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Apr 1986

Volume 79, Issue 4, pp. 895-1207

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Wave equations in linear viscoelastic materials

Jean‐Paul Charlier and Françoise Crowet

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 895-900 (1986); (6 pages) | Cited 5 times

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Conditions for writing wave equations in linear viscoelastic materials are investigated. The study is restricted to the infinitesimal theory and an application is suggested in modeling ultrasound propagation in soft biological tissues. First, a general wave equation is obtained for the displacement field in an inhomogeneous medium. Second, the propagation of ‘‘the mean principal stress’’ (i.e., minus the arithmetical mean of the principal stresses) is examined. That quantity is particularly relevant when the force per unit area is detected at the surface of a nondissipative coupling medium. If the material is homogeneous, a wave equation is always obtained for the mean principal stress. Otherwise, supplementary conditions have to be assumed on the material and possibly on the motion. Results are illustrated by examples which present linearly elastic perfect fluids and linearly elastic Newtonian viscous fluids as particular viscoelastic materials.
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43.20.Bi Mathematical theory of wave propagation
43.35.Mr Acoustics of viscoelastic materials

K‐space scattering formulation of the absorptive full fluid elastic scalar wave equation in the time domain

Behrooz Compani‐Tabrizi

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 901-905 (1986); (5 pages) | Cited 4 times

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The absorptive full fluid elastic scalar wave equation is developed by deriving the full fluid elastic scalar wave equation from the first principles and adding an absorptive term to the result. The time domain solution to the initial value forward scattering problem is developed for this equation. The solution algorithm is an exact numerical solution and is useful in pressure wave modeling for media with spatially varying velocity, density, and attenuation profiles. The number of operations per time step is of the order of N log2 N, where N is the number of spatial points into which the model has been discretized.
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43.20.Fn Scattering of acoustic waves

Reflection and refraction of elastic waves on a plane interface between two generally anisotropic media

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

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 906-918 (1986); (13 pages) | Cited 17 times

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A unified approach to the study of reflection and refraction of elastic waves in general anisotropic media is presented. Christoffel equations and boundary conditions for both anisotropic media in coordinate systems formed by incident and interface planes, rather than in crystallographic coordinates, are considered. Consideration of wave propagation in an acoustic‐axis direction is included in the general algorithm, so results can be obtained both generally and for planes of symmetry, including planes of isotropy. General features of the numerical results are discussed. Energy conversion coefficients are shown to satisfy reciprocity relations which are formulated. It is much more natural to consider intensity–conversion ratios, rather than amplitude–conversion ratios, showing the important role of ray (rather than wave‐vector) directions in describing phenomena such as grazing angles. In particular, it is shown that the incident wave vector for grazing incidence may be greater or less than 90°: The domain of incident wave‐vector angles can actually split into disjoint pieces. The reflection coefficient at grazing incidence is shown to be unity, as in the isotropic case. Critical‐angle phenomena are described naturally by this approach.
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43.20.Fn Scattering of acoustic waves

Laboratory studies of diffuse waves in plates

Richard L. Weaver

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 919-923 (1986); (5 pages) | Cited 8 times

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Measurements were conducted on the reverberant diffuse elastodynamic field in a 30‐ ×30‐ ×1.21‐cm aluminum plate, the disturbances being generated by simulated acoustic emission concentrated step loads. The acoustic response in the 50‐ to 500‐kHz range was monitored over periods of 16 ms, long compared to the 100‐μs acoustic transit time across the width or length of the plate. Accurate power spectra estimates were found to require the collection of large amounts of data and to require correction of this data for the effects of absorption, or internal friction. Comparison of the frequency, time, and spatially averaged power spectra with theoretical predictions shows substantial agreement.
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43.20.Fn Scattering of acoustic waves
43.20.Ye Measurement methods and instrumentation

Wave propagation through a thin bubbly layer

K. C. Ng and L. Ting

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 924-926 (1986); (3 pages)

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The shielding effects of a thin bubbly layer submerged in pure liquid on the propagation of acoustic waves are analyzed. By using the method of matched asymptotics, conditions across the bubbly layer are derived. They are: (1) that the pressure is continuous and (2) that the jump of normal velocity is related to the temporal derivative of pressure times a parameter representing the bulk property of the bubbly layer. This parameter is the product of a small number and a large number. The former is the wavenumber times the integral of the gas volume fraction β across the layer and the latter is the ratio of the density times the square of the speed of sound for the liquid phase to that for the gas phase. When the thin bubbly layer is adjacent to a rigid surface, their combined effect is described by an impedance boundary condition.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Hq Velocity and attenuation of acoustic waves

