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Journal of the Acoustical Society of America

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Jan 1992

Volume 91, Issue 1, pp. 1-548

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Acoustic wave propagation through periodic bubbly liquids

Anthony A. Ruffa

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 1-11 (1992); (11 pages) | Cited 10 times

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A three‐dimensional finite‐element analysis is used to determine the acoustic behavior of plane waves propagating through bubbly liquids having periodic bubble distributions. The results obtained from the model include the effective phase speed and attenuation of the medium, the acoustic field in the region of each bubble, and the virtual mass for both the monopole and dipole modes of bubble oscillation. The results are in agreement with both experimental data and previous analytical results.
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43.20.Hq Velocity and attenuation of acoustic waves
43.20.Fn Scattering of acoustic waves
43.30.Lz Underwater applications of nonlinear acoustics; explosions

Multipole sources in boreholes penetrating anisotropic formations: Numerical and experimental results

H. D. Leslie and C. J. Randall

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 12-27 (1992); (16 pages) | Cited 6 times

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A 2.5‐D velocity‐stress finite‐difference code is described that models acoustic propagation in a borehole penetrating a generally anisotropic formation. The excitation may be a dilatation (monopole), or a point force (dipole) in an arbitrary direction. The anisotropic formation is homogeneous along the axis of the borehole but may be inhomogeneous in the transverse plane. The borehole cross section and location of the source in the borehole are arbitrary. Synthetic time‐domain waveforms are displayed for arrays of monopole and dipole receivers deployed along the borehole axis in both fast and slow anisotropic formations. The specific anisotropy model employed for the numerical results is a transversely isotropic (TI) formation with its axis of symmetry inclined with respect to the borehole axis by an arbitrary angle. Flexural/shear and Stoneley wave slowness and attenuation estimates are extracted from the synthetic waveforms using a variant of Prony’s method for a range of borehole inclinations relative to the formation axis of symmetry. In a fast formation, with borehole and formation symmetry axes perpendicular, flexural mode dispersion curves for quasi‐SV and SH polarizations separate only at low frequency where moderate attenuation is also observed. In a slow formation, distinct dispersion curves are obtained for quasi‐SV and SH polarizations over the entire frequency range. Moderate attenuation is again observed at low frequency. Scaled laboratory experiments confirm the numerical procedure. Experimental and numerical waveforms for monopole and several polarizations of dipole excitation in a transversely isotropic model formation overlay with excellent agreement.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.40.Ph Seismology and geophysical prospecting; seismographs

Equivalent networks for representing the two‐dimensional propagation of dilatational and shear waves in infinite elastic plates and in stratified elastic media

Anthony J. Rudgers

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 28-38 (1992); (11 pages) | Cited 2 times

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An elastic plate (lamina) of infinite lateral extent, in which there exists a plane‐wave elastic field owing to propagating dilatational and shear waves, is represented by a four‐port equivalent network. The equations describing this equivalent network are mathematically identical to those equations taken from the theory of linear elasticity that describe the mechanical behavior of a plate with arbitrary plane‐wave excitation of its surfaces. The equivalent network comprises two coupled transmission lines, one line representing dilatational‐wave propagation and the other shear‐wave propagation within the plate. A pair of ports at each plate surface transmit the normal and the transverse stresses acting at the surfaces to the input and output ports of the two transmission lines. The surface ports are coupled to the transmission‐line ports by an arrangement that includes both multiwinding ideal transformers and gyrators. Gyrators are required in the network that is the topological equivalent of an elastic plate in order to make the network equations identical to the equations resulting from the theory of linear elasticity. Consequently, the network demonstrates that mode conversion at the boundaries of an elastic plate (i.e., the conversion of dilatational‐wave motion into shear‐wave motion and vice versa) is a nonreciprocal phenomenon. By cascade interconnection of appropriate equivalent networks of the kind reported, a network model can be constructed that fully and exactly describes two‐dimensional elastic‐wave propagation in an arbitrarily stratified medium.
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43.20.Wd Analogies
43.20.Bi Mathematical theory of wave propagation
46.25.Cc Theoretical studies
62.30.+d Mechanical and elastic waves; vibrations

Nonlinearity parameters for pulse propagation in isotropic elastomers

G. P. Carman and M. S. Cramer

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 39-51 (1992); (13 pages) | Cited 2 times

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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.
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43.25.Ba Parameters of nonlinearity of the medium

Temperature dependences of the acoustic nonlinearity parameter B/A of aqueous solutions of amino acids

