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Feb 1987

Volume 81, Issue 2, pp. 215-586

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Experimental study of forward scattering for a periodic arrangement of slotted waveguides

Maurice Amram, Louis Philippe Simard, Vick J. Chvojka, and Germain Ostiguy

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 215-221 (1987); (7 pages)

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Phase reversal sound barriers, composed of periodic slotted waveguides, have shown promising results in low‐frequency noise control for plane waves normal to the obstacle, when compared with solid barriers. The phase reversal effect results in destructive interferences in the shadow zone of the barrier. In order to introduce this new phase‐controlling device in real conditions (obliquely incident ground reflections, variable source position, etc.), it was necessary to investigate its performance at any angle of incidence. This complementary experimental study, performed in an anechoic chamber, is a verification of the previous theoretical [Mongeau et al., J. Acoust. Soc. Am. 80, 665–671 (1986)] and experimental [Chvojka et al., J. Acoust. Can. 13 (1985)] studies. The results show that, in a measuring plane normal to the slots (waveguide entrances), the performance of this new type of barrier remains quite unchanged at any oblique angle of incidence within −60 ° to +60 °. On the other hand, the studies have clearly shown that this performance is much more angle dependent in a measuring plane parallel to the slots.
Show PACS
43.20.Fn Scattering of acoustic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts

Diffraction of sound by a refracting cylindrical barrier

John E. Cole, III

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 222-225 (1987); (4 pages) | Cited 1 time

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The effect of refraction caused by a sound‐speed gradient at the surface of a diffracting obstacle is investigated by examining both exact and asymptotic solutions for the sound field behind a rigid cylinder. Depending on the sign of the gradient, the curvature due to refraction over the surface of the obstacle either adds or subtracts from the geometric surface curvature and thereby alters the shadow zone of the obstacle. Results of exact and asymptotic solutions are found to display similar trends. Implications regarding improved acoustic performance of barriers are discussed.
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43.20.Fn Scattering of acoustic waves

Transverse cusp diffraction catastrophes: Some pertinent wave fronts and a Pearcey approximation to the wave field

Philip L. Marston

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 226-232 (1987); (7 pages)

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See Also: Erratum

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Diffraction patterns characteristic of transverse cusps are known to be observable in light reflected from curved surfaces or scattered from liquid drops. It is anticipated that transverse cusps may be produced when high‐frequency sound is reflected from (or radiated by) certain curved surfaces or is refracted by inhomogeneities. An explicit description is given of a wave which propagates to produce a transverse cusp; the amplitude in the xy plane is exp[ik(g−ct)] with g=a1x2+a2y2x+a3y2, a2≠0. Propagation of this wave in a homogeneous medium is shown to yield a shear‐free transverse cusped caustic which locates a transition in the number of rays which contribute to the amplitude. The Fresnel approximation of the two‐dimensional diffraction integral is evaluated. The diffracted wave field is proportional to the Pearcey function P(X,Y) or to P∗(X,Y), depending on the sign of a1+(2z)−1, where z is the distance from the xy plane. The real parameters X, Y depend on the aj, z, k, and the transverse coordinates in the observation plane. The stationary‐phase points for the diffraction integral are discussed. The problem considered is distinct from that of acoustical longitudinal cusps which unfold along the propagation direction.
Show PACS
43.20.Fn Scattering of acoustic waves
43.20.Px Transient radiation and scattering
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance

Sound propagation within a chemically reacting ideal gas

J. P. Barton

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 233-237 (1987); (5 pages)

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The propagation of a one‐dimensional sound wave within a nondiffusive, chemically reacting, ideal gas is considered. The particular case of a dissociating diatomic gas is analyzed, though the general procedure may be applied to more complex gas mixtures. The appropriate dispersion equation is derived from fundamental considerations and expressions for the sound speed and the absorption coefficient as a function of frequency are presented. The low‐frequency (equilibrium) and high‐frequency (frozen) limits are evaluated. Results are presented for oxygen for temperatures of 2000–6000 K and pressures of 10, 100, and 1000 kPa. The calculations for oxygen indicate that absorption due to chemical reaction can be quite strong, particularly in the high‐frequency limit at high temperatures and pressures.
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43.20.Hq Velocity and attenuation of acoustic waves
51.40.+p Acoustical properties
43.35.Ae Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in gases

Uniform asymptotic solution for the Green’s function for the two‐dimensional acoustic equation

Mathew J. Yedlin

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 238-243 (1987); (6 pages)