A new expansion for the velocity potential of a circular concave piston

Takahi Hasegawa, Kiichiro Matsuzawa, and Naoki Inoue

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 927-931 (1986); (5 pages)

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This paper presents a new method for calculating the velocity potential in the nearfield of a circular concave piston source in an infinite plane baffle for both the case where the vibration is normal to the piston surface and where it is parallel to the axis. The solution is given in the form of an infinite series of spherical surface harmonics in the spherical coordinate system, taking the origin at the center of curvature. The theoretical framework has the advantage that it includes neither approximations nor numerical integrations.
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43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods

Reconstruction of one‐dimensional inhomogeneities in elastic modulus and density using acoustic dimensional resonances

Stephen J. Norton and Louis R. Testardi

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 932-941 (1986); (10 pages)

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A method is described for quantitatively reconstructing a spatial inhomogeneity along a one‐dimensional structure from measurements of its resonant frequencies (fundamental and higher modes). A relationship between the shifts in the resonant frequencies of the structure due to a material inhomogeneity (computed relative to the frequencies of the homogeneous state) and the coefficients in a Fourier expansion of the inhomogeneity, which holds to the first order in the material perturbation, is derived. If a number of successive resonant frequencies are excited and measured, the unknown inhomogeneity may then be reconstructed by Fourier summation. The material inhomogeneity recovered by this technique is the sum of the fractional changes in elastic modulus and density. For simplicity, the analysis is carried out in one dimension in the absence of damping. Compared to pulse‐echo methods, the advantages of the dimensional resonance method are that it can image slowly varying impedance variations, can utilize narrow bandwidth detection, has its signal enhanced by the resonant Q, and generally utilizes lower frequencies where problems of attenuation and scattering are less serious.
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43.20.Ye Measurement methods and instrumentation
43.20.Ks Standing waves, resonance, normal modes
43.40.Cw Vibrations of strings, rods, and beams

Transient and multiple frequency sound transmission through perforated plates at high amplitude

A. Cummings

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 942-951 (1986); (10 pages) | Cited 7 times

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The transmission of complex periodic and transient acoustic signals through orifice plates at high amplitude, and in the absence of mean fluid flow, is discussed. A simple fluid dynamical model, involving a time‐varying mass end correction, is the basis of the theory. The equation of motion for the air in the orifice is solved numerically in the time domain. For a specific instance, an analytical solution in the frequency domain is possible. Good agreement is noted between experimental and theoretical results in both time and frequency domains.
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43.25.Ts Nonlinear acoustical and dynamical systems

Diffractive corrections to the high‐frequency Kirchhoff approximation

Suzanne T. McDaniel

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 952-957 (1986); (6 pages) | Cited 1 time

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Diffractive corrections to the physical optics solution for the scattering of high‐frequency sound by a random rough pressure release surface are derived. The correction terms are obtained by applying the composite‐roughness theory to an expansion of the scattering integral. Results are presented for a three‐dimensional rough surface and are compared with those obtained using a conventional composite‐roughness approach.
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43.30.Bp Normal mode propagation of sound in water
43.30.Hw Rough interface scattering
43.20.Bi Mathematical theory of wave propagation

Source range information loss in waveguides

E. C. Shang, L. M. Lawson, and D. R. Palmer

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 958-963 (1986); (6 pages)

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In a previous study [E. C. Shang, C. S. Clay, and Y. Y. Wang, J. Acoust. Soc. Am. 78, 172 (1985)] a new method of passive source ranging in a layered waveguide was proposed. This paper investigates the reduction (loss) in range information due to phase fluctuations and to an inaccurate description of the environment (waveguide mismatch). The effects of phase fluctuations are investigated using a two‐dimensional Gaussian distribution function. A numerical normal mode code is used to study the effects of waveguide mismatching. The loss in range information caused by incorrect descriptions of both the bottom sediment type and the sound speed profile in the water column is calculated. Examples are given for a water depth of 100 m and frequencies in the range from 100–500 Hz.
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43.30.Bp Normal mode propagation of sound in water
43.20.Mv Waveguides, wave propagation in tubes and ducts

Surface‐generated noise under low wind speed at kilohertz frequencies

E. C. Shang and V. C. Anderson

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 964-971 (1986); (8 pages) | Cited 1 time

