bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflections from focused liquid-filled spherical reflectors
Authors: Marks Barry M. , Mikeska E. Eugene
Published: October 2005

Experimental measurements are presented for the target strength and directivity patterns of the reflections from stainless steel spherical shells filled with a mixture of carbon tetrachloride and freon (F113) in the frequency range 30–130 kHz. Five spheres were tested having nominal outside diameters of 6, 7, 10, 12, and 18 in. with varying wall thicknesses. Target strength measurements were made separately on echo components arising from reflections from the front and rear surfaces of the sphere; the focused rear-surface reflections showed target strengths up to 21 dB higher than those corresponding to the front surface, controlled by the sphere wall material and thickness, and by the index of refraction of the fluid.

Subject Classification: [43]30.30.
Simplified model of the spectral characteristics of high-frequency surface scatter
Authors: Swarts R. L. , Eggen C. J.
Published: October 2005

Classical wave theoretical treatments can be used to predict the general characteristics of the acoustic field scattered from a roughened time-varying sea surface. Various approximations can then be invoked to handle the so-called slightly rough and very rough surface cases. In this paper an expression for the spectrum of the scattered sound is derived for the very rough case in terms of specific surface-wave parameters. This expression is then evaluated for several surface spectra, including the fully aroused Neuman–Pierson and Pierson–Moskowitz surface wave spectra. Finally, these results for special cases of the Neuman–Pierson spectra are compared with those obtained by numerically integrating the general form for the same spectra, a technique that does not involve the very rough case approximation.

Subject Classification: [43]30.40; [43]20.15.
Acoustic phase and amplitude of a signal transmitted through a uniform flow in the deep ocean
Authors: Widtfeldt J. A. , Jacobson M. J.
Published: October 2005

Results of a previous hydrodynamical study of a uniform, deep-ocean flow are used to develop simple approximations to the sound-speed and current distributions in the flow. The behavior of sound speed with depth, surface current, and source and receiver locations is examined. The effects of the flow on ray geometry, travel time, and spreading loss are investigated for a surfaced cw sound source and bottomed receiver. Total-field amplitude and phase are determined and are found to be highly sensitive to surface-current variations and to source and receiver locations. A simple method is presented for accurately estimating amplitude and phase. Then, an approximate phase formula is developed that is proportional to surface current, linear in source location, and sinusoidal in the orientation angle of the source–receiver range.

Subject Classification: [43]30.20; [43]28.60.
Reflection of waves from a point source by an impedance boundary
Authors: Thomasson Sven-Ingvar
Published: October 2005

The problem of finding a solution of the scalar wavefield produced by a point source in the presence of an infinite ’’impedance’’ boundary is treated. The analysis is made with a method used by Ingard, which has been corrected. It is shown that it is possible to rewrite the exact solution in terms of a single integral along a steepest-descent contour and a Hankel function. Asymptotical expansions of the solution is in consistency with expansions by Wenzel, who found that in a special case expansions of his and Ingard’s solution differ by a ’’surface wave’’ term. The asymptotical expansions are given as examples. The main result, the single integral and the Hankel function, could easily be integrated numerically.

Subject Classification: [43]28.40; [43]20.15, [43]20.30, [43]20.55.
Forced longitudinal vibration of an elastic circular rod on an elastic half-space
Authors: Saito H. , Chonan S.
Published: October 2005

A solution is given for the problem of the forced longitudinal vibration of an elastic circular rod, one end of which is attached to the surface of an elastic half-space and to another end of which a periodic disturbing force is applied. Resonance curves for the motions of rods are derived using specific boundary conditions. Attention is directed to the effective damping of the motion of the rod due to dissipation of waves to infinity.

Subject Classification: [43]40.20; [43]20.22.
Analysis of nonlinear resonance in thickness-shear and trapped-energy resonators
Authors: Tiersten H. F.
Published: October 2005

Electroelastic equations containing terms up to cubic in the small mechanical displacement field, but no higher than linear in the electric variables, are applied in the analysis of nonlinear resonance in rotated Y-cut quartz oscillators. Both pure thickness-shear vibrators and essentially thickness-shear trapped-energy resonators are treated. This is a natural continuation of earlier work on intermodulation in the same resonators. Since in each equation each nonlinear term is negligible compared to an associated linear term, the solutions are obtained by employing an asymptotic iterative procedure and expanding in the eigensolutions of the associated linear problem and, in the vicinity of a resonance, retaining only that nonlinear term correcting the dominant eigensolution. Lumped parameter representations of the solutions, which are valid in the vicinity of a resonance and relate the amplitude of the dominant mode nonlinearly to the voltage across the crystal, are presented for both the pure thickness-shear and trapped energy thickness-shear problems. In each instance the expression for the current through the crystal is determined, the influence of the external circuitry is included in the analysis and, ultimately, an expression cubic in the mode amplitude and linear in the driving voltage is obtained. The analyses hold for the fundamental and odd overtone thickness-shear modes. Nonlinear resonance curves are presented for AT-cut quartz using the nonlinear coefficient γ determined in earlier work on intermodulation.

