bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous phase relations in threshold-level responses from gerbil auditory nerve fibers
Authors: Ronken Don A.
Published: October 2005

Phase-locked responses at near-threshold levels obtained from single units in the auditory nerve of gerbils show that the relation between phase lag and linear frequency often contains an unexpected microstructure. In frequency regions below 1 kHz that are also an octave or more below CF, phase curves often have multiple straight-line segments, rapid slope changes, or other major inflections. These detailed features of the phase curves are not accounted for by any identified artifact. For example, the anomalous features cannot be removed simply by lowering the stimulus level; they remain down to levels where phase locking first occurs. Phase curves for single units with the same CF recorded from different animals can have similar microstructures, suggesting that the form of the phase curves may reflect some joint effect of stimulus frequency and CF or longitudinal position.
Reference equivalent threshold levels for pure tones and 1/3-oct noise bands: Insert earphone and TDH-49 earphone
Authors: Cox Robyn M. , McDaniel D. Michael
Published: October 2005

Reference equivalent threshold sound pressure levels (RETSPLs) were determined for 20 subjects for pure tones and 1/3-oct noise bands. Two transducers were used: a Telephonics TDH-49 earphone mounted in an MX-41/AR cushion, and a Danavox SMW insert earphone coupled to an ‘‘HA-2’’ earmold. RETSPLs for pure tones transduced by the TDH-49 earphone were very similar to those published previously. For each transducer, RETSPLs for 1/3-oct noise bands were essentially identical to the RETSPLs for pure tones near the center of each band. Applications for threshold testing using the insert earphone and/or 1/3-oct noise bands are discussed.
Auditory sensitivity in preschool children
Authors: Schneider Bruce A. , Trehub Sandra E. , Morrongiello Barbara A. , Thorpe Leigh A.
Published: October 2005

Thresholds for octave-band noises with center frequencies of 0.4, 1, 2, 4, and 10 kHz, and 1/3-octave-band noises with center frequencies of 10 and 20 kHz, were obtained from children 3–5 years of age and from a comparison group of adults. Thresholds for all frequencies decreased between 3 and 5 years of age. Thresholds decreased further between 5 years of age and adulthood, except for the 20-kHz stimulus, for which children had lower thresholds than adults. These results are discussed in terms of possible age-related changes in the mechanical properties of the ear and in the efficiency of neural coding.
Speech-reception threshold in noise with one and two hearing aids
Authors: Festen J. M. , Plomp R.
Published: October 2005

The binaural free-field speech-reception threshold (SRT) in 70-dBA noise was measured with conversational sentences for 24 hearing-impaired subjects without hearing aids, with a hearing aid left, right, and left plus right, respectively. The sentences were always presented in front of the listener and the interfering noise, with a spectrum equal to the long-term average spectrum of the sentences, was presented either frontally, from the right, or from the left side. For subjects with only moderate hearing loss, PTA (average air-conduction hearing level at 500, 1000, and 2000 Hz)<50 dB, the SRT in 70-dBA noise in both ears is determined by the signal-to-noise ratio even if only one hearing aid is used. For larger hearing losses the SRT appears to be partly determined by the absolute threshold. In conditions with a high noise level relative to the absolute threshold, in which case for both ears the SRT is determined by the signal-to-noise ratio, a second hearing aid, just as a monaural hearing aid, generally does not improve the SRT. However, in the case of a high hearing level, or a low noise level, in which a monaural hearing aid is profitable, the use of two hearing aids is even more profitable. In a separate experiment, acoustic head shadow was measured at the entrance of the ear canal and at the microphone location of a hearing aid. It appeared that, for a lateral noise source and speech frontal, the microphone position of behind-the-ear hearing aids has a negative effect on the signal-to-noise ratio of 2–3 dB.
Application of stochastic analysis to ultrasonic echoes—Estimation of attenuation and tissue heterogeneity from peaks of echo envelope
Authors: He Ping , Greenleaf James F.
Published: October 2005

A study of the statistics of ultrasound speckle indicates that the noise-to-signal ratio (NSR) of the echo envelope peaks (EEP) in a B scan is monotonically related to the variance of the mean power of the backscattered echoes. If it is assumed that the backscattered echoes all have the same mean power, the NSR of the EEP’s in a B scan will be expected to reach a theoretical minimum value NSR0 (0.40∼0.42). In practical situations, the variance of the mean power of the echoes is increased due to the presence of both attenuation (including beam spreading) and the spatial variation in the backscattering cross section (BCS) of the tissue. Accordingly, the measured value of the NSR of the EEP’s is expected to be greater than the NSR0. In principle, the effects of beam pattern and the attenuation can be compensated for by system calibration and a depth-related gain function, respectively. The attenuation coefficient of the tissue may then be obtained by adjusting the gain function to minimize the NSR of the EEP’s. Due to the random nature of the heterogeneity of diseased tissue, the effect of the variation in the BCS, however, cannot be compensated for by the depth-related gain function. Therefore, the minimum value of the NSR indicates the spatial variation in the BCS and may finally correlate to the disease state of the tissue.
A general model for the absorption of ultrasound by biological tissues and experimental verification
Authors: Jongen H. A. H. , Thijssen J. M. , van den Aarssen M. , Verhoef W. A.
Published: October 2005

