bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of spherical pressure pulses by a hard cylinder
Authors: Huang H.
Published: October 2005

The transient scattering of spherical pressure pulses by an infinitely long acoustically hard circular cylinder is analyzed. The pressure in the neighborhood of the reflected wavefront is calculated by the method of series expansion in conjunction with the transport equations. From the wave equation, a simple integral formula is derived by means of which the solution to the present three-dimensional problem can be effectively constructed from the two-dimensional line source solution. Thus, the pressure in the neighborhood of the diffracted wavefront is computed based upon Friedlander’s diffraction formulas pertaining to the scatttering of a cylindrical pulse by a hard cylinder. Outside the neighborhood of the scattered wavefronts, the solution is obtained by the Fourier series and integral transform techniques and is accurately computed by this formula. By combining the various solutions, the true time histories of the scattered pressure are inferred for various locations on the cylinder. Some features of the three-dimensional resultant pressure field are also discussed.

Subject Classification: 20.30.
Comparison of sonar system performance achievable using synthetic-aperture techniques with the performance achievable by more conventional means
Authors: Cutrona Louis J.
Published: October 2005

A comparison is made of the signal-to-noise characteristics of synthetic-aperture sonar and conventional sonar. For the synthetic-aperture sonar case a design procedure is described which makes possible the choice of essentially any unambiguous range and any resolution. Often multiple beam receivers are required. It is shown for the synthetic-aperture sonar case that the horizontal aperture is the major factor affecting area coverage rate. The comparisons are made with as many parameter values as spossible identical for both the synthetic-aperture cases and the nonsynthetic-aperture cases. If identical physical aperture dimensions are used and other parameters held to identical values, the synthetic-aperture sonar gives higher signal-to-ratio than does the nonsynthetic-aperture sonar primarily because the latter must operate at higher acoustic frequencies for which signal attenuation becomes extremely large. If the sonar systems are operated at the same frequency, then the nonsynthetic aperture sonar can give a higher signal-to-noise ratio only when its physical aperture is larger than that used in the synthetic-aperture case.

Subject Classification: 30.82; 60.20.
Scattering of sound from a point source by a rough surface progressing over an isovelocity ocean
Authors: Harper E. Y. , Labianca F. M.
Published: October 2005

A perturbation procedure is applied, through the second order of approximation, to the three-dimensional problem of scattering of sound from a point source by a rough surface progressing in the wind direction over an isovelocity ocean. The results satisfy conservation of energy, in a ray-theoretic sense, and are uniformly valid throughout the field. At points in the region of surface-image interference (Lloyd’s-mirror region), the signal is shown to be strongly modulated. Results are presented which depict the power in the carrier and signal sidebands. The latter are not, in general, symmetric in amplitude about the carrier. However, it is demonstrated analytically that, on two specific planes in the field, the signal power spectrum is symmetric about the carrier.

Subject Classification: 30.40, 30.20, 30.25.
Coherent component of specular reflection and transmission at a randomly rough two-fluid interface
Authors: Kuperman William A.
Published: October 2005

The specular reflection and transmission of an acoustic plane wave at a randomly rough two-fluid interface is studied. The perturbation method of Bass is used to derive a new set of boundary conditions to replace the unperturbed boundary conditions. The new conditions are valid for surfaces characterized by arbitrary anisotropic correlation functions. Using these new boundary conditions, reflection and transmission coefficients are derived. It is shown that in the Kirchhoff approximation, the reflection and transmission coefficients reduce to those obtained earlier by Eckhart, Clay, Medwin, and Hagy. In the limit of the density of one of the fluids going to zero, the reflection coefficient for a rough pressure release surface is obtained. Results are presented using ocean surface models in terms of wind speed and direction.

Subject Classification: 30.40, 30.30, 30.25,30.20.
Low-noise chambers for auditory research
Authors: Vér István L. , Brown Robert M. , Kiang Nelson Y. S.
Published: October 2005

The experimental work of the Eaton–Peabody Laboratory of Auditory Physiology requires chambers unusually free of ambient acoustic, vibratory, and electric noise, so that small mechanical or electric signals in response to low-level sounds can be measured. This paper deals with the problems that arose in setting of criteria, the design, and the construction of such chambers, and reports on the evaluation of their performance. The ambient acoustic noise is well below the human threshold of hearing even with the ventilation system operating. The noise reduction between the control rooms and the chambers is almost 80 dB at 250 Hz and more than 90 dB above 500 Hz. The octave-band ambient vibration acceleration level at the experimental tables in the chambers is below −120 dB re lg.

