bluuebunny/crossref_metadata_2025 huggingface dataset:
The sound-producing oscillations of round underexpanded jets impinging on normal plates
Authors: Powell Alan
Published: October 2005

The results of acoustical and optical experiments in which ‘‘moderately’’ underexpanded sonic round jets impinge on flat plates normal to the jet axis are presented and analyzed. Periodic unstable oscillations of the jet flow, with the resultant radiation of sound of discrete frequencies, occur over a wide variation of control parameters, namely, pressure ratio, plate size, and spacing of the plate from the jet nozzle. For ‘‘small’’ plates, the principal oscillations with λ/D about 4 (λ=acoustic wavelength, D=nozzle diameter) occur when the standoff shock wave lies in a pressure recovery region of the periodic cellular structure of the choked jet and is, therefore, highly unstable; then the oscillations have key characteristics in common with the high-harmonic excitation of Hartmann’s acoustic air-jet generator. An analogous feedback mechanism in the standoff zone is suggested in which pressure waves reflected from the plate trigger the motion of the unstable shock wave. For ‘‘large’’ plates, acoustic feedback to the nozzle occurs, and the principal tones have λ/D about 2 with frequencies nearly independent of pressure ratio (velocity) and plate size. They exhibit the sawtooth characteristic familiar in similar situations (edge tone, hole tone, and for subsonic jets interacting with flat plates), there being at least seven stages, frequently with frequency jumps between them.

A feedback mechanism is suggested, and a formula for the frequency of oscillation is derived, the form of which is consistent with experimental data. Secondary tones also occur, at least some of those of higher frequency (λ/D≊1) appearing to be extensions of the large-plate principal tones, but those of lower frequency, while of the precisely same character, presumably are from a differing instability mode. The characteristics of these principal and secondary tones provide the means of analysis of the limited existing pertinent literature. Several sets of data can be classified into the small- and large-plate classes for ‘‘moderate’’ and ‘‘high’’ degrees of underexpansion. For ‘‘very highly’’ underexpanded jets, the mechanism for small and large plates appears to merge, and, correspondingly, there is no longer the distinction between the phenomena for small and large plates as pertains at lower pressure ratios.
Yaw and spin effects on high-intensity sound generation and on drag of whistling projectiles
Authors: Shakkottai P. , Cho Y. I. , Kwack E. Y. , Back L. H.
Published: October 2005

Projectiles containing axisymmetric ring cavities constitute aeroacoustic sources. These produce high-intensity tones that are used for coding in the simulation of area weapons effects (SAWE) system. Experimental data obtained in a free-jet facility are presented describing the effects of yaw, spin, and geometric projectile parameters on sound pressure and drag. In general, the sound pressure decreases with increasing yaw angle whereas the drag increases. Spin tends to increase sound-pressure levels because of a reduction in asymmetry of flow. Drag increases at zero yaw approximately as the 2.5 power of sound wavelength. Drag increase appears to be due to energy loss by sound radiation at low wavelengths and due to wake modification at large wavelengths.
Arctic ambient noise in the Beaufort Sea: Seasonal relationships to sea ice kinematics
Authors: Lewis James K. , Denner Warren W.
Published: October 2005

Various modes of sea ice motion in the Beaufort Sea are correlated with under-ice noise at 10, 32, and 1000 Hz. Seasonal variations are considered, and a parameterization of ice microfracturing caused by sensible heat flux is included in the correlations. During the summer, the correlations indicate that all frequencies are primarily a response to the ice rushing through the water. During the fall, 10- and 32-Hz noise correlate best with a linear combination of the speed of the ice parcel plus the total rate of change in the shape of the ice parcel. This latter factor indicates noise generation due to the individual ice floes moving past one another as they rearrange into new shapes. The correlations indicate differential motions of other forms (primarily ice convergence) become important in generating lower frequency noise only during winter. As for 1000 Hz during fall and winter, the correlations are low and the results are ambiguous. Several factors are discussed that emphasize our lack of knowledge about higher frequency arctic ambient noise.
Spherically symmetrical acoustic propagation across a fluid/fluid boundary
Authors: Buckingham Michael J.
Published: October 2005

The problem of determining the spherically symmetrical field generated by an acoustic point source at the center of a fluid sphere that itself is immersed in a second fluid medium is discussed. A method of solving for the field in the internal and external fluid regions is introduced, based on finite Hankel transforms. These transforms and their inverses are constructed in such a way that the boundary conditions (continuity of pressure and normal component of particle velocity) at the spherical interface are satisfied. In particular, the inverse transforms are integrals; that is, there is a continuum of radial wavenumbers. This contrasts with the more usual formalism, involving a Fourier–Bessel series taken over a discrete distribution of radial wavenumbers. The latter type of inversion formula is suitable only for problems involving relatively simple boundary conditions (e.g., Dirichlet or Neumann). Using the new technique, an exact analytical solution is given for the acoustic field in both the sphere and the surrounding fluid.
An examination of the spherical scatterer approximation in aqueous suspensions of sand
Authors: Sheng Jinyu , Hay Alex E.
Published: October 2005