In this paper, a closed-form expression is derived for the absorption of ultrasound by biological tissues. In this expression, the viscothermal and viscoelastic theories of relaxation processes are combined. Three relaxation time distribution functions are introduced, and it is assumed that each of of these distributions can be described by an identical and simple hyperbolic function. Several simplifying assumptions had to be made to enable the experimental verification of the derived closed-form expression of the absorption coefficient. The simplified expression leaves two degrees of freedom and it was fitted to the experimental data obtained from homogenized beef liver. The model produced a considerably better fit to the data than other, more pragmatic models for the absorption coefficient as a function of frequency that could be found in the literature. Scattering in beef liver was estimated indirectly from the difference between attenuation in in vitro liver tissue as compared to absorption in a homogenate. The frequency dependence of the scattering coefficient could be described by a power law with a power of the order of 2. A comparable figure was found in direct backscattering measurements, performed at our laboratory with the same liver samples [Van den Aarssen et al., J. Acoust. Soc. Am. (to be published)]. A model for scattering recently proposed by Sehgal and Greenleaf [Ultrason. Imag. 6, 60–80 (1984)] was fitted to the scattering data as well. This latter model enabled the estimation of a maximum scatterer distance, which appeared to be of the order of 25 μm.
Ultrasonic nonlinear parameters and sound speed of alcohol–water mixtures
Authors: Sehgal Chandra M. , Porter Burdett R. , Greenleaf James F.
Published: October 2005

Changes in the nonlinear parameter B/A caused by the addition of monohydric alcohols to water have been investigated. The measurements, made by using an aqueous solution of n-propanol, isopropanol, and t-butanol, show that as the alcohol concentration is increased, B/A decreases to a minimum at approximately 10% concentration (by volume). Further increase in alcohol concentration raises B/A rapidly to a maximum at about 80% by volume. This complex variation in B/A is attributed to solute–solvent interaction which is believed to be due to an enhancement of water structure in the water-rich region. These results suggest that the magnitude of B/A may be closely related to the quasilattice structure of water, which to a first approximation can be expressed by relative amounts of bound and unbound water.
Intensity decay laws for near-surface sound sources in the ocean
Authors: Denham R. N.
Published: October 2005

Expressions derived for the acoustic intensity decay with range in shallow water by Marsh and Schulkin [J. Acoust. Soc. Am. 34, 863–864 (1962)] and Weston [J. Sound Vib. 18, 271–287 (1971)] have been adapted to describe the intensity-range variation in the deep water situation, where the sound speed at the surface is equal to the sound speed at the base of the water column. The modified equations take account of the surface decoupling loss which occurs at frequencies below 100 Hz for source depths less than 25 m. The levels predicted by these equations are compared with experimental data obtained in deep water in the Indian Ocean. It is found that the mean difference in measured and predicted levels at frequencies of 25 and 50 Hz is less than 2 dB, and rms level differences are within 4 dB.
Surface reflection: On the convergence of a series solution to a modified Helmholtz integral equation and the validity of the Kirchhoff approximation
Authors: McCammon Diana F. , McDaniel Suzanne T.
Published: October 2005

In the problem of scattering from a pressure release boundary, the Helmholtz integral equation may be expressed as a Fredholm equation of the second kind with the unknown surface velocity as the independent variable. The method of successive approximations was employed by Meecham [J. Ration. Mech. Anal. 5, 323–333 (1956)] to obtain a series solution to this equation, where the first term of this series is, in fact, the unshadowed Kirchhoff approximation to the solution. Meecham attempted to formulate the region of validity of the Kirchhoff approximation by determining when the remaining terms of the series could be neglected, however, his arguments used to select ‘‘smallness’’ have been questioned. An exact solution to the integral equation for a sinusoidal boundary is employed to examine the series, term by term, for convergence; and it is found that (1) the alternating nature of the series does not bring convergence when the series diverges absolutely, and (2) the absence of any propagating side orders and reflection anomalies is not a sufficient condition for convergence. Finally, to highlight the extent of the error made when using the Kirchhoff approximation, comparisons are made between reflection coefficients computed using the exact solution and several terms of the series. It is found that in the shadowed regions, the Kirchhoff approximation is in reasonable agreement with the exact solution, even when Meecham’s series diverges.
Low-frequency rolloff in the response of shallow-water channels
Authors: Smith P. W.
Published: October 2005

Propagation in a shallow-water channel of constant sound speed, overlying a homogeneous viscoelastic half-space with frequency-independent loss factors, is examined as a function of range, frequency, water depth, and a parameter representing the initial rate of increase of bottom reflection loss with increasing grazing angle. Particular attention is focused on the ‘‘transition’’ frequency below which the transmission loss increases rapidly. It is found to separate a ray-theoretical domain, where the directional spectrum of transmitted sound is quasicontinuous, from a modal domain where, in fact, only the first mode carries significant energy. A simple algebraic formula is derived for this transition frequency that also yields good estimates of both the ‘‘optimum frequency’’ of Jensen and Kuperman [J. Acoust. Soc. Am. 73, 813 (1983)] and the low-frequency rolloff observed in some data.
Traveling wave and SEM representations for transient scattering by a circular cylinder
Authors: Heyman E. , Felsen L. B.
Published: October 2005