T. V. Chalikian, A. P. Sarvazyan, Th. Funck, V. N. Belonenko, and F. Dunn

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 52-58 (1992); (7 pages)

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A differential technique for evaluating the molar increments of the nonlinearity parameter B/A has been employed for investigations of aqueous solutions of the amino acids glycine, alanine, norvaline, norleucine, arginine monohydrochloride, and lysine monohydrochloride in the temperature range 18 °C–45 °C. Some regularities of temperature dependencies of the nonlinearity parameter B/A of hydration shells of charged and aliphatic groups have been found. Contributions of these groups to the value of B/A molar increments of solute versus temperature have been estimated.
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43.25.Ba Parameters of nonlinearity of the medium
43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues

Nonlinear progressive wave equation model for transient and steady‐state sound beams

Gee Pinn James Too and Jerry H. Ginsberg

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 59-68 (1992); (10 pages) | Cited 1 time

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NPE is a nonlinear progressive wave equation and associated computer code that yields a time domain solution for propagation in an acoustic waveguide. In the present study, the NPE equation is modified to describe axisymmetric sound beams in the paraxial approximation. The modified version of NPE is employed to describe three cases of radiation from a baffled piston: linear transient propagation, linear cw propagation, and nonlinear cw propagation. Alternative schemes to initialize the moving window that is convected by NPE are discussed for each type of problem. The linear transient signal or linear cw signal evaluated by NPE is compared to the direct prediction of the transient or steady‐state Rayleigh integral. The nonlinear signal evaluated by NPE is compared to experimental data in the near and far field. The results show that NPE gives good results for all three propagation problems, in some cases at close regions where the paraxial approximation was previously believed to be inaccurate.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.20.Mv Waveguides, wave propagation in tubes and ducts

Weakly nonlinear waves generated by vibration of a spherical body

Takeru Yano and Yoshinori Inoue

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 69-78 (1992); (10 pages) | Cited 1 time

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The nonlinear propagation of directional spherical waves generated in an unbounded inviscid ideal gas by vibratory motions with small but finite amplitude and moderate frequency of a spherical body is considered. Starting with a regular perturbation expansion for a velocity potential in the near field, a higher‐order problem is investigated in the far field up to the shock formation distance. It is thereby shown that, in the far field concerned, a well‐known simple far‐field equation remains valid for the radial velocity u@B|r including higher‐order corrections up to O(ϵN/r) (N<−1/ϵ ln ϵ), where r is a nondimensional radial coordinate and ϵ(≪1) is the expansion parameter of the expansion. A boundary condition appropriate to the equation, which ensures the matching of a far‐field solution with a near‐field solution, can be determined from the near‐field solution obtained by the regular perturbation procedure. As an application of the theory, the third‐order problem is solved for weakly nonlinear acoustic waves radiated by a pulsating sphere. It is further shown that, for weakly nonlinear cylindrical waves with moderate frequency, a similar far‐field equation becomes invalid at the third approximation in the far field up to the shock formation distance.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves

Particle column formation in a stationary ultrasonic field

Glenn Whitworth and W. T. Coakley

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 79-85 (1992); (7 pages) | Cited 11 times

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Acoustic radiation‐force theory for noninteracting particles predicts that when a particle suspension is exposed to a stationary ultrasonic field, the particles may become concentrated at half‐wavelength intervals. In a plane stationary field, these particle concentrations would have the shape of uniform planar sheets. Gould and Coakley have observed that particles within these sheets often redistribute to form striated columns in the direction of the ultrasonic beam. In this paper, it is shown that particle columns can result from radial nonuniformity of the ultrasonic beam. Theory is presented that describes the equilibrium distribution of particles when subjected to the lowest axially symmetric acoustic mode of a cylindrical waveguide having a pressure‐release wall. Particles with higher density and lower compressibility than that of the host medium will form a column along the axis of a wide waveguide but will migrate to the wall of a narrow waveguide. The direction of radial movement for lower density particles is a function of compressibility but not of waveguide diameter. Results of experiments carried out using aqueous polystyrene suspensions in tubes having thin walls and driven at 3 MHz with a transducer designed to excite primarily the lowest axially symmetric mode were consistent with theory.
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43.25.Uv Acoustic levitation
43.25.Gf Standing waves; resonance
43.20.Mv Waveguides, wave propagation in tubes and ducts

Ray and diffraction effects of acoustic waves when atmospheric conditions produce nonlinear acoustic velocity profiles