The available data for scattered acoustic intensity and attenuation in dilute aqueous suspensions of sand are compared with theory. In theoretical calculations, the scatterer is assumed to be spherical and elastic, or rigid and movable, or rigid and immovable. The rigid movable model provides the best fit to the data. The failure of the elastic model in comparison to the rigid sphere models indicates that resonance excitation does not occur in natural sand grains, probably because of irregularities in shape. The fact that better agreement with experiment is obtained with the rigid movable model than with the rigid immovable model indicates that the inertia of the particles is important. Additional approximate expressions for the form factor and attenuation coefficient have been constructed based on a modified form of the so-called high-pass model introduced by Johnson [J. Acoust. Soc. Am. 61, 275–277 (1977)]. The modified high-pass model provides a fit to the data that is as good as, or better than, the rigid movable case.
The measurement of through thickness plate vibration using a pulsed ultrasonic transducer
Authors: Guyott C. C. H. , Cawley P.
Published: October 2005

The use of pulsed ultrasound and digital spectral analysis to measure the through thickness vibration characteristics of plates has been investigated. It has been shown that, even at nominally normal incidence, some shear modes of the plate are excited in addition to the longitudinal modes. By modeling the propagation of an ultrasonic pulse through the plate, it has been shown that this is due to the mode conversion of the edge waves from the probe, which are always at a nonzero angle of incidence to the structure. However, not all the shear modes of the plate are excited in this way, and both the pulse propagation model described here and classical analyses can be used to predict correctly which shear modes will be observed. The results show that the use of pulse excitation and digital spectral analysis can give very accurate results and, since the testing time required is small, the technique is much more attractive for use in nondestructive testing than the conventional methods employing sine wave excitation.
The ultrasonic vibration characteristics of adhesive joints
Authors: Guyott C. C. H. , Cawley P.
Published: October 2005

The natural frequencies of the longitudinal (through thickness) modes of an adhesive joint have been predicted using receptance analysis and measured using ultrasonic spectroscopy. Excellent agreement has been obtained between the predicted and measured frequencies of joints with a wide range of adhesive thicknesses and moduli. At low adhesive thicknesses, the modes tend to occur in pairs, but, at higher thickness, this pairing no longer occurs. This phenomenon has been explained in terms of the mode shapes of the different modes and the role of the adhesive layer in determining their frequencies. The variation of the apparent vibration damping with adhesive thickness has also been explained in terms of the mode shapes of the joint. The results indicate that it should be possible to calculate the thickness and modulus of the adhesive layer from measurements of the resonant frequencies of the joint. This would represent a significant advance in the nondestructive testing of adhesive joints.
Excitation and response of piping systems
Authors: Cuschieri J. M.
Published: October 2005

A piping system can be vibration excited by a number of sources that are a consequence of the flow of the internal fluid, the pumps, and other ancillary equipment of the system. The vibrational power induced in the pipe structure will be partly radiated as noise and partly transmitted through the isolators attaching the quiet piping system to the supporting structure. The transmission of this vibrational power to the supporting structure is investigated in this article using power flow and structural mobility methods. The approach that is developed here is not limited to isolated straight pipe sections but can be applied to a number of subsections joined together by components that can be represented by structural mobility terms. The results obtained can be useful towards the design of quiet piping systems. The influence of the different structural parameters of the pipe, isolators, and support structure can be clearly demonstrated.
Electroelastic effect of crystal rods expressed by fundamental material constants
Authors: Kittinger E. , Tichý J.
Published: October 2005

A material frame theory of the influence of a dc biasing field on the resonance frequency of an electroded thin piezoelectric rod is developed, starting from the rotationally invariant nonlinear constitutive equations of electroelasticity the coefficients of which are fundamental, thermodynamically defined material constants. It is shown that, up to first order in the biasing field, third-order stiffnesses and nonlinear piezoelectric constants but no other nonlinear constants contribute to the effect. Theoretical results are applied to quartz rods of widely differing orientations. The predictions are in very good agreement with experimental results.
Detection of complex echoes in noise by an echolocating dolphin
Authors: Au Whitlow W. L. , Moore Patrick W. B. , Pawloski Deborah A.
Published: October 2005

Dolphins echolocate with short broadband acoustic signals that have good time resolution properties. Received echoes are often complex, with many resolvable highlights or components caused by reflection of the incident signal from external and internal boundaries of a target and from different propagational modes within a target. A series of experiments was performed to investigate how dolphins perceive complex echoes. Echoes were produced by a microprocessor-controlled electronic target simulator that captured each emitted click and retransmitted the signal back to the animal after an appropriate time delay. The use of this ‘‘phantom’’ target allowed for precise control of the number of highlights, the time separation between highlights, and the relative amplitudes of highlights in the simulated echoes. An echolocating dolphin was trained to perform a target detection task in the presence of masking noise using these phantom echoes. The properties of simulated echoes were systematically varied, and corresponding shifts in the dolphin’s detection threshold were observed, allowing for inferences of how the dolphin perceived echoes. The dolphin performed like an energy detector with an integration time of approximately 264 μs.
Reference thresholds for the ER-3A insert earphone
Authors: Wilber Laura Ann , Kruger Barbara , Killion Mead C.
Published: October 2005

