bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffraction from the juncture of pressure release and locally reacting half-planes
Authors: Dahl Peter H. , Frisk George V.
Published: October 2005

Solutions to two coupled half-plane problems are derived. In the first, an exact solution to the canonical problem of acoustic plane-wave diffraction from a pressure release (zero impedance) surface coupled to a perfectly rigid (infinite impedance) surface is given using the Wiener–Hopf method. The solution is expressed in terms of an angular spectrum of plane waves. In the second, the rigid surface is replaced by one characterized by a locally reacting finite impedance. Here, an approximate kernel to the Wiener–Hopf functional equation is used which leads to a complete and readily interpretable solution. This solution is expressed in terms of the canonical angular spectrum for the first problem multiplied by a function that depends on material parameters of the locally reacting surface. Polar plots of the far-field amplitude level for the diffracted field are presented.
The iterative time reversal mirror: A solution to self-focusing in the pulse echo mode
Authors: Prada C. , Wu F. , Fink M.
Published: October 2005

Accurate focusing in an inhomogeneous medium is difficult to implement. In order to focus on a reflective target we have extended the concept of optical phase-conjugate mirrors, valid for monochromatic signals, to broadband pulses such as those used in ultrasound echography. The transducer’s linear response to the acoustic pressure allows one to replace the phase conjugation by a time reversal operation on the pulse echo signals. The time reversal mirror is an array of transmit–receive transducers. A first incident wave is reflected by the target. The received signals are stored in shift registers, reversed in time, and then reemitted. The main advantage of this process is that waves distorted by the propagation through an aberrating medium are corrected by the mirror operation and the back propagation through the medium. When the medium contains several reflectors, this time reversal process can be iterated in order to focus on the most reflective one. We present theoretical results on this principle, numerical simulations, and experimental results with a 1-D array working at a central frequency of 3 MHz.
A model reference approach for implementing active structural acoustic control.
Authors: Clark Robert L. , Fuller Chris R.
Published: October 2005

A model reference active structural acoustic control (ASAC) approach is investigated as a method for replacing microphone error sensors located in the acoustic field with accelerometers located on the structure. The suggested controller is the multi-input/multi-output adaptive LMS algorithm. As opposed to driving the response of the sensor located on the structure to zero with the control inputs, the response is driven to some predetermined ‘‘reference’’ value corresponding to a cost function which originally implemented microphones or the supersonic region of the wave-number transform as error information. In effect, the uncontrolled structure is adaptively modified to behave like the reference structure. Results indicate that the identical optimal control solution can be obtained when implementing the structural sensors, and the required number of sensors must simply equal the number of control actuators. In addition, for the example studied here, significant reduction in far-field sound radiation can be achieved even when errors of ±5% are present in the reference model. A considerable level of attenuation in sound can also be achieved for a band of frequencies within ±5% of the reference frequency used to obtain the models for creating the disturbance. Thus it appears that the model reference approach is reasonably robust. [Work supported by ONR/DARPA.]
Experimental and theoretical evaluation of outdoor noise barriers including
propagation effects.
Authors: Daigle G. A. , Gabillet Y. , L’Esperance A.
Published: October 2005

This paper compares the performance of a restricted number of barrier shapes and types under controlled experimental conditions and describes theoretical models. In particular, the attenuation of absorbent barriers on ground, of finite length barriers on the ground, of parallel noise barriers, of earth berms, as well as the effects of atmospheric conditions on barrier performance outdoors are briefly reviewed. An absorbent barrier is obtained when a thin barrier is covered with absorbent material, on the source or receiver side, or both. The attenuation provided by a partial barrier is complicated by additional ray paths. Parallel barriers can degrade the performance of the single barrier; however, absorbent material can be used to recover the loss in performance. Earth berms covered with grass are particularly effective barriers at higher frequencies, however, atmospheric turbulence places a limit on the amount of attenuation achieved outdoors. At longer distances, barrier performance is degraded during an inversion or downwind propagation. The results of new theory based on the method of summation of Gaussian beams to model the diffraction of a screen on the ground in the presence of downward refraction are described and are compared with controlled measurements. [Work supported by DRET.]
The processing of envelope information in comodulation masking release (CMR) and envelope discrimination
Authors: Fantini Deborah A.
Published: October 2005

