bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of dc Current Polarization on Cochlear Harmonics
Authors: Durrant John D. , Dallos Peter
Published: October 2005

The effects of dc polarization of the cochlear partition were observed on harmonic distortion components in microphonics. The qualitative effects of negative polarization (scala vestibuli negative) were quite consistent and similar to those observed in the polarization of intermodulation distortion components. The effects of positive polarization were much more variable, but the general trends of the data suggest that when the stimulus is presented below 85–95 dB SPL, the harmonic distortion output is enhanced by both positive and negative polarizing currents. At higher intensities, these components behave much as the fundamental microphonic component. These results have been interpreted as indications that electromechanical and hydromechanical nonlinearities, respectively, dominate the distortion process over low- and high-intensity ranges.
Response of an elastic half-plane to a moving and simultaneously fluctuating indenter
Authors: Keer Leon M.
Published: October 2005

By means of integral-transform techniques, the problem of steady motion and simultaneous harmonic oscillation of a smooth flat indenter is formulated and solved. The boundaries of the indenter are assumed to be fixed with respect to a coordinate system moving with steady velocity. A low-frequency approximation for this case is obtained. The results of the approximation are subsequently used with a method of Crozier and Hunter to obtain the magnitude of the changing boundary when a curved or wedge indenter is considered.
Rytov's method and large fluctuations
Authors: Brownlee L. R.
Published: October 2005

Rytov's method has been the subject of arguments as to whether or not it has a greater domain of applicability than the method of small perturbations. In order to be able to use the result of Rytov's method one must assume that the sizes of the patches of inhomogeneity are much larger than the wavelength of the sound, i.e., λ≪l. Making use of this assumption, when we use the solution for Ψ′ to compare the discarded term |▿Ψ′|2 with the remaining terms, we discover that Rytov's method has the same domain of applicability as the method of small perturbations. Using a simple geometrical model we deduce by physical reasoning the results of Mintzer and Bergmann. This model is then used to extend the theoretical prediction for the amplitude fluctuations in the (Mintzer) range (λL)12≫L0 to cover the case where the fluctuations are large.
Auditory detection of frequency transition
Authors: Tsumura Takashi , Sone Toshio , Nimura Tadamoto
Published: October 2005

The thresholds for the detection of frequency transition were obtained for the tone bursts in which the frequency was linearly changed from the initial value of 1000 Hz either during almost the whole burst duration or during a portion of it. The onset of transient had various delays from the beginning of the tone burst. The burst durations were 32, 102, 302, and 1000 msec. It was found that the nearly constant thresholds were obtained for a given burst duration as long as W(=T1+13T2) was held constant, where T1 was the duration of the initial segment of steady frequency and T2 was the duration of frequency transition. The thresholds were greater when the transition occurred near the burst onset than when it occurred near the cutoff, and in the former case, the thresholds were influenced by a rise time of tone burst. The thresholds were smallest when the frequency transitions occurred in the middle of the tone burst. It is suggested that there are two mechanisms for auditory detection of frequency transition: one is based on the pitch difference and the other on the gliding pitch.
Dispersion of axial SOFAR propagation in the western Mediterranean
Authors: Porter Robert P.
Published: October 2005

Dispersed high-order modes have been observed at frequencies as high as 300 Hz and at ranges of 600 km for shots detonated and received on the axis of a SOFAR channel located in the western Mediterranean Sea. Spectrum analysis of shot records has revealed as many as five identifiable group-velocity profiles that correlate with modes as high as 70. Accurate prediction of observed group-velocity profiles is obtained by applying WKB mode theory to sound-velocity data. In addition, dispersion of individual resolved multipath arrivals, for which low frequencies tend to arrive later, is observed and analyzed by a modified ray theory including diffraction effects.
Theoretical design of nearfield calibration arrays
Authors: Van Buren A. L.
Published: October 2005

The Trott nearfield calibration array (NFCA) is an experimentally proven concept for determining the farfield acoustic radiation of large underwater transducers from measurements in the nearfield. Existing successful NFCAs are large planar configurations of small reciprocal transducers whose responses are amplitude-shaded to produce a nearly uniform plane wave directed normal to the NFCA throughout the volume to be occupied by the unknown transducer. Trott obtained effective shading coefficients by the use of semiempirical methods that are applicable to linear or planar arrays. In this paper a rigorous derivation of the NFCA reciprocity principle is presented for the first time. The results allow for both amplitude and phase shading and are applicable to NFCAs of any configuration. A numerical technique based on this principle is described which produces an optimum set of shading coefficients for any NFCA configuration with a prescribed plane wave direction, volume, and frequency domain. Numerical examples are presented and discussed. Included is the design of a cylindrical NFCA suitable for calibrating an enclosed cylindrical transducer without mechanical rotation.
Transglottal airflow during stop consonant production
Authors: Lubker James
Published: October 2005