Several recent studies have demonstrated that the ER-3A insert earphone may sometimes be directly substituted, without recalibrating, for a TDH-39/MX-41AR earphone. However, most available data have not been reduced to a form suitable for establishing a revised estimate of the reference threshold levels. This article reports such a data analysis performed on the results of five recent studies. The mean data from the five studies are typically within 1 dB of the provisional reference threshold SPLs given by the ER-3A manufacturer for calibration in a (HA-1) 2-cc coupler. After converting the mean data to equivalent Zwislocki-coupler-type ear simulator SPLs at each of the reported audiometric frequencies (125, 250, 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz), agreement within 1.5 dB was seen with the revised estimate of minimum audible pressures given by Killion [J. Acoust. Soc. Am. 63, 1501–1508 (1978)]. Either the manufacturer’s provisional SPLs or the average results from this study may be used with little noticeable difference for most purposes.
Dichotic fusion of two tones one octave apart: Evidence for internal octave templates
Authors: Demany Laurent , Semal Catherine
Published: October 2005

Stimuli consisting of two simultaneous and sinusoidally frequency-modulated pure tones were dichotically presented to four listeners. The two component tones of each stimulus were approximately an octave apart. They were both modulated at 2 Hz, and the frequency swing resulting from each modulation corresponded to one tenth of the carrier frequency. The listeners’ task was to detect phase differences between the modulation waveforms of the two simultaneous tones: With an adaptive 2IFC procedure, just-noticeable values of Φ, the phase angle of the modulation waveforms, were measured as a function of the interval formed by the carrier frequencies (one octave, i.e., 1200 cents, ±0, 25, 50, or 100 cents). When the carrier frequencies were not too high, just-noticeable values of Φ often varied nonmonotonically with the interval, showing a minimum at or near 1200 cents. An additional experiment indicated that most, if not all, of these octave effects were not due to some form of beat detection. As a whole, the results reported here provide evidence for the existence of internal octave templates. Such templates might play an important role in the perceptual segregation of simultaneous harmonic signals, as well as in pitch perception.
An aeroacoustic approach to phonation
Authors: McGowan Richard S.
Published: October 2005

A fluid mechanical, or aeroacoustic, point of view is followed to study possible sources of sound during phonation. Concentration is on two features of the vocal tract during phonation: abrupt area change from the glottis to the vocal tract and the finite length of the vocal tract. With these features, a source of sound distinct from the volume velocity source can be identified and a preliminary account of its effect on the acoustic field given. This source of sound is an oscillating force resulting from an interaction of rotational fluid motion with itself. Because of the schematic nature of the geometry of the model used here, this source may be considerably modified in actual phonation. It is concluded that specification of volume velocity is not enough to specify the source during phonation, even neglecting source–tract interaction.
Sound scattering by cylinders of finite length. II. Elastic cylinders
Authors: Stanton T. K.
Published: October 2005

The theoretical results of the preceding article describing scattering from finite length fluid cylinders [T. K. Stanton, J. Acoust. Soc. Am. 83, 55–63 (1988)] are extended to the case of the elastic cylinder. The same method is used: The volume flow per unit length of the scattered field of an infinitely long cylinder is integrated over a finite interval to estimate the scattered field due to a cylinder of finite length. In this article, Faran’s solution for the infinitely long elastic cylinder [J. J. Faran, Jr., J. Acoust. Soc. Am. 23, 405–418 (1951)] is used to derive the scattering from the finite elastic cylinder at angles of incidence normal and nearly normal to the axis. This rigorously derived analytical solution compares very well with backscatter data from Dural cylinders and a scattering model derived by qualitative arguments, both from Andreeva and Samovol’kin [I. B. Andreeva and V. G. Samovol’kin, Akust. Zh. 22, 637–643 (1976) and Sov. Phys. Acoust. 22 (5), 361–364 (1976)]. The conclusions of this work and from Andreeva and Samovol’kin are the same: The acoustic or effective length of a cylinder, whether it be infinitely long or of finite length, is the smaller of L or the radius of the first Fresnel zone (rλ)1/2, where L is the length of the cylinder or of the insonified ‘‘spot’’ of a longer cylinder, r is the distance from the cylinder to the field point or receiver, and λ is the acoustic wavelength.
A singular perturbation problem: Scattering by a slender body
Authors: Tran Van Nhieu Michel
Published: October 2005