In comodulation masking release (CMR), thresholds for a signal masked by a narrow-band noise are reduced when additional noise is present. To demonstrate CMR, the additional noise must have similar amplitude envelope fluctuations over time as the primary noise band masking the signal. The specific source of information that provides the reduction in masked threshold remains unclear, although it is the focus of recent interest. The envelope of the on-frequency masking band (OFB) changes with the addition of the signal at threshold; in the present work, the importance of these changes in providing the CMR has been investigated. First, CMR thresholds were collected in sinusoidally amplitude-modulated noises which varied either in the phase relationship of their envelopes or in their modulation depth. Then envelope discrimination (ED) thresholds were collected for changes in envelope phase disparity (i.e., envelope correlation) and for changes in modulation depth per se. The patterns of CMR thresholds with envelope phase disparity and with modulation depth are not similar to those of the ED thresholds. A computer simulation was conducted in which the stimulus waveforms were processed through an auditory model which comprised bandpass auditory filters, a square-law nonlinearity, and a sliding temporal window. The envelopes were then extracted from the processed waveforms to determine whether the envelope changes that occur in the signal intervals in the CMR and ED tasks may be similar. The results of this analysis indicate that discriminability of envelope correlation due to the addition of the signal at threshold in the CMR task was insufficient to explain CMR. However, the discriminability of changes in modulation depth due to the addition of the signal is in agreement with thresholds obtained from the CMR task.
Constrained-layer damping analysis for flexural waves in infinite fluid-loaded plates
Authors: Dubbelday Pieter S. , Fausett Laurene V.
Published: October 2005

In an early model by Kerwin [J. Acoust. Soc. Am. 31, 952–962 (1959)] for constrained-layer damping (CLD) of flexural waves in an infinite plate, the attenuation factor was expressed in terms of the material and geometric parameters of the three constituting layers, thus facilitating optimization studies. The Kerwin model is limited to flexural waves in thin plates and does not account for fluid loading. To remedy these restrictions, the model was extended in an earlier study [P. S. Dubbelday, J. Acoust. Soc. Am. 80, 1097–1102 (1986)] while maintaining an explicit algebraic relation between the attenuation constant and the physical and geometric parameters typical of the Kerwin model. To establish the correctness of the modification, a hybrid model was developed that treats the base plate by exact elasticity theory while describing the effect of the two additional layers according to the Kerwin model. An analysis based on applying exact elasticity theory to all three layers, with fluid loading on either or both sides, is described. The influence of fluid–plate interaction on damping efficiency is discussed. The various models are compared and discrepancies noted. The hybrid and exact models necessitate finding complex roots of transcendental equations by numerical computation, thus losing direct insight into the effect of the parameters on the attenuation offered by an explicit algebraic expression, a major advantage of the Kerwin model. It is concluded that the extended Kerwin model is quite useful for optimization of the CLD technique. However, a check by means of the hybrid or exact models may be necessary in view of the limitations of the extended Kerwin model.
The effect of frequency-selective attenuation on the speech-reception threshold of sentences in conditions of low-frequency noise
Authors: van Dijkhuizen Janette N. , Festen Joost M. , Plomp Reinier
Published: October 2005

Within a study on the merits of a multichannel automatic gain control in hearing aids, the effect of frequency-selective amplification on the masked speech-reception threshold (SRT) for sentences is measured in conditions of seriously disturbing low-frequency noise, with the effect of wideband amplification as a reference. Speech and noise are both spectrally shaped according to the bisector line of the listener’s dynamic-range of hearing, but with the noise in a single octave band (0.25–0.5 or 0.5–1 kHz) increased by 20 dB relative to this line. The increase of noise level is steady state in the first experiment, and time varying in the second experiment. Results for 12 normal-hearing and 12 hearing-impaired listeners indicate that, in both experiments, frequency-selective compression of the signal in the octave band with the 20-dB increase of noise is more beneficial than wideband compression. For the hearing-impaired group, wideband compression does not give any systematic change in intelligibility. Frequency-selective compression in steady-state conditions may, for both groups of listeners, give a decrease of masked SRT (relative to a condition without compression) of up to 4 dB for a compression factor of 100%. Roughly comparable effects are seen for frequency-selective compression in time-varying conditions. The superiority of frequency-selective over wideband compression is attributed to a more effective reduction of upward spread of masking.
Short pulse sound-wave scattering from variously arranged multiple rigid flat strips in a fluid.
Authors: Carin L. , Felsen L. B.
Published: October 2005

In a companion paper (Felsen etal., previous paper), short pulse (SP) plane-wave sound scattering from an infinite plane periodic array of rigid flat strips in a fluid is analyzed via an observable-based parametrization (OBP) that highlights the temporal evolution of the global effects of periodicity from initially well-resolved local multiple scatterings. This temporal buildup is explored here further by treating directly a finite number of strips that may be noncoplanar and have unequal size and spacing. Such a model allows study of the physical size of the local environment that suffices to simulate the effects of infinite global periodicity, and it also permits assessment of how deviations from periodicity deteriorate the wave behavior of the ideal strictly periodic configuration. The reference solution is generated via the frequency domain from a multiple scattering integral equation algorithm implemented numerically by moment methods and novel asymptotics. The resulting data are then interpreted and reconstructed by TD-OBP that homes in directly on observed features in the scattered signal. Parametric studies, associated with wave-oriented signal processing in a phase space, furnish insight into the wave phenomena operative under the stated conditions. [Work supported by ONR.]
Scattering by a finite baffled thin elastic cylindrical shell: Theory and experiment.
Authors: Schreppler Stephen C. , Maxwell J. W.
Published: October 2005