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Some experimental observations of the ocean surface under low wind speed conditions, carried out with the high gain acoustic distribution array, ADA, indicate that bubbles may play an important role in the noise generating mechanism in this wind speed regime. One of the mechanisms discussed in the theory is that of bubble collapse in the surface turbulence layer as first proposed by Furduev [Atmos. Ocean. Phys. 2, 314 (1966)]. Under typical ocean conditions, low wind speeds, and the available bubble population data, the calculated noise level agrees well with experimental results, both in magnitude and in the shape of the spectrum. The spectrum has a peak in the frequency range of 100 to 1000 Hz and an ω−2 behavior at high frequencies. Several geophysical parameters could influence the noise generation. Local wind speed probably controls the population of bubbles, and swell‐induced static pressure variations could play an important role in the critical turbulence pressure for bubble collapse. There seems to be further evidence that additional structure within the water, perhaps bubble density associated with different water masses, generates a patch type of distribution on the sea surface in the low wind speed situation.
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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
92.10.Vz Underwater sound

Rainfall measurements using underwater ambient noise

Jeffrey A. Nystuen

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 972-982 (1986); (11 pages) | Cited 8 times

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Observations are made which show that the underwater ambient noise spectrum generated by rain has a unique spectral shape which can be distinguished from other noise sources. Furthermore, the relationship between spectral level and rainfall is quantifiable. The spectral shape is dominated by a broad peak at 15 kHz, but also depends on the drop size distribution in the rain. A numerical study of the acoustic physics of a drop splash is used to explain the observed spectra. There are two contributions to underwater sound from the impact. The first contribution is from an initial acoustic water hammer pulse. The magnitude of this pulse depends on drop size, shape, and impact velocity. The contribution to the underwater sound spectrum is white and is very large for large drops. The second contribution occurs because at impact the incompressible continuity equation is not satisfied. Once this equation is satisfied, the splash is no longer an acoustic source. Numerically, the time required to closely satisfy this equation is roughly constant for all drop sizes at their terminal velocity. This time interval causes a low‐frequency rolloff at roughly 15 kHz in the sound spectrum.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.50.Pn Impulse noise and noise due to impact
43.50.Vt Topographical and meteorological factors in noise propagation
92.60.Jq Water in the atmosphere

Acoustic microscopy applied to measurements of sound absorption in liquid propane

J. O. Fossum and J. D. N. Cheeke

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 983-984 (1986); (2 pages)

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An acoustic lens has been used to study the relative change in sound attenuation for frequencies in the range 90–300 MHz between the normal freezing and boiling points of liquid propane. These are the first results for the lower part of this temperature range and they confirm the predominance of the viscous contribution to the attenuation.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

An ultrasonic power meter

Sadayuki Ueha, Minoru Kuribayashi, Yoneo Tsuda, Eiji Mori, and Yoshiki Hashimoto

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 985-989 (1986); (5 pages)

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A new ultrasonic power meter has been developed to measure the acoustic power flow of longitudinal vibration in a metallic rod as the product of particle velocity and vibration force. The technological difficulty that should be faced in measuring the vibration force by electrically obtaining the spatial differential coefficient of particle velocity has been overcome. The theory used here and the experimental verification of this method are also described.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.40.Cw Vibrations of strings, rods, and beams
43.58.Fm Sound level meters, level recorders, sound pressure, particle velocity, and sound intensity measurements, meters, and controllers

A distribution based definition of impulse noise

John Erdreich

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 990-998 (1986); (9 pages) | Cited 3 times

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Determining when a worksite exposure should be considered impulsive is a problem which has complicated both research into mechanisms of auditory pathology and protection of the exposed worker. An ideal solution requires that a definition of impulsive noise be developed which is independent of specific characteristics such as duration and amplitude. As an alternative to duration independence, a fixed time window over which a statistic is calculated may also serve as a basis for classification. Additionally, selecting this window on the basis of TTS production in the ear provides a biological basis for the definition of impulsiveness. Classification of impulsiveness based on the sample kurtosis meets the requirements of a generally applicable impulse definition.
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43.50.Ba Noisiness: rating methods and criteria
43.50.Sr Community noise, noise zoning, by-laws, and legislation

Super‐resolution imaging of finite extent objects by estimating the hologram outside an aperture

Osami Sasaki and Hirotoshi Yoshida

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 999-1002 (1986); (4 pages)