Subject Classification: [43]40.24, [43]40.30; [43]85.52.
Ear dominance and intensity independence in the perception of dichotic chords
Authors: Efron Robert , Yund E. William
Published: October 2005

The perceived pitch mixture of two tones of a dichotically presented chord was studied as a function of the difference between the intensities of the right and left ear tones (ΔI). Previous experiments have shown that, within a wide range of ΔI, the pitch mixture is independent of ΔI. This intensity independence of the pitch mixture of dichotic chords is not seen with monaural chords. Within the range of ΔI over which intensity independence is seen, the pitch mixture of the dichotic chord is determined by another property of the central pitch processor—the ear dominance function. In previous experiments the intensity independent function could only be detected in those subjects with a weak ear dominance function. In the present experiments subjects adjusted the relative intensities of the two tones of a binaural chord to match the pitch mixture of a dichotic chord. Using this method, the intensity independent function was measured directly in all subjects. In addition, the present method provides a direct measure of the magnitude of the suject’s ear dominance function and clarifies the relationship between the effects of the two functions.

Subject Classification: [43]65.75, [43]65.54, [43]65.62.
Temporal summation and decay in hearing
Authors: Irwin R. J. , Kemp S.
Published: October 2005

Two theories of temporal summation in hearing were compared. In both theories the ear performs a running average on the incoming sound in accordance with the convolution integral. In one of the theories, called the ’’rectangular’’ theory, sound is transformed by a power function and weighted by a brief rectangular function; in the other theory, called the ’’exponential’’ theory, sound is transformed so that an initial large effect decays to a steady level and it is weighted by a decaying exponential function. The rectangular theory was shown to predict that brief tone bursts and brief gaps in a tone are equally detectable if the duration of the burst and gap are equal, but the exponential theory was shown to predict that brief tone bursts are more readily detectable than brief gaps of equal duration. Experimental findings support the exponential theory: The percentage of correct responses in a two-alternative forced-choice task was greater for tone bursts than for tone gaps of equal duration. This result was obtained for tones and gaps from 25 to 200 msec in duration and for two different levels of a 1000-Hz tone. In addition, the exponential theory, with a time constant of 5 sec−1 for the weighting function, was compatible with the relation between the percentage of correct responses and the theoretical quantity determining detectability.

Subject Classification: [43]65.68, [43]65.50, [43]65.75.
Higher harmonics of finite amplitude ultrasonic waves in solids
Authors: Thompson R. Bruce , Buck O. , Thompson D. O.
Published: October 2005

Absolute measurements of the amplitude of the first four harmonicof 30-MHz finite amplitude ultrasonic waves are reported for fused silica samples of various lengths and for aluminum single crystals with different amounts of cold work. The harmonically distorted motion of the end of the sample is detected by a capacity microphone and the individual harmonics are then selected and amplified by a heterodyne receiver with flat frequency response from 30 to 250 MHz. The fused silica data are found to be in excellent agreement with a model of Fubini, originally developed for gases, which for solids depends on the second- and third-order elastic constants but none of the higher constants. A discussion is presented of the reasons for the insensitivity of the measurements to the values of the fourth- and higher-order elastic constants. Agreement with the model of Fubinin is not observed in single crystal aluminum. The quantitative differences are not fully consistent with existing models for dislocation contributions to harmonic generation.

Subject Classification: [43]25.15, [43]25.20; [43]35.26; [43]25.25.
Nonspherical acoustic lens study
Authors: Corbett Kevin T. , Middleton F. H. , Sternberg R. L.
Published: October 2005

A successful short focal length radar lens design technique was adapted to the problem of nonspherical thin underwater acoustic lens development and construction. The motivation was furnished by the many sonar requirements for small size lenses capable of operation in a scanning mode. The paper includes a discussion of the computer-aided lens design, the fabrication of casting molds, the vacuum casting process, and the pattern and gain measurements on the final rubber lenses. The design was accomplished using a lens size and frequency that would be compatible with the test tank available for the work. the lenses constructed were about 7 in. in diameter, vacuum cast from 3120 RTV rubber, and were tested using an acoustic frequency of 185 KHz. The useful scanning range of the lens in these tests turned out to be ±20° from the axis. The gain of the lens was 20 dB, the main lobe beam width about 4°, and ths side lobes were from 12 to 19 dB below the main lobe. Total absorption and reflection losses were less than 1 dB. The F number of the lens was about 1.3.

Subject Classification: [43]30.80, [43]30.82, [43]30.25.
Interpretation of multipath scintillations Eleuthera to Bermuda in terms of internal waves and tides
Authors: Dyson Freeman , Munk Walter , Zetler Bernard
Published: October 2005

Rate-of-phase and intensity spectra due to time-varying multipath interference depend essentially on a single parameter ν2 which can be interpreted as the mean-square rate-of-phase for any typical single path. MIMI 406-Hz phase and intensities are consistent with ν−1=270 and 357 sec for Eleuthera to Bermuda and Eleuthera to midstation transmissions, respectively, compared to 192 and 286 sec from a ray-geometric calculation using an internal wave model based on oceanographic observations. Internal tides play a significant but not dominant role.