The far-field scattering by a finite baffled thin elastic cylindrical shell was investigated from a theoretical standpoint using the solution outlined by Lyamshev [Sov. Phys. Dokl. 2, 332–335 (1957)]. The Lyamshev solution of the elastic equations of motion with fluid-loading impedance for a finite cylindrical shell is based on a modal series. Numerical evaluation of the solution was made using the fluid-loading impedance for a finite and infinite shell and monostatic geometry. The calculations are compared to experiment for 5.0<ka<13.0, L/a =11.75, and h/a=0.01, where k is the acoustic wave number, a is the mean shell radius, L is the shell length, and h is the shell thickness. The solution accurately confirms the membrane loci of Rumerman [M. L. Rumerman and Stephen C. Schreppler (previous abstract)] and the ‘‘aperture effects’’ observed in the experiment.
Evaluation of an adaptive beamforming method for hearing aids
Authors: Greenberg Julie E. , Zurek Patrick M.
Published: October 2005

In this paper evaluations of a two-microphone adaptive beamforming system for hearing aids are presented. The system, based on the constrained adaptive beamformer described by Griffiths and Jim [IEEE Trans. Antennas Propag. AP-30, 27–34 (1982)], adapts to preserve target signals from straight ahead and to minimize jammer signals arriving from other directions. Modifications of the basic Griffiths–Jim algorithm are proposed to alleviate problems of target cancellation and misadjustment that arise in the presence of strong target signals. The evaluations employ both computer simulations and a real-time hardware implementation and are restricted to the case of a single jammer. Performance is measured by the spectrally weighted gain in the target-to-jammer ratio in the steady state. Results show that in environments with relatively little reverberation: (1) the modifications allow good performance even with misaligned arrays and high input target-to-jammer ratios; and (2) performance is better with a broadside array with 7-cm spacing between microphones than with a 26-cm broadside or a 7-cm endfire configuration. Performance degrades in reverberant environments; at the critical distance of a room, improvement with a practical system is limited to a few dB.
Poisson’s ratio of foamed aluminum determined by laser Doppler vibrometry
Authors: Dubbelday Pieter S.
Published: October 2005

Foamed aluminum is a promising candidate in hydroacoustics as a possible pressure-release material. Previously, the measurement of its dynamic shear modulus has been reported for various densities and pore sizes of the material, [Proc. IEEE, 1985 Ultrasonics Symp. 2, 1052–1055 (1985)]. In an attempt to complete the characterization of the material, its Young’s modulus and Poisson’s ratio were measured by means of laser Doppler vibrometry. The lowest value for the ρc product found was 0.20 SI Mrayl, about 15% of the ρc product of water. Some of the samples appear to be anisotropic. An attempt was made to measure the five compliance coefficients of one foamed-aluminum type that follow from assuming uniaxial symmetry. The results did not conform to the relationships pertinent to this type of symmetry.
On the similarity of two theories of comodulation masking release
Authors: Green David M.
Published: October 2005

It is observed that two theories of comodulation masking release (MR), namely, the envelope correlation theory and the equalization and cancellation theory, are nearly the same.
Evaluation and verification of bottom acoustic reverberation statistics predicted by the point scattering model
Authors: Alexandrou D. , de Moustier C. , Haralabus G.
Published: October 2005

The point scattering model offers a parameterization of the reverberation probability density function (pdf) in terms of the coefficient of excess (kurtosis) and a coherent component represented by a harmonic process with random phase. In this paper the potential utility of this parametrization is investigated in the context of seafloor characterization. The problem of separating out the effect of each parameter is discussed. Computer simulations are used to verify model predictions on the reverberation quadrature, envelope, and phase pdf. As part of the verification study, the scatterer density was determined from the kurtosis of the reverberation quadrature pdf. A statistical analysis of this procedure points to reduced estimate accuracy with decreasing kurtosis. Additional computer simulations show that the chosen pdf family, developed under the assumption of a Poisson scatterer distribution, is flexible enough to fit reverberation data generated by non-Poisson scatterer distributions exhibiting a degree of clustering or regularity. A computer experiment demonstrates how this parametrization can be used in conjunction with a simple sonar geometry to generate acoustic signatures for seafloor classification. In addition, real reverberation data collected by a Sea Beam sonar system in two different seafloor areas are interpreted according to the chosen parametrization.
Acoustical properties of symmetric multilayers
Authors: Martin B. G.
Published: October 2005

The theory of the acoustical properties of symmetric multilayers has been presented previously [Martin, J. Appl. Phys. 66, 1931(1989)], but no experimental results were included for the purpose of comparison. In the investigation discussed below, both calculated and experimental results are presented on the use of acoustical symmetric multilayers (ASMs) as antireflection (AR) coatings for a variety of coating and substrate materials. Results indicate that there is good agreement between calculation and measurement.
Explicit angular dependence of electroelastic effect of singly rotated extensional mode quartz resonators
Authors: Kittinger E. , Tichý J.
Published: October 2005

