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Journal of the Acoustical Society of America

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Mar 1991

Volume 89, Issue 3, pp. 971-1492

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Rotational waves in the elastic response of spherical and cylindrical acoustic targets in water

Robert Hickling, R. Kirk Burrows, and James F. Ball

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 971-979 (1991); (9 pages) | Cited 1 time

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The elastic response of a solid sphere to a continuous train of plane waves is shown to consist principally of rotational waves, rather like smoke rings, where the rotational motion of a particular wave is centered at points on an annulus perpendicular to the axis of sound propagation. The rotational waves are most clearly evidenced in the standing modes of free vibration of the sphere, with the waves meshing together like a system of gears. Calculated plots of the displacement vector show how these modes are excited in the sphere by incident sound, and how, during a cycle of the excitation, a first harmonic briefly changes into the nearest fundamental as it changes direction during the oscillation. Other results are presented, including a demonstration that the rotational waves also occur in solid cylinders, with the rotation centered at points along lines parallel to the cylinder axis. It is speculated that the rotational waves occur in any closed body. © 1991 Acoustical Society of America.
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43.20.Bi Mathematical theory of wave propagation
43.20.Fn Scattering of acoustic waves
43.20.Ks Standing waves, resonance, normal modes
43.40.At Experimental and theoretical studies of vibrating systems

Sonic properties of rocks under confining pressure using the resonant bar technique

Nathalie Lucet, Patrick N. J. Rasolofosaon, and Bernard Zinszner

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 980-990 (1991); (11 pages) | Cited 7 times

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This paper presents in detail the resonant bar technique used to measure acoustic properties of materials in the sonic frequency range (≃5–20 kHz). Measurements are corrected for the effects of added mass and jacketing; extrinsic effects such as the sample diameter or the dispersion at higher frequencies can mask intrinsic properties of material and are analyzed here. When this technique is used on porous saturated media such as rocks, it is important to avoid the “Biot–Gardner–White” effect; this intrinsic effect can lead to erroneous high attenuations in unjacketed saturated samples. Experimental evidence of its occurrence on water-saturated rods is presented. Experimental results of velocity and attenuation obtained on various rock types such as limestones and sandstones show the drastic sensitivity of these measurements to effective pressure. Hertz’s theory can be applied to describe the behavior of under-consolidated sandstones. Under high confining pressure, sonic attenuation in water-saturated limestone samples is found to be very low (Q ≥ 100); attenuation in sandstones is always low (Q ≥ 50), except for some shaly sandstones. © 1991 Acoustical Society of America.
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43.20.Fn Scattering of acoustic waves
43.20.Ks Standing waves, resonance, normal modes
43.20.Hq Velocity and attenuation of acoustic waves
43.20.Ye Measurement methods and instrumentation

Regular polygonal arrays of resonant scatterers

Victor Twersky

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 991-998 (1991); (8 pages)

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Numerical results for the scattering cross section (S) of N=3–26 equally spaced monopole resonators on a circle (of radius b) indicate regularities in the values of the normalized diameter (2kb = 4πb/λ = ρ with λ as the wavelength) corresponding to maximal scattering for symmetrical excitation. The peaks S∧(N) occur for ρ = ρ∧(N) between N and 2N, i.e., for circle circumference between Nλ/2 and Nλ. With increasing N, the values of ρ∧(N) in successive alternating sets (shells) of three or four values of N are close to ρm = 2mπ−π/4; shell-1 consists of N=3–5, shell-2 of N=6–9, shell-3 of N=10–12, etc. The basis for the shell structure is delineated by a simple asymptotic approximation (for large ρ and N in the range ρ<2N) or a cylindrical wave representation for a sum of spherical waves. A simple approximation is also derived fo the shift in resonance frequency that occurs for ρ small enough for the array to respond as a collective monopole.© 1991 Acoustical Society of America.
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43.20.Fn Scattering of acoustic waves
43.30.Hw Rough interface scattering
43.20.Bi Mathematical theory of wave propagation