Subject Classification: [43]30.20, [43]30.35.
Long-range acoustic propagation through the Gulf Stream
Authors: Levenson Coleman , Doblar Randy A.
Published: October 2005

Acoustic charges were detonated on a line normal to the Gulf Stream and recorded near Bermuda. Received signals were analyzed in one-third-octave bands from 40 to 200 Hz and analyzed for rms value over an 8-sec period. Results indicate areas of low transmission associated with the North and South Walls of the stream that ranged between 4–10 dB. Highest levels were received from charges detonated north of the stream. These results can possibly be explained by varying sonic-layer depths and a deepening sound channel axis between Slope Water and deep warm layers of Sargasso Sea water. Other factors possibly related to received amplitude fluctuation may be internal waves and ’’patches’’ of water different from surrounding areas. Further experiments using cw sounds are being planned to delineate seasonal and angular factors.

Subject Classification: [43]30.20, [43]30.25.
Acoustic radiation from submerged plates. II. Radiated power and damping
Authors: Stuart Alan D.
Published: October 2005

Leaky wave poles are defined as those singularities of the acoustic admittance of a fluid-loaded infinite plate that are located on the bottom Riemann sheet of the complex wave number plane and can appear near the saddle point of the complex path of steepest descent. These poles represent only the real, propagating modes in an unloaded plate. It is shown that for a point or line-excited fluid-loaded classical and Timoshenko–Mindlin plate, the value of leaky wave poles and their location relative to the saddle point are sufficient parameters to explicitly describe the radiated power, the angle, beamwidth, amplitude, and existence of the radiation lobes, and the effect of structural damping on the radiation field.

Subject Classification: [43]30.50; [43]40.24.
Identification of random auditory waveforms. II. Interaural relationships
Authors: Pollack Irwin
Published: October 2005

Can listeners successfully identify specific waveforms, randomly selected from extremely large pools of possible signals? Can listeners also identify specific sequences of interaural relationships, randomly selected from extremely large pools of possible sequences of interaural relationships? The answer to the first question is  yes ; the answer to the second is ’’probably no.’’

Subject Classification: [43]65.62, [43]65.75, [43]65.52.
Two-tone unmasking and suppression in a forward-masking situation
Authors: Shannon Robert V.
Published: October 2005

A forward-masking situation was investigated where more energy added to the masker decreased the threshold of the signal. The signal was a single sinusoid. The masker contained two frequency components: one at the same frequency as the signal, and one at a variable frequency. For certain frequencies and intensities of this variable masker component the threshold of the signal was lower than if that component were not present.This decrease in threshold is unmasking. Unmasking is interpreted as being caused by the suppression of the fixed masker component by the variable masker component, thus producing less masking at the signal frequency. The basic pattern of masking and ummasking was qualitatively similar to the pattern of pulsation thresholds observed by Houtgast [Acustica 29, 168-179 (1973). Unmasking was not observed at absolute threshold or in a simultaneous masking situation. Unmasking was observed at all signal frequencies tested (0.5–6.0 kHz) and was not dependent on the phase of the masker components or the phase between the masker and the signal. When the frequency of the variable masker component was less than the signal frequency, unmasking was dependent on only the intensity of the variable component. However, when the variable frequency was greater than the signal frequency, unmasking was dependent on the difference in intensity between the two masker components. The existence of unmasking in a forward-masking situation does not depend on whether or not the masker and signal are turned on and off abruptly or smoothly. These characteristics of unmasking are not in conflict with the assumption that this effect is caused by the variable masker component suppressing the other masker component.

Subject Classification: [43]65.58, [43]65.68, [43]65.50.
Ultrasonic bounded beam reflection and transmission effects at a liquid/ solid-plate/liquid interface
Authors: Plona Thomas J. , Pitts Leslie E. , Mayer Walter G.
Published: October 2005

Schlieren techniques are used to show that bounded beam reflection effects occur at liquid/solid-plate/liquid (L/SP/L) interfaces which are analogous to the bounded beam reflection effects reported previously at liquid/solid (L/S) interfaces. At L/SP/L interfaces, nongeometric effects are shown to be present in both the reflected and transmitted beams when the incident angle of an ultrasonic beam corresponds to the Lamb angle. In addition, similarities between wave phenomena at L/SP/L interfaces and L/S interfaces are presented which suggest that the description of bounded beam reflection derived by Bertoni and Tamir for a L/S interface can be qualitatively applied to the L/SP/L interface case. This theory is shown to account for the lateral extent to which a leaky Lamb surface wave, excited by mode conversion, propagates.

Subject Classification: [43]35.54; [43]20.40, [43]20.30.
Direct image reconstruction of anomalies in a plane via physical optics farfield inverse scattering
Authors: Bleistein Norman
Published: October 2005

This paper shows how to process backscattered acoustic data to directly generate the image of an anomaly in a plane such as an anticline, syncline, or fault. The result is based on a physical optics farfield inverse scattering (POFFIS) identity. This identity states that a phase- and range-normalized scattering amplitude is proportional to a function which is unity in the region of the anomaly and zero outside that region.

