bluuebunny/crossref_metadata_2025 huggingface dataset:
Propagation of Transient Sound Signals into a Viscous Fluid
Authors: Norwood Frederick R.
Published: September 2005

An arbitrary excitation of the plane x = 0 sends sound signals into the half-space x ⩾ 0 occupied by the viscous fluid. The governing third-order partial differential equation is solved exactly using the Laplace transform on time and the sine transform on space. New expressions for the most general solution are derived. The specific inputs considered in detail are the Dirac delta function, the Heaviside unit function, a decaying exponential, and a sinusoidal excitation. The final expressions are given in the form of real integrals and of exact power series. Short-time approximations are also given for a general input and for the four aforementioned specific inputs. Previously obtained approximations for the case of small attenuation coefficients are corrected and extended for the decaying exponential and the sinusoidal input. The results found indicate that viscosity tends to reduce the sharpness of the propagating disturbance and thus to smooth out any initially imposed discontinuity. The presence of the disturbance is felt immediately everywhere in the medium, and, in fact, the short-time approximations satisfy the parabolic heat equation.
On the Rattling of Windows by Sonic Booms
Authors: Crandall Stephen H. , Kurzweil Leonard
Published: September 2005

Estimates are made of the dynamic stresses produced in the glass of windows whose sashes are loose in their frames, when the windows experience sonic-boom pressure pulses. For conventional sized windows with free-travel distances of less than 12 in., the dynamic magnifications induced by free travel may be significantly greater than those for a fixed window. However, the resulting stresses for presently recommended over-pressures are not sufficiently severe to make glass breakage a common occurrence when such windows are rattled by sonic booms.
Axially Symmetric Waves in an Elastic Solid of Revolution
Authors: Datta S. K. , Shah A. H.
Published: September 2005

In this paper, the problem of free harmonic waves in an isotropic elastic solid of revolution is discussed. As in the classical theory, the displacement field has been expressed in terms of a dilatational scalar potential and an equivoluminal vector potential. A method indicated by Stratton in discussing electromagnetic waves has been utilized to show that if the displacement field has the same axis of symmetry as the axis of revolution of the body, these equivoluminal modes can be expressed in terms of two potential functions—one of which corresponds to the pure torsional modes. It is found that there are two distinct families of modes of vibrations—one is torsional and the other is torsion free. As illustration, complete analysis is presented for free axisymmetric harmonic waves in a prolate spheroid. It has also been shown that, as limiting cases, solutions may be derived for waves in a sphere and in a right circular cylinder.
Filtering Action of a Blanket Dome
Authors: Maidanik G. , Reader W. T.
Published: September 2005

A sonar system may incorporate blanket to cover its transducer system in an attempt to achieve a better signal-to-noise ratio. The blanket is intended to displace the external pressure field away from the baffle—the surface in which the transducer system is flush mounted. In this paper, the propagation of pressure waves in the blanket material is assumed to have fluidlike properties. The analysis of the influence of the baffle-blanket system on the performance of the sonar system is carried out in spectral space and is expressed in terms of the filtering action of the former system. Of particular concern are the effects associated with changes in the speed of sound in the material of which the blanket is cast.
Reception by an Infinite Array of Pistons and Reflection by an Infinite Plane with Mixed Impedances
Authors: Mangulis V.
Published: September 2005

A plane wave is assumed to be incident upon an infinite array of circular pistons or infinite strips in a rigid-plane baffle. The forces on the pistons, the velocities of the pistons, the power absorbed by the array, and the amplitude of the reflected wave are calculated. Some numerical results for circular pistons are presented. Under optimum conditions, small pistons absorb the same power as large pistons.
Bottom Reverberation Measured with Explosive Charges Fired Deep in the Ocean
Authors: Merklinger H. M.
Published: September 2005

Bottom reverberation was measured at five locations in the North Atlantic using a hydrophone and explosive charges suspended near the ocean floor. Measured backscattering strengths in the frequency range from 800 Hz to 12.8 kHz show a tendency to rise moderately with frequency. The dependence on grazing angle was found to vary between a sine to the one-half and a sine-squared relation. Measurements made at several depths indicate that a portion of the reverberation originates in the subbottom layer structure directly beneath the point of measurement. At frequencies above 400 Hz, this reverberation from the subbottom appears to contribute significantly only at the steeper grazing angles.
Underwater Sound Pressure from Sonic Booms
Authors: Sawyers K. N.
Published: September 2005