The theory of the field-induced change of the resonance frequency of piezoelectric extensional mode resonators based on the rotationally invariant nonlinear equations of electroelasticity as stated so far in the literature is formulated in a way that involves sums of a rather large number of terms. This fact is usually disguised by the compact notation allowed by the use of the Einstein summation convention. This form is well suited for numerical evaluation but is not easy to interpret in a general way for its obvious lack of transparence. Using the explicit expressions for the transformed material constants and purely algebraic treatment of these summations it will be shown in a completely rigorous way that the theory may be written in a considerably simplified form for the important case of quartz resonators singly rotated about the X axis. The very concise result is fairly transparent and allows direct comparison with the older phenomenological approach to this problem.
Barrier attenuation in terms of A-weighted sound exposure level
Authors: Makarewicz Rufin
Published: October 2005

This paper considers the traffic noise attenuation produced by a very long barrier, which is described in terms of A-weighted sound exposure level. The exact solution can be obtained by numerical integration. A simple expression is derived that approximates the exact solution to within 1.5 dB. This expression allows prediction of the A-weighted sound exposure level and the time-average A-weighted sound level behind the barrier.
Exploiting sound absorption for target motion analysis
Authors: Dommermuth F. M.
Published: October 2005

Normally, sound level as a function of time originating from a target moving with constant (and, compared to the speed of sound, small) velocity, only permits the determination of angular velocity. However, sound absorption becoming important in the ultrasonic region can be exploited to estimate both target velocity and range. The theoretical estimation accuracy is investigated employing model assumptions of increasing complexity, including the exploitation of possibly available measurements of target bearing angle. The proposed procedures are applied to both simulated and real data.
A technique for ultrasonic tomography in anisotropic media
Authors: Kline R. A. , Wang Y. Q.
Published: October 2005

An iterative approach to ultrasonic tomography in anisotropic media is described. The method has been particularly developed for materials such as composites, when the origin of the anisotropy is known (e.g., reinforcing fibers). Using the equations governing wave propagation in anisotropic media and composite micromechanics theory, it is possible to develop a modified version of existing tomographic reconstruction algorithms (here ART) to account for the directional dependence of acoustic velocities in anisotropic media. Results from synthetic and experimental data are presented for a relatively simple test case of a unidirectionally reinforced composite sample with a nonuniform cure state in the matrix.
Asymmetric vibration of a heavily fluid-loaded circular plate using variational principles
Authors: Ginsberg Jerry H. , Chu Pearl
Published: October 2005

As an initial step in the extension of the surface variational principle (SVP) to an assumed modes analysis of vibratory displacement and surface pressure on submerged axisymmetric structures subjected to arbitrary nonsymmetric loading, the present study considers an arbitrary harmonic excitation of an elastic plate. Two configurations, in which the supporting baffle is a thin rigid disk or an infinite plane, are considered. Fourier series expansions of the azimuthal dependence of pressure and displacement are shown to be uncoupled, with each harmonic being governed by equations that are similar in form to those for the analogous axisymmetric problem. Recursion relations using coefficients developed in the course of solving the axisymmetric problem are shown to substantially expedite the evaluation of the additional azimuthal harmonics. Results for a force located at r=a/2 when ka=3.35, where a is the radius of the plate, are presented in terms of the radial variation associated with each harmonic, as well as overall surface distributions. It is shown that although some of the higher azimuthal harmonics contribute strongly to the surface response, the power radiated in these harmonics is negligible.
The state vector approach to the wave and power flow analysis of the forced vibrations of a cylindrical shell. Part I: Infinite cylinders in vacuum
Authors: Borgiotti Giorgio V. , Rosen Erik M.
Published: October 2005

The vibration induced by a time harmonic point excitation on an elastic circular cylindrical shell in vacuum and the power flow associated with it are analyzed by using a state vector technique. The forced vibration of the shell is identified by integrating a system of first-order differential equations satisfied by the state vector having ten components, five of them representing forces and moment resultants, and the other five representing linear and angular velocities at a shell location. The solution is expressed as a linear combination of ‘‘waveguide modes,’’ solutions of the source-free problem, periodic in the circumferential coordinate, which are either attenuating or propagating in the longitudinal direction. The shell model here used is based on the assumptions of a negligible normal radial stress and of a velocity vector varying linearly within the shell thickness and includes shear deformation and rotary inertia effects. The shell two-dimensional (2-D) intensity vector has a simple expression in terms of the components of the state vector. Propagating modes having different azimuthal numbers are orthogonal; the total power flow through the shell cross section is the sum of the individual power flows associated with each waveguide mode. Several numerical examples of vibrational velocity response to point forces and uniform rings of forces, having different directions, are presented. For a point force the longitudinal power flow associated with combinations of waveguide modes is calculated in the frequency range from (close to) zero to above the first ring resonance. The intensity vector is also calculated at various points of the shell.
Bayesian model selection and minimum description length estimation of auditory-nerve discharge rates
Authors: Mark Kevin E. , Miller Michael I.
Published: October 2005