The possibility that velopharyngeal opening may cause the transglottal pressure drop necessary for the production of normal English non-nasal voiced stop consonants was investigated. Nasal airflow rate and intraoral pressure were measured during the production of a selected speech sample, produced by three normal adult females. Results suggest that nasal airflow is not uncommon during the production of non-nasal stops by normal English speakers but that the observed airflow is most likely not due to velopharyngeal opening and therefore a velopharyngeal leak represents the least probable single mechanism for the generation of a transglottal pressure drop. The hypothesis is presented that the observed nasal airflow is due to active movements of the soft palate changing the volume of the nasal cavity. The possibility that a velopharyngeal leak might contribute, in an occassional and selective manner, to transglottal flow is recognized.
Electric network effects in the cochlea
Authors: Haas Gustav F.
Published: October 2005

Cochlear microphonics have been explained in terms of a varying resistance at the hair cells that modulates resting currents and voltages in an electric network powered by biological dc “batteries.” In this paper, the distributed electric circuit of a 2-mm-long section of the first turn of the cochlea is approximated by a lumped network consisting only of linear elements, and including both fixed and variable capacitances across membranes as well as the variable resistance. When this circuit is driven by sinusoidal parameter variations, the voltage and current analogous to the cochlear microphonic and its concomitant hair-cell current exhibit these steady-state phenomena: (1) frequency-sensitive gain; (2) frequency- and amplitude-sensitive phase shift; (3) dc shifts of both polarities in response to purely ac stimulation, analogous to the summating potential; (4) waveform distortion. These results show that an additional stage of signal processing may exist between basilar-membrane vibration and nerve spike trains, and certainly between basilar-membrane vibration and observed cochlear potentials.
Shift of ear superiority in dichotic listening to temporally patterned nonverbal stimuli
Authors: Halperin Y. , Nachshon I. , Carmon A.
Published: October 2005

The assumption that the direction of ear superiority in dichotic listening to sounds varies as a function of the number of stimulus transitions within sound sequences was tested in two experiments on 36 right-handed students. In each sequence, three sounds which varied in terms of either frequency or duration were employed. Subject's task was to report the sequences by ear. The results showed that as the number of frequency or duration transitions increased from zero to two, ear superiority shifted from left to right. The shift from left to right ear superiority as a function of the increase in the complexity of temporal patterning suggests that perception of temporal patterns might be one of the underlying mechanisms in speech perception.
Propagation of elastic waves bound to a fluid layer between two solids
Authors: Staecker P. W. , Wang W. C.
Published: October 2005

Theoretical calculations and experimental measurements for an acoustic wave bound to and guided by a fluid layer between two semi-infinite isotropic elastic solids are reported. Discussion of theory includes wave propagation characteristics, mode existence criteria, and the distribution of elastic energy in the structure, treating separately the cases where the geometry is symmetric and nonsymmetric about a plane of bisection. Experimental results include measured propagation characteristics for the layered geometry and a device realization of this particular structure.
Three-dimensional acoustic-ray tracing in an inhomogeneous anisotropic atmosphere using Hamilton's equations
Authors: Chessell C. I.
Published: October 2005

Three-dimensional ray-tracing equations are presented for tracing acoustic rays in an inhomogeneous anisotropic atmosphere which are based on Hamilton's equations for geometrical optics. The equations are converted to a form suitable for direct numerical integration. Simplified ray equations for the special case of horizontal stratification are obtained. Results of ray tracing in an atmosphere with both vertical and angular wind shear are outlined, and the formation of a shadow zone in the downwind direction is demonstrated.
Acoustic radiation from a long solid rod into a semiinfinite liquid medium
Authors: Maxwell Gerald G. , Hixson Elmer L.
Published: October 2005

An approximate numerical technique is presented whereby the pressure-radiation patterns in a liquid half-space produced by radiation from the end face of a circular cylindrical, semiinfinite, solid rod set flush in an infinite rigid baffle at the boundary of the half-space can be calculated as a function of the elastic properties of the solid rod. The method is restricted to the low-frequency range such that the lowest numbered mode in the solid rod is the only propagating mode. Axisymmetric longitudinal modes are the only ones assumed to exist in the rod. The velocity distribution of the rod end face does not have to be known or assumed. The radiation impedance of the rod end is calculated and compared with that of the rigid piston, as are the pressure radiation fields. The work here presents farfield radiation only, though the method can easily be extended to study the nearfield radiation patterns in the liquid half-space.
Interference and two-tone inhibition
Authors: Legouix Jean-Paul , Remond Marie-Claude , Greenbaum Hilda B.
Published: October 2005