An expression is derived for the sound pressure in a homogeneous fluid half-space, the surface of which is loaded by an idealized sonic-boom pressure signature. The expression is cast into dimensionless form and plotted as a function of time at three selected depths. In contrast to the abrupt beginning and end of the sonic-boom pressure variation in air, the pressure wave underwater is found to exhibit a precursor and tail. The underwater waveform is seen to be an odd function of time relative to the instant when the center of the sonic boom passes directly over the point of observation.
Reflection of Plane Oblique Air Waves from Absorbents
Authors: Ford R. D. , Landau B. V. , West M.
Published: September 2005

A review is presented of the derivation of reflection coefficients for plane waves for four different absorbent models. The first three cases, fluid, hard porous, solid, have been previously considered and are here presented in consistent form. The final case, porous solid, is derived by a technique of superposition of hard porous and solid cases. Impedances are presented as functions of normal impedance, angle of incidence, and known constants in the fluid and hard porous cases. In the remaining cases, an independent determination of transverse wave velocity (together with longitudinal wave velocity in the porous solid case) is required before impedance is a known function of normal impedance and angle of incidence.
Variables that Influence Sound Pressures Generated in the Ear Canal by an Audiometric Earphone
Authors: Erber Norman P.
Published: September 2005

The influence of outer-ear configuration on the acoustic stimulus delivered by a supra-aural earphone to a listener's tympanic membrane was investigated. A probe-tube microphone measured sound pressures generated in the ear canal by a TDH-49 earphone with constant electrical input. Acoustic and anatomical measurements obtained from the ears of Caucasian adults and children (male and female) were analyzed statistically. Mean sound levels measured in the ears of the adult male group were found to be lower than those obtained from the other three groups of ears at all eight test frequencies. Significant differences between groups were found at three of these frequencies. Variation between individuals was partly explained at specific frequencies by certain structural parameters of the ear. Implications of these results are discussed with respect to definition of international auditory standards, design of an improved artificial ear, accurate determination of the threshold of hearing sensitivity, comparisons of hearing between groups, and audiometric evaluation of patients with structurally abnormal ears.
Effects of Duration and Rise Time of Tone Bursts on Evoked V Potentials
Authors: Onishi Shinjiro , Davis Hallowell
Published: September 2005

Tone bursts of 1000 Hz with linear on and off ramps and plateaus of various durations were used to evoke cortical (vertex) potentials in five adult subjects. With 30 msec rise time, the amplitude, from N1 peak to P2 trough, and the latency to either the N1 peak or P2 trough were all independent of duration of the plateau from 0 to 300 msec. With 3 msec rise time, the amplitudes were progressively reduced when the plateau was shortened from 30 msec to 10, 3, or 0 msec. With a long plateau, the amplitudes were nearly constant for rise times of 50 msec or less. The latency of the V potential was prolonged at intensities of 45 dB (ISO) or less and also in relation to the slope of the onset ramp. With very gradual slope [300 msec to reach 45 dB (ISO)], mean latency to N1 was 169 msec while with very steep slope [3 msec to reach 85 dB (ISO)], it was 109 msec. OFF responses showed similar relations but with smaller amplitudes and shorter (by 16 msec) latencies. For evoked-response audiometry, the rise time of the test signal will not be critical if it is 30 msec or less and the plateau is at least 30 msec long, and any plateau of 30 msec or longer will be acceptable.
Monaural Loudness Functions under Masking
Authors: Richards Alan M.
Published: September 2005

Monaural sone functions are obtained for a no-noise condition and under five levels of masking noise using the method of fractionation. This method precludes the use of both ears in obtaining such functions as has been the case with dichotic loudness balance and other related procedures. The curves obtained are found to parallel previously found masked functions in one case, and in another to show a more rapid acceleration at low levels, but identical slopes above 1 sone. When the power function exponent of a 1000-Hz tone is plotted against over-all SPL of a masking noise, a “power transformation,” which parallels that found for speech in noise, is obtained. Although no numerical calculations are presented, it appears that above 60 dB of noise the exponent grows as approximately the 0.16 power of the noise.
Visualization of Noise from Cold Supersonic Jets
Authors: Lowson M. V. , Ollerhead J. B.
Published: September 2005

