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Journal of the Acoustical Society of America

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Jun 1986

Volume 79, Issue 6, pp. 1655-2108

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Methods of measuring the attenuation of hearing protection devices

E. H. Berger

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1655-1687 (1986); (33 pages) | Cited 9 times

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The published literature describing three real‐ear‐attenuation‐at‐threshold (REAT), nine above‐threshold, and four objective methods of measuring hearing protector attenuation is reviewed and analyzed with regard to the accuracy, practicality, and applicability of the various techniques. The analysis indicates that the REAT method is one of the most accurate available techniques since it assesses all of the sound paths to the occluded ear and, depending upon the experimenter’s intention, can reflect actual in‐use attenuation as well. An artifact in the REAT paradigm is that masking in the occluded ear due to physiological noise can spuriously increase low‐frequency (≤500 Hz) attenuation, although the error never exceeds approximately 5 dB, regardless of the device, except below 125 Hz. Since the preponderance of available data indicates that attenuation is independent of sound level for intentionally linear protectors, the use of above‐threshold procedures to evaluate attenuation is not a necessity. An exception exists in the case of impulsive noises, for which the existing data are not unequivocal with regard to hearing protector response characteristics. Two of the objective methods (acoustical test fixture and microphone in real ear) are considerable time savers. All objective procedures are lacking in their ability to accurately determine the importance of the flanking bone‐conduction paths, although some authors have incorporated this feature as a post‐measurement correction. The microphone in real‐ear approach is suggested to be one of the most promising for future standardization efforts and research purposes, and the acoustical test fixture technique is recommended (with certain reservations) for quality control and buyer acceptance testing.
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43.10.Ln Surveys and tutorial papers relating to acoustics research; tutorial papers on applied acoustics
43.66.Vt Hearing protection
43.66.Yw Instruments and methods related to hearing and its measurement
43.50.Hg Noise control at the ear

Diffraction of Rayleigh waves in a half‐space. II. Inclined edge crack

Vikram K. Kinra and Bien Q. Vu

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1688-1692 (1986); (5 pages) | Cited 4 times

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This paper is concerned with the diffraction of a Rayleigh surface wave by an edge crack included at an arbitrary angle to the free surface of a half‐space. The corresponding problem for a normal edge crack was studied in [B. Q. Vu and V. K. Kinra, J. Acoust. Soc. Am. 77, 1425–1430 (1985)]. The scattered field was measured on the free surface both in the vicinity of the crack and far away from it. The nearfield possesses a number of interesting features which can be used to characterize an inclined crack. The farfield transmission and reflection coefficients, AT and AR, respectively, were measured under both the steady time‐harmonic motion (tone burst) and the transient motion (spectroscopy) of the half‐space. All three regions of interest were studied: wavelengths large, equal, and small compared to the crack lengths. As expected, in the short‐wavelength limit, AR asymptotically reaches its frequency‐independent limit which is the reflection coefficient of an infinite wedge. This limit was found to agree very well with the earlier results by Viktorov for a wedge [I. A. Viktorov, Rayleigh Waves and Lamb Waves—Physical Theory and Application (Plenum, New York, 1964)]. The transmission coefficient exhibits an oscillatory dependence on frequency; this is attributed to a resonance between the crack tip and the free surface. The spacing between the peaks of AT was found to satisfy the following simple kinematic condition: wavelength equals twice the crack length. Furthermore, AT was found to be measurably identical for two complementary cracks of inclination θ and π−θ, where θ is measured from the free surface.
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43.20.Fn Scattering of acoustic waves
43.35.Pt Surface waves in solids and liquids
68.35.Gy Mechanical properties; surface strains

Sound scattering from a thin rod in a viscous medium

Wen H. Lin and A. C. Raptis

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1693-1701 (1986); (9 pages) | Cited 1 time