Effect of a resonance of the frame on the surface impedance of glass wool of high density and stiffness

Jean F. Allard, Claude Depollier, Philippe Guignouard, and Pascal Rebillard

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 999-1001 (1991); (3 pages) | Cited 8 times

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A fast variation of the surface impedance of two layers of different thicknesses of the same material has been observed at low frequencies. These variations, which are predicted by the Biot theory, appear at the λ/4 resonance of the frame. © 1991 Acoustical Society of America.
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43.20.Hq Velocity and attenuation of acoustic waves
43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
43.20.Tb Interaction of vibrating structures with surrounding medium

Modes of noncircular fluid-filled boreholes in elastic formations

C. J. Randall

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1002-1016 (1991); (15 pages) | Cited 3 times

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Dispersion curves for4 the modes of noncircular fluid-filled boreholes in homogeneous elastic formations are calculated with a boundary integral formulation. Results are displayed for the propagatory modes of several borehole shapes in both fast and slow formations. Any departure from circularity reduces the tube wave speed. Agreement with exact analytical results is obtained for elliptical boreholes, while a simple approximate relation involving borehole perimeter and area is verified for arbitrary cross sections. Higher-order surface modes such as the flexural and screw modes split into two distinct branches distinguished by their orientation with respect to the principal axes of the borehole cross section. Modal dispersion characteristics in elliptical boreholes may be approximately by scaled circular borehole results. In fast formations the effective scaled radii are related to transverse dimensions of the borehole, but in slow formations they are more closely related to local radii of curvature of the borehole. For more complex cross sections with a single axis of symmetry, dispersion of the flexural mode is well modeled by that in elliptical boreholes of similar dimensions, while that of Stoneley and screw modes is not. In asymmetrical boreholes, significant torsional and out-of-phase motion may occur. © 1991 Acoustical Society of America.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Hq Velocity and attenuation of acoustic waves
43.40.Ph Seismology and geophysical prospecting; seismographs

Effects of focusing on the nonlinear interaction between two collinear finite amplitude sound beams

Jacqueline Naze Tjøtta, Sigve Tjøtta, and Erlend H. Vefring

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1017-1027 (1991); (11 pages) | Cited 17 times

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A study of the propagation and interaction of two collinear finite amplitude sound beams, presented in a previous paper [Naze Tjøtta et al., “Propagation and interaction of two collinear finite amplitude sound beams,” J. Acoust. Soc. Am. 88, 2859–2870 (1990)] is extended to include the effects of focusing. The validity of the parabolic equation when applied to strongly focused sound beams is discussed. Equations and algorithms based on a transformed parabolic equation are presented and used to compute the interaction between two collinear, focused sound beams, and between one plane wave and a focused sound beam. Numerical results are shown, with special emphasis on parametric generation and parametric reception of sound.© 1991 Acoustical Society of America.
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43.25.Lj Parametric arrays, interaction of sound with sound, virtual sources
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

Effects of absorption on the nonlinear interaction of sound beams

Corinne M. Darvennes, Mark F. Hamilton, Jacqueline Naze Tjøtta, and Sigve Tjøtta

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1028-1036 (1991); (9 pages)

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Nonlinearity in the propagation and interaction of sound beams in real fluids is considered, with special emphasis on the effects of absorption. Asymptotic formulas are derived for the sum and difference frequency sound generated by two harmonic sound beams. The amplitude and phase conditions of the sources are arbitrary, within the limits imposed by the parabolic approximation. A distinction is made between two main contributions to the nonlinearly generated sound in the far field, the continuously pumped sound and the scattered sound. The relative amplitudes of the pumped and scattered waves are shown to depend critically on the frequency dependence of the absorption coefficients. Numerical results are presented for the noncollinear interaction of Gaussian primary beams, and also for second harmonic generation in the field of a circular uniform piston source.© 1991 Acoustical Society of America.
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43.25.Lj Parametric arrays, interaction of sound with sound, virtual sources