The acoustic field of small, cold supersonic jets has been studied by shadowgraph visualization. Preliminary experiments showed the importance of choosing an optimum film position for the visualization of sound waves. The interpretation of shadowgraphs is discussed. The apparent radiation field from the supersonic region of the flow is of relatively high frequency. In this field the order of dominance of the sound sources in the present case is (i) radiation from the nozzle, (ii) radiation from shock-turbulence interaction in the flow, and (iii) Mach-wave radiation. When the jet flow is deflected, the jet-deflector interaction becomes the principal noise source. The significance of the nozzle radiation is believed to result from the small scale of the jet used and demonstrates the necessity for care when extrapolating model scale acoustic data. The comparative in significance of Mach-wave radiation is probably due to the lower exhaust velocity of the cold jets. It is suggested that Mach reflection of spherical waves may be an important factor in the generation of “Mach waves.”
Dual Rôle of Frequency Spectrum in Determination of Auditory Distance
Authors: Coleman Paul D.
Published: September 2005

Manipulation of frequency content of click stimuli shows apparent distance of sound source from an observer is decreased by increasing high frequency content.
On Assessing Threshold of the “Better-than-Normal” Hearing Population
Authors: Egan James J. , Metz David A.
Published: September 2005

The ISO calibration standards for pure-tone audiometers are based upon thresholds of a young, normally hearing, pathology-free population of individuals obtained under optimum audiometric testing conditions. It has been clinically noted that individuals often respond to 100% correct identification of pure-tone stimuli at ISO audiometric zero. The term threshold demands a 50% correct response to tonal stimuli; thus, classical threshold is not obtained for those people with better than ISO hearing. Several shortcomings utilizing audiometers that do not make provisions for testing below audiometric zero are discussed. The recommendations are made that all audiometers be manufactured to allow for more sensitive presentation levels and that present audiometers without this provision have an attenuation pad inserted between the oscillator and the earphones.
Exponent in the Power Law and Loudness or Noisiness Calculation
Authors: Green David M. , Bishop Dwight E. , Parnell John E.
Published: September 2005

Calculations of loudness or noisiness assume some relation between changes in sound pressure p and changes in the psychological attribute, either loudness (in sones) or noisiness (in noys). We call this relation the power law, since Stevens has presented considerable data indicating that loudness is proportional to the intensity of the physical stimulus raised to some power. The purpose of this letter is to show that the calculation of loudness level in phons or perceived noise level in PNdB is remarkably unaffected by assumptions about the exponent of the power law, provided that the weighting given the loudest or noisiest frequency band with respect to the loudness or noisiness contributed by the remaining frequency bands is changed appropriately. The Letter concludes with a discussion of some implications of this fact.
Heat-Conduction Effects in Gas-Filled Cavities
Authors: Delany M. E.
Published: September 2005

Analysis of the acoustic impedance of a gas-filled rigid-walled cavity under nonadiabatic conditions is well established. A recent American Standard gives a single normalized curve for heat-conduction effects for air, hydrogen, and helium, and apparently fails to take account of the dissimilar ratio of specific heats (γ) of these gases. Corrected values are tabulated for a cylindrical gas-filled cavity for γ = 1.402 and γ = 1.666.
Axisymmetric Vibrations of a Thin Circular Plate Having Parabolic Thickness Variation
Authors: Barakat Richard , Baumann Elizabeth
Published: September 2005

The axisymmetric vibrations of thin circular plates having a parabolic thickness variation are studied for plates with fixed boundary conditions and simply supported boundary conditions. The Ritz Galerkin method of solution is employed.
Finite-Amplitude Distortion of 150-kHz Acoustic Waves in Water
Authors: Browning David G. , Mellen Robert H.
Published: September 2005

Finite-amplitude acoustic theory holds that sinousoidal plane wave becomes sawtoothed in shape as it propagates. Experiments showing the progressive distortion of a 150 kHz sine wave radiated from a square (40 × 40 cm) projector and detected by a 0.8-mm diam probe hydrophone are described. With an initial peak pressure of approximately 1 bar, the distortion becomes highly developed in the 8-m water path as expected from plane wave theory, but the waveform also shows evidence of phase distortion that is not considered in the theory.
Phase Characteristics of Continuous-Wave Transmissions in Shallow Water
Authors: Huff Lloyd C.
Published: September 2005

Three temporal scales of phase stability are evident in shallow-water acoustic propagation of 1700-Hz CW signals transmitted across Block Island Sound.
Formulas for the Calculation of Underwater Pressure in Acoustics
Authors: Leroy Claude C.
Published: September 2005