When observed over long observation times, scattered returns from targets illuminated by broadband acoustic signals reveal distinctive features in the early and late time regimes. The features can be explained in terms of the different wave phenomena, progressive and oscillatory, that are dominant during these respective intervals. The former represent wave front arrivals, and the latter full body resonances. A hybrid theory, recently developed by Heyman and Felsen [IEEE Trans. Antennas Propag. AP-31, 426–437 (1983)], has formalized the connection between them and has provided new interpretations that have not emerged from more conventional treatments. These interpretations can clarify issues which have arisen within the resonance expansion procedure, in particular, the adequacy of the expansion at early times. In this paper, the canonical problem of scattering by a circular cylinder serves as a rigorous test for general observations made elsewhere [E. Heyman and L. B. Felsen, IEEE Trans. Antennas Propag. AP-31, 706–718 (1985)], concerning the traveling wave interpretation of the resonance series, and especially the role of the entire function in the complex frequency plane that is included to repair resonance series deficiencies of the Singularity Expansion Method (SEM).

The resonance series of damped global oscillatory wave fields corresponding to the complex resonant frequencies represents, collectively, the multiple effects of diffracted (creeping) waves traveling around the cylinder in the positive and negative directions, but it cannot incorporate the specularly reflected field in the lit region, which has not sampled the obstacle surface as a whole. This contribution remains as a free term that can be identified in the complex frequency plane as an intrinsic (nonremovable) entire function. The analysis also shows how delaying the turn-on time of the resonance series, by retaining some early creeping wave front arrivals intact, can generate, in addition, a nonintrinsic (i.e., removable) entire function. These considerations, having rigorous foundation and appealing physical content, aid in the understanding of wave phenomena associated with broadband scattering from targets observed over early and late time periods.
Acoustic resonance frequencies of deformed spherical resonators. II
Authors: Mehl James B.
Published: October 2005

The effects of imperfect spherical shape on the modes of a spherical acoustic resonator are considered. The resonator boundary is described by a series of spherical harmonics r=a+εa∑ clkYlk, where ε is a small parameter. It is convenient to summarize the results by considering deformations which do not change the resonator volume. Earlier work showed, for pure radial modes subject to axisymmetric shape perturbations, that the fractional shift of the resonance frequency is proportional to ε2. This work extends this result to arbitrary shape perturbations. Nonradial modes, for which the acoustic pressure is proportional to jn (kns r) Ynm (θ, φ) with n≥1 are (2n+1)-fold degenerate for a perfect spherical resonator. Deformation of the resonator normally shifts the resonance frequencies by an amount which is linear in ε. However, the average shift of a degenerate set of modes with indices {ns} is of order ε2. Axisymmetric shape perturbations normally reduce the degeneracy of the nonradial modes to (n+1)-fold, and arbitrary deformations normally lift the degeneracy completely. The modes with indices {ns} are sensitive only to the terms clk with even values of l in the range l≤zn. A formalism for quantitative estimates is developed. Numerical results are obtained for some n=1 and n=2 cases.
Beyond bathymetry: Mapping acoustic backscattering from the deep seafloor with Sea Beam
Authors: de Moustier Christian
Published: October 2005

In its standard mode of operation, the multibeam echo sounder Sea Beam produces high resolution bathymetric contour charts of the seafloor surveyed. However, additional information about the nature of the seafloor can be extracted from the structure of the echo signals received by the system. Such signals have been recorded digitally over a variety of seafloor environments for which independent observations from bottom photographs or sidescan sonars were available. An attempt is made to relate the statistical properties of the bottom-backscattered sound field to the independently observed geological characteristics of the seafloor surveyed. Acoustic boundary mapping over flat areas is achieved by following trend changes in the acoustic data both along and across track. Such changes in the acoustics are found to correlate with changes in bottom type or roughness structure. The overall energy level of a partial angular-dependence function of backscattering appears to depend strongly on bottom type, whereas the shape of the function does not. Clues to the roughness structure of the bottom are obtained by relating the shape of the probability density function of normal-incidence echo envelopes to the degree of coherence in the backscattered acoustic field.
The effects of variations in sound speed on coupling coefficients between acoustic normal modes in shallow water over a sloping bottom
Authors: Hall Marshall
Published: October 2005