The scattering of sound waves by rigid slender bodies of revolution are investigated by an approach based on the matched asymptotic method. The reduced wavenumber Ka is assumed to be of the order of unity. The scattered field is represented at the scale of the body length by a superposition of sectorial spherical harmonics whose distributions are determined by matching them with the solution of the local problem characterized by a typical length scale of the order of the maximum body cross-section radius. Asymptotic expressions are obtained for the scattered pressures. Comparison of the scattered farfield is made with other methods and numerical computations of the directivity functions of a slender prolate spheroid are presented for several values of angles of plane wave incidence.
Shallow seismic experiments using shear waves
Authors: Stoll R. D. , Bryan G. M. , Flood R. , Chayes D. , Manley P.
Published: October 2005

During the summer of 1986, a series of seismo-acoustic experiments was carried out in shallow water off the New Jersey shore. The purpose of these experiments was to measure the geoacoustic properties of the ocean sediments that comprise the upper few hundred meters of the sediment column. Seismic sources and receivers were deployed at or very near the bottom in order to excite shear waves in the sediment and minimize the effects of interference from waterborne propagation. The experiments were performed at several sites where prior field work had established physical properties and a detailed profile of the sediments. By using conventional air guns deployed in an unconventional way, strong interface and diving shear waves were generated; these data were inverted to obtain shear wave velocity as a function of depth. The inversion results were then compared with the predictions of a geoacoustic model that accounts for the effects of voids ratio, overburden pressure, and other physical parameters. The in situ measurements from experiments and the gradients predicted by the model were in good agreement, suggesting a strong dependence of velocity on overburden pressure near the water–sediment interface.
Comparison of walleye pollock target strength estimates determined from i
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u measurements and calculations based on swimbladder form
Authors: Foote Kenneth G. , Traynor Jimmie J.
Published: October 2005

The target strength of walleye pollock (Theragra chalcogramma) at 38 kHz has been determined in each of two ways: (1) in situ measurement with dual-beam and split-beam echo sounders, and (2) theoretical calculation based on the swimbladder form. Respective probability density functions of target strength are compared. The several estimates of mean target strength (T̄S̄) determine the relation T̄S̄=20 log l−66.0, where l is the fish fork length in centimeters.
Pulse scattering by baffled cavity-backed membranes
Authors: Baker William P. , Kriegsmann Gregory A. , Reiss Edward L.
Published: October 2005

A flexible membrane backed by a rigid cavity is set into an infinite plane baffle. The membrane lies in the plane, and the cavity is in the lower half-space. The upper half-space contains a homogeneous acoustic fluid. The cavity is filled with another homogeneous acoustic fluid. A pulse, which satisfies the acoustic wave equation in the upper half-space, is incident on this baffled membrane. Asymptotic expansions as ε→0 that are uniformly valid in t are obtained for the membrane’s motion and the scattered and cavity acoustic fields. Here, ε≪1 is the ratio of the density of the fluid in the upper half-space to the membrane’s density. If the bandwidth of the pulse’s spectrum is sufficiently narrow, so that it is free of any of the resonant (natural) frequencies of the membrane or of the cavity, then the pulse is essentially reflected as though the baffled, cavity-backed membrane is rigid. However, if the pulse’s spectrum is sufficiently broad, so that it contains cavity and membrane resonant frequencies, an additional scattered field is produced by its interaction with the membrane’s motion and the acoustic field inside the cavity. This scattered field insonifies distant observation points after the rigidly reflected pulse arrives. It is a complicated sum of slightly damped and oscillating outgoing spherical waves. The damping occurs on the two time scales εt and ε2t. Some of these damped spherical waves are perturbations, due to the cavity fluid, of the ‘‘decayed ringing’’ of the vacuum-backed, baffled membrane. Application is given to the circular membrane that is backed by a cylindrical cavity, of the same radius as the membrane, and insonified by the normally incident, plane, spiked pulse. Graphs of the membranes motion are presented.
Acoustic localization and resonant scattering
Authors: Condat C. A.
Published: October 2005

The properties of the renormalized speed of sound and of the scattering and transport mean-free paths in two- and three-dimensional media containing random distributions of identical, finite-size scattering centers are analyzed. In particular, the connections between the frequency dependence of these parameters and the structure of the exact single-scatterer cross section are investigated. Since a careful evaluation of the mean-free paths is necessary for the accurate prediction of localization phenomena, the implications of the results to the localization of acoustic excitations are discussed in detail.
Lateralization and sequential relationships in the octave illusion
Authors: Deutsch Diana
Published: October 2005

Subjects made lateralization judgments concerning sequences of dichotic chords whose components stood in octave relation. In condition 1, each ear received a sequence consisting of 400- and 800-Hz tones in alternation, such that when one ear received the 400-Hz tone, the other ear simultaneously received the 800-Hz tone. Condition 2 was identical to condition 1, except that the alternating tones were at 600 and 1200 Hz instead. In condition 3, dichotic chords at 400 and 800 Hz alternated with dichotic chords at 600 and 1200 Hz. In all conditions, the amplitude relationships between the higher and lower tones were varied, and the percent lateralization to the higher frequency signal was plotted as a function of these amplitude relationships. In all conditions, when the tones at the two ears were equal in amplitude, lateralization tended to be toward the ear receiving the higher frequency signal. Averaged across subjects, this tendency in condition 1 was overcome only when the lower frequency signal was 12 dB higher in amplitude, and, in condition 2, when it was 9 dB higher. However, in condition 3, the tendency was overcome when the lower frequency signal was 3 dB higher in amplitude. The lateralization effect was thus shown to be influenced by the sequential relationships between the frequencies presented to the two ears.
Vibrational modes of Chinese two-tone bells
Authors: Rossing Thomas D. , Hampton D. Scott , Richardson Bernard E. , Sathoff H. John , Lehr Andre
Published: October 2005