An equation is presented that makes it possible, from the knowledge of depth and latitude only, to calculate the absolute pressure in the oceans with sufficient accuracy for use in underwater acoustics. The equation has a universal use, with the exception of the Black Sea and the Baltic, for which separate equations are given.
Phase Changes and Pulse Deformation in Acoustics
Authors: Tolstoy I.
Published: September 2005

Acoustic waves generated by a point source in the ocean or atmosphere may be reflected due to total internal reflection by regions of increasing sound velocity- i.e., by the bending back of ray paths at turning points. This phenomenon is usually accompanied by the simultaneous formation of caustics. The relationship between caustics and turning point effects can be explored by the use of WKB and stationary phase approximations for the case of a harmonic point source in a homogeneous fluid overlying a stratified section. If one examines the behavior of reflected waves traveling along a given ray path, one sees that the conditions for formation of a caustic in the stratified section and for a −π/2 phase shift occurring within this section are identical. If, on the other hand, the point source is removed to infinity, one recovers the plane-wave case: The caustic becomes the horizontal turning-point plane and the −π/2 phase shift becomes a turning-point effect. These features are reviewed; and it is concluded that, in stratified media, the −π/2 phase shift due to a turning point is simply the plane-wave limit of the caustic effect, a limit that is approached asymptotically when the source is removed to great distances.
Tube-Cavity Resonance
Authors: Troke Robert W.
Published: September 2005

Mathematical definitions of all tube cavity vibration modes are developed from experimental results. The crossover from one mode to another is defined in terms of pertinent design parameters. A simple, accurate, and first time-presented solution is developed for the spring-mass vibration mode. The higher harmonics associated with the sping-mass resonators, commonly called Helmholtz resonators, are identified from experimental data. Tube cavity limit conditions of zero length as well as zero and infinite volumes are included in this study. The resonance modes observed are spring mass, half-wave, and quarter-wave. Using the new solution for the spring-mass mode, natural resonances are found to be bracketed by the limit conditions of the adiabatic and isothermal processes. The classical works of Von Helmholtz and Rayleigh concerning Helmholtz resonators is extended to include boundary-layer theory, which theory was not introduced by L. Prandtl until 1904, a considerable time after the work of Von Helmholtz and Rayleigh.
Equivalent Peak Level: A Threshold-Independent Speech-Level Measure
Authors: Brady Paul T.
Published: September 2005

Previous research showed that the logarithm of the absolute voltage of a speech waveform is nearly uniformly distributed between same arbitrary threshold and a peak. In the present study, the equivalent peak level (epl) of a speech sample is defined as that peak of a log-uniformly distributed random variable that would have produced the same rms above threshold as was measured from the speech sample. Measurements on 116 speech samples show that if threshold is varied over a range of at least 35 dB on repeated measurements of the same speech sample, the epl varies ±1 dB. Equivalently, if the measuring threshold is held constant, the epl will follow known speech level changes on a decibel-for-decibel basis to within ±1 dB over a 35-dB range. The epl may be measured with any facility having means of obtaining rms-above-threshold.
Intelligibility of Vowels Altered in Duration and Frequency
Authors: Daniloff Raymond G. , Shriner Thomas H. , Zemlin Willard R.
Published: September 2005

This study was conducted to examine the differential effects upon vowel intelligibility of various degrees of time compression (TC) and frequency division (FD), with and without time restoration. A male speaker and a female speaker were used. For a given percentage of distortion, FD degrades vowel intelligibility more severely than TC. Restoring time to normal for FD speech produced by slow playing via the Fairbanks speech compressor does not enhance intelligibility. Vowel confusions under TC are related to duration; those for FD conditions appear to be closely related to the perception of Vowel Formant 2 and to a lesser degree, Vowel Formant 1. Patterns of male and female vowel confusions are generally much alike for all conditions and types of distortion. Results tentatively indicate superior female vowel intelligibility under all conditions of distortion, the advantage being largest for FD, somewhat less for TC. These results suggest that over a limited range of frequency division (up to 40%), vowel phonemic quality is relatively unaffected by proportionate shifting of fundamental frequency and formant structure, indicating that a “relative-vowel” hypothesis of vowel phonemic quality may hold for limited shifts in the frequency of vowel spectra.
Attenuation of High-Frequency Elastic Waves in Quartz and Fused Silica
Authors: Lewis M. F.
Published: September 2005

