlled thin plate
Authors: Tanaka Nobuo , Snyder Scott D. , Hansen Colin H.
Published: October 2005

It is the purpose of this paper to elucidate quantitatively the generation mechanism of structural intensity patterns induced in an actively controlled thin plate vibrating harmonically in a steady state. Particular emphasis is placed upon the vortex-type intensity response pattern, which has a potential for confining the vibration power into a specific area of the plate. First, a formulation is developed for minimizing structural kinetic energy with active vibration control on a planar structure. The results are used to develop expressions for vibration intensity in the controlled structure, which are then used as the basis for investigating intensity distributions in an actively controlled rectangular panel excited harmonically. It is shown that when a vortex pattern exists, the plate response is dominated by two vibration modes. The vibration intensity field associated with these two vibration modes is defined, and both an approximate energy stream function and a vortex function are derived. It is shown that the vibration intensity vector is tangential to the contour of the approximate energy stream function, and that fundamental characteristics such as the number and direction of the vortices can be determined from the approximate energy stream function. Finally, it is found that the major vortex with multiple subvortices inside appearing in the structural intensity field is a derivative or an image of subvortices, and does not carry the characteristics of the vortex from the viewpoint of fluid dynamics.
Three-component recording of ultrasonic transient vibration by optical heterodyne interferometry
Authors: Bayón A. , Rasolofosaon P. N. J.
Published: October 2005

The generation and detection of elastic waves by photoelastic methods, called ‘‘laser ultrasonics,’’ is now a rather commonly used method in research. The aim of this paper is to adapt an existing method, based on laser speckle interferometry, in order to record the three components of transient vibration induced by an ultrasonic wave at a point on the surface of a solid model. A detailed description of the method is given. The reliability of the method is experimentally demonstrated. As an illustration, maps of the local three-dimensional transient vibration and of the particle trajectories of different points at the surface of a solid are reported.
Experimental observation of elastic-wave dispersion in bounded solids of various configurations
Authors: Kwun H. , Bartels K. A.
Published: October 2005

Dispersion characteristics of multiple longitudinal modes of elastic-wave propagation in bounded solids of various configurations were observed using a simple and efficient experimental technique. The technique involves (1) transmitting a short elastic-wave pulse into the material using a noncontacting magnetostrictive sensor (MsS), (2) detecting transient waveforms of the transmitted wave using another MsS, and (3) performing time-frequency analysis on the detected signals using the short-time Fourier transform (STFT). Data acquired from a solid cylinder, cylindrical tube, square rod, reinforcing rod, and seven-wire strand are given and discussed based on known theories.
The influence of microphone vents on measurements of acoustic intensity and impedance
Authors: Li Jing-Fang , Pascal Jean-Claude
Published: October 2005

The pressure equalization vents of conventional microphones introduce bias errors in measurements of the sound intensity. Two error terms in the estimated active intensity are derived using a low-frequency model of microphone. The first error term is associated with the lower-limiting frequency of the microphones (1 to 2 Hz) and is proportional to the reactive sound intensity. It is shown here that the difference between limiting frequencies of the two microphones causes the second error term to be proportional to the mean-square pressure and to be of comparable importance at low frequencies. The amplitudes of errors due to the vents are analyzed in a quasistanding wave. Unlike the first error, the second can be corrected at the same time as the phase error between measurement channels, and several correction techniques are examined. For the error proportional to the reactive intensity, a correction method in a standing wave tube is suggested, using the joint measurement of several other energetic quantities. Examples of the influence of these errors on typical parameter values for half-inch microphones are presented in the case of measuring the acoustic impedance of materials using a two-microphone probe.
Acoustics in long enclosures with multiple sources
Authors: Kang Jian
Published: October 2005

The subject of this paper is long enclosures, where one dimension is much greater than the other two, although the other two are still relatively large compared to the acoustic wavelength. A computer model is given for calculating the acoustic indices in long enclosures with multiple sources. Calculations in two long enclosures show that the reverberation at a receiver can be significantly increased by adding sources beyond a single source and could be decreased by adding sources between a single source and the receiver. The efficiency of reducing the reverberation of multiple sources by more absorption and directional sources is analyzed. It is also demonstrated that for a multiple loudspeaker public address system, depending on room and loudspeaker conditions, there is an optimal loudspeaker spacing for the speech transmission index (STI).
Validation of a diffraction correction model for through-transmission substitution measurements of ultrasonic absorption and phase velocity
Authors: Zeqiri Bajram
Published: October 2005