Effects of boundary conditions on the nonlinear interaction of sound beams

Jacqueline Naze Tjøtta, James A. TenCate, and Sigve Tjøtta

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1037-1049 (1991); (13 pages) | Cited 1 time

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Weak nonlinearity in the propagation and interaction of real sound beams in a lossless fluid is considered. Special emphasis is given to the effects produced by various boundary conditions at the sound sources and other bounding surfaces. Asymptotic formulas and numerical results are presented for the second harmonic, and for the scattered sum and difference frequency sound generated by two harmonic beams that intersect at an arbitrary angle. The results are derived from a general theory presented earlier [Naze Tjøtta and Tjøtta, J. Acoust. Soc. Am. 83, 487–495 (1988)], which is valid for any source separation and amplitude distribution. In situations where the parabolic approximation is not legitimate (large angles, broad beams), properly accounting for the boundary conditions may be crucial. Also discussed are implications for the parametric emitting and receiving arrays. © 1991 Acoustical Society of America.
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43.25.Lj Parametric arrays, interaction of sound with sound, virtual sources
43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves

Higher-order Padé approximations for accurate and stable elastic parabolic equations with application to interface wave propagation

Michael D. Collins

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1050-1057 (1991); (8 pages) | Cited 25 times

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Higher-order Padé approximations are applied to derive accurate and stable parabolic equations for sound propagation in oceans bounded below by an elastic bottom or bounded above by ice cover. Accuracy is achieved by placing constraints on the derivatives of the Padé approximations at the point corresponding to the reference wave number. Stability is achieved by requiring that the Padé approximations map part of the lower-left quadrant of the complex plane into the upper half of the complex plane. Elastic parabolic equations based on these Padé series can handle problems involving compressional, shear, and interface waves, very wide propagation angles, and large depth variations and weak range variations in the seismoacoustic parameters. A finite-difference spectral solution is developed for generating reference solutions and starting fields. The rotated elastic parabolic equation is used to investigate the accuracy of the elastic parabolic equation for range-dependent problems.© 1991 Acoustical Society of America.
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43.30.Bp Normal mode propagation of sound in water

The problem of energy conservation in one-way models

Michael B. Porter, Finn B. Jensen, and Carlo M. Ferla

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1058-1067 (1991); (10 pages) | Cited 24 times

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It is shown that the standard stair-step representation of a sloping bottom may result in significant prediction errors. In fact, current parabolic equation implementations are not energy conserving. The problem is shown to derive from the approximate treatment of the interface conditions at vertical boundaries along the stair steps. Several improved interface conditions are proposed.© 1991 Acoustical Society of America.
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43.30.Bp Normal mode propagation of sound in water

A higher-order energy-conserving parabolic equqation for range-dependent ocean depth, sound speed, and density

Michael D. Collins and Evan K. Westwood

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1068-1075 (1991); (8 pages) | Cited 46 times

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Outgoing solutions of the wave equation, including parabolic equation (PE) and normal-mode solutions, are usually formulated so that pressure is continuous with range for range-dependent problems. The accuracy of normal-mode solutions has been improved by conserving energy rather than maintaining continuity of pressure [Porter et al., “The problem of energy conservation in one-way equations,” J. Acoust. Soc. Am. 89, 1058–1067 (1991)]. This approach is applied to derive a higher-order energy-conserving PE that provides improved accuracy for problems involving large ocean bottom slopes and large range and depth variations in sound speed and density. A special numerical approach and complex Padé coefficients are applied to suppress Gibbs’ oscillations. The back-propagated half-space field, an improved PE starter, is applied to handle wide propagation angles. Reference solutions generated with a complex ray model and with the rotated PE are used for comparison.© 1991 Acoustical Society of America.
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43.30.Bp Normal mode propagation of sound in water

Sound generation in the vicinity of the sea surface: Source mechanisms and the coupling to the received sound field

Douglas H. Cato

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1076-1095 (1991); (20 pages) | Cited 1 time