We have used Mason and Bateman's formulation of the Akhiezer mechanism to compute the ultrasonic attenuation in quartz. The results are compared with the experimental measurements of various workers. For the seven pure-mode ultrasonic waves that propagate on the x, y, and z axes in quartz the agreement between the calculated and measured attenuation coefficients is always to better than a factor of 2. This is the first extensive calculation of its kind on a trigonal crystal, and it is particularly gratifying that the theory explains the approximate equality of the attenuations of longitudinal and transverse waves. We have also performed similar calculations on fused silica, but in this case the measured attenuation exceeds the Akhiezer attenuation by more than an order of magnitude. It appears that some other relaxation mechanism dominates the attenuation in this material.
Design of High-Amplitude Resonators
Authors: Martner J. G. , Hanagud S. V.
Published: September 2005

The design parameters and operation of a new type of ultrasonic resonator are described. The resonator consists of a solid cylindrical body that contains a centrisimetric conic cavity and is driven by a piezoelectric disk bonded to the base of the body. The system thus generated vibrates in a radial mode, and the maximum amplitude is measured at the rim of the system. Optimum vibration conditions are obtained when the ratio of height to radius of the resonator is 1.24. An approximate equation is derived for the frequency of vibration as a function of the properties of the material and the physical dimensions. A number of models were constructed, and their capabilities as atomizers were studied. Aerosol conversion capabilities were found to be in excess of 1350 ml of waterlike liquid per minute with an aerosol-generating area of approximately 24 cm2 for the fundamental-mode-type resonator. The edsign of fourth enharmonic resonators whose cross sections are similar to the ones described is discussed briefly.
On Optimum Waveforms for Correlation Detection in the Sonar Environment: Reverberation-Limited Conditions
Authors: Kincaid Thomas G.
Published: September 2005

This study is concerned with optimum waveforms for correlation detection in the sonar environment. The selection of optimum waveforms for combating random multipath under noise-limited conditions was considered previously [T. G. Kincaid, J. Acoust. Soc. Am. 43, 258–268 (1968)]. In this paper, the same problem is considered under reverberation-limited conditions. The optimum waveforms are required to maximize the ratio of expected signal to expected reverberation plus noise under a fixed-energy constraint. Necessary and sufficient conditions for the optimum waveforms are derived. As under noise-limited conditions, it has only been possible to develop a technique for finding waveforms that satisfy a necessary condition. However, it is conjectured that this technique produces optimum waveforms. Conjectured optimum waveforms are found for selected examples, and their performance is compared to that of two conventional (CW and chirp) waveforms.
Effect of Signal Duration on Detection for Gated and for Continuous Noise
Authors: Tucker Ann , Williams Paul I. , Jeffress Lloyd A.
Published: September 2005

A series of two-alternative forced-choice experiments showed that for short durations, the detection of a tonal signal in noise when the two are gated synchronously is superior to the detection of the signal in a background of continuous noise. The experiments also showed that for gated signal and noise, there is a steady improvement in detection as the duration is shortened, provided that highly practiced observers are employed in the task. Naïve observers exhibit a similar trend, but their performance drops at the short durations (5 and 10 msec) where the listening task becomes very difficult.
On the Negative Potential within the Organ of Corti
Authors: Dallos Peter
Published: September 2005

When recording with relatively large electrodes from within the organ of Corti, a high negative resting potential is obtained. It is argued that this potential is an injury phenomenon and, as such, it has no significance in the hearing process.
Apical Cochlear Responses to Pulse Trains
Authors: Glattke Theodore J.
Published: September 2005

Studies of the characteristics of the cochlear microphonic during presentation of periodic stimuli have produced apparently contradictory results with respect to the contribution of the apical coils to the cochlear response. The present study investigated cochlear responses using paired electrodes placed in Turns I and III of the cochlea (Guinea pig) during stimulation with periodic stimuli derived from exciting a filter with a rectangular pulse train. Marked differences in the potentials observed in the third turn were apparent when records taken under monopolar recording conditions were compared with those obtained through a bipolar technique. Further exploration suggested that the third turn responses to modulated stimuli, as recorded by monopolar techniques, may be principally neural in origin.
Miniature Piezoelectric Transducers for Broad-Band Noise Measurements
Authors: Hennen H. A. , Lambert R. F.
Published: September 2005

The development and calibration of a minature piezoelectric ceramic transducer suitable for broad band wall pressure-fluctuation measurements is described. The ceramic has a physical diameter of 0.020 in., a length of 0.040 in., and, when coupled to a high-impedance preamplifier, exhibits a flat response (less than ±14 dB, from 10 to 100 kHz. The absolute sensitivity (about −110 dB re 1 V/μbar) is most critically dependent on the shunt capacitance of the preamplifier and connecting cable.
Comments on “Transient Acoustic Fields Generated by a Body of Arbitrary Shape” [C. L. S. Farn and H. Huang, J. Acoust. Soc. Am. 43, 252–257 1968)]
Authors: Junger Miguel C.
Published: September 2005