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Sound waves incident on a thin elastic rod whose radius is smaller than the wavelength of the incident sound induce flexural and uniform compressional oscillations in the rod. These elastic oscillations, in turn, radiate sound waves into the fluid medium and affect the scattered waves. This paper deals with an analytic study on sound scattering by, and acoustoelastic vibrations of, a thin elastic unbound rod in a viscous fluid. The shear viscosity of the fluid is considered in the solutions to boundary value problems concerning the sound scattering and the elastic response of the rod. Results show that the scattered compressional waves consist of the rigid‐rod scattering of compressional waves, monopolar waves due to the uniform pulsating of the rod, and dipolar waves due to the flexural vibration of the rod. The scattered viscous waves consist of the rigid‐rod scattering of viscous waves and dipolar waves due to the flexural vibration of the rod. Acoustic resonances occur when the effective inertia force of the rod balances the stiffness force of the rod. The fluid viscosity and the scattering of sound give rise to damping effects for the rod vibrations and signficantly affect the acoustic resonances.
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43.20.Fn Scattering of acoustic waves

Synthesis of backscattering from an elastic sphere using the Sommerfeld–Watson transformation and giving a Fabry–Perot analysis of resonances

Kevin L. Williams and Philip L. Marston

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1702-1708 (1986); (7 pages) | Cited 4 times

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The Sommerfeld–Watson transformation (SWT) was recently applied to the acoustic backscattering from elastic spheres in water having ka≫1 [K. L. Williams and P. L. Marston, J. Acoust. Soc. Am. 78, 1093–1102 (1985)]. Expressions for the scattering due to each class of elastic surface wave (e.g., the Rayleigh wave) were interpreted in terms of contributions from repeated circumnavigations. In the present paper, these expressions are summed in closed form as in the analysis of Fabry–Perot resonators. The form function is synthesized by adding this sum to the specular reflection. The procedure is confirmed by comparison with the exact form function f for a tungsten carbide sphere in the range 10≤ka≤80. In this case, the interference of the specular and Rayleigh contributions produces the underlying structure in ‖f(ka)‖, while the whispering gallery wave resonances produce a finer superposed structure. Phase shifts and coupling coefficients are identified which affect the signatures in ‖f(ka)‖ of the Rayleigh wave resonances.
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43.20.Fn Scattering of acoustic waves

Acoustic attenuation in fluid‐saturated porous cylinders at low frequencies

Keh‐Jim Dunn

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1709-1721 (1986); (13 pages) | Cited 5 times

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Laboratory measurements on the elastic moduli and the acoustic attenuation of fluid‐saturated porous rock cylinders are frequently affected by the boundary conditions of the rock sample, i.e., whether the curved surface of the cylindrical sample is exposed to air or properly sealed. In this paper, the analytical solutions of these problems for the extensional, torsional, and flexural modes are derived, and several numerical examples are computed. It was found that there exists an ‘‘artificial’’ attenuation caused by the open‐pore boundary condition, whose relaxation frequency, in the case of extensional mode, is directly proportional to the permeability of the rock and inversely proportional to the viscosity of the pore fluid and the square of the sample radius. This attenuation exists in both the extensional and the flexural modes but not in the torsional mode.
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43.20.Hq Velocity and attenuation of acoustic waves

On the mode‐splitting of Love waves in a rough layer

I. Lerche

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1722-1733 (1986); (12 pages)

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Using the technique of mean‐field renormalization, it is shown that the general effect of surface roughness on Love waves is to cause not only a splitting of the mode frequency but also an effective attenuation because of multiple scattering from the rough surface. The precise amounts of splitting and attenuation are shown to be dependent on the power spectrum of the surface roughness as well as on the normal mode. The calculation is restricted to the two‐dimensional problem where the roughness varies in one spatial direction only so that coupling of the Love modes to P–SV waves is strictly forbidden. For surface roughness, of rms amplitude 〈 f 2〉1/2, occurring on a scale that is long when compared to the Love mode wavelength, both the frequency splitting and effective attenuation are of fractional order ω〈 f 2〉1/2(s21−s22)12/2, where ω is the angular frequency and s1 and s2 are the slowness on either side of the rough boundary. For a surface roughness dominating the evaluation of certain basic integrals occurring in the mean‐field dispersion relation, it is shown that the modes couple nonlinearly to the rough fluctuations so that both resonant scattering of the modes amongst themselves, as well as nonresonant scattering to ‘‘background’’ oscillations, takes place. These analytic calculations have been done to both illustrate the broad range of diverse phenomena that can arise as well as to provide formulas for later comparison against numerical experiments and synthetic seismograms.
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43.20.Hq Velocity and attenuation of acoustic waves
43.20.Ks Standing waves, resonance, normal modes
43.40.Ph Seismology and geophysical prospecting; seismographs