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A uniform asymptotic expansion in the frequency domain is derived for the Green’s function of the two‐dimensional acoustic equation. The expansion is uniform in that it is valid near the source region. It is not valid for caustics, which can arise due to rapid changes in the gradients of the material parameters, the density, or the bulk modulus. The Green’s function which is obtained describes only the body wave acoustic arrivals in a smoothly varying whole space. Other wave types, such as surface waves or critically refracted (head) waves, are not included in this expansion.
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43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.20.Bi Mathematical theory of wave propagation

Measurement of sound propagation downslope to a bottom‐limited sound channel

William M. Carey, Istvan B. Gereben, and Burlie A. Brunson

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 244-257 (1987); (14 pages) | Cited 4 times

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Signal transmission loss and spatial coherence data for source–receiver separations between 100 and 250 km were acquired in the Gulf of Mexico with a calibrated seismic‐streamer measurement system at 400‐m depth, a towed projector at 100‐m depth which emitted 67‐ and 173‐Hz tones, and a moored Webb sound source at 988‐m depth driven at 175 Hz. Range‐dependent bathymetry and sound velocity profiles and other environmental data were measured. The 67‐Hz data showed a persistent sound transmission with a mean of measured range‐averaged loss values (corrected for cylindrical spreading) of 41 dB ranging between 37 and 45 dB; the 173‐Hz data showed several pronounced transmission loss minima with a mean measured range‐averaged loss value of 51 dB ranging between 41 and 60 dB as well as a rapid increase in loss over the slope at ranges greater than 225 km and water depths less than 1.2 km. Slope enhancements were found to be on the order 2–4 dB at 67 Hz and 6 dB at 173 Hz when compared to flat bottom calculations. Pair wise coherence data showed the effect of signal‐to‐noise ratio variations due to multipath interference. Estimates of signal coherence length from the coherent summation of streamer hydrophones yielded coherence lengths ranging between 70 m (8λ) and 300 m (35λ) with an average of 181 m (20λ) at a frequency of 173 Hz (λ=8.67 m). Fast asymptotic coherent and normal mode transmission loss calculations produced results in qualitative agreement with measured data for the deep flat portion of the measurement track when measured geoacoustic profiles or the derived bottom loss curves were used. The results of implicit finite difference parabolic equation calculations were consistent with range‐averaged data for the flat portion of the track as well as on the slope. These results show that if proper descriptions of the subbottom velocity profiles are used, then computations employing either parabolic equation or normal mode techniques provide qualitative agreement with experimental results.
Show PACS
43.30.Bp Normal mode propagation of sound in water
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.30.Sf Acoustical detection of marine life; passive and active

Measurement and modeling of downslope acoustic propagation loss over a continental slope

S. E. Dosso and N. R. Chapman

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 258-268 (1987); (11 pages) | Cited 4 times

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Measurements of propagation loss were obtained in an experiment to study downslope acoustic propagation over the continental slope off the Canadian west coast. The propagation was strongly influenced by the bathymetry and a downslope enhancement was observed at a receiver in the deep sound channel for shallow explosive charges deployed over the continental slope. The maximum enhancement was observed for sources near the edge of the continental shelf at a range of about 110 km, where conversion to low‐loss water column propagation paths by bottom interaction occurred at a depth approximately equal to the sound channel axis. The propagation loss measured for these sources was as much as 15 dB less than that estimated for propagation over a flat ocean bottom, and was equivalent to levels recorded for sources at only 25–30 km. The data were interpreted by examining the structure of the signals received from the charges deployed over the slope, and by using ray theory to determine the propagation paths. The range dependence of the propagation loss was modeled using a wide‐angle parabolic equation method with a realistic geoacoustic model of the environment which included sound speed, density, and attenuation profiles. The model results were in excellent agreement with the measured values over the entire frequency band of the measurements.
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43.30.Bp Normal mode propagation of sound in water
43.30.Cq Ray propagation of sound in water
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
92.10.Vz Underwater sound

Shear wave effects on propagation to near‐bottom and sub‐bottom receivers

Robert A. Koch and Paul J. Vidmar

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 269-274 (1987); (6 pages)