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A super‐resolution imaging method is proposed which utilizes the finite extent of the object to estimate the hologram data outside the limited aperture from the hologram data detected at a small number of the points in the aperture by using the regularized singular value decomposition algorithm. The characteristics of this method are made clear by computer simulations, and the experiments show the usefulness of the method.
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43.60.Cg Statistical properties of signals and noise
43.60.Sx Acoustic holography

Standing wave patterns in the human ear canal used for estimation of acoustic energy reflectance at the eardrum

B. W. Lawton and Michael R. Stinson

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1003-1009 (1986); (7 pages) | Cited 3 times

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Standing wave patterns were measured in the unoccluded ear canals of 13 human subjects, for applied pure tones of 3 to 13 kHz. Measurements were made, using a probe microphone technique, over a region which could be approximated as a duct of constant cross‐sectional area. Analysis of the patterns allowed the reflective properties of the middle ear to be determined in terms of an acoustic energy reflection coefficient, or reflectance, at the eardrum. Over all subjects the trend of the results was for the energy reflection coefficient to rise from about 0.3 at 4 kHz up to 0.8 at 8 kHz, and continue at this value to 13 kHz. There was, however, significant intersubject variation, especially at frequencies greater than 7 kHz.
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43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Yp Instruments and methods
43.20.Ks Standing waves, resonance, normal modes

Frequency selectivity of single cochlear‐nerve fibers based on the temporal response pattern to two‐tone signals

Steven Greenberg, C. Daniel Geisler, and Li Deng

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1010-1019 (1986); (10 pages) | Cited 1 time

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The physiological basis of auditory frequency selectivity was investigated by recording the temporal response patterns of single cochlear‐nerve fibers in the cat. The characteristic frequency and sharpness of tuning was determined for low‐frequency cochlear‐nerve fibers with two‐tone signals whose frequency components were of equal amplitude and starting phase. The measures were compared with those obtained with sinusoidal signals. The two‐tone characteristic frequency (2TCF) is defined as the arithmetic‐center frequency at which the fiber is synchronized to both signal frequencies in equal measure.
The 2TCF closely corresponds to the characteristic frequency as determined by the frequency threshold curve. Moreover, the 2TCF changes relatively little (2%–12%) over a 60‐dB intensity range. The 2TCF generally shifts upward with increasing intensity for cochlear‐nerve fibers tuned to frequencies below 1 kHz and shifts downward as a function of intensity for units with characteristic frequencies (CF’s) above 1 kHz. The shifts in the 2TCF are considerably smaller than those observed with sinusoidal signals. Filter functions were derived from the synchronization pattern to the two‐tone signal by varying the frequency of one of the components over the fiber’s response area while maintaining the other component at the 2TCF. The frequency selectivity of the two‐tone filter function was determined by dividing the vector strength to the variable frequency signal by the vector strength to the CF tone. The filter function was measured 10 dB down from the peak (2T Q10 dB) and compared with the Q10 dB of the frequency threshold curve. The correlation between the two measures of frequency selectivity was 0.72. The 2T Q10 dB does change as a function of intensity. The magnitude and direction of the change is dependent on the sharpness of tuning at low and moderate sound‐pressure levels (SPL’s). The selectivity of the more sharply tuned fibers (2T Q10 dB>3) diminishes at intensities above 60 dB SPL. However, the broadening of selectivity is relatively small in comparison to discharge rate‐based measures of selectivity. The selectivity of the more broadly tuned units remains unchanged or improves slightly at similar intensity levels. The present data indicate that the frequency selectivity and tuning of low‐frequency cochlear‐nerve fibers are relatively stable over a 60‐dB range of SPL’s when measured in terms of their temporal discharge properties.
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43.64.Pg Electrophysiology of the auditory nerve

Auditory filter shapes in subjects with unilateral and bilateral cochlear impairments

Brian R. Glasberg and Brian C. J. Moore

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1020-1033 (1986); (14 pages) | Cited 53 times