The conventional method for determining the coupling coefficient between acoustic normal modes in shallow water over a hard sloping bottom gives an incorrect result because it assumes the derivative normal to the bottom to be equal to the depth derivative. This problem can be circumvented by measuring depth normal to the bottom. The coupling coefficients determined in this manner are found to be at least three times smaller or larger than the corresponding conventional results (the exact ratio depends on the mode numbers). For well-trapped modes in isospeed water over a sloping bottom with a finite sound speed, the coupling coefficient is approximately the same as would occur if there were a virtual pressure release surface at a fixed distance beneath the actual seafloor. This distance is typically about 30% greater than the cutoff water depth for the frequency under consideration. If the water column is not isospeed, then the depth functions of the modes can be expressed as perturbation series of the sinusoidal functions that correspond to the isospeed case. A negative sound-speed gradient increases the coupling coefficients and, providing the sound speed does not exceed the phase velocity of the unperturbed modes, the increase is proportional to the relative variability of the sound-speed profile.
Hamiltonian perturbation theory for acoustic rays in a range-dependent sound channel
Authors: Miller Jack C.
Published: October 2005

A perturbation theory for acoustic ray propagation is presented which is based on the analogy between Hamilton’s Principle of Least Action (independent variable: time) and Fermat’s Principle of Least Time (independent variable: space coordinate). In a vertical ocean section with x positive to the right and z positive upward, the Lagrangian variables z and ż (a dot denotes differentiation with respect to x; ż=dz/dx) are first replaced by the canonical variables (z, p) of the corresponding Hamiltonian formulation. For the zeroth-order case, where the sound c(x,z) reduces to the form c0(z), a canonical transformation, z, p → ω0, J0, can be made. The new variables are the analogs of angles-action variables in dynamics, and are constants. The generator for this transformation is just the Eikonal function for zeroth order and, hence, is recognized as the travel time between a source and receiver of sound. Finally, when the x-dependent perturbations are turned on, ω0 and J0 cease to be constants and a second, infinitesimal, canonical transformation, ω0, J0 → ω, J, is made. For range-dependent sound channels, ω=ω(x) and J=J(x). The canonical equations for these variables are exhibited, and how they may be solved by standard perturbation theory techniques is shown. Finally, some examples of the theory as applied to perturbations which vary slowly in x or, alternatively, which vary rapidly in x compared with the basic variation in the range-independent channel are given. The various perturbations to travel time are included in these calculations.
Acoustic scattering by ocean irregularities: Aspects of the inverse problem
Authors: Uscinski B. J.
Published: October 2005

Expressions are derived for the autocorrelation and structure functions of the acoustic refractive index for ocean internal waves in the presence of fine structure. The transverse autocorrelation and structure functions required in acoustic scattering formulas are obtained from these. The spectra and correlation functions of acoustic phase, complex amplitude, and intensity are considered in the case of multiple scattering, and it is shown that the effect of fine structure on the fourth moment of the acoustic field is fundamentally different from that exerted on the second moment or the phase. The problem of deducing the correlation function of ocean irregularities from the acoustic signal is considered, and it is shown that, under certain circumstances, the full inverse problem can be solved by using the second moment of acoustic complex amplitude. Finally, the effect of tides on the phase, second moment, and the spectrum of intensity fluctuations of the acoustic signal is considered. It is shown that this effect must be taken into account when seeking a solution to the inverse problem.
An experimental study of the penetration of a water–sediment interface by a parametric beam
Authors: Wingham Duncan J. , Pace Nicholas G. , Ceen Robert V.
Published: October 2005

A recent theoretical study [D. J. Wingham, J. Acoust. Soc. Am. 76, 1192–1200 (1984)] presented calculations of the farfield secondary pressure in sediment due to a parametric array incident on a water–sediment interface, assuming the array to be completely truncated at the interface. An experimental investigation of this theory is undertaken and the measured secondary pressure contours throughout the sediment are compared with the theoretical estimates. The theory is shown to provide good estimates of the secondary field. The measured secondary pressure variation as a function of beam incidence angle at various ranges is presented and it is apparent that only when the array is truncated in its primary nearfield does the performance of the parametric array differ significantly from a conventional array. It is concluded that the anomalous behavior of parametric arrays, at postcritical angles, relies on virtual sources which are both close to the interface and suitably phased to radiate into the sediment.
Deep sound channel noise from high-latitude winds
Authors: Bannister R. W.
Published: October 2005

The contribution to underwater ambient noise from the persistent winds which blow at high latitude is discussed and estimated. Energy is ducted into low-loss paths in the deep sound channel by favorable horizontal sound-speed gradients. A concept of ‘‘wind-noise lanes’’ is developed into a simple model which is used to predict the resulting underwater ambient noise levels as a function of season and latitude. Three main oceans are considered—the Pacific, Atlantic, and Indian Oceans. In general terms, predicted omnidirectional levels at 50 Hz lie between 65 and 75 dB re: 1 μPa2/Hz and are comparable to those generally associated with light-to-moderate ship traffic. The spectral shape of high-latitude wind noise is also similar to that associated with ships. High-latitude wind noise arrives within ±15° of horizontal, and the predicted magnitude of this low-angle component also matches measurements well. It is concluded that the component of noise associated with high-latitude winds can be significant at low frequencies. Properties of omnidirectional noise, as well as vertical and horizontal directivity, may be dominated by this component under some conditions. It appears, however, to have been often overlooked in the interpretation of data.
The representation of steady-state vowel sounds in the temporal discharge patterns of the guinea pig cochlear nerve and primarylike cochlear nucleus neurons
Authors: Palmer A. R. , Winter I. M. , Darwin C. J.
Published: October 2005