Auditory-nerve fiber discharges are modeled as self-exciting point processes with intensity given by the product of a stimulus-related function and a refractory-related function. Previous methods of estimating these two functions, based on the maximum-likelihood principle, have the problem of estimating more parameters than the data can support. A new procedure, based on a Bayes criterion for choosing the complexity of the model in addition to estimating the parameters, solves the over-parametrization problem. This procedure is seen to relate asymptotically to Rissanen’s minimum description length (MDL) criterion. A performance comparison of the MDL procedure with previous maximum-likelihood algorithms promotes the adoption of the MDL procedure for simultaneous estimation of the stimulus and recovery properties of auditory-nerve discharge.
Elastic wave scattering by an isotropic noncentrosymmetric sphere
Authors: Lakhtakia Akhlesh , Varadan Vasundara V. , Varadan Vijay K.
Published: October 2005

In an isotropic, noncentrosymmetric elastic solid, the displacement field u has to be supplemented by the independent microrotation field φ. In this mirror-asymmetric (or chiral) medium, six different wave numbers are possible: Of these, two represent longitudinal fields, and the remaining four are (circularly) handed. This paper is concerned with the scattering of elastic waves by a chiral sphere, and the effect of the chiral parameter on its scattering response.
Evaluating acoustic absorption coefficients by comparative analysis—Theory part
Authors: Mills Charles A. , Spiekermann Charles E.
Published: October 2005

An analytical model has been developed for use in evaluating normal incidence acoustic absorption coefficients of materials. The model describes an acoustic impedance tube having a closed and partially absorptive boundary, corresponding to an absorber specimen mounted within an endcap affixed to the tube. The other boundary contains an acoustic excitation. Additionally, the model incorporates internal acoustic dissipation effects of the tube, which can be significant. Acoustical frequency response functions are computed based on the amounts of the two dissipation mechanisms. This composite analytical model is to be used for comparison to experimentally measured acoustic pressure magnitudes so as to evaluate the acoustic absorption coefficient.
Study of a thermoacoustic prime mover below onset of self-oscillation
Authors: Atchley Anthony A. , Bass Henry E. , Hofler Thomas J. , Lin Hsiao-Tseng
Published: October 2005

The frequency response of a thermoacoustic prime mover has been measured as a function of the mean gas pressure and temperature gradient across the prime mover stack. The quality factor Q and resonance frequency can be determined from the response. As the temperature gradient is increased, the Q increases, indicating a decrease in attenuation across the stack. At sufficiently large temperature differences (∼300 K), the resonator goes into self-oscillation, indicating negative attenuation. Measurements are reported for helium and argon at pressures ranging from 170–500 kPa and temperature gradients ranging from zero to that required for onset of self-oscillation. The results are explained in terms of a counterpropagating, plane-wave analysis, based on techniques commonly used in porous media investigations. In general, the predictions of the analysis are in good agreement with experiment. The predictions of Q and the change in resonance frequency with mean gas pressure are within approximately 5% and 0.4% of measured values for the no temperature gradient cases. In the cases where temperature gradients are present, the agreement is quite good for the two highest mean pressures reported (370 and 500 kPa). There are some noticeable discrepancies at the lowest pressure (170 kPa). The reasons for these discrepancies are unknown.
Near-field acoustic scattering from simulated two-dimensional, wind-driven sea surfaces
Authors: Caruthers Jerald W. , Keiffer Richard S. , Novarini Jorge C.
Published: October 2005

The Helmholtz integral has been evaluated numerically in the near field for simulated two-dimensional (2-D), randomly rough surfaces and point sources. Surfaces chosen for simulation were wind-driven sea surfaces having a Pierson–Moskowitz directional spectrum (wind speeds of 8 and 11 m/s). Estimates of the complex scattered field along with higher-order statistical moments are calculated as ensemble averages. Predictions via this approach are compared over the frequency range from 0.2–2.0 kHz with analytic and numerical solutions obtained for the specular direction after applying the Fraunhofer approximation to both the source and receiver. Results indicate that the transition between far field and near field as well as from smooth to rough surfaces occurs at frequencies in reasonable agreement with predictions based on simple estimates. The technique is also used to show that the true 2-D nature of the sea surface is important in the analysis of near-field scattering from it. Differences between the out-of-specular scattering for up/down and cross-wind cases are shown to be significant.
Ray and diffraction effects of acoustic waves when atmospheric conditions produce nonlinear acoustic velocity profiles
Authors: Osborne C. F.
Published: October 2005