Subject Classification: [43]20.30, [43]20.15; [43]40.50.
Temporal auditory summation for pure tones and white noise in the house mouse (M
u
s m
u
s
c
u
l
u
s)
Authors: Ehret Günter
Published: October 2005

The dependence of the absolute auditory threshold on signal duration was measured by means of behavioral methods in the house mouse (Mus musculus). Twelve frequencies between 1 kHz and 120 kHz and white broad-band noise were tested while seven pulse durations between 1 and 3000 msec were used. In any case temporal summation follows the function I⋅tb=const until, at a critical duration tc, a constant value is reached where thresholds become independent from signal duration. The critical durations are frequency-dependent following the general function: tc=p⋅fq (with q<0). This frequency-dependent nonlinearity could alos be extracted from available data on human hearing. The present results and respective data of the human ear are discussed with reference to a critical-band-related summation theory assuming fixed critical bands even for very short signal durations.

Subject Classification: [43]65.68, [43]65.75, [43]65.35; [43]80.50.
Temporal masking-level differences: The effect of mask duration
Authors: Lakey J. Radford
Published: October 2005

Psychometric functions were obatained for the interaural conditions NoSo and NoSπ in both forward and backward masking using masks of different durations. In addition, data were collected for the Sm, Sπ and So conditions without an external mask. The slope parameter k and the signal level required for 76% correct detection were computed with a least-squares technique. The results were that both temporal masking and temporal masking-level differences (MLDs) increased monotonically with longer mask durations. This mask-duration effect was more pronounced for forward masking than for backward masking. Without an external mask, the signal was about 3 dB more detectable in the So configuration than in the Sπ configuration, and it was about 4 dB more detectabe in the Sπ configuration than in the Sm configuration. The psychometric functions were generally steeper for the NoSπ condition than for the NoSo condition in forward masking, but not in backward masking. They were also steeper for the Sπ condition than for either the Sm or So conditions without an external mask. The temporal properties of a typical detection model consisting of a filter centered at the stimulus frequency followed by a rectifier and a final ’’leaky’’ integrator were found to explain much of existent temporal masking data. Signal:500Hz, 8 msec; interstimulus interval: 5–10 msec; mask: wide-band noise; method: two-interval forced choice.

Subject Classification: [43]65.62, [43]65.58, [43]65.68.
Acoustic fluctuations in the open ocean—A measurement using a fixed refracted path
Authors: Ewart Terry E.
Published: October 2005

Amplitude and phase (transit time) fluctuations in pulses sent between a fixed transmitter and a fixed receiver over a wholly refracted 17.2-km path were recorded for 144.5 h. The sites were the southwest flank of Cobb Seamount and a lesser peak 17.2 km away, both at 1000 m depth. Eight-cycle pulses at 4166 Hz and 16-cycle pulses at 8333 Hz were sent alternately every 15.7 sec and received at three receivers located at 0, 5, and 15 m along a horizontal arm located perpendicular to the transmission path. Power spectra have been computed from the time series of phase and amplitude at a single receiver and the phase difference between two receivers. Extreme care was used in the analysis of the data to ensure that the time series obtained represented a single path. The power spectra of the phase data exhibit dominant tidal peaks at 24, 12.4, and 6.2 h; the power spectra of the amplitudes show less evidence of the tides. Between the inertial frequency and the Väisälä frequency, the power spectra of the phase, amplitude and phase difference fall off at approximately ω−3, ω−1, and ω−1/2, respectively. The power spectra of the phase differences for the 15-, 10-, and 5-m spacings scale according to a plane wave arrival. The phase-difference variance is below theoretical predictions, and the amplitude variance is above theoretical predictions. The high-amplitude variance is tentatively identified as ’’micro’’ multipath interference. Evidence is presented to show that the oceanographic regime of the Cobb Seamount area is typical of the open ocean environment.

Subject Classification: [43]30.20, [43]30.25.
Temporal masking of a click by noise in diotic and dichotic listening conditions
Authors: Berg Kathleen , Yost William A.
Published: October 2005

Forward, backward, and combined forward–backward masking of a 1-msec click by noise bursts were examined for diotic and dichotic stimulus configurations. The silent interval between the noise masker and the click ranged from 0 to 40 msec for forward and backward masking conditions. For combined forward–backward masking the silent interval between the two noise maskers ranged from 1 to 60 msec, and the click was positioned at 10-msec intervals within this gap. Masking level differences (MLD’s) were obtained for all temporal conditions studied, but were largest for backward masking when the interval between the masker and click was 0 msec. For the combined forward–backward masking procedure, the effects of forward and backward maskers were roughly equivalent in the homophasic condition, but for the antiphasic condition the backward masker was considerably less effective than the forward masker. For homophasic stimuli, the magnitude of additional masking was dependent upon masker intensity. There was little or no evidence of additional masking for antiphasic stimuli.