Subject Classification: 55.40; 65.10.
The five distractors experiment: exploring the critical band with contaminated white noise
Authors: Kaplan Howard L.
Published: October 2005

Three observers tried to detect a 500-Hz target in white noise in one of two temporal intervals. A distractor tone was added to the target interval on half of the trials and to the nontarget interval on the remainder. When the distractor was within about 40 Hz of 500 Hz, the 80% correct threshold for the target was elevated or depressed depending on whether the distractor was added to the nontarget or target interval. Thus, the critical band around 500 Hz is estimated to be about 80 Hz wide. It is possible to compare the relative sizes of the two threshold shifts against the predictions of two models of detection: the classical, integrated-energy model, and a model emphasizing contrast among the energy of the components within the band. To make these predictions, simulated observers were run under the identical procedure. Within the limits of experimental error, the simulation matched the data well only under the integrated-energy model. Under that model, the observers are performing about 2. to 3 dB worse than what the simulation predicts, which provides an estimate of the internal noise as nearly equal to the external noise.

Subject Classification: 65.58, 65.75; 50.70.
Spiral membrane speaker enclosure
Authors: Kaiser Jr. Julius A.
Published: October 2005

Acoustical transmission lines formed into a spiral configuration possess the latent property of having different lengths along adjacent lines when traversing along a radius: for an acoustical spiral, sound waves in adjacent transmission lines will progress from an antiphase relation at the center of the spiral to an in-phase relation at some radius r (λ) from the center. This is a transformation dependent only upon wavelength. When those transmission - line walls that are facing the environment are covered with a low-mass, tightly stretched membrane, radiation from this secondary surface will occur at the appropriate time. Radiation of a transverse wave rotating about the spiral axis occurs when sound waves in adjacent transmission lines are in phase. In this paper, several radiation modes and phasing properties are discussed. Owing to automatic adjustment of aperture size with change in frequency, the spiral membrane enclosure has a broad and constant beamwidth. An acoustical source, such as a loudspeaker cone each side of which is contiguous to the end of an acoustical transmission line, generates within those transmission lines longitudinal waves that are antiphase relative to each other. Constant loading of the source occurs over a wide range of frequencies, providing uniform electrical/acoustical performance. An experrimental model is described.

Subject Classification: 85.60; 20.40.
An accurate method for the experimental evaluation of the acoustical impedance of a black box
Authors: Kathuriya M. L. , Munjal M. L.
Published: October 2005

Among different methods, the transmission-line or the impedance tube method has been most popular for the experimental evaluation of the acoustical impedance of any termination. The current state of method involves extrapolation of the measured data to the reflecting surface or exact locations of the pressure maxima, both of which are known to be rather tricky. The present paper discusses a method which makes use of the positions of the pressure minima and the values of the standing-wave ratio at these points. Lippert’s concept of enveloping curves has been extended. The use of Smith or Beranek charts, with their inherent inaccuracy, has been altogether avoided. The existing formulas for the impedance have been corrected. Incidentally, certain other errors in the current literature have also been brought to light.

Subject Classification: 85.20.
Real-time ultrasonic imaging methodology in nondestructive testing
Authors: Knollman G. C. , Weaver J. L. , Hartog J. J. , Bellin J. L.
Published: October 2005

Acoustic imaging techniques are described for real-time nondestructive testing of highly attenuative material having irregular shape. Specific application is made to rapid, on-line inspection of tapered cylindrical billets for display of interior spherical voids as small as 2.5 mm. Basic parameters for sonovision operation and function are presented first, including unfocused and focused shadow imaging of a void versus backscatter imaging. A fixed-focus acoustic lens of appropriate focal depth and image resolution is advanced for shadow imaging of minimum-size or larger voids. A focused insonification system is described, and both single-element and linear-array solid-state acoustic receivers are presented as imaging devices. Methods for mechanical scan of object and/or ultrasonic transducers are outlined together with the accompanying real-time cathode ray tube display. Aqueous glycerol solution constitutes an immersion fluid for enhancement of acoustic imaging in the nondestructive test of many solid materials. Two sonovision systems for on-line nonintrusive inspection are presented based on helical scan. Special features of the ultrasonic imaging arrangements include pulse operation, receiver gating, acoustic shielding, and automatic contrast control.

Subject Classification: 85.10; 35.65, 35.26.
X-ray measurement of an ultrasonic wave amplitude in a crystal
Authors: Lazara Kenneth , Zayas Jose M. , Zajac Alfred
Published: October 2005

The effect of an ultrasonic wave on the integrated intensity in the Borrmann effect has been used to calculate the ultrasonic wave amplitude in a silicon crystal.

Subject Classifications: 85.22; 35.65, 35.68.
Ray-theoretic analysis of a mathematical model for SOFAR propagation
Authors: Goda M. A. A. , Rao C. R. A.
Published: October 2005

The problem of acoustic wave propagation in an underwater sound channel has been discussed using the ray theory for a model consisting of two semi-infinite liquid media in which the propagation velocity increases exponentially in both directions from the interface. The results predicted by this model are in good agreement with the results of experimental work.