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Some effects of shear wave processes in a multilayered ocean bottom are examined. Normal mode theory is used to calculate the stress and displacement components at receivers in and on the bottom. The effects of the seafloor on normal modes are contained in a bottom boundary condition involving the impedance derived from the plane‐wave reflection coefficient. Shear wave processes are included when the reflectivity is calculated using a solid description of the bottom. Comparisons of the range dependence of stresses and displacements calculated using fluid and solid descriptions of the seafloor indicate that shear wave processes significantly affect the phase of all acoustic field components, both on and in the bottom. Within the bottom, all acoustic component amplitudes may be 10 dB greater if the solid, instead of the fluid, seafloor description is used. On the seafloor, the only acoustic component amplitude substantially affected by shear wave processes is the vertical displacement, which may be 10 dB smaller for a solid bottom than for a fluid one.
Show PACS
43.30.Bp Normal mode propagation of sound in water
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.20.Bi Mathematical theory of wave propagation

Downslope propagation of normal modes in a shallow water wedge

C. T. Tindle, H. Hobaek, and T. G. Muir

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 275-286 (1987); (12 pages) | Cited 3 times

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Experimental results are presented for the downslope propagation of acoustic normal modes in a shallow water wedge with a penetrable bottom and a slope of up to 9°. A 7‐element line source was used to generate individual low‐order normal modes. To obtain single modes in a wedge it was necessary to align the line source to form an arc of a circle centered on the wedge apex. The resulting normal modes propagate with wave fronts which are also curved into arcs of circles centered on the wedge apex. These ‘‘wedge modes’’ propagate without coupling. The amplitudes, mode functions, and group velocities of the wedge modes are described by simple adiabatic normal mode theory, but the wave front curvature is not.
Show PACS
43.30.Bp Normal mode propagation of sound in water
43.20.Ks Standing waves, resonance, normal modes

Normal mode filtering for downslope propagation in a shallow water wedge

C. T. Tindle, H. Hobaek, and T. G. Muir

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 287-294 (1987); (8 pages) | Cited 7 times

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Experiments to measure downslope sound propagation in a shallow water wedge with a penetrable bottom have been conducted in an indoor tank. Mode filtering has been applied to the signals received on a vertical array to extract the waveforms of individual normal modes. Results show that the normal modes of the wedge propagate with wave fronts which are curved into arcs of circles centered on the wedge apex. These wedge modes propagate downslope without coupling and are therefore the true normal modes of the wedge. Conventional normal modes with vertical wave fronts show coupling effects for slopes of 2° and higher. The group velocities of the wedge modes are strongly dependent on the slope and water depth and are in agreement with adiabatic normal mode theory. Modes which are not trapped in the water depth at the source can become trapped when the water depth is sufficient to support them.
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43.30.Bp Normal mode propagation of sound in water
43.20.Ks Standing waves, resonance, normal modes

Decorrelation of acoustic energy propagated over disjoint paths in a turbulent ocean

C. C. Yang and Suzanne T. McDaniel

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 295-300 (1987); (6 pages)

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The path integral technique is applied to investigate the effects of internal waves and temperature fine structure on multipath propagation in the ocean. The novel feature of this study is the use of ray tracing to evaluate the stationary paths between source and receiver. An expression for the correlation of the acoustic pressure propagated along disjoint paths is derived which describes both deterministic and random effects. Numerical results are obtained for the interference of two rays in the presence of a bilinear sound‐speed profile. These results clearly demonstrate that internal waves rather than oceanic fine structure govern the decorrelation of acoustic energy propagated along the two paths.
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43.30.Ft Volume scattering
43.30.Cq Ray propagation of sound in water
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect

Acoustic resonance scattering by viscoelastic objects

V. M. Ayres and G. C. Gaunaurd

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 301-311 (1987); (11 pages) | Cited 5 times

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In this paper acoustic scattering from a viscoelastic sphere accurately modeled by means of the Kelvin–Voigt model is studied. The approach based on a single impedance‐type or Cauchy boundary condition used in the past to account for losses in the body, is reconciled with the exact approach of viscoelasticity, which accounts for material losses via complex field equations, complex propagation vectors, and a set of three realistic boundary conditions on the surface of the sphere. Using the exact approach of viscoelasticity theory, the effect of viscoelastic losses on the various quantities of interest is determined. The Resonance Scattering Theory (RST) is ideally suited to isolate features of the acoustic spectrum which are dependent upon material composition. In order to use the RST for the combination of a viscoelastic object in a liquid medium, an impedance‐matched background is required, and it is developed here for the first time. Subtraction of this background successfully isolates the resonances in the present case. Finally, an exact expression for the specific surface impedance of the sphere, which depends in a complicated way on frequency, on mode order, and on the four parameters controlling the viscoelastic properties of the sphere is derived. The effect of all these quantities on the sonar cross section of the sphere, or on the modal contributions contained within it is studied, and many pertinent results are displayed.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.35.Mr Acoustics of viscoelastic materials
43.20.Ks Standing waves, resonance, normal modes