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The shape of the auditory filter was estimated at three center frequencies, 0.5, 1.0, and 2.0 kHz, for five subjects with unilateral cochlear impairments. Additional measurements were made at 1.0 kHz using one subject with a unilateral impairment and six subjects with bilateral impairments. Subjects were chosen who had thresholds in the impaired ears which were relatively flat as a function of frequency and ranged from 15 to 70 dB HL. The filter shapes were estimated by measuring thresholds for sinusoidal signals (frequency  f ) in the presence of two bands of noise, 0.4 f  wide, one above and one below  f . The spectrum level of the noise was 50 dB (re: 20 μPa) and the noise bands were placed both symmetrically and asymmetrically about the signal frequency. The deviation of the nearer edge of each noise band from  f  varied from 0.0 to 0.8 f. For the normal ears, the filters were markedly asymmetric for center frequencies of 1.0 and 2.0 kHz, the high‐frequency branch being steeper. At 0.5 kHz, the filters were more symmetric. For the impaired ears, the filter shapes varied considerably from one subject to another. For most subjects, the lower branch of the filter was much less steep than normal. The upper branch was often less steep than normal, but a few subjects showed a near normal upper branch. For the subjects with unilateral impairments, the equivalent rectangular bandwidth of the filter was always greater for the impaired ear than for the normal ear at each center frequency. For three subjects at 0.5 kHz and one subject at 1.0 kHz, the filter had too little selectivity for its shape to be determined.
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43.66.Dc Masking
43.66.Sr Deafness, audiometry, aging effects

Frequency discrimination as a function of tonal duration and excitation‐pattern slopes in normal and hearing‐impaired listeners

Richard L. Freyman and David A. Nelson

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1034-1044 (1986); (11 pages) | Cited 9 times

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Frequency difference limens were determined as a function of stimulus duration in five normal‐hearing and seven hearing‐impaired subjects. The frequency DL duration functions obtained from normal‐hearing subjects were similar to those reported by Liang and Chistovich [Sov. Phys. Acoust. 6, 75–80 (1961)]. As duration increased, the DL’s improved rapidly over a range of short durations, improved more gradually over a middle range of durations, and reached an asymptote around 200 ms. The functions obtained from the hearing‐impaired subjects were similar to those from normal subjects over the middle and longer durations, but did not display the rapid changes at short durations. The paper examines the ability of a variation of Zwicker’s excitation‐pattern model of frequency discrimination to explain these duration effects. Most, although not all, of the effects can be adequately explained by the model.
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43.66.Fe Discrimination: intensity and frequency
43.66.Sr Deafness, audiometry, aging effects

Auditory profile analysis of irregular sound spectra

Gerald Kidd, Jr., Christine R. Mason, and David M. Green

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1045-1053 (1986); (9 pages) | Cited 13 times

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The discrimination of changes in the shapes of sound spectra is reported. The change was always an intensity increment to the 948‐Hz component of a multitone complex. First, the ability of naive listeners to learn to discriminate a change in a ‘‘regular’’ background or reference spectrum (equal‐level tones equally spaced in logarithmic frequency) was measured as a function of the number of trials. On the average, threshold improved about 10 dB over 3000 trials, with about 50% of the decrease in threshold occurring during the first 750 trials. In a subsequent series of experiments, the overall pattern of spectral shape of the background was varied randomly. Two kinds of perturbations in spectral shape were employed: (1) Randomly choosing the frequencies of the reference spectra and (2) randomly choosing the amplitudes of the components of the reference spectra. The experimental manipulations involved fixing the random spectra across a block of trials, varying the reference spectra from interval to interval of each trial, and providing extensive practice in discriminating specific randomly perturbed reference spectra. The results of the spectrum‐learning and random perturbation experiments provide insight into the roles of critical band filtering, sensory variability, and short‐term and long‐term memory representations in auditory profile analysis. Further, the appropriateness of the generalization of a simple energy detection model is discussed
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43.66.Fe Discrimination: intensity and frequency
43.66.Ba Models and theories of auditory processes
43.66.Jh Timbre, timbre in musical acoustics
43.66.Dc Masking

Critical modulation frequency based on detection of AM versus FM tones

E. Schorer

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1054-1057 (1986); (4 pages) | Cited 4 times