A systematic study has been undertaken of the influence of diffraction on ultrasonic absorption coefficient and phase velocity measurements made using the through-transmission substitution technique. A diffraction correction model dealing explicitly with the interaction of the sample with the plane- and edge-wave components of the acoustic field of a piston transducer is introduced. The National Physical Laboratory ultrasonic materials characterization facility has been used to validate the model using a pulsed technique covering the frequency range 1–15 MHz. In the validation, absorption coefficient and phase velocity measurements are presented for test specimens of cross-linked polystyrene of various thickness. Strong diffraction effects have been demonstrated in the measurements, particularly for the absorption coefficient where measured values can be typically a factor of 2–3 higher than plane-wave values. Excellent agreement is demonstrated between theory and measurement for both absorption and phase velocity under a wide range of measurement conditions.
Effects of aging on the fine structure of the 2f1−f2 acoustic distortion product
Authors: He Ning-ji , Schmiedt Richard A.
Published: October 2005

The fine structures of 2f1−f2 acoustic distortion products (ADP) were measured in four groups of human subjects: (1) young with normal hearing, (2) aged with normal or near-normal hearing, (3) aged subjects with more severe hearing loss above 2000 Hz, and (4) young with hearing similar to those of the normal- or near-normal-hearing aged group. The purpose of this study was to investigate how ADP fine structure changes with age and hearing loss. Results show that the fine structure is observable whenever the ADP is measurable, and its sharpness, defined as the peak-to-peak frequency distance, is independent of age, hearing loss, and longitudinal amplitude change. There is a larger variance in ADP peak amplitudes in aged subjects with or without hearing loss as compared to young normal-hearing subjects, the aged group generally having lower peak amplitudes than those of the young group. According to an ANOVA analysis with absolute threshold as covariate, the null hypothesis stating that there is no aging effect on the ADP peak responses cannot be ruled out, a conclusion similar to that made by Stover and Norton [J. Acoust. Soc. Am. 94, 2670–2681 (1993)]. On the other hand, threshold changes cannot explain all the differences in ADP amplitude. It is clear that the relationship between ADP amplitudes and behavioral thresholds can differ between young and aged populations. At primary levels of 50 dB SPL, almost normal ADP magnitudes are often found in aged subjects even when associated with a 35-dB hearing loss, whereas for young subjects ADPs typically were not measurable when associated with the pure-tone thresholds of 20 dB HL or higher. This dichotomy may be explained by the different etiologies of the cochlear pathologies predominant in the two groups.
The ratio of elastic moduli of cochlear outer hair cells derived from osmotic experiments
Authors: Ratnanather J. Tilak , Zhi Man , Brownell William E. , Popel Aleksander S.
Published: October 2005

Outer hair cells (OHCs) were subjected to three different hypo-osmotic challenges which induced shape changes in OHCs. The longitudinal and circumferential strains, εz and εc, respectively, were extracted from a morphometric analysis of video images of the cells. A value of εz/εc=−0.72 was obtained and was found to be independent of the applied osmotic gradient. Using an elastic isotropic membrane model for the OHC lateral wall, the ratio of the elastic shear modulus μ to the elastic area expansion modulus K was calculated yielding a value of 0.054. The contribution of this ratio to OHC mechanics is discussed.
Long-term adaptation in cat auditory-nerve fiber responses
Authors: Javel Eric
Published: October 2005

Driven responses of cat auditory-nerve fibers to long-duration characteristic-frequency (CF) tones could decrease substantially over time periods ranging from seconds to minutes. In extreme cases, the discharge rate could fall below the pre-stimulation spontaneous rate (SR). Reductions in response were characterized by two processes, each of which followed a decaying exponential function. Long-term adaptation affects the discharge rate in the first several seconds following stimulus onset. The average amount in high-SR fibers was 42.5% for tones at 20–40 dB SL, and the mean time constant was 3.64 s. Long-term adaptation increased significantly with sensation level (SL, or level above threshold), decreased with SR, and was not significantly correlated with CF or fiber response threshold. Time constants did not depend on CF, SR, or SL. Very-long-term adaptation refers to further, smaller reductions in the discharge rate that accumulate over a period of minutes. Fiber responses formed two groups. The larger group adapted with a mean time constant of 45.22 s for CF tones at 20–40 dB SL, and the smaller group did not adapt over very long terms.