Subject Classification: 30.20; 20.20.
Spectrum of phase fluctuations caused by multipath interference
Authors: DeFerrari Harry , Leung Ricky
Published: October 2005

Fluctuations of CW phase caused by time-varying multipath interference are simulated with fully coherent ray propagation models. Fixed-system measurements of fluctuations of CW transmission are presented and compared for three ocean ranges. When the sound-speed perturbation used for model inputs are adjusted to give the same statistics of transmission-loss fluctuations (decorrelation time, variance, and mean-square bandwidth) as observed, then the associated fluctuations of CW phase also have the same statistics as the experimental results. Phase fluctuations are shown to be strongly influenced by the nonlinear multipath process. For low-frequency internal waves (less than 1 cycle/h), and especially for internal tides, linear or direct fluctuations influence the phase spectrum, but for higher frequencies it seems likely that nonlinear effects dominate. Therefore, the possibility of a direct linear relationship between the internal-wave spectrum and the spectrum of phase fluctuations is unlikely.

Subject Classification: 30.35, 30.20; 20.20.
Distortion of short-duration stress pulses propagating in solids and liquids
Authors: Felix M. P.
Published: October 2005

Short-duration, laser-generated, compressive stress pulses were propagated in a variety of solid and liquid materials; and the initially compressive pulses were observed to develop tensile ’’tails’’ for propagation distances of less than 6 cm. This type of pulse distortion cannot be attributed solely to geometric dispersion or material attenuation. It is shown that the observed pulse distortion can be explained using elementary diffraction theory. Since the transition distance from the Fresnel region (nonattenuative) to the Fraunhofer region (1/z attenuation) is dependent upon the wavelength of the acoustical radiation, stress pulses composed of many wavelengths are distorted and not merely attenuated during propagation. Numerical results are presented to substantiate this observed effect and to provide a convenient means of predicting the shape of a stress pulse at any distance in a nondispersive, nonattenuative medium given the shape initially.

Subject Classification: 35.65, 35.24, 35.26; 25.22.
Acoustic radiation force on fused silica spheres, and intensity determination
Authors: Hasegawa Takahi , Yosioka Katuya
Published: October 2005

The advantages of using fused silica spheres as the target in the radiation force method of acoustic intensity determination are considered. Experimental determination of the radiation force function, for fused silica spheres in water in the range of ka 2–24, was carried out. The experimentally obtained values of the radiation force function agree within 2% of those calculated from the theory of the radiation force on solid elastic spheres. This makes possible determination of ultrasonic intensity and calibration of acoustic probes with uncertainties <2% to values of ka=24, where the accuracy of the radiation force method with stainless steel spheres becomes reduced. The experimental conditions necessary for the realization of this accuracy are discussed.

Subject Classification; 25.45; 30.80; 35.80; 85.22.
Sabine’s reverberation time and ergodic auditoriums
Authors: Joyce W. B.
Published: October 2005

It is shown in geometrical acoustics that ergodic specular enclosures do exist and that in such auditoriums, but not in general, 4V/S′ is the exact mean directed path length (V is volume and S′ is any part of surface area S). Sabine’s expression is then demonstrated to yield the exact reverberation time, provided the enclosure is mixing and provided the inhomogeneous anisotropic surface absorptivity is sufficiently weak. It is further proven that the functional form of Sabine’s expression cannot be modified so as to become correct for large absorption. In an attempt to reassign credit and to reconcile these results with influential findings to the contrary, a short historical account is added. Conditions imposed upon the surface reflectivity—whether the reflectivity be reversible (specular or other) or irreversible (statistical) —by the second law of thermodynamics and by the principle of detailed balance are evaluated. Extensions (e.g., mean length of curved paths in an ergodic auditorium with a thermal gradient) and other applications (electroluminescent-diode design) are noted.

Subject Classification: 55.20, 55.30, 55.55.
Optimum array detection in fluctuating ambient noise fields
Authors: Adams S. L. , Nolte L. W.
Published: October 2005

In practical underwater signal detection problems using an array, the statistics of the ambient noise field vary spatially and temporally. This paper considers the problem of detecting a farfield signal source of known location and waveform which generates a known signal field at an array aperture. The power of the ambient noise field is considered to be a random function of space and time and the Bayes approach is used to derive optimum receiver structures and their performance. For all cases considered, the optimum array processor either requires spatial filtering which is not accomplished by a beam former or requires spatial processing in addition to that provided by a beam former. The loss of detection performance due to uncertainty in the parameters of the ambient noise field is determined for several specific cases.

Subject Classification: 60.20; 25.35.
Influence of rotary inertia and shear deformation on acoustic transmission through a plate
Authors: Stepanishen Peter R.
Published: October 2005

The reflection and transmission of a harmonic acoustic plane wave from a fluid-loaded plate is investigated using the Timoshenko–Mindlin plate equation. In contrast to the classical plate theory, the effects of rotary inertia and shear deformation are included in the Timoshenko–Mindlin theory. The usual acoustic coincidence frequency and angle based on the classical theory are shown to depart from the present results based on the Timoshenko–Mindlin theory as the frequency–plate thickness product increases. Furthermore, an additional acoustic coincidence frequency and angle are also noted in the present analysis for large frequency-plate thickness products. Several numerical results are presented to illustrate the effects of the incident angle, frequency, plate thickness, and damping on the transmission of an incident acoustic plane wave through a steel plate in water.