We have recorded the responses of fibers in the cochlear nerve and cells in the cochlear nucleus of the anesthetized guinea pig to synthetic vowels [i], [a], and [u] at 60 and 80 dB SPL. Histograms synchronized to the pitch period of the vowel were constructed, and locking of the discharge to individual harmonics was estimated from these by Fourier transformation. In cochlear nerve fibers from the guinea pig, the responses were similar in all respects to those previously described for the cat. In particular, the average-localized-synchronized-rate functions (ALSR), computed from pooled data, had well-defined peaks corresponding to the formant frequencies of the three vowels at both sound levels. Analysis of the components dominating the discharge could also be used to determine the voice pitch and the frequency of the first formants. We have computed similar population measures over a sample of primarylike cochler nucleus neurons. In these primarylike cochlear nucleus cell responses, the locking to the higher-frequency formants of the vowels is weaker than in the nerve. This results in a severe degradation of the peaks in the ALSR function at the second and third formant frequencies at least for [i] and [u]. This result is somewhat surprising in light of the reports that primarylike cochlear nucleus cells phaselock, as well as do cochlear nerve fibers.
NBS-9A coupler-to-eardrum transformation: TDH-39 and TDH-49 earphones
Authors: Cox Robyn M.
Published: October 2005

A transformation was derived to convert sound-pressure levels referenced to an NBS-9A coupler to corresponding eardrum sound-pressure levels. It was found that the same transformation may be used for male and female adults and for both TDH-39 and TDH-49 earphones in MX-41/AR supra-aural cushions. It was determined that from 250–2000 Hz the transformation provides an eardrum sound-pressure level estimate that is within 6 dB of the actual eardrum level for 95% of individuals. However, in the 4000–6300-Hz range, the accuracy deteriorates to ±12 dB of actual eardrum level for 95% of individuals.
On the tangentially and radially polarized piezoceramic thin cylindrical tube transducers
Authors: Wang Hong-zhang
Published: October 2005

The electric admittance equations of the tangentially and radially polarized piezoceramic thin circular cylindrical tube in the unloaded case have been derived approximately. On the basis of these equations, a method to calculate the main electromechanical parameters is suggested. With the same assumptions, the equations of vibration of the tube in water and the formulas for the responses of the radiation and receiving corresponding to a wider frequency range have also been derived. A further discussion about the influence of radiation impedance, Poisson’s ratio, piezoelectric constant ratio, and coupling coefficient to the response of receiving sensitivity of the piezoceramic thin circular cylindrical tube has been given.
Reply to ‘‘Comments on ‘Theory, ingenuity, and wishful wizardry in loudspeaker design—A half-century of progress?’ ’’ [J. Acoust. Soc. Am. 7
7, 1303–1308 (1985)]
Authors: Augspurger G. L.
Published: October 2005

In this letter, the author responds to comments on a former article.
Comments on ‘‘Harmonic and transient scattering from time varying obstacles’’ [J. Acoust. Soc. Am. 7
6, 1527–1534 (1984)]
Authors: Piquette Jean C. , Van Buren A. L.
Published: October 2005

Censor [J. Acoust. Soc. Am. 76, 1527–1534 (1984)] considered the acoustic interaction of an incident wave of angular frequency ω with a surface which is vibrating uniformly and harmonically at angular frequency Ω. He used the linear wave equation together with time-dependent boundary conditions to derive his solutions, and obtained results that predict scattered spectral components at frequencies ω−qΩ, where q=±1,±2, ... . A recent paper [J. C. Piquette and A. L. Van Buren, J. Acoust. Soc. Am. 76, 880–889 (1984)] investigated the same problem using the nonlinear wave equation to account for the intrinsic medium nonlinearity. The results, repeated here, show that, within a fraction of a wavelength of the surface, the scattered wave predicted by Censor becomes negligible in comparison to that generated by the medium nonlinearities. The problem of acoustic scattering from vibrating surfaces is inherently nonlinear (i.e., it cannot be linearized in any physically meaningful way). Reduction of the wave amplitudes, or varying any other parameters of the problem to decrease the effects of medium nonlinearity, also decreases the effect predicted by Censor by exactly the same factor.
High-energy impulsive noise assessment
Authors: Schomer Paul D.
Published: October 2005