Resonance spectra of elongated elastic objects

H. Überall, Y. J. Stoyanov, A. Nagl, M. F. Werby, S. H. Brown, J. W. Dickey, S. K. Numrich, and J. M. D’Archangelo

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 312-316 (1987); (5 pages) | Cited 3 times

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The eigenfrequencies at which smooth convex objects resonate under the incidence of an acoustic wave correspond to the real parts of those complex frequency values at which circumferential waves generated by the incident signal phase‐match after repeated circumnavigations around the object [H. Überall, L. R. Dragonette, and L. Flax, J. Acoust. Soc. Am. 61, 711 (1977)]. A resonance condition based on this principle is formulated, and applied to the case of elastic prolate spheroids and cylinders with hemispherical endcaps. Using then the known phase velocities of surface waves on elastic spheres, with a radius equal to the local radius of curvature along the surface path, the elastic resonance frequencies of these objects can be predicted. This was done for the Rayleigh wave on a prolate spheroid, where comparison with resonances in the scattering amplitude as obtained by a T‐matrix calculation led to good agreement.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.20.Px Transient radiation and scattering
43.20.Fn Scattering of acoustic waves

Thermoacoustic radiation of sound by a moving laser source

Yves H. Berthelot and Ilene J. Busch‐Vishniac

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 317-327 (1987); (11 pages) | Cited 9 times

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The generation of sound by a moving laser source is investigated both theoretically and experimentally. The analysis is restricted to sound waves generated exclusively through the thermal mechanism. The model is based on the impulse response of a thermoacoustic source as described in a previous paper [J. Acoust. Soc. Am. 78, 2074–2082 (1985)]. The results presented here include pressure waveforms, directivity patterns, sound level dependence on source velocity, and spreading curves for subsonic, transonic, and supersonic source velocities. In general, experimental results are in good agreement with theoretical predictions.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Intensity fields of continuous‐wave axisymmetric transducers

H. D. Mair, D. A. Hutchins, and P. A. Puhach

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 328-334 (1987); (7 pages) | Cited 3 times

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The intensity fields of disk, bowl, and conical transducers have been evaluated theoretically throughout their nearfield regions at a single frequency. The results have been compared to the fields resulting from the square of the pressure (P2). It is shown that the two types of fields differ most markedly on axis and close to the transducer face. The direction of energy flow has also been analyzed, and it is demonstrated that parallel flow lines occur in regions where P2 is the closest to intensity.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.38.Ar Transducing principles, materials, and structures: general

Dynamic response of a two‐dimensional elastic solid of arbitrary shape having a circular cavity subjected to a transient pressure along the cavity

Kosuke Nagaya and Humihiko Niiyama

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 335-345 (1987); (11 pages)

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This paper is concerned with a method for solving response problems of an elastic solid of arbitrary shape with a circular cylindrical cavity subjected to a transient pressure along the cavity. In the analysis, the exact solutions which satisfy the boundary conditions along the cavity are obtained by applying the Laplace transformation to the equations of motion of elastic solids based on the two‐dimensional theory of elasticity. The boundary conditions along the outer surface of arbitrary shape are satisfied by means of the Fourier expansion collocation method. The Laplace transform inversion integral is obtained from the residue theorem. Reasonably accurate results are obtained when the integration for finding the coefficients of the Fourier series and the numerical differentiation are carried out appropriately. To discuss the accuracy of the present analysis, results are compared with those from an exact method for circular rings. Numerical calculations are carried out for sample cases.
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43.40.At Experimental and theoretical studies of vibrating systems
43.40.Cw Vibrations of strings, rods, and beams
46.25.Cc Theoretical studies

Transient response of plates with arbitrary shape in contact with a fluid subjected to general dynamic pressures on a fluid surface

Kosuke Nagaya and Katsumi Nagai

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 346-356 (1987); (11 pages)

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This paper is concerned with a method for solving dynamic response problems of arbitrarily shaped plates in contact with a fluid. By utilizing the Fourier expansion and the Laplace transform methods for disposing of general dynamic pressures, and by applying the Fourier expansion collocation method for satisfying the boundary conditions, expressions for the dynamic response of displacement and bending moment are obtained in a general form which is applicable to general dynamic pressures and arbitrarily shaped plates. Numerical calculations have been carried out for circular plates, rectangular plates, rectangular plates with round corners, and oval plates. The results obtained in certain plates are compared with the exact ones.
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43.40.Dx Vibrations of membranes and plates