C. F. Osborne

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 86-90 (1992); (5 pages)

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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.
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43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors

The wall‐pressure spectrum in turbulent flow over a randomly inhomogeneous elastic solid

M. S. Howe

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 91-98 (1992); (8 pages)

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The characteristics of the low‐wave‐number and acoustic domains of the turbulent boundary layer wall‐pressure spectrum are critically dependent on the structural properties of the wall. This dependence is examined in this paper in terms of a theoretical model of turbulent flow of water over an elastomeric material containing a random distribution of rigid (but movable) filaments. The interaction of hydrodynamic, convective boundary layer pressure fluctuations with the filaments generates a secondary pressure field by scattering. The intensities of the secondary pressures are negligible compared to the convective pressures responsible for their generation, but may nonetheless be large enough to produce significant changes in the relatively weak, low‐wave‐number region of the wall pressure. The magnitude of the changes depends on the relative mass density of the material of the filaments, on their diameters relative to the boundary layer thickness, and on their fractional volume density. Numerical results indicate that increases of the order of 10–20 dB (compared to theoretical estimates for the homogeneous elastomer) can be produced by filaments occupying only 1% by volume of the elastomer. Predictions of this kind suggest that experimental data relating to the low‐wave‐number and acoustic domains are easily contaminated by the presence of relatively small nonuniformities in wall properties.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.30.Lz Underwater applications of nonlinear acoustics; explosions
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
43.50.Nm Aerodynamic and jet noise

Backscattering from rough interfaces and the parabolic approximation

Suzanne T. McDaniel

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 99-106 (1992); (8 pages)

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Iterative solutions of coupled parabolic wave equations are examined to determine the validity of applying this method to predict low‐frequency ocean acoustic reverberation. Solutions for backscattering from a random rough interface between two media of differing wave number are obtained in the form of an expansion in powers of the rough interface excursion from its mean value. This expansion is found to differ significantly from the corresponding expansion obtained by applying perturbation theory to the full elliptic wave equation.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Hw Rough interface scattering
43.20.Fn Scattering of acoustic waves

Marine sediment classification using the chirp sonar

Lester R. LeBlanc, Larry Mayer, Manuel Rufino, Steven G. Schock, and John King

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 107-115 (1992); (9 pages) | Cited 4 times

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The chirp sonar is a calibrated wideband digital FM sonar that provides quantitative, high‐resolution, low‐noise subbottom data. In addition, it generates an acoustic pulse with special frequency domain weighting that provides nearly constant resolution with depth. The chirp sonar was developed with the objective of remote acoustic classification of seafloor sediments. In addition to producing high‐resolution images, the calibrated digitally recorded data are processed to estimate surficial reflection coefficients as well as a complete sediment acoustic impulse profile. In this paper, surficial sediments in Narragansett Bay, RI are used to provide ground truth for an acoustic model. Quantitative acoustic returns from the chirp sonar are used to estimate surficial acoustic impedance and to predict sediment properties. A robust acoustic sediment classification model that uses core samples to account for the local depositional environment has been developed. The model uses an estimate of acoustic impedance to predict surficial density, porosity, compressibility, and rigidity. The comparisons show a high correlation between the core‐determined sediment properties and the estimates obtained from acoustic measurements.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Vh Active sonar systems

Sonar attenuation modeling for classification of marine sediments

Lester R. LeBlanc, Satchidanan Panda, and Steven G. Schock

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 116-126 (1992); (11 pages) | Cited 4 times

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An attenuation‐based model for classification of marine sediments is developed for the chirp sonar operating in the frequency range of 2–10 kHz. A relaxation‐time model is proposed that combines the various dissipative energy loss mechanisms of sound in marine sediments into a single parameter. Historical data were analyzed by converting attenuation values reported in ‘‘dB/m@kHz’’ to a single relaxation time value. Analysis of these previous attenuation measurements supports the use of a relaxation‐time model. Based on this large collection of data, an empirical equation is developed that relates relaxation time to grain size (in phi units). Using this model, very little phase dispersion is observed for a correlated chirp pulse traveling through 40 m of sand, silt, or clay. Yet, this is not so for a pulse in the ultrasonic frequency range (0.2–1.0 MHz) traveling through only 10 cm of clay. Here, significant dispersion is noted. Because of the unique Gaussian‐like shape of the correlated chirp pulse power spectrum, pulse elongation due to attenuation is minimized. Using the center frequency shift in the pulse spectrum, a new ‘‘instantaneous frequency’’ method of attenuation estimation is proposed that overcomes the problems associated with interfering reflections. Based on the relaxation‐time model, the correlated chirp pulse was synthetically attenuated to establish a relation between the relaxation time and the center frequency shift. In situ sediment‐type predictions from chirp sonar data using the instantaneous frequency method and analyses of core samples taken in the Narragansett Bay, Rhode Island are in good agreement.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Tg Navigational instruments using underwater sound