The vibrational modes of a modern copy of an ancient Chou dynasty bell have been studied by means of holographic interferometry and by scanning the sound field near the bell. The modes are compared to those observed in church bells, carillon bells, and handbells, as well as other ancient Chinese bells. Modes tend to occur in pairs, one with a node at the xian or spine, and one with an antinode there; the frequencies of the two doublet members differ by about 3% to 10%. Bells of this type emit two distinctly different notes, depending upon where they are struck.
Frequency importance functions for a feature recognition test material
Authors: Duggirala Vasanta , Studebaker Gerald A. , Pavlovic Chaslav V. , Sherbecoe Robert L.
Published: October 2005

The relative importance of different parts of the auditory spectrum to recognition of the Diagnostic Rhyme Test (DRT) and its six speech feature subtests was determined. Three normal hearing subjects were tested twice in each of 70 experimental conditions. The analytical procedures of French and Steinberg [J. Acoust. Soc. Am. 19, 90–119 (1947)] were applied to the data to derive frequency importance functions for each of the DRT subtests and the test as a whole over the frequency range 178–8912 Hz. For the DRT as a whole, the low frequencies were found to be more important than is the case for nonsense syllables. Importance functions for the feature subtests also differed from those for nonsense syllables and from each other as well. These results suggest that test materials loaded with different proportions of particular phonemes have different frequency importance functions. Comparison of the results with those from other studies suggests that importance functions depend to a degree on the available response options as well.
Low-frequency ultrasound absorption in aqueous solutions of hemoglobin, myoglobin, and bovine serum albumin: The role of structure and pH
Authors: Barnes Christopher , Evans J. Anthony , Lewis T. John
Published: October 2005

New measurements on ultrasound absorption of aqueous solutions of the three globular proteins, bovine hemoglobin, horse heart myoglobin, and bovine serum albumin, at 20 °C are reported for the frequency range below 1.2 MHz and, in the case of hemoglobin and bovine serum albumin, to a limited extent for the range 2–30 MHz. The effect of protein conformation has been investigated by use of a range of denaturants and by change of pH. A much more detailed description of protein interactions emerges from the low-frequency studies than was possible hitherto. Specific absorption processes for myoglobin and bovine serum albumin peak in the neighborhood of pH 4.2. The process for myoglobin has a relaxation frequency between 1 and 2.6 MHz, while for bovine serum albumin the frequency is as low as 70 kHz. Both processes can be related to conformational changes in the molecules. In the case of hemoglobin, an absorption process with a relaxation frequency of 600 kHz is found that can be attributed to the dissocation equilibrium of the quaternary structure of the molecule and can be considerably enhanced by denaturants or pH change from neutral to acid conditions. Measurements at frequencies down to 200 kHz have also permitted a more thorough investigation of proton-transfer reactions at carboxyl and amino groups in these proteins and of the effect of pH on these reactions.
Specific acoustic impedances of piezoelectric ceramic and polymer composites used in medical applications
Authors: Bui Tuan , Chan Helen L. W. , Unsworth Joe
Published: October 2005

The specific acoustic impedance of the piezoelectric composites over the frequency range of 0.5–7.5 MHz was measured using the reflection, the echo-shift, and the resonance techniques. There was a significant difference between the values obtained by the reflection technique in comparison with the other two techniques. It is argued that the difference is inherent in the measurement techniques and they measure different properties of the composite such as acoustic impedance and reflectivity. The specific acoustic impedance and the reflectivity were found to be a function of the volume fraction of the ceramic and not a function of frequency.
Error analysis of two-microphone measurements in ducts with flow
Authors: Åbom Mats , Bodén Hans
Published: October 2005

In an earlier work [H. Bodén and M. Åbom, J. Acoust. Soc. Am. 79, 541–549 (1986)] the influence of errors on two-microphone measurements in ducts without flow has been studied. The aim of this article is mainly to extend the earlier work to include the effects of mean flow and also of attenuation during the sound propagation. First, a short review of the various existing two-microphone methods is made. The errors in the measured input data are then analyzed and special attention is paid to the effects of neglected attenuation, nonideal microphones, and flow noise. The influence of errors on the calculated quantities has been investigated and the conclusions from the earlier work have been extended to the case with flow. It is also shown that the neglect of attenuation between the microphones leads to a low-frequency limit for the applicability of the two-microphone method. Finally, a new technique for measuring the Mach number using a two-microphone method is suggested.
Experimental determination of cascade parameters of a hearing-aid microphone via the two-load method
Authors: Egolf David P. , Haley Brett T. , Bauer Kenneth M. , Howell Henry C. , Larson Vernon D.
Published: October 2005