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The ratios between the modulation index (η) for just noticeable FM of a sinusoidally modulated pure tone and the degree of modulation (m) for just noticeable AM at the same carrier and the same modulation frequency were measured at carrier frequencies of 0.125, 0.25, 0.5, 1, 2, 4, and 8 kHz. Signal levels were 20 dB SL and 50 dB SPL or 80 dB SPL. At low modulation frequencies, for example, 8 Hz, AM and FM elicit very different auditory sensations (i.e., a fluctuation in loudness or pitch, respectively). In this case, η and m show different values for just noticeable modulation. Since both stimuli have almost equal amplitude spectra if η equals m ( m<0.3), the difference in detection thresholds reflects differences in the phase relation between carrier and sidebands in AM and FM. With increasing modulation frequency, the η–m ratio decreases and reaches unity at a modulation frequency called the ‘‘critical modulation frequency’’ (CMF). At modulation frequencies above the CMF, the same modulation thresholds are obtained for AM and FM. Therefore, it can be concluded that the difference in phase between the two types of stimuli is not perceived in this range. At center frequencies below 1 kHz, where phase errors caused by headphones and ear canal presumably are small, the CMF is useful in estimating critical bandwidth.
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43.66.Fe Discrimination: intensity and frequency
43.66.Nm Phase effects
43.66.Ba Models and theories of auditory processes

Temporal integration in two species of Old World monkeys: Blue monkeys (Cercopithecus mitis) and grey‐cheeked mangabeys (Cercocebus albigena)

Charles H. Brown and Christopher G. Maloney

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1058-1064 (1986); (7 pages) | Cited 2 times

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Changes in auditory sensitivity as a function of signal duration were studied in two species of Old World monkeys. Testing was conducted under free‐field conditions with pure tones 250, 800, 1600, and 4000 Hz in frequency. Test stimuli ranged in duration from 35–2000 ms. The results showed that the temporal integration functions for the blue monkeys were similar to those reported for rhesus monkeys [T. D. Clack, J. Acoust. Soc. Am. 40, 1140–1146 (1966)], but differed significantly from those for mangabey monkeys and human subjects tested in the same apparatus, by the same procedure. Integration functions for humans and mangabeys did not differ. It was concluded that some taxonomic groups of primates exhibit temporal integration times that are much longer than those characteristic of humans, while others do not, and that interspecific differences in temporal integration are not readily related to species differences in their vocal repertoires.
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43.66.Gf Detection and discrimination of sound by animals
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

The use of acoustical test fixtures for the measurement of hearing protector attenuation. Part I: Review of previous work and the design of an improved test fixture

Juergen Schroeter

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1065-1081 (1986); (17 pages) | Cited 2 times

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This paper gives a comprehensive progress report on the development of objective methods for measuring the attenuation of hearing protection devices (HPD’s), and focuses on the use of acoustic test fixtures (ATF’s), i.e., artificial heads. While there are many publications on ATF’s for the evaluation of circumaural HPD’s (earmuffs), only one serious attempt to construct an ATF for the evaluation of intra‐aural HPD’s (earplugs) could be found. Consequently, no ATF for testing earplugs has been standardized so far, while two standardized ATF’s currently exist for testing earmuffs [see ANSI S3.19‐1974 (1975) and ISO/DIS 6290 (1983)]. Both ATF’s are suited, however, only for production testing and are not designed for HPD‐type testing. It is believed that both ATF’s do not provide sufficiently high accuracy for HPD‐type testing. A new ATF with appropriate circumaural and intra‐aural flesh simulations was constructed, including a suitable ear simulator and a cast of an average pinna. Objectives for design and construction of the new ATF are discussed. The effect of using artificial flesh on the insertion loss of earmuffs (max. 5 dB at 125 and/or 250 Hz) and the effect of using a pinna (max. 12 dB lower insertion loss at 2 kHz) were evaluated.
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43.66.Vt Hearing protection
43.66.Yw Instruments and methods related to hearing and its measurement

Envelope detection of amplitude‐modulated high‐frequency sinusoidal signals by skin mechanoreceptors

P. J. J. Lamoré, H. Muijser, and C. J. Keemink

J. Acoust. Soc. Am. Volume 79, Issue 4, pp. 1082-1085 (1986); (4 pages) | Cited 3 times

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High‐frequency (1000–2000 Hz) sinusoidal vibrations of the skin, which are normally imperceptible, induce distinct sensations when amplitude modulation is applied in the frequency region around 200 Hz. This phenomenon appears to be initiated in the mechanoreceptor, as a result of rectification in the mechanoelectrical transduction process. The curve for sensitivity to modulation frequency resembles the frequency‐sensitivity curve of the Pacini receptor system. The low‐frequency slope is flatter than that of comparable psychophysical frequency‐threshold curves for sinusoidal stimuli. This finding suggests that mechanical filtering (in the capsule of the Pacinian corpuscle and the surrounding skin tissue) contributes to the detection threshold. The characteristics of such a mechanical filter are estimated.
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43.66.Wv Vibration and tactile senses
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