Several experiments to determine the effects of two-tone interaction in the cochlea are described. Nonlinear effects result when the cochlear partition is stimulated by a sinusoid whose frequency falls in a very narrow frequency band surrounding, but not including, the resonant frequency at the point under the recording electrode. These nonlinear effects are manifested as a negative shift in the dc potential accompanied by a partial or complete suppression of the cochlear microphonic potential to a second tone presented at the same time. This suppression is best seen in the first and second turns of the cochlea. Similar suppression effects accompanying a dc shift are obtained by artificially displacing the basilar membrane from its resting position by an asymmetrical change in hydrostatic pressure in the perilymph. The functional relations governing suppression were determined and the results compared with those obtained in two-tone inhibition experiments in auditory nerve fibers. The results support the conclusion that inhibitory effects seen in nerve fibers, stimulated by two tones simultaneously, reflect mechanical events in the cochlear partition and subsequent changes in the effective stimulating waveform triggering the auditory nerve.
dBA attenuation of ear protectors
Authors: Waugh R.
Published: October 2005

The adoption of dBA-type hearing damage risk criteria and the consequent use of A-weighted sound levels to identify areas of auditory hazard have created a need for a measure of the dBA attenuation of ear protectors. In Study 1, the dBA attenuation values of 30 ear protectors are calculated in 619 industrial noise spectra. It is found that the same ear protector may offer 20 dB more dBA attenuation to one noise than to another but that noises of like C-A value are subjected to approximately the same dBA attenuation. Noises are therefore sorted into five classes according to C-A value, and average dBA attenuation values for each class are calculated for each ear protector. This type of information makes it possible to select adequate ear protectors even though only the C- and A-weighted sound levels of the noise environment are known. In Study 2, a simple procedure is developed for calculating the dBA attenuation values of any ear protector for the five C-A classes defined in Study 1. The procedure incorporates correction factors which ensure that, for the average protector, the calculated dBA attenuation values are obtained in 90% of spectra.
Elastic wave propagation in granular media
Authors: Eden H. Frank , Felsenthal P.
Published: October 2005

Some measurements of the propagation of ultrasonic pulses through packs of spherical and nonspherical particles of different diameters are reported. The packings include evacuated and compressed media. The values of sonic velocity measured together with the measured bulk elastic properties of one such packing yield a reasonable value for Poisson's ratio, tending to 0.5 for the assembly. Increasing contact pressure between particles, or the presence of interstitial air affect the properties considerably.
Pressure radiations from an infinite two-layered elastic plate with point and shear force excitations
Authors: Lai Jai-Lue
Published: October 2005

Pressure radiations generated from a two-layered elastic plate by time-varying point and shear forces are obtained analytically. The plate made of two different isotropic and homogeneous materials of uniform thickness is bounded on one side by a fluid medium and another side by a vacuum. Both the fluid and the plate are assumed to be infinite in extent. The effects of transverse shears and rotary inertias in both layers are included in the equations governing the plate motion. The solution is obtained with the aid of Hankel transforms for spatial coordinate and Laplace transform for time variable. “Saddle-point” technique is used to carry out the inverse Hankel transform for farfield radiations. Numerical results for pressures generated by time-harmonic point or shear force are presented.
Babinet's principle for elastic waves
Authors: Gangi Anthony F. , Mohanty Bibhuti B.
Published: October 2005

Babinet's principle for elastic waves gives a relationship between the displacement fields due to complementary diffracting screens. The relationship has been derived using the seismic representation theorem as the starting point. The relationship for rigid complementary screens, for stress-free complementary screens, and for mixed rigid-stress-free complementary screens in each case has the same form. In deriving the relationship it is necessary to assume that the “jumps” across the complementary screens are the same as those that would exist when both complementary screens are present. This assumption has been tested in a seismic modeling experiment that utilized both stress-free and rigid screens. The experiments show that the assumption is valid within the accuracy of the experiment and, consequently, that Babinet's principle for elastic waves is valid to the same degree of accuracy.
Nonlinear transient stress-waves in cylindrical and conical shells
Authors: Lahe Andres , Nigul Uno
Published: October 2005

In this paper a nonlinear Timoshenko-type theory of shells is used to analyze the transient axisymmetric stress waves produced in elastic cylindrical and truncated conical shells by an input at one edge. The analysis utilizes the method of characteristics and an asymptotic method. Prior work in this area has been based on linear shell theories and on the exact equations of linear elasticity. The methods suggested here allow one to establish how in the course of time the nonlinearities affect the linear solutions.
Nearfield effects in end-fire line arrays
Authors: Berktay H. O. , Shooter J. A.
Published: October 2005

An “exact” closed-form solution for the acoustic field from a continuous end-fire line array is presented. Interactions between the array elements are ignored, but no approximations are made regarding the position of the field point. (This model lends itself particularly well to the study of the response of parametric receivers.) The results are presented in the form of beam patterns as a function of range. It is shown that the range where the transition between the nearfield and the farfield is obtained depends only on the length of the array and that the beam patterns within the nearfield can be substantially more narrow than the farfield beam patterns.
Solid-liquid compound hydroacoustic lens of low aberration
Authors: Tannaka Yasuaki , Koshikawa Tsuneji
Published: October 2005