Seasonal variations of the sediment compressional wave‐speed profile in the Gulf of Mexico

Subramaniam D. Rajan and George V. Frisk

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 127-135 (1992); (9 pages) | Cited 1 time

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The seasonal variation of the sediment compressional wave‐speed profile due to temperature variability in the water column is investigated for shallow‐water regions, where large temperature fluctuations can occur during the course of a year. For example, in water depths of less than 30 m in the Gulf of Mexico, field observations indicate that the annual fluctuation of the ocean bottom temperature is approximately sinusoidal with a peak‐to‐trough value of about 15 °C. The heat flow across the water/sediment interface results in the variation of the pore water temperature with season. It is shown that the compressional wave speed varies approximately linearly with pore water temperature, an effect which is, to first order, independent of both the porosity and given sediment type. Further, the velocity ratio (ratio of sound speeds in the water and the sediment at the water/sediment interface) is shown to be independent of temperature but dependent on sediment type. The effect of variations in water column temperature on sediment compressional wave speed is demonstrated by inversions of two data sets. The data were obtained at the same location in the Gulf of Mexico but at different seasons. Finally, the importance of these variations is studied by considering their effect on (a) the prediction of the pressure field in the water column and (b) the errors introduced in source localization by matched‐field processing.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

On the possibility of monitoring El Niño by using modal ocean acoustic tomography

E. C. Shang and Y. Y. Wang

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 136-140 (1992); (5 pages) | Cited 4 times

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The possibility of monitoring El Niño by using the modal acoustic tomography (MOAT) is discussed. It is found that the inversion of El Niño profile with linear inversion scheme is less successful than the mid‐ocean eddy case indicated by the condition number of the kernel matrix. However, based on a simple yet realistic acoustic model of El Niño, it appears that it might be possible to detect temperature fluctuations associated with El Niño’s by examining a proper set of modal features of the acoustic field. Numerical simulation illustrated that a fair reconstructed El Niño profile could be obtained by using the ‘‘damped least‐squares’’ inversion incorporating the singular value decomposition (SVD) analysis.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

Improving performance for matched field processing with a minimum variance beamformer

John M. Ozard, Gary H. Brooke, and Peter Brouwer

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 141-150 (1992); (10 pages) | Cited 2 times

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Matched field processing (MFP) employing reduced minimum variance beamforming (RMVB) has been described in the literature as being robust to signal phase errors for vertical line arrays in modal noise. These techniques are extended to horizontal line arrays and evaluated for both horizontal and vertical arrays. The evaluation of RMVB is also more general in that it is extended to white and modal noise fields in the presence of phase or amplitude errors. Two phase error models were employed, one corresponding to constant sensor‐position errors the other to short‐term fluctuations of mode phase during the covariance matrix estimation. For minimum variance beamforming (MVB), in the presence of both types of random phase errors, array gain, peak‐to‐sidelobe ratios, and peak‐to‐background ratios all decreased in a modal noise field. Performance was far less sensitive to phase errors in spatially white noise than in modal noise. MVB was modified by reducing the number of eigenvectors employed in the matching. For the modified forms performance was improved over that of MVB with an attendant reduction in the number of computations. The equispaced horizontal arrays consistently outperformed and were more robust than the equispaced vertical arrays. Similar results were obtained with amplitude errors that were constant during the estimation.
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43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.60.Gk Space-time signal processing, other than matched field processing

High‐frequency ultrasonic wave propagation in polycrystalline materials

S. I. Rokhlin, T. K. Bolland, and L. Adler

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 151-165 (1992); (15 pages) | Cited 1 time

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Ultrasonic propagation through a multigrained anisotropic medium is studied in the high‐frequency (geometric) region via supercomputer simulation. The grains and their boundaries are considered randomly oriented. Material texture is also included in the model. A ray‐tracing approach is used with an exact solution for reflection and transmission of ultrasonic waves at grain boundaries. Transmission losses are studied for both phase‐sensitive and phase‐insensitive receiving transducers. Dependence of transmission loss and wave phase distribution on grain size and anisotropy is considered. It is shown that at high anisotropies the transmission loss for a fixed distance between transmitter and phase‐sensitive receiver passes through a minimum as a function of the grain size. The wave‐front orientation angles and the beam deviations at the receiving transducer are also found.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Contributions to the vibratory excitation of gear systems from periodic undulations on tooth running surfaces