The propagation of acoustic pulses in a medium with refractive index n=(a+be−αz)ν, where a, b, ν, α are constants, is discussed within both the ray and diffraction analysis. This work is of relevance to the propagation of acoustic pulses in media which have temperature gradients and/or wind gradients. It is shown that both treatments are amenable to exact solution. A new class of analytical solutions are presented that are of relevance to scientists working in the area of wave propagation in the atmosphere. In the ray treatment a generalization of the linear gradient is obtained that suggests greater bending as compared to the linear case, while in the diffraction limit, the solutions of the wave equation are shown to be particular examples of confluent hypergeometric and Papperitz functions. Qualitative discussions of the solutions are presented.
Acoustic cavitation produced by microsecond pulses of ultrasound: A discussion of some selected results
Authors: Crum L. A. , Roy R. A. , Dinno M. A. , Church C. C. , Apfel R. E. , Holland C. K. , Madanshetty S. I.
Published: October 2005

Because of its extensive utilization in clinical practice, and because the subjects examined are often fragile and sensitive to trauma, the safety of diagnostic ultrasound has always been of concern. Of the various mechanisms through which ultrasound could act in a manner deleterious to a patient, acoustic cavitation, should it occur, appears to possess significant potential for biological damage. This paper reviews several recent reports of progress by our two groups and demonstrates the conditions under which cavitation has been observed by microsecond pulses of ultrasound. Although these results give no indications that diagnostic ultrasound may pose a true risk to a patient, they do indicate that in vivo cavitation may occur under certain conditions.
Stabilization of perceived echo amplitudes in echolocating bats. I. Echo detection and automatic gain control in the big brown bat, E
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Authors: Hartley David J.
Published: October 2005

Previous research on echo detection in bats has suggested that the effective threshold is a function of the acoustic clutter in the experimental environment, as might be expected given the low ambient noise levels typical of such psychophysical research. This paper demonstrates that theory of signal detectability (TSD) methodology is applicable to bats and uses it to show that an important element of clutter limiting in Eptesicus fuscus and Noctilio leporinus is backward masking of phantom targets by the real echo from the loudspeakers used to generate them. This information suggests that a previous estimate of the magnitude of automatic gain control (AGC) is too high, due to variable backward masking inherent in the experimental method used. A re-examination of gain control using a masking-free method shows that it reduces auditory sensitivity by 6 to 7 dB per halving of target range, rather than 11 dB as previously thought.
Sonar gain control and echo detection thresholds in the echolocating bat, E
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Authors: Simmons James A. , Moffat Anne J. M. , Masters W. Mitch
Published: October 2005

The echolocating bat, Eptesicus fuscus, detects sonar echoes with a sensitivity that changes according to the time elapsed between broadcasting of each sonar signal and reception of echoes. When tested in an electronic target simulator on a two-choice echo-detection task, the bat’s threshold improved by 11.5 dB as echo delay changed from 2.3 to 4.6 ms (target ranges of 40 and 80 cm). Earlier experiments measured the change in detection threshold for delays from 1 to 6.4 ms (target ranges from about 17 to 110 cm) and obtained about 11 dB of improvement per doubling of delay. The new experiments used electronic delay lines to simulate echo delay, thus avoiding movement of loudspeakers to different distances and the possible creation of delay-dependent backward masking between stimulus echoes and cluttering echoes from the loudspeaker surfaces. The slope of the threshold shift defines an echo gain control that keeps echoes from point targets at a fixed sensation level—reducing sensitivity by 11 to 12 dB as echo amplitude increases by 12 dB per halving of range during the bat’s approach to the target. A recent experiment using loudness discrimination of echoes at 70 to 80 dB SPL (roughly 50 dB above threshold) found a slope of about 6 dB per halving of range, so the gain-control effect may be level dependent. The observed effect is operationally equivalent to forward masking of echoes by the transmission, but any events correlated with vocalization which impair hearing sensitivity for a short interval following transmissions could cause a decline in sensitivity to echoes. Contractions of the bat’s middle-ear muscles synchronized to transmissions may account for the observed threshold shift, at least for a span of echo delays associated with the most critical portion of the approach stage of pursuit. Forward masking by the sonar transmissions may contribute to the threshold shift, too, but middle-ear muscle contractions do occur and must be a significant part of the cause.
Nonlinearity parameters for pulse propagation in isotropic elastomers
Authors: Carman G. P. , Cramer M. S.
Published: October 2005

The propagation of one-dimensional shear waves in isotropic hyperelastic materials is examined. Both compressible and incompressible materials subject to arbitrarily large shear prestrains are considered. The nonlinear evolution equation governing small disturbances on prestrained undisturbed states is derived. The prestrain is seen to change the nonlinearity from the cubic form found in the unstrained case to the stronger quadratic form governed by the conventional Burgers’ equation. Additional results include explicit and general expressions for the quadratic and cubic nonlinearity parameters. Numerical estimates are also provided for natural rubber and foamed polyurethane. It is demonstrated that the quadratic nonlinearity parameter does not increase monotonically with prestrain and may actually vanish at nonzero values of the prestrain.
Comment on ‘‘Analysis of weights in multiple observation tasks’’ [J. Acoust. Soc. Am. 8
6, 1743–1746 (1989)]
Authors: Lutfi Robert A.
Published: October 2005