Presented in this article is a computer-aided experimental method for obtaining the cascade parameters of the two-port model of a miniature hearing-aid microphone. The method is an adaptation of the ‘‘two-load’’ method [D. P. Egolf and R. G. Leonard, J. Acoust. Soc. Am. 62, 1013–1023 (1977)] to acoustoelectric, rather than electroacoustic, transducers. The cascade parameters of a particular microphone, determined by this method, were within 2.5 dB of the manufacturer’s published open-circuit sensitivity data. In an attempt to further verify the numerical cascade-parameter data, a two-port model of the microphone was used to simulate experimental voltages developed across two different complex electrical load impedances attached to the microphone. The results showed experimental/simulation differences of no greater than 3.0 dB at any frequency. The two-port microphone model and associated cascade parameters are currently being incorporated into a computer-based plan for mathematical simulation of an entire in situ hearing aid.
Frequency specific susceptibility to acoustic trauma in the budgerigar (M
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Authors: Hashino Eri , Sokabe Masahiro , Miyamoto Kensaku
Published: October 2005

The effects of intense noise exposure on hearing in the budgerigar were examined by behavioral audiometry. After binaural exposure to an intense broadband noise, auditory threshold shifts (TS) of the birds were continuously measured at frequencies between 0.125 and 8 kHz using an avoidance conditioning technique. Temporary threshold shifts (TTS) were observed at frequencies higher than 1.5 kHz and considerable permanent threshold shifts (PTS) were observed at frequencies below 1 kHz. This pattern of threshold shifts is contrary to that observed in mammals.
Two-mass model of the vocal folds: Negative differential resistance oscillation
Authors: Conrad William A. , McQueen David M.
Published: October 2005

The vocal folds and glottis are analyzed as a single system rather than as two separate but interacting systems, i.e., an aerodynamic one (the glottis) and a mechanical one (the vocal folds). Simplified steady flow calculations based on the two-mass model, and similar to those of Ishizaka and Matsudaira [SCRL Monograph No. 8, Santa Barbara, CA (1972)], are made except that flexible walls are assumed for both dc and ac flows. A negative differential resistance is found for steady flow when the coupling spring is weak compared to the spring of the upper mass and when the displacement of the upper mass is small compared to that of the lower mass. Dynamic transverse motion of the masses is represented by two transverse series resonant circuits in parallel within the glottis. The vocal tract is represented by a lumped resistance and inertance in series. Sustained, self-excited, small-amplitude oscillations can be obtained when the magnitude of the negative differential resistance is equal to the real part of the impedance of the rest of the circuit. The oscillation frequency depends only on the elasticity and mass of the vocal folds. The present analysis differs from Ishizaka and Matsudaira’s analysis because their oscillation frequency decreases as dc volume velocity increases.
The moving thermoacoustic array: A theoretical study
Authors: Chotiros N. P.
Published: October 2005

A theoretical study of the moving thermoacoustic array as an underwater sound projector is presented. The movement imparts to the acoustic signal a Doppler shift which is direction dependent. Extremely high Doppler shifts are achievable because it is a noncontact source. While the moving thermoacoustic array has certain interesting features compared to conventional acoustic projectors, notably the noncontact property and the direction-dependent Doppler shift, its thermoacoustic energy conversion efficiency is found to be no better than that of the stationary thermoacoustic array. It was found that the thermoacoustic conversion was most efficient when the laser energy was delivered as an impulse train. The efficiency is fundamentally limited by the physical properties of the medium, particularly the coefficient of thermal expansion and the specific heat.
The dynamic shear modulus of marine sediments
Authors: Bryan G. M. , Stoll R. D.
Published: October 2005

The dynamic shear modulus of marine sediments (μ) as a function of overburden pressure (p) and voids ratio (e) can be represented approximately by the expression μ=μ0(p/p0)n ×exp(−Γe), where μ0, n, and Γ are constants. Available laboratory results for sands, silts, and clays over a pressure range of 24 to 700 kPa and a voids ratio range of 0.35 to 1.5 lead to the values: n=0.45, Γ=1.50 and, if p0 is taken as 1 atm, μ0=2526 atm. For bentonite, an expandable clay with high cation-exchange capacity, the voids ratio dependence is similar (Γ=1.60) but the pressure has relatively little effect (n=0.08). Secondary effects due to quasistatic stress history and dynamic shear strain amplitude may modify these values somewhat for low-amplitude acoustic signals in in situ sediments.
Measurement of the temporal fluctuations of cw tones propagated in the marginal ice zone
Authors: Dahl Peter H. , Baggeroer Arthur B. , Mikhalevsky Peter N. , Dyer Ira
Published: October 2005