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This paper presents a theory of the mechanisms of sound generation in fluids containing moving fluid interfaces, i.e., discontinuities in density and sound speed, following the approach of Lighthill [Proc. R. Soc. London Ser. A 211, 564–587 (1952)]. It is shown that in addition to the expected volume distributions of quadrupoles, motion of the discontinuities radiate sound equivalent to that from distributed monopoles and dipoles in place of the surfaces. These sources account both for the generation of sound and for the effect of the surfaces on the radiation of that sound. The results are applied to sound generation in the vicinity of the sea surface. All sources are inherent in the theory. The second part of this paper derives a direct relationship between the sound pressure spectrum in the ocean and the frequency wave-number spectra of the near surface fluid processes responsible for generating the sound, on the assumption that these fluid processes are statistically homogeneous in the horizontal plane. The effects of refraction and bottom reflections are ignored. The results are given in terms of “coupling factors” that are measures of the extent to which the source field copules to the received sound field. The coupling factors are evaluated and the results give some insight into the source characteristics required to ensonify the far field.© 1991 Acoustical Society of America.
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43.30.Lz Underwater applications of nonlinear acoustics; explosions
43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Theoretical and measured underwater noise from surface wave orbital motion

Douglas H. Cato

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1096-1112 (1991); (17 pages) | Cited 1 time

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This paper develops a theory of sound generation by orbital motion of sea surface waves (as distinct from motion directly resulting from wave breaking such as bubble oscillation) and compares the noise predictions with measurements in a carefully controlled experiment. Theory and measurement were found to agree within the experimental errors. The mechanism is also known as the nonlinear interaction of surface waves and has been addressed by a number of authors. The approach of this paper differs from other models in that it avoids the use of the commonly applied perturbation expansion, and calculates the total noise field whereas others have limited their estimates to sound production from standing waves and waves that closely approximate standing waves. It is shown that while standing waves result in distributed dipoles with vertical axes, other wave interactions result in dipoles with axes inclined to the vertical so that there are components with both horizontal and vertical axes. The relative contribution of the horizontal dipole components to the noise field is of the same order of magnitude as that of the vertical dipole components. This paper therefore predicts higher noise levels and different directionalities, and also determines the contribution from the evanescent or near field that dominates for receiver depths less than several hundred meters (depending on frequency) resulting in substantially higher noise levels at shallow receivers. On the basis of this and previous work there seems little doubt that this mechanism is a significant source of noise in the ocean, usually dominant from about 0.2 to 5 Hz. © 1991 Acoustical Society of America.
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43.30.Lz Underwater applications of nonlinear acoustics; explosions
43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Expansion of integral equations arising in scattering theory

Suzanne T. McDaniel and Phyllis R. Krauss

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1113-1118 (1991); (6 pages)

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Solutions to integral equations for the field on the boundary surface are obtained for the special case of scattering from a one-dimensional periodic pressure release surface. The results, which are expressed as an expansion in powers of hk, differ for different formulations of the boundary integral equation. Of the three integral equations considered, only one yields physically acceptable reflection coefficients, and these are identical to those obtained using the small waveheight approximation. © 1991 Acoustical Society of America.
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43.30.Hw Rough interface scattering
43.20.Fn Scattering of acoustic waves

Acoustic tomography via matched field processing

A. Tolstoy, O. Diachok, and L. N. Frazer

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1119-1127 (1991); (9 pages) | Cited 12 times

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This paper suggests a new approach based on narrow-band, low-frequency data using air-deployed shots recorded on widely distributed large aperture vertical arrays. This approach uses fast, cheap, and high S/N data. Results to date with a simulated three-dimensional (3-D) eddy environment show that efficient characterization of the environment plus careful selection of the source/array geometry can lead to highly accurate estimates of the 3-D sound-speed profiles, e.g., maximum errors less than 0.2 m/s.© 1991 Acoustical Society of America.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

Arctic abyssal T phases: Coupling seismic energy to the ocean sound channel via under-ice scattering

Ruth Eta Keenan and Lynn Renee Lineback Merriam

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1128-1133 (1991); (6 pages) | Cited 1 time