Acoustical properties of partially reticulated foams with high and medium flow resistance

Jean‐F. Allard, Achour Aknine, and Claude Depollier

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1734-1740 (1986); (7 pages) | Cited 8 times

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A new method for measuring impedance has been used for evaluating the normal surface impedance of three foams in free field. The results have been interpreted using the Biot theory, the two dilatational waves being taken into account. It has been pointed out from the theory that, for high flow resistance, the ratio of the acoustical velocities of the frame and the air is close to 1 at the surface of the foam. This ratio decreases with flow resistance but is never negligible for the studied foams. For foams with high flow resistance, the contributions of the two waves must be taken into account when calculating the impedance, and a description with only one wave would not be realistic. For foams with medium flow resistance, the one‐wave approximation for calculating the surface impedance is a good approximation in the whole range of acoustical frequencies.
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43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.58.Bh Acoustic impedance measurement

The existence of caustics and cusps in a rigorous ray tracing representation

Edward R. Floyd

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1741-1747 (1986); (7 pages) | Cited 1 time

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With rigorous ray tracing, caustics and their associated cusps in addition to those of classical ray tracing are encountered. These additional caustics are associated with classical (WKB) vertex points. Rigorous ray tracing also confirms those caustics that exist under a classical ray tracing representation, albeit both displaced from the classical locations into the classical shadow zone and perhaps deformed with additional cusps.
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43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.20.Bi Mathematical theory of wave propagation
43.30.Cq Ray propagation of sound in water
43.20.Dk Ray acoustics

Applications of multifold Kirchhoff–Helmholtz path integrals to sound propagation in the ocean. Part I: Theory

L. Neil Frazer

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1748-1759 (1986); (12 pages)

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Kirchhoff–Helmholtz theory is used to derive a generalized ray theory, called the multifold path integral (MFPI) method, that enables the calculation of frequency‐dependent ray theoretical amplitudes at caustics and shadows where ordinary ray theory (geometrical acoustics) fails. The method is then applied to some problems of acoustic propagation in an ocean whose sound‐speed profile, bathymetry, and bottom characteristics are all range dependent. Specifically, considered are: (a) rays with multiple bounces between the surface and a bottom that is rough on a scale much larger than a wavelength of the signal; (b) rays in a sound‐speed channel whose axis height varies with range; and (c) rays around an obstacle such as a seamount. Modeling examples will be presented in a subsequent paper but included here is a discussion of various methods for evaluating the multifold integrals.
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43.30.Cq Ray propagation of sound in water
43.20.Bi Mathematical theory of wave propagation
43.20.Dk Ray acoustics

Simulation of bottom interacting waveforms

David P. Knobles and Paul J. Vidmar

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1760-1766 (1986); (7 pages) | Cited 1 time

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Current understanding of the acoustic processes occurring in the seafloor is used to develop a detailed ray approach for simulating the received time series of a broadband acoustical signal interacting once with the seafloor. The environment is assumed to be horizontally stratified, and the seafloor is described in terms of a geoacoustic profile. The frequency response is constructed from the superposition of the individual responses of each of the eigenrays. The ray approach includes the effects of reflection from the water–sediment interface, penetration into the sediment, refraction due to a constant compressional sound‐speed gradient in the sediment, absorption within the sediment, phase shifts due to caustics, and multipaths. The one‐bounce time series is constructed from the inverse Fourier transform of the product of the source spectrum and the eigenray frequency response. As an example application, the one‐bounce time series for an explosive source in a deep water environment is calculated and analyzed in terms of acoustical processes. Excellent agreement with measured time series is demonstrated.
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43.30.Cq Ray propagation of sound in water
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
91.50.Ey Seafloor morphology, geology, and geophysics
43.20.Dk Ray acoustics