The frequency dispersion of hour-long acoustic tonal signals, stepped in frequency between 25 and 200 Hz, is measured via the covariance method. This method is computationally efficient and relatively unexploited for this purpose. The signals are from MIZEX 84 and have propagated through a partially ice-covered 100-km path. Source/receive drift-induced Doppler shift compares favorably with available navigational data. The dispersion is expressed in terms of the parameter ν, which is a function of a host of possible oceanic processes dynamically perturbing the sound field.
Cavitation threshold measurements for microsecond length pulses of ultrasound
Authors: Fowlkes J. B. , Crum L. A.
Published: October 2005

The acoustic cavitation threshold of an aqueous solution has been measured at megahertz frequencies as a function of pulse width and pulse repetition frequency for various combinations of these quantities. The fluid tested was a 0.1M KOH–H3BO3 buffer solution with pH 10.9, which contained luminol, was saturated with argon, and filtered to 25 μ. The presence of cavitation was detected by a photomultiplier tube that required the emission of visible light that was both larger in magnitude and longer in duration than a preset criterion. It was observed that the cavitation threshold of water under pulse conditions decreases both when the pulse width is fixed and the pulse repetition frequency is increased, and when the pulse repetition frequency is fixed and the pulse width is increased. Acoustic cavitation thresholds measured in aqueous solutions are significantly less than those acoustic pressures associated with instruments that are currently in widespread use in medicine.
Inhomogeneous plate driven by distributed load
Authors: Pierucci Mauro , Le Tuan , Fang Tiantong
Published: October 2005

The vibrational characteristics of an infinite plate with structural inhomogeneities represented by a stiffness that varies periodically in space are considered. The plate properties and the forcing function selected all vary in the same direction so that the inhomogeneous plate equation reduces to the inhomogeneous beam equation. The coupled fluid–structure interaction problem then results in a linear ordinary differential equation with varying coefficients. This equation is then transformed into Fourier space and it results in a difference equation for the transformed plate displacement. The difference equation is then solved in the Fourier space for the distributed loading function, and the inverse of the transform of the plate displacement is then obtained. Typical results are presented.
A finite element procedure for design of cavity acoustical treatments
Authors: Bernhard Robert J. , Takeo Seiji
Published: October 2005

The design of acoustical treatments for small or close-fitting cavity enclosures is significantly complicated by nearfield effects and standing wave behavior. In this article, the finite element method is used to model the acoustical behavior in such situations. Additional calculations are made to compute the sensitivity of certain acoustical design objective functions, particularly radiated power through apertures or total energy in the cavity, to certain design parameters, in this case, the reactance and resistance of the acoustical treatment materials. The sensitivity calculation results are used to identify which design parameters are most effective and which design philosophy most effectively improves the objective function. The article illustrates two examples of the application of the design sensitivity information to an automated design optimization.
Two-sensor methods for the measurement of sound intensity and acoustic properties in ducts
Authors: Seybert A. F.
Published: October 2005

A unified theoretical approach to the development of two-sensor methods is presented. It is shown that various methods developed in the last 10 years for sound intensity measurement and for the measurement of acoustic properties in ducts may be systematically derived from a general decomposition theory. In the decomposition theory, the incident and reflected wave auto and cross spectra are obtained from a set of decomposition equations using the measurement of the total acoustic pressure at two arbitrary points in a one-dimensional steady, random sound field. The application of the wave spectra to the measurement of sound intensity and acoustic properties follows directly. It is further shown that the decomposition theory predicts a set of characteristic wavenumbers at which two-sensor methods fail to yield meaningful data. Experimental data are presented showing the application of the decomposition theory to acoustic property determination, sound intensity measurement, and the estimation of sound pressure and particle velocity in a duct.
Characteristics of marine seismic survey sounds in the Beaufort Sea
Authors: Greene Charles R. , Richardson W. John
Published: October 2005

Geophysical survey vessels emit very intense pulses of underwater sound at intervals of several seconds; these noise pulses are sometimes detectable at very long ranges. Sound pulses from geophysical surveys were recorded in shallow parts of the Beaufort Sea during August and September of 1980–1984. Hydrophones deployed from a quiet boat were the primary sensors, but aircraft-deployed sonobuoys were also used. Water depths for the boat-recorded data were 9–130 m, but mostly <50 m. Sources studied included a single air gun and arrays of sleeve exploders, open bottom gas guns and air guns. Peak source levels were said to be as high as 248 dB re: 1 μPa-m. Received levels from air gun arrays were as high as 179 dB re: 1 μPa at range 1.9 km. For ranges >4 km, best-fit equations for maximum (rms) received levels in dB generally were obtained by assuming cylindrical spreading [−10*log(range)] and a term linear in range corresponding to an absorption loss or scattering term. The coefficients of the linear term varied from −0.61 to −2.33 dB/km, increasing in magnitude for shallower water. Pulses received at ranges greater than 3–4 km were usually 0.25–0.75 s long. These pulses often began with a bottom-traveling wave whose energy was concentrated below 100 Hz. The waterborne energy showed the geometrical dispersion that results from the summation of many sound rays that are reflected between the surface and the bottom: high frequencies (generally below 500 Hz) arrived first, followed by gradually lower frequencies. The result was a down-frequency chirplike sound. At short ranges the signal energy was concentrated at frequencies below 100 Hz. The reactions of bowhead whales to these signals are described in a companion article [Richardson et al., J. Acoust. Soc. Am. 79, 117–1128 (1986)].
Further experimental studies on the transfer-function technique for impedance tube measurements
Authors: Chu W. T.
Published: October 2005