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Earthquakes along the mid-arctic ridge radiate earthborne compressional and shear waves that couple into the waterborne arctic acoustic channel and propagate as T phases. The T-phase energy is transmitted above the epicenter through the seafloor at near-vertical angles. Scattering from the ice surface couples some of this energy into waterborne angles. At 5 Hz, the coupled energy is about 40 dB down from the incident levels, and at 15 Hz it is about 30 dB down. Scattering accounts for the characteristic spectral shape of the abyssal T phase that is more energetic at 15 Hz than 5 Hz. Several T-phase arrivals were recorded on hydrophones during the FRAM II experiment. From the measured acoustic levels, a transmission loss prediction between source and receiver, and the scattering conversion losses, the microearthquake acoustic source level in the water column is estimated to be about 250 dB re 1 μPa2-m/Hz at 5 Hz and 235 dB re 1 μPa2-m/Hz at 15 Hz. These levels lead to a crustal attenuation estimate of 0.52 dB/km at 5 Hz, which is consistent with FRAM II refraction measurements. © 1991 Acoustical Society of America.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Hw Rough interface scattering
43.40.Ph Seismology and geophysical prospecting; seismographs

Energetics of the deep ocean’s infrasonic sound field

G. L. D’Spain, W. S. Hodgkiss, and G. L. Edmonds

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1134-1158 (1991); (25 pages) | Cited 8 times

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Simultaneous measurements of infrasonic (0.5–20 Hz) acoustic particle velocity and acoustic pressure made by the Marine Physical Laboratory’s set of freely drifting Swallow floats are analyzed in terms of the energetics of acoustic fields. Results from a recent deep-ocean deployment indicate that the midwater column’s acoustic potential and kinetic energy density spectra are equal above 1.7 Hz since, away from the ocean boundaries, the sound field is locally spatially homogeneous. Near the ocean bottom, the vertical spatial inhomogeneity is statistically significant between 0.6–1.4 Hz and 7–20 Hz. In the lower band, the pressure autospectrum decreases with increasing distance from the ocean bottom, whereas in the upper band, it increases due to the deep sound channel’s ability to trap acoustic energy at the higher infrasonic frequencies. For ship signals, the signal-to-noise ratio in the active intensity magnitude spectrum is 3–6 dB greater than in either of the two energy density spectra due to the vector nature of acoustic intensity. Although smaller than the net horizontal flux above a few hertz, a statistically significant net vertical flux density of energy occurs across the whole frequency band, from the ocean surface into the bottom. The direction of the net horizontal flux density for various discrete sources, e.g., a magnitude 4.1 earthquake, a blue whale, and commercial ships, is discussed. The net horizontal flux density of the background sound field between 5 and 12 Hz may have been determined by the surrounding ocean bottom topography in one experiment; its direction approximately coincides with the center of a topographic window. However, it also matches the heading toward a 4000-km-distant hurricane. A third possibility of an unknown, broadband source cannot be eliminated with the available data. © 1991 Acoustical Society of America.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field

A two-dimensional Fourier transform method for the measurement of propagating multimode signals

D. Alleyne and P. Cawley

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1159-1168 (1991); (10 pages) | Cited 50 times

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A technique for the analysis of propagating multimode signals is presented. The method involves a two-dimensional Fourier transformation of the time history of the waves received at a series of equally spaced positions along the propagation path. The technique has been used to measure the amplitudes and velocities of the Lamb waves propagating in a plate, the output of the transform being presented using an isometric projection which gives a three-dimensional view of the wave-number dispersion curves. The results of numerical and experimental studies to measure the dispersion curves of Lamb waves propagating in 0.5-, 2.0-, and 3.0-mm-thick steel plates are presented. The results are in good agreement with analytical predictions and show the effectiveness of using the two-dimensional Fourier transform (2-D FFT) method to identify and measure the amplitudes of individual Lamb modes. © 1991 Acoustical Society of America.
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43.35.Mr Acoustics of viscoelastic materials
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.40.Dx Vibrations of membranes and plates