Rough surface elastic wave scattering in a horizontally stratified ocean

W. A. Kuperman and Henrik Schmidt

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1767-1777 (1986); (11 pages) | Cited 8 times

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A previously developed boundary perturbation method [W. A. Kuperman, J. Acoust. Soc. Am. 58, 365–370 (1975)] is extended to treat scattering at a randomly rough interface which separates viscoelastic media. This method is then combined with a full wave treatment of sound propagating in a stratified ocean described by a system of fluid and elastic layers [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813–825 (1985)]. The net result of combining the extended boundary perturbation method with the full wave solution technique is to define a set of effective potentials which, when inserted in the full wave solution algorithm, yield the coherent components of the compressional and shear wave fields which decay with range due to boundary roughness scattering into incoherent compressional and shear waves. A natural outcome of this model is also the option to calculate the coherent reflection coefficient for an arbitrarily arranged layered system of fluid/solid media separated by randomly rough interfaces. Numerical examples of reflection coefficients and sound propagation in an ocean described by a stratified waveguide are presented.
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43.30.Bp Normal mode propagation of sound in water
43.30.Hw Rough interface scattering
43.20.Fn Scattering of acoustic waves

Surface velocity, shadowing, multiple scattering, and curvature on a sinusoid

Diana F. McCammon and Suzanne T. McDaniel

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1778-1785 (1986); (8 pages) | Cited 1 time

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The Kirchhoff approximation is frequently invoked in the solution of scattering problems because it greatly reduces the computational complexity. This paper compares the actual surface velocity distribution on a sinusoidal pressure release surface to that assumed by the Kirchhoff approximation and examines more closely the reasons for its successes and failures. Corrections designed to improve the result by including the effects of shadowing, surface curvature, and multiple scattering are also investigated. In the cases examined, curvature correction appears to offer the most improvement while the multiple scattering contribution is practically negligible.
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43.30.Bp Normal mode propagation of sound in water
43.30.Hw Rough interface scattering

Real‐time study of frequency dependence of attenuation and velocity of ultrasonic waves during the curing reaction of epoxy resin

S. I. Rokhlin, D. K. Lewis, K. F. Graff, and Laszlo Adler

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1786-1793 (1986); (8 pages) | Cited 8 times

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The frequency dependence of the phase velocity and attenuation of ultrasonic waves were measured as a function of time during the polymerization (curing) reaction of epoxy resins. The phase velocity and attenuation were evaluated from the amplitude and phase spectra of ultrasonic signals transmitted through a layer of curing epoxy resin. The measurements were made in the frequency range of 2–20 MHz. From the experimental data follows an important conclusion: The attenuation coefficient increases linearly with frequency at all stages of the curing reaction from the viscous liquid to the solid state. The slope of the attenuation coefficient as a function of frequency is strongly dependent on the time of cure (degree of cure). The linear behavior of attenuation versus frequency suggests that the attenuation effect cannot be explained by classical viscothermal absorption or relaxation theory. This type of behavior (so‐called hysteresis behavior) is poorly understood on the molecular level and was found previously for some highly viscous liquids, for solid polymers, and for biological tissue. The phase velocity data were evaluated from the phase spectrum of the transmitted signal. The ultrasonic velocity changes with time according to an S‐shaped curve. It is also moderately dependent on the frequency.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
82.35.-x Polymers: properties; reactions; polymerization

Diffraction correction for a radiation force measurement on an infinite plane target

Peter B. Nagy

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1794-1797 (1986); (4 pages) | Cited 1 time

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A discussion is given of a rigorous diffraction correction for acoustic dosimetry by a radiation force measurement on an infinite plane target. As an example, analytical results are presented for circular radiators of different velocity distributions and diameter‐to‐wavelength ratios, including baffled rigid piston, simply supported piston, clamped piston, and Gaussian radiators.
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43.35.Yb Ultrasonic instrumentation and measurement techniques

The response of a semi‐infinite fiber to a pulse applied asymmetrically to its end

Lynn O. Wilson

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1798-1810 (1986); (13 pages) | Cited 1 time