In 1977 and again in 1981, the National Research Council (NRC) concluded that the C-weighted Day–Night Level was the best available measure with which to assess community response to high-energy impulse noise. Rattles in homes were the major adverse factor indicated by sonic boom and blast noise studies and cited by the NRC reports. Studies, since 1981, by the U. S. Army further support the NRC conclusions. Despite this wide consensus, there remain advocates for using only the A-weighting for measuring noise in the community—including that from high-energy impulses. This letter covers issues not considered in the NRC reports and provides additional rationale for the use of C-weighting, based on measurability and mitigation implications. This letter shows that impulsive noise is commonly hidden in other neighborhood sources when using A-weighting, but only rarely hidden when using C-weighting. There is a 10-dB improvement in signal to noise when using C-weighting. Also, A-weighting can mislead the public since it implies large benefits (up to 15 dB) for mitigation techniques such as barriers or forests. Low-frequency impulse energy, which rattles houses, is not attenuated by barriers or forests. Thus no large benefit is gained. C-weighting predicts the correct answer—only a few decibels of attenuation.
Sound attenuation of TDH-39 earphones in a diffuse field of narrow-band noise
Authors: Arlinger Stig D.
Published: October 2005

The sound attenuation characteristics of the audiometric earphone Telephonics TDH-39 with cushion MX-41/AR have been tested, using the hearing threshold method according to the International Standard ISO 4869-1981 (‘‘Acoustics—Measurement of sound attenuation of hearing protectors—Subjective method’’). This method specifies 1/3-oct bands of noise as test signals and a diffuse sound field. This is in contrast to the use of pure tones in a frontally incident free sound field, by means of which most earlier attenuation data have been obtained. The mean sound attenuation values obtained from a group of 20 normal-hearing subjects were up to 3–5 dB lower than those previously reported for pure tones in a free field.
Diffraction of an explosive transient
Authors: Raspet Richard , Ezell Jean , Coggeshall Stephen V.
Published: October 2005

Blast walls and barriers are often proposed for reducing noise from explosives or artillery fire. The calculation of blast noise reduction by three-dimensional finite difference flow field codes is expensive and computer time intensive. For many cases, the source strength at the barrier is neither very strong nor very weak (acoustical). In this paper, a combined theoretical and experimental model study to investigate the range of validity of linear transient diffraction theory is described. Also, this paper further investigates the use of a finite wave propagation program to extend the utility of the linear calculation. This study demonstrates that the linear theory, with an accurate input waveform, can predict the insertion loss to within 1.5 dB for peak sound-pressure levels less than 162 dB at the barrier. For the source levels greater than 162 dB, the prediction significantly underestimates the insertion loss.
The interaction of airborne sound with the porous ground: The theoretical formulation
Authors: Sabatier James M. , Bass Henry E. , Bolen Lee N. , Attenborough Keith , Sastry V.V.S.S.
Published: October 2005

The surface of the ground is modeled as that of an air-filled poroelastic soil layer of known thickness overlying a semi-infinite nonporous elastic substrate. Using a modified form of the Biot–Stoll differential equations for wave propagation in fluid-saturated porous media, propagation constants for the two possible dilatational waves and the shear wave in the poroelastic layer are determined. The dilatational waves are identified as a fast wave, moving predominately in the solid frame, and a slow wave, moving predominately in the pore air. The elastic moduli in the substrate are assumed to be those of the solid grains of which the poroelastic soil layer is composed. Intergranular friction in the soil and substrate is assumed to be negligible. Boundary conditions at the air–soil interface and at the porous soil–substrate interface are applied to determine, numerically, the displacement amplitudes of the allowed wave motions. From the incident and reflected amplitudes at the air–soil interface, the normalized ground surface impedance is calculated as a function of angle of incidence and of frequency. In this paper, the response of the pore fluid and frame to airborne acoustic waves is considered and those ideas will be pursued in a later publication. The predicted impedance at normal incidence is compared with measurements of the impedance of a sandy soil for which measurements of the various parameters required by the theory are also available. The predictions of impedance are found to be in tolerable agreement both with measured data and with predictions of a simpler model of the surface as that of a rigid porous semi-infinite homogeneous medium. Calculations of the surface impedance as a function of angle of incidence suggest that the porous medium is locally reacting.
The acoustic transfer function at the surface of a layered poroelastic soil
Authors: Attenborough Keith , Sabatier James M. , Bass Henry E. , Bolen Lee N.
Published: October 2005

A model for the response of a poroelastic layered soil to an incident plane wave developed in a previous paper [Sabatier et al., J. Acoust. Soc. Am. 79, 1345–1352 (1986)] is used to predict the complex sound pressure within the upper poroelastic layer. The predictions both of phase velocity and attenuation of the slow wave associated primarily with propagation in the pore fluid are compared with measurements made with a specially constructed probe microphone. The agreement between theory and experiment is good. The predictions for a layered poroelastic soil model are compared numerically with those of a semi-infinite rigid porous soil model and are found to differ only at frequencies higher than 1000 Hz. Analysis of the sensitivity to the theoretically predicted propagation constants in the poroelastic soil to the assumed value for the bulk rigidity modulus of the soil predicts that over the known range of rigidity moduli for soils it is possible to obtain a switchover between fast and slow propagation modes. This switchover occurs at the lower end of the possible range of values of the shear modulus. It is suggested that probe microphone measurements in air-filled soils offer a way of measuring flow resistivity and of deducing the structural parameters required for application of the Biot–Stoll model to water-saturated sediments.
The transient wave fields in the vicinity of the elliptic, hyperbolic, and parabolic umbilic caustics
Authors: Brown Michael G.
Published: October 2005