Subject Classification: 20.60; 40.24; 20.30.
Damping constants for nonresonant bubbles
Authors: Fairbank William M.
Published: October 2005

The damping constants for nonresonant bubbles calculated by Eller must be corrected by a factor (ω0/ω)2 in order to conform to the usual definition of the damping constants. The source of this confusion in definition is explained.

Subject Classification: 30.60.
Excitation of a Helmholtz resonator by a turbulent boundary layer
Authors: Panton Ronald L. , Miller John M.
Published: October 2005

A turbulent boundary layer on the fuselage of a glider was used to excite a Helmholtz resonator. The resonator orifice was flush with the surface and smaller than the boundary-layer thickness. Resonator frequencies were chosen so they would tune with different portions of the boundary-layer wall pressure spectrum. The resonators were excited at both the Helmholtz frequency and a standing wave frequency. The results show a shift in the Helmholtz frequency when the boundary layer is present. This shift indicates the degree to which the turbulence interacts with the acoustic motion in the orifice and modifies the end correction. Four of the nine resonators tested were ’’strongly’’ excited and radiated considerable acoustic sound. This phenomenon occurs when turbulent eddies about the size of the orifice are convected past the orifice with the proper velocity to impose a frequency that matches a resonant frequency of the resonator. Turbulent eddies which are either smaller or larger than the orifice will not produce strong excitation.

Subject Classification; 28.65, 28.60; 85.32; 20.40.
Energy evaluation of wide-band SOFAR transmission
Authors: Porter Robert P. , Leslie H. D.
Published: October 2005

Transmitted energy levels for wide-band SOFAR transmission are calculated for arbitrary sound-speed profiles using ray-mode analysis [R. P. Porter, J. Acoust. Soc. Am. 54, 1081–1091 (1973)]. The analysis of the received field has been generalized to include arbitrary normal modes and range-varying, sound-speed profiles. It is shown that computations of wide-band propagation based on ray-mode analysis require an order of magnitude fewer calculations than do calculations by harmonic analysis. A computer code has been developed and used to estimate the wide-band loss for profiles from the Mediterranean and the North Atlantic. Comparisons with continuous tone, normal-mode calculations yield agreement to within 3 dB.

Subject Classification: 30.20, 30.25; 20.20, 20.40.
Sampling statistics for cylindrical modes of higher order
Authors: Jones Kenneth E. , Waterhouse Richard
Published: October 2005

The distribution functions are considered for the random sampling in space of a three-dimensional acoustic mode. Expressions are obtained for the probability density and cumulative functions for a single mode excited in an ideal elastic fluid contained in a right-circular cylindrical enclosure. In earlier work, axisymmetric modes of lower order were treated; here the work is extended to some modes of higher order, and in addition the rms values of the modal function are sampled, as well as the mean-square vales. The rms modal function ‖J0(⋅) ‖ contains cusps on the abscissa, and these cause the distribution functions to differ from those pertaining to the square of the modal function. In both cases, however, the density functions have a number of poles which increases with the order of the mode. Computed values of the functions are presented, together with values of the variances of the distributions.

Subject Classifications: 45.30; 55.20.
Automatic segmentation of speech into syllabic units
Authors: Mermelstein Paul
Published: October 2005

As a first step toward automatic phonetic analysis of speech, one desires to segment the signal into syllable-sized units. Experiments were conducted in automatic segmentation techniques for continuous, reading-rate speech to derive such units. A new segmentation algorithm is described that allows assessment of the significance of a loudness minimum to be a potential syllabic boundary from the difference between the convex hull of the loudness function and the loudness function itself. Tested on roughly 400 syllables of continuous text, the algorithm results in 6.9% syllables missed and 2.6% extra syllables relative to a nominal, slow-speech syllable count. It is suggested that inclusion of alternative fluent-form syllabifications for multisyllabic words and the use of phonological rules for predicting syllabic contractions can further improve agreement between predicted and experimental syllable counts.

Subject Classification: 70.40, 70.60.
Effect of delayed channel on the perception of dichotically presented speech and nonspeech sound
Authors: Porter Robert J.
Published: October 2005

Subjects were asked to identify dichotically competing pairs of CV syllables and two types of acoustically comparable nonspeech sounds. Dichotic signals were presented with onset asynchronies ranging from 0 to 150 msec. Subjects identified lagging signals more accurately and reported them as clearer than the leading signals at asynchronies between 30 and 75 msec. This advantage for the lagging signal was larger, more reliable, and had a different form for the speech sounds than for the nonspeech sounds. Similarities in the pattern of results for speech and nonspeech were interpreted in terms of the forward-, backward-, and simultaneous-masking effects occurring early in the central processing of auditory events. The differences in speech and nonspeech results, on the other hand, were seen as reflecting the particular sensitivity of later stages of speech processing to the masking effects. This sensitivity may be related to the way in which the phonetic message is encoded in the sound stream and the special speech processing occasioned by this encoding.