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McKenna and Simpkins [J. Acoust. Soc. Am. 78, 1675–1683 (1985)] have developed a normal mode theory concerning wave propagation down a semi‐infinite or finite elastic cylinder due to a time‐dependent load applied at one or both ends. To test the practicality of applying this theory, a nontrivial model problem concerning the dynamic response of a glass fiber to a certain pulse applied at its end representing tensile fracture is studied. After considerable analytical effort, the expansion coefficients for the modes are computed. Calculations concerning displacements and strains of the dominant modes are presented. When necessary, additional asymptotic analyses are done. It is possible to obtain a comprehensive description of the fiber’s response to the pulse. However, the effort required to apply the theory to a general problem is extensive. If the problem formulation admits considerable simplification of the expressions for the modal expansion coefficients, the theory is probably both elegant and meaningful.
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43.40.Cw Vibrations of strings, rods, and beams
43.20.Ks Standing waves, resonance, normal modes
43.40.At Experimental and theoretical studies of vibrating systems

An analysis of doubly rotated quartz resonators utilizing essentially thickness modes with transverse variation

D. S. Stevens and H. F. Tiersten

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1811-1826 (1986); (16 pages) | Cited 12 times

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Closed‐form asymptotic expressions for the frequency–wavenumber dispersion relations in doubly rotated quartz plates vibrating in the vicinity of the odd pure thickness frequencies are derived from the equations of linear piezoelectricity and the associated boundary conditions on the major surfaces. The usual assumptions of small piezoelectric coupling and small wavenumbers along the plate are made and it is supposed that the pure thickness frequencies are sufficiently different that one pure thickness wave is dominant at a time. In the treatment the mechanical displacement is decomposed along the eigenvector triad of the pure thickness solution to facilitate the asymptotic analysis. The fact that the wavenumbers along the plate are restricted to be small significantly reduces the complexity of the equations without neglecting any transformed elastic constants. The resulting asymptotic dispersion equation enables the construction of a scalar differential equation describing the transverse behavior of essentially thickness modes of vibration in doubly rotated quartz plates. The scalar equation is applied in the analysis of both trapped energy resonators with rectangular electrodes and contoured crystal resonators using established procedures. In particular, calculations performed for the contoured SC cut and a number of other doubly rotated orientations are shown to be in excellent agreement with experiment. Since the differential equation for each harmonic family depends on the order of the harmonic and in the general doubly rotated case contains mixed derivatives in the plane of the plate, a different transformation is required for each harmonic family to obtain the coordinate system in which the mixed derivatives do not appear and, hence, the equation is separable. An interesting consequence of this transformation is that since the nodal planes of the anharmonics of each harmonic family of the contoured SC‐cut quartz resonator are oriented along the transformed coordinate system for that harmonic family, they are oriented differently for each harmonic family.
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43.40.Dx Vibrations of membranes and plates

Acoustical comparison of three theaters

J. S. Bradley

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1827-1832 (1986); (6 pages)

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Three theaters, including both thrust stage and proscenium arch designs, are evaluated using acoustical measures not yet in common use. The unique characteristics of each theater are considered and include a partially covered orchestra pit and a music shell. A computer model is used to estimate the detrimental effects of excessive ceiling lighting holes.
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43.55.Gx Studies of existing auditoria and enclosures
43.55.Hy Subjective effects in room acoustics, speech in rooms

Transmission loss optimization in acoustic sandwich panels

Spilios E. Makris, Clive L. Dym, and J. MacGregor Smith

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1833-1843 (1986); (11 pages) | Cited 1 time

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Considering the sound transmission loss (TL) of a sandwich panel as the single objective, different optimization techniques are examined and a sophisticated computer program is used to find the optimum TL. Also, for one of the possible case studies such as core optimization, closed‐form expressions are given between TL and the core‐design variables for different sets of skins. The significance of these functional relationships lies in the fact that the panel designer can bypass the necessity of using a sophisticated software package in order to assess explicitly the dependence of the TL on core thickness and density.
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43.55.Rg Sound transmission through walls and through ducts: theory and measurement
43.55.Ti Sound-isolating structures, values of transmission coefficients
43.58.Ta Computers and computer programs in acoustics