With the intention of improving the resolving power of underwater acoustic imaging systems, hydroacoustic lenses of the solid-liquid compound type were investigated with special attention to their aberrations and F number. The solid and liquid materials used were, respectively, a plastic and a silicone fluid, thus forming an interface of higher refractivity than those between a plastic and water, or a silicone and water. The ray-tracing computations of the aberration showed that the meridional and sagittal aberrations of the solid-liquid compound lens of aspherical type designed and constructed in the present research were much reduced. The results of measurements on Fraunhofer diffraction patterns showed that an F number as small as F/1.0 was realized by the solid-liquid compound lens of aspherical type, and this in turn considerably improved the least resolvable separation on the focal plane of the lens for a given sound wavelength, and the resolving power of the lens for a given sound wavelength and a given focal length.
Synthesis of helicopter rotor tips for less noise
Authors: Lyon Richard H. , Mark William D. , Pyle Robert W.
Published: October 2005

Theoretical and computational studies of rotor-tip sound radiation have been conducted for the purpose of designing rotor tips that radiate less sound in specified frequency bands. Consideration is given to radiation due to lift and thickness effects. Effects of unsteady vortex shedding on lift radiation are examined. It is shown that lift radiation is generally negligible in comparison with thickness radiation. A computational algorithm is developed for the synthesis of tip shapes that cause minimum thickness radiation in specified frequency bands. Numerical results are obtained for tip shapes that minimize high-frequency radiation, and a substantial reduction of radiation in comparison with existing shapes is shown. The uncertainty principle is used to establish a fundamental relationship between the tip section chord length and the minimum possible cutoff frequency for effective suppression of high-frequency sound. Factors that affect tradeoffs between choices on airfoil section and planform are discussed.
Effectiveness of continuous spatial averaging in a diffuse sound field
Authors: Lubman David , Waterhouse Richard V. , Chien Chi-Shing
Published: October 2005

The effectiveness of spatial averaging in an ideal diffuse field is examined, with intended application to pure-tone reverberant sound power measurement. A theoretical measure of spatial averaging effectiveness is proposed, based on the variance of the spatial average, which is determined analytically from the shape and size of the intended path. Three cases, examined here in detail, are: continuous averaging on a line, a circle, and the surface of a disk. Results show that for greatest effectiveness, the path of averaging must extend over a region of space whose dimensions are large with respect to a wavelength. In particular, it is shown that averaging on a line segment of given length will be more effective if the line is straight rather than circular. Surprisingly, it is also shown that averaging on the surface of a disk will be less effective than averaging on its perimeter if the disk is small compared to a wavelength. This last result is employed to illustrate the dangers of oversampling (the use of highly correlated samples) which might otherwise go unrecognized.
Acoustically induced vibrations of slender rods in a cylindrical duct with parallel flow
Authors: Hine M. J.
Published: October 2005

The effect of parallel flow on acoustically induced rod vibrations in a cylindrical duct is predicted and measured. The flow is shown to modify the axial fluid wavelength, which is a critical factor in determining rod response.
Initial Reaction of a Submerged Shell to Acoustic Waves
Authors: Rein Charles R.
Published: October 2005

The propagation of a peripheral wave around a submerged metallic shell was studied experimentally. Data were obtained with a shell mounted accelerometer and with an acoustic projector and hydrophone. The phase velocity of the peripheral wave in the shell was measured and the peripheral wave was determined to be the source of a wave reradiated to the water.
Electromagnetic leakage in high-frequency continuous-wave ultrasonics
Authors: Miller J. G.
Published: October 2005

Electromagnetic leakage or cross talk between transmitter and receiver represents a severe limitation on the usefulness of continuous-wave (CW) ultrasonic methods at high frequencies. The problem of leakage is, however, entirely eliminated by use of a scheme known as the sampled-CW technique. The role of the sampled-CW technique in eliminating leakage is explicitly demonstrated by contrasting the results of CW and sampled-CW measurements under a variety of conditions.
Ultrasonic studies in binary solutions of pyridine with water, methanol, and ethanol
Authors: Thomas K. N. , Stumpf F. B.
Published: October 2005

The velocity and absorption of ultrasound at 19.5 MHz were studied as a function of the concentration in binary solutions of pyridine with water, methanol, and ethanol. In addition, the compressibility and volume viscosity were calculated. Molecular processes are suggested to explain the variation of the ultrasonic properties of these binary solutions with respect to concentration.
High-speed method for computing the exact solution for the pressure variations in the nearfield of a baffled piston
Authors: Lockwood J. C. , Willette J. G.
Published: October 2005

A method is presented whereby the pressure variations at any point in the field of a baffled piston may be efficiently calculated. If a solution for the impulse response of a piston of a given geometry is known, then for harmonic excitation the steady-state field may be computed by evaluating the driving-frequency component of the Fourier transform of the impulse response. This method involves a single integration, whereas the direct numerical solution requires a double numerical integration. An exact, closed-form solution for the impulse response of a rectangular piston is derived. With this solution and the known solution for the impulse response of a circular piston the steady-state solutions for these two geometries are obtained. Three-dimensional and contour plots of data obtained for a circular piston and for a plane of symmetry of a rectangular piston field are presented. The plots for the circular piston compare favorably with previously published plots of data calculated by a double integration.
Low-frequency scattering
Authors: Senior T. B. A.
Published: October 2005