Subject Classification: 70.30; 65.58; 65.75.
Interaural–intensive differences and dichotic listening
Authors: Speaks Charles , Bissonette Linda J.
Published: October 2005

Interaural-intensive differences were introduced in a dichotic-listening experiment with CV syllables. Six listeners with a right-ear advantage (REA) in syllable-identification scores were tested. In one condition, speech level in the right ear was attenuated in 8-dB steps from each of four reference intensities for the left ear: 80, 70, 60, and 50 dB SPL. In a second condition, speech level in the left ear was amplified in 8-dB steps from the same four reference intensities for the right ear. The right-ear advantage was canceled by attenuation of signal level in the right ear, but the amount of attenuation required to cancel the REA varied with reference intensity. For the three higher reference intensities, amplification of speech level in the left ear did not overcome the REA. The REA was canceled with amplification of the left-ear signal only for the 50-dB reference.

Subject Classification: 70.30.
Computer-based sound spectrograph system
Authors: Strong William J. , Palmer E. Paul
Published: October 2005

Sound spectrographs based on digital computers are of interest because of the versatility they offer in generating and displaying sound spectrograms. A particular computer-based sound spectrograph is described in which digitized time waveforms stored on disk memory are spectrally analyzed and the resulting data stored back on disk for later display. Analyses are also performed to obtain the voicing fundamental frequency and the overall-intensity level of the signal which are displayed time registered with the spectrogram. While viewing the spectrographic display, the user is able to tailor the display before making hardcopy. This permits the user to specify a spectral threshold level, the dynamic range represented in the display, spectral contrast, and spectral emphasis.

Subject Classification: 70.62, 70.40; 85.32.
Hearing thresholds of the horn shark, H
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Authors: Kelly Joseph C. , Nelson Donald R.
Published: October 2005

Horn sharks were conditioned to pure-tone audio signals in two different laboratory test situations. In the first experiment, conducted in a small, air-speaker-driven enclosure, four sharks were conditioned to cross a barrier to avoid electrical shock. The sharks responded from 25 to 160 Hz, with the lowest pressure threshold at 40 Hz. The second experiment, conducted in a large tank with an underwater speaker, used four different sharks and employed a heart-rate technique in which shock and sound were paired to elicit conditioned bradycardia. These sharks responded over a similar frequency range of 20 to 160 Hz. When tested at two subject-to-transducer distances, their acoustic pressure thresholds increased with distance while their acoustic particle-motion thresholds remained the same. The lowest pressure threshold was at 40 Hz (12 dBμb), and the lowest particle-motion threshold was at 80 Hz, with a displacement of 1.4×10−6 cm and a velocity of 7×10−4 cm/sec (104 μvar).

Subject Classification: 80.50, 80.60; 65.50.
STL–Ionophone: Transducer properties and construction
Authors: Fransson Frans J. , Jansson Erik V.
Published: October 2005

The STL–Ionophone is a simple electroacoustical transducer well suited to many applications in an acoustic laboratory, even one with modest equipment. Its transducer element consists of a glow discharge in the atmospheric air, which is initiated and maintained by a highly stable dc power supply and a large current-limiting resistor. The discharge emits sound when an ac current is superimposed on the dc current. The STL–Ionophone is a sound emitter of small dimensions, of high acoustical impedance, and has constant source strength (volume velocity) from infra- to ultrasonic frequencies. It can also register sound down to zero frequency as voltage variations. In this report, we describe how the correct discharge is obtained, present basic transducer properties of the discharge, and give practical construction hints together with applications in which the STL–Ionophone has been used. The information presented is sufficient for design and use of the STL–Ionophone.

Subject Classification: 85.40, 85.60, 85.62.
Coarticulatory effects of voiced stops on the reduction of acoustic vowel targets
Authors: Ohde Ralph N. , Sharf Donald J.
Published: October 2005

Five male subjects recorded three samples of the American English vowels /i/ and /u/ and two lists of CVCV utterances, one in which the vowels /i, u/ and consonants /b, d, g/ were used symmetrically and one in which the vowels /i, u/ were used symmetrically but the consonants /b, d, g/ were used asymmetrically with /h/ always in the other consonant position. In addition, one of the subjects recorded a list of hVC utterances using the same vowels and consonants. Vowel targets were established for each subject on the basis of spectrographic measurements of F2 from the isolated vowels. Vowel reduction was determined by comparing these target values with spectrographic measurements made from steady-state portions of vowels in context. Right-to-left (R to L) effects were determined from utterances in which /b, d, g/ were the second consonants and left-to-right (L to R) effects were determined from utterances in which /b, d, g/ were the initial consonants. The results were as follows: (1) L to R effects of consonants on vowel reduction were considerably greater than R to L effects; (2) R to L effects on vowel reduction in hVC utterances were no greater than those in hVCV utterances; (3) vowel reduction for combined hVCV and CVhV utterances was somewhat greater than for symmetrical CVCV utterances, and (4) all utterances reflected greater influence of /d/ on vowel reduction than other consonants and greater reduction of /u/ than of /i/. The results are discussed in terms of models of speech production and the apparent paradox in the relationship between the greater L to R acoustic effects and the assumed primacy of R to L perception.