Determination of natural frequencies of a thick spinning annular disk using a numerical Rayleigh–Ritz’s trial function

Sunil K. Sinha

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 357-369 (1987); (13 pages) | Cited 4 times

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See Also: Erratum

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Consideration is given in this paper to the problem of a thick, spinning, annular disk constrained at its inner radius. Mindlin’s transverse shear deformation and rotary inertia terms are included in the eigenvalue formulation. In the modified Rayleigh–Ritz method used here, the ‘‘admissible’’ or ‘‘trial functions’’ are developed numerically by an iterative scheme so that all the forced, as well as natural, boundary conditions are fully satisfied. The natural frequencies for different mode shapes of the disk have been computed and are presented in a nondimensional form as a function of rotating speed.
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43.40.Dx Vibrations of membranes and plates
43.20.Ks Standing waves, resonance, normal modes

Measuring helmet sound attenuation characteristics using an acoustic manikin

Elizabeth S. Ivey, G. Patrick Nerbonne, and Gilbert C. Tolhurst

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 370-375 (1987); (6 pages)

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The sound attenuation characteristics of two military helmets were measured using an acoustic manikin as the test apparatus. The manikin results are compared to the results of attenuation measurements made on human subjects wearing identical helmets. The testing room and instrumentation were the same for both the manikin and human subjects. Procedures in ANSI S3.19‐1974 were used in the real‐ear attentuation at threshold (REAT) part of this study. The results are encouraging as they suggest that the manikin may be used in place of a panel of human subjects to evaluate the hearing protection characteristics of military head gear.
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43.50.Hg Noise control at the ear
43.50.Yw Instrumentation and techniques for noise measurement and analysis
43.66.Vt Hearing protection

The tight‐coupled monopole (TCM) and tight‐coupled tandem (TCT) attenuators: Theoretical aspects and experimental attenuation in an air duct

W. K. W. Hong, Kh. Eghtesadi, and H. G. Leventhall

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 376-388 (1987); (13 pages) | Cited 1 time

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Active noise attenuators have been developed for use in an industrial air duct. A theory is presented for calculating the attenuation of tight‐coupled attenuators, where the microphone and loudspeaker are in close proximity. Practical and theoretical aspects of a tandem system have been developed, utilizing a cascade of two simple monopole attenuators. A theoretical model suitable for use in the computation of the attenuation from both types of tight‐coupled attenuators is presented. The tight‐coupled tandem attenuator can provide a minimum attenuation of 20 dB for more than three and one‐half octave bands from 30 to 330 Hz. Also, the attenuators could provide significant attenuation in the presence of airflow. The attenuation patterns in front of the attenuator loudspeaker are investigated. Good agreement between the measured attenuation and the computed results validates the proposed theory and the model for the calculation of the attenuation from tight‐coupled systems.
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43.50.Ki Active noise control
43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.

Generalized nearfield acoustical holography for cylindrical geometry: Theory and experiment

Earl G. Williams, Henry D. Dardy, and Karl B. Washburn

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 389-407 (1987); (19 pages) | Cited 28 times

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From the measurement of the acoustic pressure on a cylindrical, two‐dimensional contour located close to the surface of an underwater, vibrating cylinder, the complete three‐dimensional sound field can be reproduced (reconstructed) with the aid of a computer. This reconstruction technique, called GENAH (generalized nearfield acoustical holography), is unlike conventional holography because it provides a super resolution image of the sound‐pressure field from the surface of the cylinder to the farfield. At the same time, GENAH reconstructs, from this two‐dimensional measurement, the vector velocity and the vector intensity fields (energy flow) in the nearfield of the source, and identifies modes of surface vibration of the cylinder. Experimental results are provided and the accuracy of GENAH is demonstrated by comparison with the two‐hydrophone technique.
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43.60.Sx Acoustic holography
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

On Riccati equations describing impedance relations for forward and backward excitation in the one‐dimensional cochlea model

Christian Kaernbach, Peter König, and Thomas Schillen

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 408-411 (1987); (4 pages)