Dynamic interaction of a poroelastic layer and a half-space

M. Tajuddin and Syed Iqbal Ahmed

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1169-1175 (1991); (7 pages) | Cited 2 times

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The dynamic interaction of a poroelastic layer and a half-space is investigated using the analytical model based on Biot’s theory of wave propagation in fluid-saturated porous media. The wave velocity equations are derived and discussed in the case of welded and smooth contacts, each for pervious and impervious surfaces. In the limiting case of wave number, the problem reduces to more simplified forms discussed in previous works. © 1991 Acoustical Society of America.
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43.40.Dx Vibrations of membranes and plates
43.20.Tb Interaction of vibrating structures with surrounding medium

A comparison of three classical concert halls

J. S. Bradley

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1176-1192 (1991); (17 pages) | Cited 2 times

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Values of newer auditorium acoustics quantities are presented for measurements in three well-known classical concert halls: the Amsterdam Concertgebouw, the Vienna Grosser Musikvereinssaal, and the Boston Symphony Hall. The measured octave band quantities included reverberation time, early decay time, sound strength or level, early/late sound ratios, and lateral energy fractions. Hall average values from the measured unoccupied conditions are presented as well as estimated occupied values. The variation of parameters with both source and receiver position is examined in detail. The results help to define the range of conditions that are to be expected in good concert halls, and reveal some of the detailed differences among these halls. © 1991 Acoustical Society of America.
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43.55.Gx Studies of existing auditoria and enclosures
43.55.Mc Room acoustics measuring instruments, computer measurement of room properties

Estimation of the parameters of the Rice distribution

Kushal K. Talukdar and William D. Lawing

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1193-1197 (1991); (5 pages)

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This paper deals with the problem of estimating the parameters of the Rice distribution. The distribution has applications in sonar and radar signal processing and a proper estimation procedure with associated confidence intervals is important. Using the sample second moment as an estimate of the second moment of the distribution, two techniques, viz., methods of moments and maximum likelihood are applied to synthetic envelope data of known signal-to-noise ratios, in order to estimate the parameter from different sample sizes. It is concluded that the sample second moment is an unbiased estimate of the theoretical second moment and for the signal-to-noise ratio parameter both methods work without any significant bias and satisfy the criterion of maximum efficiency. However, the method of moments is simpler, easier to apply and therefore recommended as the method of choice. © 1991 Acoustical Society of America.
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43.60.Cg Statistical properties of signals and noise

A non-iterative time mapping algorithm for linear motion in 3-space

D. W. Ricker

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1198-1200 (1991); (3 pages)

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The modeling of signal propagation or communication channels when the source-receiver or scatterer are moving at relativistic speeds is often complicated by time base distortion. In order to synthesize the received waveform, it is usually necessary to map time of signal reception to time of transmission recursively for each received time series sample. This laborious procedure which can severely limit the ability to carry out real time modeling may be considerably foreshortened if a piece-wise linear approximation is made to the motion in 3-space. Then, the recursive computation reduces to a 2-step closed-form algorithm. © 1991 Acoustical Society of America.
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43.60.Gk Space-time signal processing, other than matched field processing

Modeling synchronization and suppression of spontaneous otoacoustic emissions using Van der Pol oscillators: Effects of aspirin administration

Glenis R. Long, Arnold Tubis, and Kenneth L. Jones

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1201-1212 (1991); (12 pages) | Cited 17 times

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Many of the aspects of the interaction of spontaneous otoacoustic emissions with external tones (suppression and synchronization) can be qualitatively simulated by the behavior of a single driven Van der Pol oscillator. Analytical and numerical investigations of a model of spontaneous otoacoustic emissions based on such an oscillator (with appropriate parametric changes in the nonlinear and negative damping components) lead to predictions of the nature of the changes in suppression and synchronization (frequency-locking) tuning curves when the levels of spontaneous otoacoustic emissions are modified. Observations of the suppression and synchronization of spontaneous otoacoustic emissions by external tones of different frequencies and levels were obtained while the levels of spontaneous emissions were altered by aspirin administration. Modeling an emission as a single Van der Pol oscillator qualitatively accounts for: (1) the reduction of the level of an external tone required to suppress the emission by a decibel amount equivalent to the level reduction induced by aspirin administration; (2) the broadening of the frequency-locking tuning curve of an emission whose level is reduced; and (3) the pulling of the emission frequency by an external tone. It does not account for: (1) the observed asymmetry in the slopes of the external-tone suppression curves (more gradual for frequencies of the suppressor tone higher, rather than lower, than that of the emission); and (2) the frequency pushing of the emission by an external tone. © 1991 Acoustical Society of America.
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43.64.Bt Models and theories of the auditory system
43.64.Jb Otoacoustic emissions