More refined measurements of the complex reflection coefficients using single-frequency excitation and a lock-in amplifier for data analysis have revealed a limitation in the two-microphone transfer function technique for impedance tube measurements. A fixed choice of microphone positions for all frequencies as suggested by the current standard ASTM E1050-86 will compromise the accuracy of measurements. For accurate measurements, one of the microphone positions has to be close to a minimum pressure point of the standing-wave pattern, preferably the first minimum point. The choice of the other microphone position does not seem to be critical as long as the separation of the two positions is not close to a half-wavelength. The procedure employed in this study uses sequential sampling with one microphone instead of simultaneous sampling with two microphones. It presents a technique that is better than the existing standard methods for impedance tube measurements.
An algorithm for adaptive augmented array beamforming
Authors: Godara L. C. , Gray D. A.
Published: October 2005

In the theory of augmented array beamforming, a spatial invariance property of the noise field is exploited in order to constrain the beam pattern of the array at more points than the number of elements in the array. This results in weight vectors of the augmented array with the dimensions greater than the number of elements. Due to the larger dimensionality, the constrained least-mean-square (LMS) algorithm in the usual form cannot be used to adaptively estimate these weights. This article presents an algorithm to iteratively estimate the optimal weights of an augmented array.
Resonance-frequency discrimination
Authors: Gagné Jean-Pierre , Zurek P. M.
Published: October 2005

Measurements of the just-noticeable change in resonance frequency ∼(ΔF)r of a second-order filter are reported. The source signal was either periodic, with or without a smooth change in fundamental frequency, or it was random white noise. These differences in the nature of the source had little effect on ∼(ΔF)r. Over the investigated ranges of reference resonance frequency (Fr=300 to 2000 Hz) and filter selectivity (Q=1 to 36), the results are well summarized by ∼(ΔF)r=0.079 Fr/(Q)1/2. The data were used to evaluate filter-bank models employing different filter shapes and performance-prediction schemes. A good fit to the resonance-discrimination data was obtained with filters derived in a masking study by Patterson [J. Acoust. Soc. Am. 55, 802–809 (1974)] and with performance based on use of the maximum level difference over all bands. The latter finding indicates that listeners may not make optimal use of small level differences distributed over multiple bands.
The contribution of the near and far ear toward localization of sound in the sagittal plane
Authors: Humanski Richard A. , Butler Robert A.
Published: October 2005

Eight listeners were required to locate a train of 4.5-kHz high-pass noise bursts emanating from loudspeakers positioned ±30, ±20, ±10, and 0 deg re: interaural axis. The vertical array of loudspeakers was placed at 45, 90, and 135 deg left of midline. The various experimental conditions incorporated binaural and monaural listening with the latter utilizing the ear nearest or ear farthest from the sound source. While performance excelled when listening with only the near ear, the contribution of the far ear was statistically significant when compared to localization performance when both ears were occluded. Based on head related transfer functions for stimuli whose bandwidth was 1.0 kHz, four spectral cues were selected as candidates for influencing location judgments. Two of them associated relative changes in energy across center frequencies (CFs) with vertical source positions. The other two associated an absolute minimum (maximum) energy for specific CFs with a vertical source position. All but one cue when measured for the near ear could account for localization proficiency. On the other hand, when listening with the far ear, maximum energy at a specific CF outperformed the remaining cues in accounting for localization proficiency.
Preliminary evaluation of a multichannel electrotactile speech processor
Authors: Cowan R. S. C. , Alcantara J. I. , Blamey P. J. , Clark G. M.
Published: October 2005

Speech discrimination testing, using both open- and closed-set materials, was carried out with four severely to profoundly hearing impaired adults and seven normally hearing subjects to assess performance of a wearable eight-channel electrotactile aid (Tickle Talker). Significant increases in speechtracking rates were noted for all subjects when using the electrotactile aid. After 70 h of training, mean tracking rate in the tactile plus lipreading condition was 55 words per minute (wpm), as compared with 36 wpm for lipreading alone, for the normally hearing group. For the hearing impaired group, the mean tracking rate in the aided condition was 37 wpm, as compared with 24 wpm for lipreading alone, following 35 h of training. Performance scores on Central Institute for the Deaf (CID) everyday sentences, Consonant Nucleus Consonant (CNC) words, and closed-set vowel and consonant identification were significantly improved when using the electrotactile aid. Performance scores, using the aid without lipreading, were well above chance on consonant and vowel identification and on elements of the Minimal Auditory Capabilities Battery. Two hearing impaired subjects have used the device satisfactorily in the home environment.