Subject Classification: 70.20, 70.30, 70.70.
Noise and children: A review of literature
Authors: Mills John H.
Published: October 2005

The document is a review of information which deals directly and indirectly with the effects of noise on children. Potential problem areas are identified and recommendations for research are stated.

Subject Classification: 10.60; 50.70; 65.10.
Sound radiation from a simple source in circular and helical motion
Authors: Chandrashekhara N.
Published: October 2005

The analysis of sound radiation from a time-varying simple source in uniform circular and helical motion is made. The expressions for the mean-square farfield sound pressure and the overall sound-power output are derived. The retarded time approach is used and illustrates the relative significance of the time rate of pulsations and the acceleration due to rotation of the source.

Subject Classification; 20.15, 20.55; 30.50.
Improved efficiency in the parametric transmitting array
Authors: Merklinger Harold M.
Published: October 2005

It is shown that the efficiency of the parametric transmitting array may be improved over that obtained where two equal amplitude-frequency components are employed in the primary wave. Through suitable periodic shaping of the envelope of the primary wave, available improvements in the output at the ’’difference’’ frequency of between 2.1 and 6.0 dB are possible in principle. The degree of available improvement depends upon whether the transmitter is peak power or average power limited and whether finite-amplitude attenuation of the primary wave is significant. It is proposed that the on–off modulation of a single-frequency carrier provides a simple, practical method through which near optimum efficiencies may be obtained under most circumstances. A bandwidth greater than the ’’difference’’ frequency is required at the transducer in order to achieve this improvement.

Subject Classification: 25.35; 30.75.
Effect of flow on the acoustic resonances of an open-ended duct
Authors: Ingard Uno , Singhal Vijay K.
Published: October 2005

The effect of flow on the acoustic resonances of an open-ended, hard-walled duct is analyzed. The flow produces acoustic losses both in the interior of the duct and at the ends. Unless the duct is very long, typically 100 times the diameter, the losses at the ends dominate. At flow Mach numbers in excess of 0.4 the losses are so large that axial duct resonances are almost completely suppressed. The plane-wave Green’s function for the duct with flow is expressed in terms of the (experimentally determined) pressure reflection coefficients at the ends of the duct, and the flow dependence of the complex eigenfrequencies of the duct is obtained. Some observations concerning the noise produced by the flow in the duct are also reported.

Subject Classification: 28.60.
Study of the measurement of transducer directivity with a planar measurement array
Authors: Baker D. D. , Smith D. A.
Published: October 2005

An experimental study was conducted to investigate directivity measurements made in the farfield of a conventional sonar transducer with a planar array of probe transducers. The principal questions investigated were (1) how closely must measurement probes be spaced for directivity measurements to be of useful accuracy and (2) how does one process and display the data in a useful format. Full-scale experiments were conducted with a probe transducer positionable over a grid of measurement points to simulate a multiprobe array. Measurements were made at probe spacings varying from 0.1 to 0.4 times ψHP, the half-power beamwidth of the sonar transducer. The data were processed by computer and displayed with contour plots, which proved quite easy to use and easy to interpret. The data obtained from the experimental measurements were compared with conventional beam patterns of the transducer; results were encouraging and, in fact, somewhat better than expected, generally. Discrete data taken at 0.1 and 0.2 times ψHP defined all features of the directivity function to within the measurement accuracy of conventional directivity measurements. Data obtained at the spacing equal to 0.4 times ψHP resolved major characteristics of the pattern to within ±2 dB and ±2°. It is believed that the use of more sophisticated interpolation techniques in processing the data prior to contour plotting would improve the accuracy.

Subject Classification: 30.85, 30.82; 85.40.
Wave propagation in a viscoelastic rod with temperature-dependent properties
Authors: Ting Edward C.
Published: October 2005

In this paper the unidirectional wave propagation in a rod made of viscoelastic material of the Maxwell type is considered. The rod is subjected to nonuniform temperature gradients and its mechanical properties are assumed to be temperature-dependent. A perturbation technique incorporated with the usual Laplace transform method is employed to obtain the analytical solution in series form. The strong temperature-history effect on the attenuation of the wavefront is demonstrated in simple examples for the case where a stress discontinuity due to constant velocity impact propagates along the rod.