The caustics of high-frequency wave propagation may be classified using catastrophe theory. In this paper, we examine the transient wave fields in the vicinity of the elliptic, hyperbolic, and parabolic umbilic catastrophes. Analytical results are presented which describe the time-dependent wave field due to an impulsive source on and at large distances in each control direction away from the most singular point of each of these three catastrophes. Numerical results are presented which show the smooth variation of these transient wave fields as each control parameter is independently varied. These results are compared to previously derived results on the transient wave fields in the vicinity of the cuspoid catastrophes (the cuspoid and umbilic catastrophes have coranks 1 and 2, respectively). It is found that the transient wave fields in the vicinity of the cuspoid and umbilic catastrophes differ with regard to the temporal structure of the wave field on the most singular point of each catastrophe, the manner in which these temporal structures unfold, and the phase shifts which individual rays undergo as a result of touching one of the catastrophes.
Application of the composite roughness model to high-frequency bottom backscattering
Authors: Jackson Darrell R. , Winebrenner Dale P. , Ishimaru Akira
Published: October 2005

The composite roughness model is applied to bottom backscattering in the frequency range 10–100 kHz. For angles near normal incidence, the composite roughness model is replaced by the Kirchhoff approximation which gives better results. In addition, sediment volume scattering is treated, with account taken of refraction and reflection at the randomly sloping interface. In applying the model to published data it is found that sediment volume scattering is dominant in soft sediments except at small and large grazing angles. For coarse sand bottoms, roughness scattering dominates over a wide range of grazing angles. Implications for acoustic remote sensing are discussed.
Thermoacoustic generation in anisotropic media
Authors: Hildebrand John A.
Published: October 2005

The generation of acoustic waves by a modulated thermal source is examined for anisotropic materials. A wave equation is developed to include the effect of a thermoacoustic source for the anisotropic case. The dependence of the thermoacoustic source term upon the material elastic constants is identified for a thermal source varying in one dimension. This dependence is examined for several classes of crystalline anisotropy and it is found that thermoacoustic generation varies with crystallographic orientation. The directions of maximum and minimum thermoacoustic generation are not consistent for a given crystal class and are dependent upon the specific values of the elastic constants for the material.
Comparison of frequency estimators for underwater acoustic data
Authors: Barrett R. F. , McMahon D. R. A.
Published: October 2005

A number of high-accuracy frequency estimators have been critically compared using simulated and real passive sonar data. Techniques considered are the standard Prony method, the extended Prony method of Marple, the Kumaresan–Prony algorithm, the Pisarenko algorithm, the maximum likelihood approach, and a phase interpolation method developed by the authors. The latter two techniques appear to offer the most promise for the analysis of sonar data.
The shape of the nonlinearity generating the combination tone 2f1−f2
Authors: Strube Hans Werner
Published: October 2005

If the level behavior of the cubic difference tone is explained by a static nonlinear characteristic, the correspondence between this characteristic and certain components and quantities of the basilar membrane must be clarified. This is attempted here for a nonlinearity compatible with the idea of an active undamping feedback mechanism saturating at high levels. The relation between asymptotic behavior of the nonlinearity and the measured CDT level dependence is established. Agreement with psychoacoustic data requires a very ‘‘softly’’ compressing characteristic; linear or logarithmic asymptotes are ruled out. The psychoacoustically known level dependence is well reproduced for small primary-frequency differences by cancellation experiments with a digitally simulated basilar-membrane model.
Confusion effects with sinusoidal and narrow-band noise forward maskers
Authors: Neff Donna L.
Published: October 2005

In some forward-masking conditions, signal thresholds may be elevated by the listener’s inability to distinguish the signal from the preceding masker. In this study, such ‘‘confusion’’ effects are investigated for both sinusoidal and narrow-band noise forward maskers combined with sinusoidal signals of varying duration. Results for the sinusoidal maskers show effects of off-frequency listening for brief signals and possibly small effects of confusion for longer signals. Results for the narrow-band noise maskers show a marked influence of confusion over a wide range of signal durations. This range is in good agreement with that predicted from previous work with ‘‘pulsing’’ maskers [D. Neff, J. Acoust. Soc. Am. 78, 1966–1976 (1985)]. These results suggest that studies using narrow-band noise forward maskers or studies of psychophysical suppression should include direct tests for confusion effects in key conditions.
Pure-tone pitch anomalies. II. Pitch-intensity effects and diplacusis in impaired ears
Authors: Burns Edward M. , Turner Christopher
Published: October 2005