Berg’s method [J. Acoust. Soc. Am. 86, 1743–1746 (1989)] for assessing the weights observers give to multiple observations is not independent of assumptions regarding internal noise.
Hearing protection against high-level shooting impulses in relation to hearing damage risk criteria
Authors: Pekkarinen Jussi O. , Starck Jukka P. , Ylikoski Jukka S.
Published: October 2005

The earmuff attenuation of acoustic impulses produced by large-caliber weapons was measured with a high-speed microcomputer controlled unit. The estimated accuracy was ±1 dB in peak sound-pressure level measurements. The peak levels outside earmuffs were 184 dB for the heavy bazooka and 172 dB for the hand-held bazooka (re: 20 μPa). Heavy bazooka impulse peak levels were attenuated from 7 to 19 dB by the earmuffs depending on the mass and volume of the measured three types of earmuffs. Hand-held bazooka impulse peak levels were attenuated by the earmuffs from 9 to 15 dB. The risk limits for hearing loss from a single impulse were exceeded in spite of the use of earmuffs when the criteria of CHABA (USA) or Pfander (Germany) were applied. The unexpectedly low attenuation was due to the low-frequency waveform of the high-level impulses. The earmuffs were found to prolong the impulse duration, which may reduce the benefit otherwise achieved by attenuation of the peak levels.
Responses to amplitude-modulated tones in the auditory nerve of the cat
Authors: Joris Philip X. , Yin Tom C. T.
Published: October 2005

Sinusoidally amplitude-modulated (AM) tones are frequently used in psychophysical and physiological studies, yet a comprehensive study on the coding of AM tones in the auditory nerve is lacking. AM responses of single auditory-nerve fibers of the cat are studied, systematically varying modulation depth, frequency, and sound level. Synchrony-level functions were nonmonotonic with maximum values that were inversely correlated with spontaneous rate (SR). In most fibers, envelope phase-locking showed a positive gain. Modulation transfer functions were uniformly low pass. Their corner frequency increased with characteristic frequency (CF), but changed little for CFs above 10 kHz. The highest modulation frequencies to which phase locking occurred were more than 0.8 oct lower than the highest frequencies to which phase locking to pure tones occurs. Cumulative, or unwrapped, phase increased linearly with modulation frequency: The slope was inversely related to CF, and slightly higher than group delays reported for pure tones. High SR, low CF fibers showed the poorest envelope phase locking. In some low CF fibers, phase locking increased at high levels, associated with ‘‘peak-splitting’’ phenomena. Changes in average rate due to modulation were small, and could be enhancement or suppression.
The role of frequency selectivity in measures of auditory and vibrotactile temporal resolution
Authors: Formby C. , Morgan L. N. , Forrest T. G. , Raney J. J.
Published: October 2005

The purpose of this study was to compare the role of frequency selectivity in measures of auditory and vibrotactile temporal resolution. In the first experiment, temporal modulation transfer functions for a sinusoidally amplitude modulated (SAM) 250-Hz carrier revealed auditory modulation thresholds significantly lower than corresponding vibrotactile modulation thresholds at SAM frequencies ≥100 Hz. In the second experiment, auditory and vibrotactile gap detection thresholds were measured by presenting silent gaps bounded by markers of the same or different frequency. The marker frequency F1=250 Hz preceded the silent gap and marker frequencies after the silent gap included F2=250, 255, 263, 310, and 325 Hz. Auditory gap detection thresholds were lower than corresponding vibrotactile thresholds for F2 markers ≤263 Hz, but were greater than the corresponding vibrotactile gap detection thresholds for F2 markers ≥310 Hz. When the auditory gap detection thresholds were transformed into filter attenuation values, the results were modeled well by a constant-percentage (10%) bandwidth filter centered on F1. The vibrotactile gap detection thresholds, however, were independent of marker frequency separation. In a third experiment, auditory and vibrotactile rate difference limens (RDLs) were measured for a 250-Hz carrier at SAM rates ≤100 Hz. Auditory RDLs were lower than corresponding vibrotactile RDLs for standard rates >10 Hz. Combination tones may have confounded auditory performance for standard rates of 80 and 100 Hz. The results from these experiments revealed that frequency selectivity influences auditory measures of temporal resolution, but there was no evidence of frequency selectivity affecting vibrotactile temporal resolution.
Effects of temporal separation and masker level on binaural analysis in forward masking
Authors: Yama Mark F.
Published: October 2005