Subject Classification: [43]65.58, [43]65.62, [43]65.68.
Consonant environment specifies vowel identity
Authors: Strange Winifred , Verbrugge Robert R. , Shankweiler Donald P. , Edman Thomas R.
Published: October 2005

Past studies have shown that, while vowels can be produced with static vocal tract configurations, the resulting steady-state tokens are misidentified frequently by naive listeners. The first experiment compared the perception of isolated vowels with vowels spoken in a fixed consonantal frame by the same set of 15 talkers. Vowels in /p–p/ syllables were identified with far greater accuracy than were comparable isolated vowels in both single and multiple-talker conditions. Acoustical analyses of the test tokens showed that the poor intelligibility of isolated vowels could not be attributed to talkers’ failure to produce these vowels correctly. In a second experiment, vowels in syllables in which the initial and final stop consonant varied unpredictably from item to item were still identified with greater accuracy than were isolated vowels. These results offer strong evidence that dynamic acoustic information distributed over the temporal course of the syllable is utilized regularly by the listener to identify vowels.

Subject Classifications: [43]70.30, [43]70.40, [43]70.70.
Toward a more general integral formulation of the pressure field of an echosonde aperture antenna
Authors: Adekola S. A.
Published: October 2005

The basis for improvements in acoustic echo-sounding (echosonde) antenna characteristics is analyzed. The results are based on a more general radiation integral formulated from the time-independent wave equation for an acoustic wave, using a cylindrical antenna as a model. Employing common forms of aperture field distributions across the upper transmitting aperture of the antenna, a Fresnel-region field quantity, which is expressed in a closed form using Lommel’s series, is obtained. An echosonde antenna design meeting the requirements of previous specifications is made from the numerical results of the farfield patterns in order to show the validity of the results. The design permits the operation of the antenna in urban environments since irritating noise levels are kept low. The height of the antenna shielding cuffs reduces the 90° side-lobe level (ground level) by 3.85 dB at the height of 1 ft through 40 dB at 13 ft. A 90° side-lobe reduction of 38.6 dB, which agrees with predictions, is obtained for the more appropriate height of 12 ft; diameters of 4 and 12 ft for the lower illuminating—and upper transmitting—apertures, respectively. The results, reported for acoustic carrier frequencies of 2 and 5 kHz, indicate that small values of the antenna height are untenable in echo-sounding operation.

Subject Classification: [43]85.40; [43]20.15, [43]20.30, [43]20.55.
Harmonic vibrations of isotropic, elastic, and elastic/viscoelastic three-layered plates
Authors: Durocher L. L. , Solecki R.
Published: October 2005

A fourth-order equation has been derived that is suitable for analyzing symmetrically constructed, isotropic three-layer plates. The formulation includes the effects of shear deformation in each layer, as well as the rotatory inertia of the composite while enforcing continuity of displacements and shear stresses at layer interfaces. From virtual work considerations, the natural boundary conditions are also derived in an invariant form. Since the equations of motion and boundary conditions are tensor equations, an arbitrarily shaped plate can be analyzed using the most convenient coordinate system. Natural frequency comparisons have shown that the current theory is in excellent agreement with an exact elasticity solution, at least in the range where such data exists. By using the complex modulus concept or the correspondence principle, the governing equation can be used in analyzing composite plates that consist of (a) a viscoelastic core sandwiched between similar elastic faces and (b) an elastic plate with two symmetric viscoelastic coatings. Several examples have been analyzed to illustrate the damping that can be obtained by the use of a viscoelastic inner layer.

Subject Classification: [43]40.20, [43]40.24.
Deep-ocean dynamics for environmental acoustics models
Authors: Watson J. G. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

A hydrodynamic model for flows in the deep ocean is developed in order to determine the velocity field and sound-speed distribution for use in acoustic transmission problems. A scaling of the governing equations is constructed that explicitly includes sound speed. A subsequent perturbation expansion yields a set of approximate equations for motions nearly in geostrophic and hydrostatic balance, such as large-scale, quasisteady currents and Rossby waves. The quasigeostrophic potential vorticity equation or a simpler limiting case of this equation arises from the perturbation scheme to govern higher-order dynamics of the stream function for these flows. The results of the analysis are used to obtain a significant simplification of the ray equations of geometrical acoustics for moving media. For the particular class of flows considered here, the model equations are applicable if the ocean depth is about 1 km or greater and if the spatial and temporal scales of variation of the motions are of the order of 100 km and 10 days, respectively. A solution for a flow such as the Antilles current is derived. Isospeed curves for this solution are shown in a plane perpendicular to the current, and specific features of the curves are discussed and interpreted.

Subject Classification: [43]30.25, [43]30.20; [43]28.60.
Experiments with two types of electromagnetic ultrasonic transducers
Authors: Kawashima Katsuhiro
Published: October 2005

Two types of electromagnetic ultrasonic transducers were made and tested on mild steel, stainless steel, and aluminum. One of the transducers generates and detects a relatively large amount of longitudinal wave and simultaneously a small amount of radially polarized transverse wave in nonmagnetic metal. The other is for a large amount of radially polarized transverse wave and a small amount of longitudinal wave, also in nonmagnetic metal. Both transducers showed different characteristics for ferromagnetic metal, giving greater efficiency to the radially polarized transverse wave. It was also shown experimentally with an electromagnetic transducer that the mode conversion between longitudinal waves and radially polarized transverse waves occurs fairly efficiently at a vertical reflection.