The leading terms in the low-frequency expansions for acoustically soft and hard bodies are examined and the relevance of the magnetic polarizability tensor is discussed. For a hard, rotationally symmetric body, two tensor elements, functions only of the geometry, are now sufficient to specify the entire low-frequency scattering behavior in just the same way as the electrostatic capacity suffices for a soft body. Even these quantities are subject to known constraints and computed data for a variety of bodies are presented.
Free and forced response of a laminated ring
Authors: DiTaranto R. A.
Published: October 2005

A free- and forced-vibration analysis is made of a three-layer laminated ring consisting of an inner and outer elastic layer with a core capable of transmitting only shear. The Variational Method is used to obtain the equations of motion. Analytical expressions are obtained for the response and the natural frequencies of the laminated ring having an elastic core material. Curves are obtained which demonstrate the variation of the natural frequencies of the laminated ring for specific values of the core thickness and shear parameters with a change in the elastic thickness parameter for the first four circumferential bending modes. The resonance response is investigated and analytical expressions are obtained for the system having a viscoelastic core. Curves are obtained relating the resonant-frequency parameter and the composite-loss factor to the geometrical and physical properties of the ring vibrating in the fundamental circumferential bending mode.
Vibration analysis of thick-walled spheres and cylinders
Authors: Rose J. L. , Chou S. C. , Chou P. C.
Published: October 2005

A wave-propagation approach is employed to determine the fundamental frequency of hollow spheres and long hollow cylinders (plane strain state). The study was initiated in order to study the periodic response of such specimens as a function of the number of wave reflections off the inner and outer surfaces as well as the thickness-to-inside radius ratios, (h/Ri). It was hoped to achieve a relationship similar to that obtained in the classical longitudinal step loading bar problem. In the bar case, the material response is periodic for either two or four complete reflections, depending on whether the bar has a free or a fixed end. In the hollow sphere and cylinder problem, however, the analysis is not as simple. The motion is approximately periodic. It was found that the number of wave reflections for one cycle was some irrational number, the number being a function of (h/Ri). This unusual observation led to the development of useful design curves and equations for determining the fundamental frequencies of thick-walled spheres and cylinders. Comparisons of results from the vibration and wave propagation approaches are used to establish regions of validity of the approaches as a function of (h/Ri).
Pressure dependence of sound attenuation in the Pacific Ocean
Authors: Bezdek H. F.
Published: October 2005

Measurements of the attenuation of sound at a nominal frequency of 75 kHz have been made over vertical and horizontal acoustic paths located between depths of 700 and 3400 m in the Pacific Ocean. Results indicate that the equation used to predict attenuation overestimates the values actually encountered at these frequencies and depths. (Compare calculated values of 27.3 and 22.7 dB/km to measured values of 19.9±0.5 and 13.3±0.5 dB/km at depths of 910 and 3350 m, respectively.) The measurements definitely establish the decrease of attenuation with increasing pressure. However, the magnitude of the pressure coefficient of attenuation is almost twice as large as previously suspected (12.3±1.1×10−4/bar, or approximately 12.3×10−4/atm, compared to 6.54×10−4/atm).
Acoustic transmission in an ocean surface duct
Authors: Eden H. Frank , Nicol James
Published: October 2005

An analysis is presented of acoustical transmission measurements which were performed in the oceanic surface duct in two areas of the Pacific Ocean. Three frequencies, three transmitter depths, and three receiver depths were employed. Both areas demonstrated a persistent surface duct but the water mass was more variable in one area than the other. The thermal surveys were inadequate to establish that either area represented the actual thermal front between different water masses. Experimental transmission-loss curves gave good agreement with theoretical curves based upon normal-mode theory. It was not possible to distinguish between the acoustic properties of the two areas either by the experimental transmission-loss data or by an analysis of the observed signal variability.
Acoustic backscattering from a rough surface at extremely low grazing angles
Authors: Gardner R. R.
Published: October 2005

This study is concerned with the wide discrepancy between published experimental data and existing theories for acoustic backscattering at low grazing angles. A new theoretical development based on the Helmholtz theorem is presented which is valid at low grazing angles and which includes the effect of shadowing. At low grazing angles a scattering strength nearly independent of grazing angles and an inverse relationship between scattering strength and wind speed is predicted. A low-grazing-angle experiment was performed at sea on a stable platform where conditions approximated those found in the open ocean. Observations were obtained on the acoustic backscattering of the sea surface as a function of grazing angle down to 1.5° and wind speed from 5 to 20 knots. The effect of shadowing was observed with acoustic radiation. The sea surface was measured with a wave staff to obtain the rms slope of the surface and the wave-height spectrum. Previous theories are shown to give incorrect results because of improper use of rough-surface boundary conditions. It is also shown that the effect of shadowing needs to be included, but a relatively simple correction is adequate.
Intensity calculations along a single ray
Authors: Krol H. R.
Published: October 2005