William D. Mark

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 166-186 (1992); (21 pages) | Cited 2 times

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The transmission error is widely recognized to be the principal source of vibratory excitation arising from meshing gear pairs. Periodic machining errors (undulation errors) on gear teeth can provide an important contribution to the transmission error of wide‐face helical gears. A method is described for using complex sinusoids to represent such periodic errors on individual gear teeth. Expressions are derived for the Fourier series expansion coefficients of the contributions from such errors to the transmission error. A model describing the relative phase relation on successive teeth of the individual sinusoidal components of such errors is postulated which is believed to provide a valid representation of the phase of most, if not all, such errors generated by imperfections in the rotating elements of gear manufacturing apparatus. For particular parameter values of the phase model, it is shown that such periodic errors can contribute to: (1) tooth meshing harmonics only, (2) rotational harmonics only, or (3) both tooth meshing and rotational harmonics. Two cases of practical interest are analyzed in detail—namely, periodic errors caused by imperfections in worktable rotational and translational drives. The rotational drive imperfections give rise to one dominant rotational harmonic in the transmission error spectrum; whereas, the translational drive imperfections contribute, primarily, to the tooth meshing harmonics of the transmission error spectrum.
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43.40.At Experimental and theoretical studies of vibrating systems
43.50.Ed Noise generation

Phonoscopy: An acoustical holography technique for plane structures radiating in enclosed spaces

M. Villot, G. Chavériat, and J. Roland

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 187-195 (1992); (9 pages) | Cited 4 times

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The present paper provides a modification of near‐field acoustical holography (NAH) enabling reconstruction of sound fields in a room in order to study plane structures radiating in enclosed spaces; the new technique is called phonoscopy. A description of the measurement laboratory is given; a single microphone scanner is used to measure the pressure on the hologram plane. Three examples of measurement are presented: a point source located on a rigid wall, a homogeneous wall, and a window mounted in a wall. Maps of the velocity of the structure and of the acoustic intensity radiated are given. The accuracy of phonoscopy is demonstrated by comparison with the accelerometer methods (for measuring vibration velocities) and the two‐microphone technique (for measuring acoustic intensities). Some K‐space spectra are also presented and analyzed, giving more information about the physics of the vibrator.
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43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Hearing protection against high‐level shooting impulses in relation to hearing damage risk criteria

Jussi O. Pekkarinen, Jukka P. Starck, and Jukka S. Ylikoski

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 196-202 (1992); (7 pages) | Cited 1 time

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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.
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43.50.Hg Noise control at the ear
43.50.Qp Effects of noise on man and society
43.50.Pn Impulse noise and noise due to impact
43.66.Vt Hearing protection

Short‐term poststimulatory response characteristics of the human acoustic stapedius reflex: Monotic and dichotic stimulation

Anthony T. Cacace, Robert H. Margolis, and Evan M. Relkin

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 203-214 (1992); (12 pages)

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Two experiments were performed to study short‐term poststimulatory response characteristics of the human acoustic stapedius reflex in the time and intensity domains. In experiment 1, monotic magnitude‐intensity functions (MIFs) were obtained for a 20‐ms test stimulus preceded by a conditioning stimulus varying in duration (20, 50, 100, 500 ms) and level (−10, 0, +10 dB re: stapedius‐reflex threshold) and temporally separated from the test stimulus by various interstimulus intervals (ISIs) (0, 20, 50, 100, 500 ms). Experiment 2 was similar in design except that conditioner and test stimuli were presented dichotically and fewer ISIs were used. Both experiments demonstrated that a prior conditioning stimulus produced significant increases in test‐stimulus response magnitude. These poststimulatory effects were characterized by complex interactions among stimulus variables (conditioner duration, conditioner level, and interstimulus interval) with similar interactions occurring for both monotic and dichotic stimuli. A simple superposition effect of the responses to the conditioner and test stimulus does not account for the effect of prior stimulation since responses often exceeded the sum of the responses to the conditioner and the test stimulus alone.
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43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Ri Evoked responses to sounds
43.64.Qh Electrophysiology of the auditory central nervous system