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Recent experimental observations of otoacoustic emissions suggest the existence of spontaneous emitters of sound on the basilar membrane. These tend to send off waves not only in the normal direction of propagation. It is therefore significant to study the environmental conditions such an emitter finds inside the cochlea. The impedance relations seen by these emitters are described by the Riccati equation for an inhomogeneous transmission line. The results reported in this paper differ considerably for forward and backward excitation. This reflects the quite different behavior of the cochlea pertaining to waves traveling forward and backward. Because of reflections, backward waves cannot be treated with the Liouville–Green approximation.
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43.64.Bt Models and theories of the auditory system

Auditory brain stem responses from human adults and infants: Wave V tuning curves

Richard C. Folsom and Michael K. Wynne

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 412-417 (1987); (6 pages) | Cited 5 times

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Decrement in ABR wave V amplitude was measured in the presence of simultaneous tonal maskers. Probe stimuli were 1.0, 4.0, and 8.0‐kHz third‐octave‐filtered clicks. Adults and 3‐month‐old infants served as subjects. The resultant amplitude‐decrement functions for each tonal masker were fit with regression lines. The sound pressure level (SPL) required to reduce wave V to 50% of the unmasked probe amplitude was plotted for each masker to develop tuning curves. The tuning curves were quantified by calculations of tip‐to‐tail difference, Q10, and SPL at maximum masker frequency (MMF). Tuning curves for adult and infant subjects were similar for the 1.0‐kHz probe. For the high‐frequency probes (4.0 and 8.0 kHz), smaller tip‐to‐tail differences and lower Q10 values were observed for the infant subjects. Ranges of MMF level were similar across adult and infant subjects. For the 8.0‐kHz probe, tuning curves from infant subjects consistently showed maximum masker frequencies which were lower than the probe.
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43.64.Ri Evoked responses to sounds
43.66.Dc Masking

A release from masking by continuous, random, notched noise

Robert P. Carlyon

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 418-426 (1987); (9 pages) | Cited 5 times

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Thresholds for 10‐ms sinusoids simultaneously masked by bursts of bandpass noise centered on the signal frequency were measured for a wide range of signal frequencies and noise levels. Thresholds were defined as the signal power relative to the masker power at the output of an auditory filter centered on the signal frequency. It was found that the presentation of a continuous random noise, with a spectral notch centered on the signal frequency, produced a reduction in signal thresholds of up to 11 dB. A notched noise spectrum level of 0–5 dB above that of the masker proved most effective in producing a masking release, as measured by a reduction in masked threshold. A release from masking of up to 7 dB could be obtained with a continuous bandpass noise. The most effective spectrum level of this noise was 5 dB below that of the masker. The effect of the continuous notched noise was to reduce signal‐to‐masker ratios at threshold to about 0 dB, regardless of the threshold in the absence of continuous noise. Thus the greatest release from masking occurred when ‘‘unreleased’’ thresholds were highest. The release from masking is almost complete within 320 ms of notched noise onset, and persists for about 160 ms after notched noise offset, regardless of notched noise level. The phenomenon is similar in many ways to the ‘‘overshoot’’ effect reported by Zwicker [J. Acoust. Soc. Am. 37, 653–663 (1965)]. It is argued that both effects can be largely attributed to peripheral short‐term adaptation, a mechanism which is also believed to be involved in forward masking.
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43.66.Ba Models and theories of auditory processes
43.66.Dc Masking
43.66.Fe Discrimination: intensity and frequency
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Individual differences in auditory capabilities. I.

David M. Johnson, Charles S. Watson, and Janet K. Jensen

J. Acoust. Soc. Am. Volume 81, Issue 2, pp. 427-438 (1987); (12 pages) | Cited 4 times

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Twenty‐eight audiometrically normal adult listeners were given a variety of auditory tests, ranging from quiet and masked thresholds through the discrimination of simple and moderately complex temporal patterns. Test–retest reliability was good. Individual differences persisted on a variety of psychoacoustic tasks following a period of training using adaptive threshold‐tracking methods, and with trial‐by‐trial feedback. Large individual differences in performance on temporal‐sequence‐discrimination tasks suggest that this form of temporal processing may be of clinical significance. In addition, high correlations were obtained within given classes of tests (as, between all tests of frequency discrimination) and between certain classes of tests (as, between tests of frequency discrimination and those of sequence discrimination). Patterns of individual differences were found which support the conclusion that individual differences in auditory performance are, in part, a function of patterns of independent abilities.
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43.66.Ba Models and theories of auditory processes
43.66.Cb Loudness, absolute threshold
43.66.Dc Masking
43.66.Fe Discrimination: intensity and frequency
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