Subject Classification: 40.22; 35.50.
Backward recognition masking
Authors: Massaro Dominic W.
Published: October 2005

Backward recognition masking refers to the interference of a second sound on recognition of another sound presented earlier in time. Previous experiments have demonstrated backward recognition masking in an absolute judgment task. In those experiments, all of the experimental conditions were varied randomly within a test session. In the first experiment reported here, backward-masking functions generated between blocks of trials were compared to those determined within an experimental session. The results showed backward masking using both experimental procedures. The next two experiments evaluate backward-masking effects in a two-interval forced-choice task and a successive-comparison task. Backward masking was observed in both experiments. The final experiment showed that selectively attending to the ear of the test tone presentation does not attenuate the backward-masking effects of a second tone presented to the opposite ear.

Subject Classification: 65.22, 65.58, 65.75.
Acoustic impedance of an annular capillary
Authors: Backus John
Published: October 2005

The behavior of an acoustic impedance formed by a capillary of annular cross section was investigated. The configuration used in previous work consisted of a cylindrical rod spaced concentrically within a cylindrical tube. Experimentally, this configuration was found to have an impedance magnitude which remained reasonably constant with frequency up to values for which the length of the capillary was comparable to the wavelength. This was checked numerically; computer calculations based on the relevant equations showed that for certain ranges of lengths and annulus thicknesses, the impedance magnitudes are reasonably constant over a useful frequency range. Graphs of impedance magnitudes and phases are displayed for representative values in these ranges.

Subject Classification: 75.40; 85.20; 75.35.
Improved efficiency of an acoustic parametric source
Authors: Eller Anthony I.
Published: October 2005

The efficiency of a parametric source can be increased through use of a multicomponent primary signal in place of the customary two-component primary. The results indicated in this letter form a special case of a general analysis by Merklinger [J. Acoust. Soc. Am. 58, 784–787 (1975)] and offer independent confirmation of part of his paper.

Subject Classification: 25.35; 60.20.
Wave propagation at unbonded interface between two elastic half-spaces
Authors: Murty G. S.
Published: October 2005

The question whether a Stoneley mode can exist at an unbonded interface between two elastic half-spaces is examined theoretically. Explicit conditions for its existence are derived when the two half-spaces are incompressible or Poisson solids whose elastic constants and material densities are approximately equal.

Subject Classification: 35.26; 20.15.
Vocal frequency and vertical larynx positioning by singers and nonsingers
Authors: Shipp Thomas , Izdebski Krzysztof
Published: October 2005

Measurements were taken from lateral still photographs of the vertical larynx position of four professional singers and four nonsingers. Subjects sustained phonation at seven discrete intervals between 90 and 350 Hz. Nonsingers generally positioned their larynx upward with increased voice frequency and tended to maintain a level at or above the larynx physiologic rest position throughout their vocal range. Singers usually maintained a laryngeal position below the physiologic rest level throughout their vocal frequency range.

Subject Classification: 70.20; 75.70.
Difference frequency pressure within the interaction region of a parametric array
Authors: Rolleigh Richard L.
Published: October 2005

A theoretical model that predicts difference frequency pressure within the interaction region of a parametric array is presented. Linear and nonlinear attenuation are neglected, and it is assumed that the primary signals are spherically spreading throughout the interaction region. It is shown that with these assumptions the three-dimensional scattering integral can be reduced to a single integral if the primary pressure fields are axially symmetric. Analyses of the error introduced by assuming the primary fields are spherically spreading and by neglecting linear attenuation are presented. Theoretical results compare favorably to p’revious experimental results. The results indicate that diffraction effects are more important than attenuation when the observation point is within the interaction region and when primary signal level reduction is due more to spherical spreading than attenuation.

Subject Classification: 25.35; 20.30, 20.15.
Sound attenuation by commonly available membranes used for moisture protection of microphones
Authors: Kaye David H.
Published: October 2005

Rubber condoms have been used to protect microphones used outdoors, but the technical literature includes no evaluation of the effects of this application. We have measured attenuation versus frequency for combinations of foam windscreen and condom and find that the attenuation can be both significant and unpredictable, variable between brands and between methods of application. Because a microphone cannot be acoustically calibrated with currently available portable calibrators after it has been sheathed, we believe that using a condom-protected microphone is likely to result in erroneous data. Another commonly available membrane, the plastic sandwich bag, produces similar erratic results.

Subject Classification; 50.85; 85.24, 85.62.
Loudness and the acoustic reflex
Authors: Margolis Robert H. , Popelka Gerald R.
Published: October 2005

The hypothesis that loudness is constant at acoustic-reflex threshold is examined. Acoustic-reflex thresholds were measured in five normal-hearing adult subjects for octave frequencies from 250 to 4000 Hz, for a narrow-band noise (BW=50 Hz) centered at 500 Hz, and for a wide-band noise. After acoustic-reflex threshold was determined, the loudness of the reflex-threshold stimulus was measured utilizing a monaural loudness-balance procedure employing a 1000-Hz comparison tone and a Method of Constant Stimuli. Results indicate that for the activating stimuli used in this experiment, loudness at acoustic-reflex threshold varies over a 17-dB range. The range would probably increase if lower frequency activating stimuli were used. The data suggest that the acoustic reflex is not dependent on some critical loudness of the activating stimulus.