Subject Classification: [43]35.60, [43]35.80; [43]85.40, [43]85.48.
Experiments involving sonification of liquid helium at 4.2 K in the cathode–anode interspace of a photodiode tube
Authors: Smith C. W. , Burke G. F. , Rooney J. A.
Published: October 2005

An experimental study of the photo-injection of electrons into liquid helium at 4.2 K during sonification shows a dramatic increase in the observed photocurrent. The increase in photocurrent results from a sonically induced increase of the electron bubble mobility and a reduction in mean thermalization time due to an increase in local density fluctuations in the vicinity of the photocathode. The increase in mobility of the electron bubbles in the sound field has the same functional dependence as static pressurization, suggesting an effective rectification mechanism. Studies in which the sound field is abruptly turned off show that the half-life of potential cavitation nuclei within the microbubble field is 7.6 sec. These sonically induced changes in the electron microbubble photocurrent provide a unique method for the study of the formation and population dynamics of cavitation nuclei.

Subject Classification: [43]35.47, [43]35.32.
Susceptibility to auditory fatigue: Comparison of changes in cochlear nerve potentials in the guinea pig and chinchilla
Authors: Mitchell Curt
Published: October 2005

The susceptibilities of the guinea pig and chinchilla to acoustic fatigue are compared. For this comparison they were exposed to a 6-kHz tone. The exposures were within the range of 60–110 dB SPL. The N1 potential of the cochlear nerve and the cochlear potential were recorded before and after exposure. Both species suffered greatest N1 changes a 1/2 octave above the exposure tone. No appreciable changes in cochlear potential were observed. In agreement with previous studies for equal SPL’s, the chinchilla was found to be more susceptible to fatigue than the guinea pig. However, when the exposures are based on maximum cochlear-potential output, these animals suffer similar losses in N1. This suggests that impedance differences in their ears accounts for the susceptibility difference. Nerve fatigue is described and found related to hair cell distortion.

Subject Classification: [43]65.66, [43]65.40, [43]65.42.
Spatial coherence in multipath or multimodal channels
Authors: Smith P. W.
Published: October 2005

An integral expression for the spatial coherence function of pure-tone sound fields is formulated under hypotheses that the component fields of individual paths or modes are locally plane waves and mutually incoherent in the average. The total field is not assumed to be a Gaussian random variable. The resulting coherence is quasi or locally homogeneous, varying slowly with average position as the strength of the component fields change. Statistical estimates for the contributions of these components are taken from existing literature on average transmission loss. The expression for coherence has an explicit dependence on the environmental parameters, the range, and the depths of source and receivers. Numerical results and approximate expressions are developed for channels characteristic of shallow and deep water.

Subject Classification: [43]20.15; [43]60.20.
Attenuation of shear waves in marine sediments
Authors: Hamilton Edwin L.
Published: October 2005

The objectives of this report are to review selected published measurements of the attenuation, or energy damping, of low-strain shear waves in surficial water-saturated sands and silt clays (mud) which might occur as marine sediments. In various computations, a linear viscoelastic model is favored in which velocity dispersion is negligible, the linear attenuation is proportional to the first power of frequency, and the specific dissipation function, 1/Q, and the logarithmic decrement are independent of frequency. The logarithmic decrement is favored as a measure of energy damping because of research in soil mechanics. The very sparse data indicate that in water-saturated sands and silt clays, the logarithmic decrements are mostly between 0.1 and 0.6. If approximate values of shear wave energy losses are required for generalized computations, it is suggested that a value for the logarithmic decrement of 0.30±0.15 be assumed for sands, and 0.2±0.1 for silt clays. Measured logarithmic decrements of compressional waves in sands average about 0.10±0.03; in silt clays about 0.02±0.01. The average values of the ratio of compressional-to-shear-wave logarithmic decrements, using the above average values, would be 0.3 for sands and 0.1 for silt clays.

Subject Classification: [43]30.20; [43]40.50, [43]30.30.
High-frequency model for sound transmission from an airborne source into the ocean
Authors: Meecham William C.
Published: October 2005

The problem of the transmission of sound from an airborne source into the ocean, through the rough ocean surface, is considered. A high-frequency approximation is adopted, requiring for its validity that the sound wavelength in air be (much) less than typical radii of curvature and than typical displacements of the ocean surface. This condition is approximately met in many applications. Attention is focused on observation directions with small grazing angles. The result is approximately unaffected by surface roughness when the grazing angle is greater than the rms surface slope, and approaches a limit (proportional to the variance of the surface slope) when the grazing angle is less than the slope. The result is independent of the source height, under the stated approximations, as is also the case for the transmission through a plane surface. The enhancement due to surface roughness, even at moderate wind speed, ranges up to 10 dB.