Considerable variability in amounts of long-term and very-long-term adaptation was observed in similarly tuned fibers from the same ear. This suggests that long-term effects do not arise from cochlear mechanics or middle ear muscle activity. No long-term effects were observed in responses of fibers directly stimulated by high-intensity electrical pulses presented at rates up to 500/s through a cochlear implant. This suggests that the effects do not arise from fundamental differences in spike-generating properties of spiral ganglion cells. The data suggest that long-term adaptation may occur either when neurotransmitter utilization at inner hair cell synapses exceeds the rate at which it is replenished from global stores or uptake mechanisms, or when metabolic resources influencing neurotransmitter release become depleted. The neural data are related to perceptual findings in human listeners, in which unusually large amounts of tone decay may be observed at high frequencies, and they indicate that the perceptual effects originate peripherally.
Acoustical resonances of assorted ancient structures
Authors: Jahn Robert G. , Devereux Paul , Ibison Michael
Published: October 2005

Rudimentary acoustical measurements performed inside six diverse ancient structures revealed that each sustained a strong resonance at a frequency between 95 and 120 Hz, despite major differences in chamber shapes and sizes. The resonant modal patterns all featured strong antinodes at the outer walls, with appropriately configured nodes and antinodes interspersed toward the central source. In some cases, interior and exterior rock drawings resembled these acoustical patterns. Since the resonance frequencies are well within the adult male voice range, one may speculate that some forms of human chanting, enhanced by the cavity resonance, were invoked for ritual purposes.
Acoustic scattering from a rough circular disk
Authors: Jansson Per-Åke
Published: October 2005

Scattering of an acoustic wave from a thin rough circular disk is studied using an integral equation method. The T matrix (transition matrix), which governs the relation between the incident and scattered fields, is determined using an integral representation of the Helmholtz equation. The rough surface is modeled by a superposition of a number of sinusoidal surfaces that are randomly translated and rotated with respect to each other. Some numerical results for the scattered field are presented in the case of an incident plane wave. One conclusion is that the amplitude of the backscattered field is not only dependent on parameters like frequency, angle of incidence, and overall characteristics of the surface like rms height and correlation function. The exact geometry of the rough object is also vitally important for its scattering properties, which implies that a statistical approach to the problem is of limited value.
Radiation force on a spherical object in an axisymmetric wave field and its application to the calibration of high-frequency transducers
Authors: Chen Xucai , Apfel Robert E.
Published: October 2005

The general formulation for the radiation force on a spherical object in an axisymmetric acoustic field is provided. The sphere is described in general by three parameters: its density, compressional wave speed, and shear wave speed. Other types of spheres, including the rigid and immovable sphere and the infinitely soft sphere (void), are treated as limiting cases. Specialized formulations of the radiation force function are provided for several types of incident waves of common interest. A low-frequency expansion for each case is provided for comparison with results from the literature. Among the solutions provided are the scattering function of an elastic sphere in a focused acoustic field and the radiation force on the sphere. The radiation force function is used to calibrate high-frequency transducers. Experimental data are provided for a focused transducer for frequencies up to 10 MHz, where the size of the elastic sphere is comparable to or larger than the −3-dB beamwidth of the sound field.
Radial wave thermoacoustic engines: Theory and examples for refrigerators and high-gain narrow-bandwidth photoacoustic spectrometers
Authors: Arnott W. Patrick , Lightfoot Jay A. , Raspet Richard , Moosmüller Hans
Published: October 2005