In the present study detection under diotic (NoSo) and dichotic (NoSπ) listening conditions in a forward masking paradigm was investigated. Both the level of a noise masker and the temporal separation between the masker and a 250-Hz tone burst served as independent variables. Results showed that most of the variance in the data could be accounted for by the amount of masking in the NoSo condition, independent of the value of the temporal parameter, which itself accounted for only 1.4% of the variance that remained. Once the data were corrected for NoSo masking effectiveness, the MLD was found to decrease by only 1.4 dB as temporal separation increased from 5–100 ms, which is consistent with a very long time constant for the binaural system. Consistent with this finding, it was shown that slope changes of the growth of masking functions, for simultaneous as compared to forward masking, were similar for both the NoSo and NoSπ conditions.
Effects of noise on detection of amplitude increments of sinusoidal vibration of the skin
Authors: Gescheider George A. , Verrillo Ronald T. , Pelli Denis G.
Published: October 2005

Vibrotactile thresholds for detecting a 300-Hz signal in the presence of both a 300-Hz sinusoidal pedestal and a background noise were measured as a function of the amplitudes of the pedestal and noise. Threshold increased monotonically as a function of the amplitude of the noise, but was a nonmonotonic function of the amplitude of the sinusoidal pedestal. Negative masking, in which the pedestal facilitated detection of the test stimulus, was observed in the absence of background noise and in the presence of subthreshold background noise when the pedestal was near or below threshold. Negative masking disappeared when the experiment was conducted in the presence of moderately intense to intense background noise. The results are consistent with a peripheral high-energy threshold for taction.
Underwater scattering targets made of polystyrene foam
Authors: Suiter H. R.
Published: October 2005

A versatile method is described of casting expandable polystyrene beads in small quantities for laboratory use as surface scattering targets. The method requires no specialized equipment and does not require careful process control. The making of one such target is described, a four-period sawtooth wedge grating. Backscattering was measured and compared favorably with a one-dimensional Fresnel–Kirchhoff model.
The role of interaural time difference and fundamental frequency difference in the identification of concurrent vowel pairs
Authors: Shackleton Trevor M. , Meddis Ray
Published: October 2005

The ability of subjects to identify both components of a concurrent vowel pair was determined when vowel fundamental frequency difference and an interaural time difference (ITD) in one of the vowels were introduced. In agreement with earlier studies it was found that introduction of a fundamental frequency difference significantly improved detection performance (by 22% for a 1 semitone difference). Identification performance improved as the ITD was made larger but this improvement was small compared to the fundamental frequency difference effect (7% improvement between 0 and 400 μs).
Annoyance caused by simultaneous impulse, road-traffic, and aircraft sounds: A quantitative model
Authors: Vos Joos
Published: October 2005

In this study, total annoyance caused by different simultaneous environmental sounds is investigated. In spite of a number of puzzling data in the literature, it is fairly well established that in combinations in which the annoyance of one source is considerably higher than that of another source, total annoyance is equal to the maximum annoyance of the separate sources. For combinations in which both sounds are about equally annoying, total annoyance seems to be higher than the maximum source-specific annoyance. The available data, however, are too rough to model total annoyance in these conditions. The present laboratory studies were therefore designed to explore further possible procedures to quantify total annoyance. Subjects rated the (total) annoyance caused by various combinations of impulse, road-traffic, and aircraft sounds.

The results support a simple model which predicts the overall or total rating sound level Lt for combinations of several types of sounds. Here, Lt is numerically equal to the A-weighted equivalent sound level Leq of road-traffic sound with the same annoyance as caused by the combination of sounds. In the model, the sound exposure caused by the impulse and/or aircraft sounds is first expressed in the Leq of equally annoying road-traffic sound. With the help of source-specific dose–effect relationships, this is achieved by adding level-dependent penalties to the Leq of the respective sources. Weighted summation of the corrected Leq’s of the various sources then results in Lt. An optimal overall fit of the data from two separate experiments was obtained when the weighted summation of the corrected Leq’s was performed with the parameter k in k log{∑10(corrected Leq of source j)/k} set to 15. The standard deviation of the differences between the experimental results and the model predictions with k=15 was equivalent to the small change in annoyance produced by a 1.5-dB shift in the Leq of road-traffic sound. Adoption of k=15 implies that after correction, two equal Leq’s yield a total rating sound level which is 4.5 dB higher than each single-source corrected Leq.
New empirical equations for sound propagation in rigid frame fibrous materials
Authors: Allard Jean-F. , Champoux Yvan
Published: October 2005

New expressions are given that can be used instead of the phenomenological equations of Delany and Bazley. They provide similar predictions in the range of validity of these equations, and in addition are valid at low frequencies where the equations of Delany and Bazley provide unphysical predictions. These new expressions have been worked out by using the general frequency dependence of the viscous forces in porous materials proposed by Johnson et al. [J. Fluid Mech. 176, 379 (1987)], with a transposition carried out to predict the dynamic bulk modulus of air. The model used suggests how sound propagation in fibrous materials can depend both on the diameter of the fibers and on the density of the material.