Subject Classification: [43]30.25.
Comments on ’’Sabine’s reverberation time and ergodic auditoriums’’ [J. Acoust. Soc. Amer. 58, 643–655 (1975)]
Authors: Gomperts M. C.
Published: October 2005

Joyce’s paper is, in fact, a confirmation of the author’s standpoint that, generally, Sabine’s formula does not hold. A reverberation formula from recent literature, referred to by Joyce, is shown to be false. Instead, a more correct formula is given here.

Subject Classification: [43]55.20, [43]55.30, [43]55.55.
Vibrations of an infinite plate with a frequency independent Q
Authors: Caputo Michele
Published: October 2005

The dissipation in an elastic medium is represented by a dissipation mechanism which is similar to one used in an earlier paper [M. Caputo, Geophys. J. R. Astron. Soc. 13, 529–539 (1967)], but is simpler and has a frequency-independent Q−1. The vibrations of a plate are studied by obtaining the eigenfrequencies, the amplitude of the displacement, the dispersion relation, the Q−1, the hysteresis cycle, and the yield stress.

Subject Classification: [43]40.24.
Comfortable effort level: An experimental variable
Authors: Brown W. S. , Murry Thomas , Hughes David
Published: October 2005

It is not uncommon to read in speech studies that subjects were instructed to produce speech samples at a ’’comfortable effort level.’’ In many cases the experiments have made the assumption that this level of effort is more or less constant over repeated occurrences. The purpose of this study was to test the constancy of comfortable effort level in speakers’ utterances across experimental sessions. Sixteen speakers were recorded on each of five successive days while producing a series of vowels and phrases. The only instruction to the speakers was to repeat the utterances at a comfortable effort level. Measures of speaking fundamental frequency (SFF) and vocal intensity (SPL) were obtained from the recordings. Results indicate that variability in both SFF and SPL occurred in the utterances; in many cases (especially for SPL) this variability was considerable. These results suggest that experiments desiring constant vocal productions must be more specific in providing instructions to subjects since comfortable effort level can not be assumed to be constant from one experimental session to the next (especially from day to day).

Subject Classification: [43]70.40, [43]70.20.
The contribution of fundamental frequency and voice onset time to the /zi/-/si/ distinction
Authors: Massaro Dominic W. , Cohen Michael M.
Published: October 2005

Functional measurement was utilized to study the acoustic cues that contribute to the perception of the voicing difference in /zi/ and /si/. Rather than simply varying the acoustic signal along a single dimension and observing the effect on perception, changes along two acoustic dimensions were covaried in a factorial manner. The time between the onset of the syllable and the onset of vocal-cord vibration called voice onset time (VOT) was covaried with the fundamental frequency (F0). Observers were asked to indicate where each stimulus fell on a scale from /zi/ to /si/. The results showed that both VOT and F0 contribute to the perception of voicing. Sounds were judged as more /zi/-like with decreases in VOT and with decreases in the F0. The frequency contour of F0 during the syllable had very little effect beyond that accounted for by the frequency of F0 at the onset of vocal-cord vibration. Another experiment showed that the role of F0 could not be attributed to the possibility that there was less energy at the first formant with higher frequency values of F0. A quantitative model assuming that VOT and F0 are perceived independently provided a good description of the observed judgments.

Subject Classification: [43]70.30, [43]70.20, [43]70.70.
Spectral transformations by an infinite clipper
Authors: de Boer E.
Published: October 2005

Several manifestations of auditory nonlinearity indicate that the percentage of distortion does not vary much over a wide range of stimulus intensities. Accordingly, there has been some interest in ’’essential nonlinearities’’ (nonlinear devices of which the percentage of distortion is independent of level) for modeling purposes. In this note the genesis of the cubic difference tone (CDT) by such a device is treated. The extreme case of an infinite clipper is chosen for reasons of simplicity. In the simplest case the stimulus signal has two components with frequencies f1 and f2 (f2≳f1) of which the upper one is the weaker of the two. This signal shows both amplitude (AM) and phase modulation (PM). The clipping removes the AM and the remaining PM causes the signal to have at least three components. The newly generated third component is the CDT with frequency 2f1−f2. It is as if the original upper component is split into two components; one with the original frequeny f2 and the other with the frequency 2f1−f2. Each of these has half the original amplitude, hence the infinite clipper produces one form of two-tone suppression as well. The method by which the results are obtained suggests a generalization to multicomponent and to stochastic signals. This may allow a fruitful strategy to be developed for a comprehensive analysis of cochlear nonlinearity.

Subject Classification: [43]65.35, [43]65.56.
Natural frequencies of orthotropic rectangular plates with varying thickness
Authors: Sakata Toshiyuki
Published: October 2005

An approximate formula is derived for the estimation of the fundamental natural frequency of the simply supported orthotropic rectangular plate with thickness varying linearly in one direction. The accuracy of the formula and the influence of the flexural rigidity D*1 on the natural frequency are discussed.