High‐resolution beamforming by fitting a plane‐wave model to acoustic data

R. S. Hebbert and L. T. Barkakati

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1844-1849 (1986); (6 pages)

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The problem addressed in this paper is the representation of the acoustic field at an array of hydrophones as a background plus a small number of plane waves. As data, assume that a narrow‐band covariance matrix has been observed. The covariance matrix implied by the model (i.e., background plus small number of plane waves) is adjusted to obtain the least‐squares fit to the observed covariance matrix. Since the number of plane waves is not known, one plane wave is initially assumed and others added in succession until the error is no longer reduced. Each plane wave is described by two parameters: power and bearing. However, the power may be eliminated formally. The problem remaining is one of multidimensional optimization with bearings as unknowns.
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43.60.Gk Space-time signal processing, other than matched field processing
43.30.Yj Transducers and transducer arrays for underwater sound; transducer calibration

Representation of system response using expansions of Hermite and Beranek functions

Richard H. Lyon

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1850-1856 (1986); (7 pages)

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A new representation of system functions in the time and frequency domains using Hermite functions is introduced. The properties of such a representation are compared and contrasted with the well‐known Laguerre expansion of system temporal response introduced by Y. W. Lee [Statistical Computation Theory (Wiley, New York, 1960), Chap. 19]. It is argued that the Hermite functions are more relevant representations of systems with many degrees of freedom, and offer other mathematical and conceptual advantages as well. A new set of functions related to Hermite functions by the Hilbert transform are introduced, and are named Beranek functions. The use of these representations is illustrated by an application to the transfer function for a lossy acoustical pipe.
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43.60.Gk Space-time signal processing, other than matched field processing
02.30.Gp Special functions
43.20.Mv Waveguides, wave propagation in tubes and ducts

What is ‘‘Synchrony suppression’’?

Donald D. Greenwood

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1857-1872 (1986); (16 pages) | Cited 3 times

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Synchrony of discharge of auditory neurons to two‐tone stimuli and ‘‘synchrony suppression’’ have been analyzed by examining the implications of the definition of vector strength. Synchrony suppression, defined as the reduction in the vector strength for one component when a second is introduced, occurs by definition when partial (‘‘half‐wave’’) rectification occurs in an otherwise linear system. It does so with the usual shifts (on the abscissa) of empirical vector strength curves, disproving any necessity for compressive or other nonlinearities. Synchrony suppression, is sometimes defined incompatibly as the shift in dB of a vector strength curve—said to be the magnitude of suppression. That this conception is incorrect is shown by the identification of partial rectification with vector strength reduction and curve shift, but it can be shown to be a logical fallacy as well. The vector strength definition was also applied to the complex waveform obtained at the output of an instantaneous amplitude compressive nonlinearity. The shifts of vector strength growth and decay curves (at their crossover points) necessarily equal those in the linear case for any compressive nonlinearity that compresses equal inputs equally. But such a compressive nonlinearity is not without noticeable effects on vector strengths. If the input levels lie in the range leading to compressed outputs, differences in the relative input levels will be accentuated in the relative output levels in the period histogram. Compression thus contributes to greater differences in the vector strengths, for unequal input levels, than in the linear case. More visible effects on vector strength curves result from waveform distortion, which reduces vector strength saturation and crossover values and causes them to recede at higher input levels.
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43.64.Bt Models and theories of the auditory system

Compound action potential thresholds and tuning curves in the alligator lizard

Robert G. Turner and Neil T. Shepard

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1873-1882 (1986); (10 pages)

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Compound action potential (AP) thresholds and tuning curves were measured in the alligator lizard using techniques similar to those used with the mammal. For tone burst stimuli, the AP was a major component of the gross response, the electrical response to sound recorded by a wire electrode near the cochlea. The AP thresholds agreed well with threshold estimates based on single‐fiber data. A forward masking paradigm produced AP tuning curves which resemble single‐fiber tuning curves. A simultaneous masking paradigm produced curves which match the boundaries of single‐fiber two‐tone rate suppression. The AP thresholds and tuning curves provide useful information about the peripheral physiology of the ear of the alligator lizard.
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43.64.Nf Cochlear electrophysiology
43.64.Tk Physiology of sound generation and detection by animals