Pitch-intensity functions and psychophysical tuning curves (PTC’s) were measured in ten listeners with sensorineural impairments of presumed cochlear origin. Masking patterns, frequency jnd’s, diplacusis measurements, and octave adjustments were also obtained for selected conditions in selected listeners. The results showed a tendency for increased frequency jnd’s and increased pitch-matching variability in frequency regions where frequency resolution, as determined by PTC Q10 estimates, was degraded. The results also showed exaggerated pitch-level effects, both in regions where frequency resolution was degraded and, in many cases, in regions where thresholds and frequency resolution were apparently normal. The usual manifestation of exaggerated pitch-level effect was an abnormally large negative pitch shift with increasing level, particularly at low frequencies. The limited data from diplacusis measurements and octave adjustments suggest that the exaggerated negative pitch shifts are the consequence of a large increase in pitch at low stimulus levels which ‘‘recruits’’ at higher levels. These results are difficult to explain with simple tonotopic models, or presently formulated temporal models, of pure-tone pitch encoding.
Wave equations in linear viscoelastic materials
Authors: Charlier Jean-Paul , Crowet Françoise
Published: October 2005

Conditions for writing wave equations in linear viscoelastic materials are investigated. The study is restricted to the infinitesimal theory and an application is suggested in modeling ultrasound propagation in soft biological tissues. First, a general wave equation is obtained for the displacement field in an inhomogeneous medium. Second, the propagation of ‘‘the mean principal stress’’ (i.e., minus the arithmetical mean of the principal stresses) is examined. That quantity is particularly relevant when the force per unit area is detected at the surface of a nondissipative coupling medium. If the material is homogeneous, a wave equation is always obtained for the mean principal stress. Otherwise, supplementary conditions have to be assumed on the material and possibly on the motion. Results are illustrated by examples which present linearly elastic perfect fluids and linearly elastic Newtonian viscous fluids as particular viscoelastic materials.
A new expansion for the velocity potential of a circular concave piston
Authors: Hasegawa Takahi , Matsuzawa Kiichiro , Inoue Naoki
Published: October 2005

This paper presents a new method for calculating the velocity potential in the nearfield of a circular concave piston source in an infinite plane baffle for both the case where the vibration is normal to the piston surface and where it is parallel to the axis. The solution is given in the form of an infinite series of spherical surface harmonics in the spherical coordinate system, taking the origin at the center of curvature. The theoretical framework has the advantage that it includes neither approximations nor numerical integrations.
Transient and multiple frequency sound transmission through perforated plates at high amplitude
Authors: Cummings A.
Published: October 2005

The transmission of complex periodic and transient acoustic signals through orifice plates at high amplitude, and in the absence of mean fluid flow, is discussed. A simple fluid dynamical model, involving a time-varying mass end correction, is the basis of the theory. The equation of motion for the air in the orifice is solved numerically in the time domain. For a specific instance, an analytical solution in the frequency domain is possible. Good agreement is noted between experimental and theoretical results in both time and frequency domains.
Rainfall measurements using underwater ambient noise
Authors: Nystuen Jeffrey A.
Published: October 2005

Observations are made which show that the underwater ambient noise spectrum generated by rain has a unique spectral shape which can be distinguished from other noise sources. Furthermore, the relationship between spectral level and rainfall is quantifiable. The spectral shape is dominated by a broad peak at 15 kHz, but also depends on the drop size distribution in the rain. A numerical study of the acoustic physics of a drop splash is used to explain the observed spectra. There are two contributions to underwater sound from the impact. The first contribution is from an initial acoustic water hammer pulse. The magnitude of this pulse depends on drop size, shape, and impact velocity. The contribution to the underwater sound spectrum is white and is very large for large drops. The second contribution occurs because at impact the incompressible continuity equation is not satisfied. Once this equation is satisfied, the splash is no longer an acoustic source. Numerically, the time required to closely satisfy this equation is roughly constant for all drop sizes at their terminal velocity. This time interval causes a low-frequency rolloff at roughly 15 kHz in the sound spectrum.
The null-field approach in series form—The direct and inverse problems
Authors: Boström Anders
Published: October 2005

The direct and inverse scattering problems in two-dimensional acoustics at a fixed frequency are considered. It is shown how the null-field approach can be modified so that the Q matrix (which in a straightforward manner gives the transition matrix) is obtained as a series instead of an integral. For an obstacle which is a perturbation of a circle this series form gives an approximate, very explicit, expression for the transition matrix. A few numerical examples are given to show the utility and limitations of this approximation. For the inverse problem, the series form of Q gives a system of nonlinear polynomial equations which are solved by the imbedding method. Some numerical examples show that quite accurate results are obtained by this method in cases where the system of equations can be kept small. The linear approximation of the system of polynomial equations yields a method that works surprisingly well and which is also promising for the more difficult three-dimensional and vector problems.
Tests of the accuracy of a data reduction method for determination of acoustic backscatter coefficients
Authors: Insana Michael F. , Madsen Ernest L. , Hall Timothy J. , Zagzebski James A.
Published: October 2005

The accuracy of a new method for measuring ultrasonic backscatter coefficients was tested, using narrow-band pulses and well-defined media having scatterers randomly distributed in space. Experimentally determined values agree very well with theoretical values for wide ranges of experimental parameters, these ranges being applicable in measurements made on human soft tissues. An important outcome is that the method yields accurate results for scattering media positioned anywhere from the nearfield through the farfield of the nonfocused transducers employed. In addition, backscatter coefficients can be determined for a broad range of gate durations.