Responses to amplitude‐modulated tones in the auditory nerve of the cat

Philip X. Joris and Tom C. T. Yin

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 215-232 (1992); (18 pages) | Cited 30 times

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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.
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43.64.Pg Electrophysiology of the auditory nerve
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Modeling the identification of concurrent vowels with different fundamental frequencies

Ray Meddis and Michael J. Hewitt

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 233-245 (1992); (13 pages) | Cited 42 times

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Human listeners are better able to identify two simultaneous vowels if the fundamental frequencies of the vowels are different. A computational model is presented which, for the first time, is able to simulate this phenomenon at least qualitatively. The first stage of the model is based upon a bank of bandpass filters and inner hair‐cell simulators that simulate approximately the most relevant characteristics of the human auditory periphery. The output of each filter/hair‐cell channel is then autocorrelated to extract pitch and timbre information. The pooled autocorrelation function (ACF) based on all channels is used to derive a pitch estimate for one of the component vowels from a signal composed of two vowels. Individual channel ACFs showing a pitch peak at this value are combined and used to identify the first vowel using a template matching procedure. The ACFs in the remaining channels are then combined and used to identify the second vowel. Model recognition performance shows a rapid improvement in correct vowel identification as the difference between the fundamental frequencies of two simultaneous vowels increases from zero to one semitone in a manner closely resembling human performance. As this difference increases up to four semitones, performance improves further only slowly, if at all.
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43.66.Ba Models and theories of auditory processes
43.66.Hg Pitch
43.71.Qr Neurophysiology of speech perception
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech

Intensity and frequency resolution: Masking of absolute identification and fixed and roving discrimination

Shuji Mori and Lawrence M. Ward

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 246-255 (1992); (10 pages) | Cited 1 time

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Auditory intensity and frequency resolution were studied in three paradigms under masking conditions. Absolute identifications of single stimuli (one‐interval paradigm) and 2IFC judgments of fixed‐ and roving‐level pairs of stimuli (two‐interval paradigm) were obtained from the same experienced observers. Judgments were made under optimal (no mask) conditions, in the presence of a broadband noise mask (simultaneous mask), and when the stimulus(i) to be judged were either preceded (forward mask) or followed (backward mask) by a broadband noise mask. Substantial masking of intensity resolution was found in all mask conditions. Only a simultaneous mask affected frequency resolution. In the no mask condition, performance was best for fixed‐level (or frequency) 2IFC discrimination, followed by roving‐level (frequency) 2IFC, and finally absolute identification. These differences were maintained under masking for frequency resolution, but not for intensity resolution. The results are discussed in terms of the Braida and Durlach (1988) model of intensity resolution. A similar model is suggested for frequency resolution with differences suggested by the differences in neural coding of sound intensity and frequency.
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43.66.Dc Masking
43.66.Fe Discrimination: intensity and frequency
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Auditory filter shapes at low center frequencies in young and elderly hearing‐impaired subjects

Robert W. Peters and Brian C. J. Moore

J. Acoust. Soc. Am. Volume 91, Issue 1, pp. 256-266 (1992); (11 pages) | Cited 13 times

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Auditory filter shapes were measured for two groups of hearing‐impaired subjects, young and elderly, matched for audiometric loss, for center frequencies ( fc) of 100, 200, 400, and 800 Hz using a modified notched‐noise method [B. R. Glasberg and B. C. J. Moore, Hear. Res. 47, 103–138 (1990)]. Two noise bands, each 0.4fc wide, were used; they were placed both symmetrically and asymmetrically about the signal frequency to allow the measurement of filter asymmetry. The overall noise level was either 77 or 87 dB SPL. Stimuli were delivered monaurally using Sennheiser HD424 earphones. Although auditory filters for the hearing‐impaired subjects were generally broader than for normally hearing subjects [Moore et al., J. Acoust. Soc. Am. 87, 132–140 (1990)], some hearing‐impaired subjects with mild losses had normal filters. The filters tended to broaden with increasing hearing loss. There were not any clear differences in filter characteristics between young and elderly hearing‐impaired subjects. The signal‐to‐noise ratios at the outputs of the auditory filters required for threshold (K) tended to be lower than normal for the young hearing‐impaired subjects, but were not significantly different from normal for the elderly hearing‐impaired subjects. The lower K values for the young hearing‐impaired subjects may occur because broadened auditory filters reduce the deleterious effects on signal detection of fluctuations in the noise.
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43.66.Dc Masking
43.66.Cb Loudness, absolute threshold
43.66.Sr Deafness, audiometry, aging effects
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