Acoustic response and tuning in saccular nerve fibers of the Goldfish (carassius auratus)

Richard R. Fay and Timothy J. Ream

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1883-1895 (1986); (13 pages) | Cited 1 time

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The acoustic frequency selectivity of over 500 saccular nerve fibers of the goldfish was studied using automated threshold tracking based on spike rate increments defined statistically. Saccular fibers of the goldfish show great variation in (1) best sensitivity (−26 to +35 dB re: 1 dyn/cm2), (2) best frequency (below 100 to 1770 Hz), (3) spontaneous rate (0 to over 200 spikes/s), (4) spontaneous type (silent, regular, irregular, burst), and (5) degree of tuning (Q10 dB from <0.1 to 2). Saccular fibers may be grouped into four nonoverlapping categories based on tuning and best frequency: (1) untuned (less than 10‐dB variation in sensitivity between 100 and 1000 Hz), (2) low frequency (BF from below 120 to 290 Hz), (3) midfrequency (BF between 330 and 670 Hz), and (4) high frequency (BF between 790 and 1770 Hz). Within each category, all spontaneous rates and types, and all degrees of tuning can be observed. The least sensitive fibers within each group have zero spontaneous rates. The goldfish is like all other vertebrates studied in that the peripheral auditory system is adapted for frequency selectivity throughout the animal’s entire frequency range of hearing. Peripheral tuning most likely accounts for behavioral determinations of the ‘‘auditory filter’’ and for the detectability of signals masked by noise. The signal‐to‐noise ratio enhancement provided by these peripheral filters is likely to be of primary biological significance. A ‘‘place principle’’ of sound quality analysis based on lines ‘‘labeled’’ according to best frequency in the brain cannot be ruled out on the basis of the peripheral physiology.
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43.64.Pg Electrophysiology of the auditory nerve

A temporal analysis of auditory‐nerve fiber responses to spoken stop consonant–vowel syllables

Laurel H. Carney and C. Daniel Geisler

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1896-1914 (1986); (19 pages) | Cited 1 time

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Auditory‐nerve fiber spike trains were recorded in response to spoken English stop consonant–vowel syllables, both voiced (/b,d,g/) and unvoiced (/p,t,k/), in the initial position of syllables with the vowels /i,a,u/. Temporal properties of the neural responses and stimulus spectra are displayed in a spectrographic format. The responses were categorized in terms of the fibers’ characteristic frequencies (CF) and spontaneous rates (SR). High‐CF, high‐SR fibers generally synchronize to formants throughout the syllables. High‐CF, low/medium‐SR fibers may also synchronize to formants; however, during the voicing, there may be sufficient low‐frequency energy present to suppress a fiber’s synchronized response to a formant near its CF. Low‐CF fibers, from both SR groups, synchronize to energy associated with voicing. Several proposed acoustic correlates to perceptual features of stop consonant–vowel syllables, including the initial spectrum, formant transitions, and voice‐onset time, are represented in the temporal properties of auditory‐nerve fiber responses. Nonlinear suppression affects the temporal features of the responses, particularly those of low/medium‐spontaneous‐rate fibers.
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43.64.Pg Electrophysiology of the auditory nerve
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech

Discrimination of spectral density

W. M. Hartmann, Stephen McAdams, Andrew Gerzso, and Pierre Boulez

J. Acoust. Soc. Am. Volume 79, Issue 6, pp. 1915-1925 (1986); (11 pages) | Cited 2 times

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Experiments were performed to determine the ability of human listeners to discriminate between a sound with a large number of spectral components in a band, of given characteristic frequency and bandwidth, and a sound with a smaller number of components in that band. A pseudorandom placement of the components within the band ensured that no two sounds were identical. The data suggested that discrimination is primarily based upon the perception of temporal fluctuations in the intensity of the sound and secondarily upon resolved structure in the spectrum, perceived as tone color. Experiments using clusters of complex harmonic sounds showed that listeners are able to use the information in upper harmonic bands to discriminate spectral density.
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43.66.Ba Models and theories of auditory processes
43.66.Fe Discrimination: intensity and frequency
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
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