Subject Classification: [43]40.24.
Radiation from a spherical acoustic source near a scattering sphere
Authors: Thompson William
Published: October 2005

The radiation from a spherical source vibrating with an arbitrary, axisymmetric, time-harmonic velocity distribution while positioned at an arbitrary point wholly outside a fluid sphere while both are embedded in another infinite fluid medium, is computed. The translational addition theorem for spherical wave functions is used to express series of wave modes centered at one sphere in terms of modes centered at the other, thereby facilitating the task of satisfying the boundary conditions. By letting the fluid sphere become either infinitely dense or infinitely compliant, the special cases of a spherical source radiating in the presence of a perfectly reflecting spherical scatterer are obtained. The source output and farfield directional response pattern are computed as a function of source and fluid sphere separation for some representative values of relative fluid density and sound speed. Numerous results are presented showing the modification of the radiation load on monopole and dipole sources of various wavelength sizes due to a nearby rigid or pressure release, spherical scatterer of the same size. The effect of the perfect scatterer is only important when the source and scatterer are very close and the pressure-release scatterer has considerably more effect than the rigid one.

Subject Classification: [43]20.30, [43]20.55.
On the attenuation of sound by turbulence
Authors: Brown E. H. , Clifford S. F.
Published: October 2005

We present a theory of attenuation of sound by turbulence. The mechanism underlying this theory is the turbulence-induced broadening of finite beams of sound. It is thus conjectured that attenuation of sound by turbulence is not an intrinsic property of the medium, nor even of its dynamic state, but depends on the particular details of the experiment, such as beamwidth, beam orientation, etc. This point of view is at odds with that of some other theories, in which attenuation by turbulence is regarded primarily as a scattering process. Some conceptual flaws in these other theories are pointed out. It is shown that the present theory yields results which are in qualitative agreement with observations.

Subject Classification: [43]28.40, [43]28.60; [43]20.35.
Determination of source depth from the spectra of small explosions observed at long ranges
Authors: Mitchell Stephen K. , Bedford Nancy R. , Weinstein Marvin S.
Published: October 2005

The acoustic pressure versus time signature of an underwater explosive source is a sensitive function of the charge weight and the depth of the explosion. If those parameters are known, then the amplitude of the primary shock pulse and the amplitudes and spacings of the following bubble pulses may be accurately predicted. The power spectrum of the signal is characterized by a scalloped form, which also is determined by the charge weight and depth. Even though the signal observed at long range is distorted due to propagation effects, the scalloped spectral structure is preserved. By using power cepstrum techniques, it is possible to determine the characteristic period of the spectrum. From the relation between the spectral period and the bubble pulse period, the exact detonation depth may be determined from a received shot signal if the charge weight is known. An example of such a measurement is presented in this paper. A series of signals from 1.8 lb Mk 61 SUS charges detonated at nominal depths of 60 ft was examined. The bubble pulse period of each source was determined from recordings made onboard the ship from which the shots were deployed. Shots were received at ranges of 250–310 NM at one location and at ranges of 625–700 NM at another location. The depths, as estimated at the remote receiver, were distributed about the onboard measurements with standard deviations of 0.49 ft at the shorter ranges and 0.52 ft at the longer ranges.

Subject Classification: [43]30.75.
Influence of auditory fatigue on masked pure-tone thresholds
Authors: Parker Donald E. , Tubbs Randy L. , Johnston Peggy A. , Johnston Linda S.
Published: October 2005

Thresholds for detection of a 3-kHz tone embedded in a 2121–4242-Hz octave band of masking noise or a 6-kHz tone in 4243–8486-Hz masking noise were determined before and after fatiguing noise exposure. Masking-noise levels were varied from 0 to 90 dB (re 20 μN/m2). The fatiguing noise was a 1414− to 2828-Hz or a 2829–5658-Hz octave band of noise set at intensities between 90 and 115 dB. Each observation included the following parts: (1) prefatigue threshold determination, (2) 3-min exposure to intense noise, (3) 90-sec delay, and (4) postfatigue threshold determination. The results of a series of observations employing the above procedure indicate that tone thresholds were elevated following the fatiguing-noise exposure by up to 22 dB when the tones were embedded in 0−dB masking noise (TTS2=22 dB). However, tone thresholds were elevated only slightly following fatiguing-noise exposure when the tone was embedded in 45–90-dB masking noise. Possible mechanisms that might account for these observations are considered.

Subject Classification: [43]65.58, [43]65.66, [43]65.50, [43]65.75.
Sound production by organ flue pipes
Authors: Fletcher N. H.
Published: October 2005

A nearly exact, nonparametric treatment is devised to allow calculation of the transient and steady-state acoustic spectra of a flue organ pipe, given the geometry of its construction and the pressure variation in its foot. Explicit formulation is given for the fundamental and the first and second upper partials. A scaling law is set out, relating the behavior of pipes of different fundamental frequencies, and several illustrative calculations are performed. Comparison between theory and experiment for a limited number of cases shows satisfactory agreement in semiquantitative terms but indicates that a more careful treatment of air jet behavior is required at low jet velocities.

Subject Classification: [43]75.60.