A theoretical analysis of radial wave thermoacoustic engines in cylindrical resonators is developed. Impedance and pressure translation equations are presented for open sections of the resonator and for heat exchangers. Coupled first-order differential equations are given for pressure and impedance in the temperature gradient supporting engine section (stack). These quantities are used to calculate heat and work flows and to predict engine performance. Theory and design of a variable quality factor resonator for enhanced photoacoustic spectroscopy are presented. The short stack approximation is developed for the radial geometry and is used along with plane-wave equations to compare refrigerator performance for these two geometries. Results of the comparison are that engines in the plane-wave geometry are better overall refrigerators when maximizing the coefficient of performance and cooling capacity together.
Comparison of measured and predicted lateral distribution of sonic boom overpressures from the United States Air Force sonic boom database
Authors: Lee Robert A. , Downing J. Micah
Published: October 2005

In 1987 the United States Air Force (USAF) collected the lateral distribution of sonic booms produced by 43 supersonic flights of military aircraft near Edwards Air Force Base (EAFB). These flights were accomplished using eight different aircraft at several Mach number and altitude combinations. The flights were planned for steady and level operation, but unsteadiness and maneuvering in some of the flight profiles caused variability and focusing of the propagated booms along the lateral measurement array. The full sonic boom waveforms collected during this study are included in a digital database, BoomFile, which is accessible to researchers. The database also includes the aircraft tracking and local weather profiles. A comparison of the measured to predicted peak overpressures along the lateral spread of the boom carpet demonstrates the results from this study agree as expected with previous sonic boom studies. The measurements are compared with predictions calculated by Carlson’s simplified sonic boom model and a sonic boom ray tracing model. The analysis demonstrates that, in general, the predictions are in good agreement with the measured data, but the models overestimate the overpressures as the lateral cutoff is approached. Moreover, the comparison reveals that Carlson’s method is a robust tool for predicting sonic booms produced by nonmaneuvering flights.
Theoretical model of in-plane scatter from a smooth sediment seabed
Authors: Hines Paul C.
Published: October 2005

The author has previously reported [J. Acoust. Soc. Am. 88, 324–334 (1990)] on a model for acoustic backscatter from the volume beneath a smooth sediment seabed. In the present paper, the model is generalized to an in-plane scattering model such that the source and receiver need not be colocated but must lie in the same vertical plane. In the model, scattering is caused by fluctuations in sediment porosity. The model allows for penetration of the incident wave into the bottom at subcritical grazing, and retransmission of scattered spherical waves through the (planar) interface. The frequency and grazing angle dependence of the acoustic scatter are determined primarily by the correlation function of the porosity fluctuations, whereas the magnitude of the scatter is controlled by the porosity variance. Results are obtained from the model over the frequency band 5–200 kHz, for a variety of incident and scattered grazing angles, using two sample porosity correlation functions. The first is an exponentially decaying correlation function and the second is a point scatterer correlation function. The results obtained illustrate the significance of the correlation function in determining the scattering strength of the bottom volume.
Multifilament source model for short-range underwater acoustic problems involving penetrable ocean bottoms
Authors: Murphy Joseph E. , Li Gongqin , Chin-Bing Stanley A. , King David B.
Published: October 2005

Accurate numerical solutions generated with a new computational model are presented for several range-dependent underwater acoustic problems involving penetrable ocean bottoms. The multifilament source model [Boag et al., ‘‘Analysis of acoustic scattering from fluid cylinders using a multifilament source model,’’ J. Acoust. Soc. Am. 83, 1–8 (1988)], originally developed to treat acoustic scattering by arbitrarily shaped cylinders embedded in an infinite medium, has been extended to solve short-range ocean acoustic problems. Source model solutions for two different range-dependent problems agree with solutions that were obtained with Evans’ COUPLE model [R. B. Evans, ‘‘A coupled mode solution for acoustic propagation in a waveguide with stepwise depth variations of a penetrable bottom,’’ J. Acoust. Soc. Am. 74, 188–195 (1983)]. These comparisons demonstrate the source model’s ability to describe propagation in a shallow water environment with rapidly varying bathymetry and a lossy, penetrable bottom.