A method is presented for the calculation of sound intensity using only one ray. The sound-velocity profile is assumed to be continuous up to the second derivative and it is supposed that the ray equations are solved numerically. An example is given.
Calibrations of oceanographic research velocimeters
Authors: Mackenzie Kenneth V.
Published: October 2005

Calibrations of two precision velocimeters were performed by four different laboratories for the purpose of determining acceptable calibration criteria for accurate oceanographic measurements. Analysis of results indicated that a standard error of estimate of 20 mm/sec can be achieved or exceeded for individual calibrations. Sound-speed differences generally spread less than 0.15 m/sec. A precision better than 0.05 m/sec is attainable with rigorous 8-point calibrations from 1°C to 35°C. With stringent controls, absolute accuracies of 0.10 m/sec are within the realm of possibility for at-sea data.
Numerical modeling of acoustic-wave scattering from randomly rough surfaces: an image model
Authors: Novarini J. C. , Caruthers J. W.
Published: October 2005

A technique for studying wave scattering from randomly rough surfaces by computer simulation is presented. Scattering of 1.0- and 1.5-kHz acoustic waves from numerical models of wind-driven sea surfaces having Neumann-Pierson spectra for a 5 m sec−1 wind speed is reported. The surfaces were generated using the theory of linear systems in two dimensions. Scattering was simulated by forming facets in the surface, applying laws of reflection at each facet, and accumulating the rays, with due regard to phase and spreading, onto a rectangular grid of 63 simulated hydrophones. The results are presented in terms of total, coherent, and incoherent intensities, amplitude and phase fluctuations, and degree of coherence all in specular and nonspecular directions, and spatial correlations in horizontal and vertical directions. Also presented is a study of incoherent sea-surface scattering of high-frequency waves emitted from a point source at infinity and having various position angles with respect to the zenith and the wind direction on the surface.
Estimating ocean wind wave spectra by means of underwater sound
Authors: Williams Robert G.
Published: October 2005

Measurements of the spectrum of ocean surface reradiated acoustic signals generated by an omnidirectional, sinusoidal source are used to estimate the ocean surface wave-height spectrum, and the results are compared with wave-staff measurements made simultaneously in the scattering area. Plane-wave physical optics theory is applied to a long-crested sea surface model to verify Marsh's hypothesis that for low sea states the spectrum of acoustic waves reradiated by the rough, moving sea surface consists of a specular component at the transmitted frequency and a scattered component, which is the weighted surface wave-height spectrum. The approach employs theories by Parkins, Clay and Medwin, and Pierson. The weighting function applied to the surface spectrum depends on signal frequency, experimental geometry, and mean-square wave height. Continuous-wave signals at 127 and 1702 Hz were transmitted from fixed, omnidirectional sources to receivers 4.5 and 31 km downrange. Additionally, wave height was monitored continuously by resistance wave staff. The time series records of sound-pressure level and ocean wave height were analyzed for spectral content. Agreement between theory and experiment is good when the acoustic sideband levels are not more than 25 dB below the level of the specular component. The experimental results are also interpreted in light of Parkins' spherical wave theory, and the differences between the plane and spherical wave theories are discussed.
Laboratory simulation of development of superbooms by atmospheric turbulence
Authors: Ribner H. S. , Morris P. J. , Chu W. H.
Published: October 2005

A jet flow was used to model roughly a localized region of atmospheric turbulence, simulating a single idealized “eddy.” The jet was arranged in the UTIAS 80-ft sonic-boom generator horn so as to blow either against or with the direction of boom propagation. The two cases produced spiked and rounded boom signatures, respectively, qualitatively in accord with theory. The resemblance to signatures resulting from supersonic flight under turbulent atmospheric conditions was especially marked with the spiked “superbooms.”
Ultrasonic scattering from polycrystalline solids and plates
Authors: Diachok O. I. , Mayer W. G.
Published: October 2005

Relative maxima in ultrasonic backscattering were observed at critical angles of incidence that correspond to Lamb modes on brass plates located between air and water. Critical angles were determined utilizing schlieren visualization of beam displacement. Results are compared to backscattering the Rayleigh angle at a brass bulk solid-water interface.
Backscatter measurements of acoustic waves scattered from statistically known inhomogeneous rough media
Authors: Tu C. M. , Fung A. K.
Published: October 2005