A computational model of afferent neural activity from the cochlea to the dorsal acoustic stria

M. J. Pont and R. I. Damper

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1213-1228 (1991); (16 pages) | Cited 2 times

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The first comprehensive computational modelof the precortical mammalian auditory system to include afferent neural processing up to the level of the dorsal acoustic stria (DAS) is described. The model consists of two scissile stages simulating (1) the cochlea and the auditory nerve (AN) and (2) the dorsal cochlear nucleus (DCN). The model derives its input from a 128-channel cochlear filterbank. Cochlear transduction, rectification, logarithmic compression, and two-tone suppression functions are performed at the first stage of the simulation. The 512 artificial neurons employed model the cell at the level of transmembrane potential and have interconnections that follow closely those reported in recent anatomical and physiological studies of the cat AN and DCN. The responses of the model to pure-tone stimuli (at various sound-pressure levels) and noise stimuli (at various levels and bandwidths) are reported in detail and compare well with published results. The model is being used to investigate the representation of initial English stop consonants (differing in voice-onset time) in the DAS; this work is briefly described. © 1991 Acoustical Society of America.
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43.64.Bt Models and theories of the auditory system
43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Kc Cochlear mechanics
43.64.Pg Electrophysiology of the auditory nerve

Finding the impedance of the organ of Corti

George Zweig

J. Acoust. Soc. Am. Volume 89, Issue 3, pp. 1229-1254 (1991); (26 pages) | Cited 46 times

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Measurements of the nonlinear response of the basilar membrane to a pure tone are shown to have a simple form for moderate membrane velocities:   
math
where the response V is the velocity of the membrane at measurement position x, Vu is the umbo velocity, f is the frequency of the stimulus, and fc(x) is the local characteristic frequency. The frequency dependence of the functions ν(x,f) and math(x,f) is determined from the data, and ν(x,f) and ln math(x,f) are shown to be analytic functions in the lower half of the complex frequency plane, with Re{ν(x,f)} a monotonically increasing function of f at fixed x. The linear limit of basilar membrane motion is characterized by a transfer function T(x,f) = (math/V1)ν/(1−ν), estimated by extrapolating V(x,f;Vu)/Vu to a small membrane velocity V1. T(x,f) and ln T(x,f) are shown to be analytic functions in the lower half of the complex frequency plane. The inverse of the amplitude of the transfer function, which has both a deep dip at f ≈ fc(x) and a broad shoulder at lower frequencies, bears a striking resemblance to the neural threshold tuning curve. The functional form of T(x,f) is used to deduce the equation governing the motion of a section of the organ of Corti. Each section acts like a negatively damped harmonic oscillator stabilized at time t by a feedback force proportional to the velocity at the previous time t−τ. The time delay τ is proportional to the oscillator period [τ = 1.75/fc(x)]. Like a laser, the organ of Corti pumps energy into harmonic traveling waves. Unlike the laser, the direction of energy flow abruptly reverses as the traveling wave approaches the point of maximum membrane velocity [fc(x) ≈ f]. All accumulated wave energy is then pumped back into a small section of the organ of Corti where transduction presumably occurs. Outer hair cells are conjectured to be active elements contributing to the negative damping and feedback of the cochlear amplifier. © 1991 Acoustical Society of America.
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43.64.Bt Models and theories of the auditory system
43.64.Kc Cochlear mechanics
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