Subject Classification: 65.50, 65.22, 65.75.
Comments on summarization of the findings of Liberman e
t a
l. regarding the role of formant transitions in the perception of voiceless stops
Authors: Winitz H. , LaRiviere C. , Herriman E.
Published: October 2005

In a recent paper [LaRiviere et al., J. Acoust Soc. Am. 57, 470–475 (1975)], the term ’’vocalic transition’’ was introduced with reference to an hypothesis generated by the authors. In this letter, a distinction is drawn between vocalic transition and formant transition with respect to literature citations.

Subject Classification: 70.30, 70.70.
Problems with absorption measurements of inhomogeneous solids
Authors: Marcus Peter W. , Carstensen Edwin L.
Published: October 2005

The use of phase-sensitive receiver can lead to errors in the measurement of the acoustic absorption coefficients of inhomogeneous samples. The problem can be avoided by use of a radiation force or an acoustoelectric receiver.

Subject Classification: 80.30, 80.20.
Acoustic wave propagation in a viscoelastic fluid undergoing a simple steady shearing motion
Authors: Schwarz W. H.
Published: October 2005

The theory for the prediction of the absorption and dispersion of forced acoustic waves propagating through a viscoelastic fluid in a steady simple shearing motion is presented. The stress tensor is represented by an approximate constitutive equation for a simple fluid obtained by a functional expansion about the basic state of a motion with a constant-stretching history. The linear terms are written as integrals, having kernels identified as shear and compressional relaxation functions. The absorption and dispersion depends on the direction of acoustic propagation relative to the shearing axis. Two cases are examined and the appropriate relaxation functions, or alternatively, the complex viscosity functions, obtained. These forms are compared to the shear relaxation functions obtained from shear oscillation experiments. The special case of acoustic wave propagation through a viscoelastic fluid, otherwise at rest, is considered and the results are compared to existing theories and experimental data.

Subject Classification: 35.50, 35.24.
Optimal primary spectra for parametric transmitting arrays
Authors: Clynch James R.
Published: October 2005

The use of more than two spectral components in the primary signal of a parametric endfire array is considered. Equations are developed for the spectra of N components which maximize the farfield SPL for shock-free primaries in dispersionless media. Effects of the variation of attenuation with frequency are shown to have a considerable influence on the shape of the optimal spectra. For the case of attenuation proportional to the square of the frequency, the optimal spectra are functions only of the downshift ratio R and the number of components N, and not functions of the absolute value of the frequencies. The optimal spectra and waveforms for several sets of R and N values are shown. It is found that a 3-dB increase over a two-component primary can be obtained with three or four components for a wide range of downshift ratios. At extremely high primary powers, an increased tendency toward shock formation may negate this gain. Beamwidths were found to be essentially unaffected.

Subject Classification: 25.35; 60.10.
Parametric acoustic receiving array. I. Theory
Authors: Truchard James J.
Published: October 2005

Closed-form solutions are derived for several configurations of the parametric receiving array. First, the solution for the interaction of a high-frequency spherical wave from a point source and a low-frequency plane wave is obtained theoretically by using a two-dimensional stationary phase solution of Westervelt’s scattering integral. The result is in turn used to generate the solution for parametric receiving arrays with various pump transducers, including a truncated line source, a rectangular piston, and a circular piston. In each case, the observer is assumed to be in the farfield of the pump transducer, but the result includes the effects of interaction in the nearfield of the pump transducer. The solution of the parametric receiving array with a point source pump and a truncated line receiver is also found. The theoretical solutions include the effects of misalignment of either the pump or receiving transducer.

Subject Classification; 25.35; 30.85.
Parametric acoustic receiving array. II. Experiment
Authors: Truchard James J.
Published: October 2005

A series of experiments was conducted with a 48-ft parametric receiving array at a pump frequency of 90 kHz. An omnidirectional transducer was used with either a rectangular or a square piston transducer. Each of the three transducers could be used as either pump or receiver, so that a variety of parametric receiving array configurations could be realized. The piston transducer could be independently rotated, to examine the effects of misalignment. Theoretical and experimental results are compared for the parametric receiving array with several transducer arrangements. With either the pump transducer or the receiver misaligned, the difference frequency beam pattern is asymmetrical and is the mirror image of the sum frequency beam pattern. The agreement between theory and experiment was excellent.

Subject Classification: 25.35; 30.85.
Calculation of the effect of internal waves on oceanic sound transmission
Authors: Flatté Stanley M. , Tappert Frederick D.
Published: October 2005

The signal received by a hydrophone in the ocean many kilometers from a steady sound source fluctuates dramatically due to variations of the speed of sound in sea water. By inserting an empirical model of internal-wave-generated sound-speed variations into an acoustic-transmission computer code, we have shown that internal waves cause significant variations in sound transmission at 100 Hz, comparable in size and frequency to the variations observed in field experiments. We have also studied the usefulness of vertical hydrophone arrays.

Subject Classification: 30.25, 30.82; 28.60.