Backscatter measurements were made, at frequencies of 0.5, 1.0, and 1.5 MHz, of waves scattered from three different targets: (1) an inhomogeneous medium with a plane boundary, (2) a homogeneous medium with a rough boundary, and (3) an inhomogeneous medium with a rough boundary. The surface roughness of targets 2 and 3 is the same and so are the inhomogeneous properties of targets 1 and 3. It is found that for the cases studied surface roughness is more sensitive to frequency than the inhomogeneities and that the inhomogeneities contribute more significantly to the backscattered power at large incident angles than surface roughness.
Effect of spherical scatterers on the radiation resistance of a transducer at an air-water surface
Authors: Stumpf F. B. , Bulger C. R.
Published: October 2005

The radiation resistance of a small sonar transducer at an air-water surface has been measured in the presence of a hard or soft sphere placed in the water. The diameter of the sphere was nearly a wavelength. The sphere was shown to have substantial effect when placed within two wavelengths of the transducer and might have usefulness as a device to control the radiation impedance of transducers used in sonar arrays.
Binaural interaction of transients: interaural time and intensity asymmetry
Authors: Babkoff Harvey , Sutton Samuel , Barris Michael
Published: October 2005

When subjects are required to make a forced choice between pairs of pulses dichotic with respect to time (Δt ) from pairs of pulses dichotic with respect to intensity (ΔI), the resultant data appear as V-shaped functions relating discrimination accuracy to interaural time asymmetry (ΔI). The sharpness of the limbs (the spread of the functions), the appearance of a well-defined minimum, the Δt at which the minimum point is found, and the accuracy of discrimination at the minimum point of the function depend upon the parameters of summed binaural sensation level, and the interaural intensity asymmetry. The interaural time asymmetry (Δt) associated with the minimum point of the function can be used as an index of the degree to which Δt can be matched to ΔI when the parameters of ΔI and summed binaural sensation level are varied. The ratio of Δt associated with the minimum of the function to ΔI, i.e., Δt/ΔI in microseconds/dB, is found to be inversely related to summed binaural sensation level.
Monaural loudness adaptation
Authors: Wiley Terry L. , Small Arnold M. , Lilly David J.
Published: October 2005

Monaural loudness-adaptation measurements were made at several suprathreshold levels for 500 and 4000 Hz with normal-hearing subjects. A unique procedure used the subject as a null device and adaptively varied the signal level over time until no change in loudness was indicated. The results indicated no monaural loudness adaptation. These findings support similar data obtained by other investigators using delayed-balance procedures. It was concluded that the adaptation effects observed in experiments using some form of simultaneous, binaural stimulation apparently are due to binaural interaction and may reflect central as well as peripheral influences.
Gradient microphone performance within a gas mask
Authors: Morrow Charles T.
Published: October 2005

It has been shown previously that a gradient microphone close to the lips is capable of providing an intelligible speech signal in spite of standing waves within a diving mask. It keeps most spectral levels close to their natural balance, but it does not compensate for detuning of the first formant by limited mask cavity volume. The present study is an investigation of a simulated diving mask and speech transmitter, whose distortion of speech is primarily by detuning of the vocal tract. It splits the first two formants into a triplet and de-emphasizes the uppermost frequency of the triplet. The gradient microphone restores emphasis to the uppermost frequency and de-emphasizes the middle frequency. This results in a formant structure similar to that of undistorted speech, with high intelligibility and most of the hollowness suppressed.
Guidelines for determination of the average sound power radiated by discrete-frequency sources in a reverberation room
Authors: Maling George C.
Published: October 2005

When a source of discrete-frequency sound is placed in a reverberation room, the sound-power output depends on the source position and frequency. In addition, the measured sound-pressure level depends on microphone position. In this paper, some experimental data are presented that are relevant to both the microphone path length required for an accurate determination of the space/time average mean-square pressure in the room, and the variations of sound-power output with source position in the room. Based on theoretical and experimental results, some guidelines are proposed for the determination of the sound-power radiated by discrete-frequency sources in a reverberation room.
A sensitive test of speech communication quality
Authors: Nakatani Lloyd H. , Dukes Kathleen D.
Published: October 2005

Small differences in quality may affect the ease with which various speech samples can be understood even though they are all highly intelligible according to articulation tests. Such quality differences were reliably discriminated by a speech-interference test which determined how easily the speech samples could be heard against a background of interfering speech. The communication quality of a degraded speech sample was measured by the difference, A = T − T0, where T and T0 were the interference thresholds for the degraded and reference speech, respectively. An interference threshold was defined as the value of the signal-to-interference intensity ratio where the signal speech was 50% intelligible in the presence of interfering speech. Q measures and subjective quality ratings were obtained for speech degraded by low- and high-pass filtering, additive noise, and transmission over a telephone line. The Q measures successfully discriminated differences in speech quality, and were monotonically related to the ratings, thereby validating the speech interference test for speech-quality evaluation.
Diffraction of a Bleustein-Gulyaev wave by a conductive semi-infinite surface layer
Authors: van der Pauw L. J.
Published: October 2005

The diffraction of a Bleustein-Gulyaev surface wave by a semi-infinite conductive surface layer is investigated. It is assumed that the direction of propagation is normal to the edge of the semi-infinite conductive layer. It appears that, if the dielectric constant ε1 of the piezoelectric material is large compared with the dielectric constant ε0 of the adjacent half-space, the relative power flow associated with the reflected surface wave is of the order (ε0/ε1)2. The relative power flow of the transmitted surface wave is of the order ε0/ε1. Hence, if ε0/ε1 ≪ 1, the largest part of the incident power is converted into a bulk wave. The angular power distribution of the diffracted bulk waves appear to be very asymmetric and concentrated preponderantly in a direction making an angle κ2/(1 + ε1/ε0) with the incident wave, κ being the piezoelectric coupling coefficient.
Higher-order finite-element analysis of topographic guides supporting elastic surface waves
Authors: Lagasse P. E.
Published: October 2005

A method of computing the eigenmodes of acoustic waveguides of arbitrary cross section is described. It is a finite-element technique, based on a variational formulation of the guided-wave problem. The accuracy of the method is assessed by comparing numerical and experimental results for a few specific structures. In particular we describe an acoustic surface ridge waveguide with low dispersion over a broad band.
Anisotropy, diffraction scaling, surface wave lenses, and focusing
Authors: Mason I. M.
Published: October 2005

Anisotropic beamsteering and diffraction enhancement-retardation effects are analyzed. An anisotropic scaling theorem and an analytic, anisotropic lens maker's equation are deduced. Experimental results, illustrating near- and farfield diffraction pattern scaling, and contrasting aberration-corrected and cylindrical surface wave lenses are presented.
Directive harmonic generation in the radiation field of a circular piston
Authors: Lockwood J. C. , Muir T. G. , Blackstock D. T.
Published: October 2005

An experimental and theoretical investigation is presented of farfield distortion of a finite-amplitude wave generated by a circular-piston source. Nearfield distortion is neglected. Thus the boundary condition is that the acoustic signal at the beginning of the farfield is a pure sine wave of amplitude proportional to the small-signal directivity factor for the piston. The method of applying weak-shock theory to obtain directivity patterns and propagation curves is outlined. A criterion for the maximum range at which weak-shock theory is valid is derived for each harmonic. An ad hoc method of matching at this range the small-signal solution, with absorption included, to the weak-shock solution is proposed. Data obtained for a fundamental frequency of 450 kHz and source levels of 109 and 127 dB (re 1 μbar at 1 yd) are presented. Theoretical and experimental beam patterns are in good agreement. Propagation data presented for the 127-dB source level are in poor agreement with the predictions of unmodified weak-shock theory but in good agreement with the matched solution. In general, the experimental data support the hypothesis that harmonic generation in waves from directive sources may be described by specifying a boundary condition for each direction and then assuming that the distortion developing in that direction is not affected by distortion along any other direction.
Error analysis of velocity and direction measurements of plane waves using thick large-aperture arrays
Authors: Clay C. S. , Hinich M. J. , Shaman P.
Published: October 2005

The statistical properties of estimators for plane-wave parameters are discussed. A thick large-aperture array is assumed to be detecting a signal emanating from an unknown continuous wave source. The signal is assumed to be a plane wave embedded in a spatially incoherent Gaussian noise field. Maximum-likelihood estimators of velocities and directions are derived and their root-mean-square errors are obtained, for single and multiple arrivals for linear arrays and square arrays with a large number of sensors. The rms errors of the propagation parameter estimators are proportional to K−1 for a square-lattice array of K sensors and to K−3/2 for a linear array of K sensors. The rms error of the waveform estimator, however, is proportional to K−1/2 in each case. Thus, for the propagation parameters, the figure of merit for rms signal-to-noise gain of the array is K for a square array of K sensors and K3/2 for a linear array of K sensors.
Measurement of sound intensity applied to the determination of radiated sound power
Authors: Burger J. F. , van der Merwe G. J. J. , van Zyl B. G. , Joffe L.
Published: October 2005

A system for measuring sound intensity is described which can also be used for measuring very low sound levels.
Effect of the closed-response format on modified rhyme test scores
Authors: Williams Carl E. , Levin Barbara Woods , Hecker Michael H. L.
Published: October 2005

An experiment was performed to determine whether high scores typically obtained with the Modified Rhyme Test (MRT) in the evaluation of speech-communication systems can be attributed to the closed-response format of the test. The 300-word MRT vocabulary was recorded by an adult male speaker and administered to two groups of listeners at two signal-to-noise ratios. The first group came for five test sessions during each of which they heard the six MRT lists at each test condition and utilized an open-response (write-down) format. The second group came for one test session and heard the six MRT lists at each test condition; they utilized the regular closed-response (multiple-choice) format. Test scores obtained from the listeners utilizing the open-response format and having considerable exposure to the test vocabulary were not appreciably different from test scores obtained from the listeners utilizing the regular closed-response format having no previous exposure to the test vocabulary. Additional tests administered to two other groups of listeners showed that MRT scores do not rise as listening experience is acquired.