The paper under discussion compares a universally applicable, numerical approach with existing analytical solutions. It is pointed out here that a numerical technique may be required even when the source configuration admits, in principle, an analytical solution. A third approach, equally general, but approximate except near the pulse front, is described and its results compared to those presented in the subject paper.
Reflection of Finite-Amplitude Ultrasonic Waves. I. Phase Shift
Authors: Van Buren A. L. , Breazeale M. A.
Published: September 2005

When an ultrasonic wave is reflected from an interface, a phase shift that is dependent on the angle of incidence may occur. If the wave is nonsinusoidal, this phase shift causes relative spatial shifting of the Fourier harmonic components. The assumption of independent reflection of the Fourier harmonics allows the use of linear theory to calculate the change in the phase angle between the fundamental and the second-harmonic components in the distorted wave. A pulse technique is used to measure this change in phase angle. Agreement between theory and experiment is good for the phase shift upon reflection from water-copper, from water-duralumin, and from water-mica-glycerin interfaces when correction is made for finite-amplitude effects between the interface and the receiving transducer.
Reflection of Finite-Amplitude Ultrasonic Waves. II. Propagation
Authors: Van Buren A. L. , Breazeale M. A.
Published: September 2005

The reflection of a finite-amplitude ultrasonic wave from an interface was described by assuming that the Fourier Components in the wave are shifted in phase as though they were independent waves (Part I). In Part II, the behavior of the distorted wave after reflections that produce nonzero component phase shifts is predicted using a computer model. The progress of these “unstable” waves toward the “stable” waveform is described. Experimental results obtained using a pulse technique are in good agreement with the computer results.
Ray Method for Sound-Wave Reflection in an Open-Ended Circular Pipe
Authors: Felsen L. B. , Yee H. Y.
Published: September 2005

Modal reflection and coupling coefficients are calculated for a semi-infinite flanged and unflanged hard-wall circular tube excited by one of the propagating modes. The calculation is performed by a ray method wherein the incident mode is decomposed into local plane waves impinging on the rim. Consequent diffraction effects establish the reflected waves and are represented equivalently in terms of radiation from a nonisotropic ring source having a radiation pattern determined by the local scattering properties of the rim. The rays emitted by the nonisotropic ring source and reflected repeatedly from the tube wall are summed into modal form, the quality of the resulting asymptotic mode series being improved by comparison with the exact solution for an isotropic ring source. Reflection and coupling coefficients are provided by the modal amplitudes in this representation and are determined for primary diffraction due to the incident mode only and also for multiple diffraction due to interaction across the mouth of the tube. Comparison with exact computations for the thin-walled tube shows that the multiple interaction ray-acoustical calculation is capable of high accuracy not only at high frequencies but even in the dominant mode regime. Data are also presented for flanged terminations for which no exact solution is available.
Diffraction of Plane Acoustic Pulses by Obstacles of Arbitrary Cross Section with an Impedance Boundary Condition
Authors: Shaw Richard P.
Published: September 2005

The diffraction of an arbitrary acoustic pulse by an arbitrary scattering obstacle with an impedance boundary condition is treated by the same techniques used by the author in previous diffraction studies [e.g., “Diffraction of Acoustic Pulses by Obstacles of Arbitrary Shape with a Robin Boundary Condition,” J. Acoust. Soc. Am., 41, 855–859 (1967)]. The problem is formulated as an integrodifferential equation on surface values of pressure or velocity; this equation is then solved numerically for the specific geometry of a long cylinder of square cross section struck laterally by a step pulse in pressure. A useful economy is that the coefficients used in the approximation are independent of the boundary condition and are identical to those used for previous studies involving the same geometry. Results indicate that the surface pressure decreases from the rigid body solution for infinite impedance to an almost constant level for the boundary impedance equal to the fluid impedance.
Low-Frequency Scattering by Hard and Soft Bodies
Authors: Van Bladel J.
Published: September 2005

A reciprocity theorem is used to show that the first two terms in the power expansion of the farfield can be determined once the leading term is known on the scatterer. The parameter of the expansion is the wavenumber k.
Seismic Waves Generated by Sonic Booms: A Geoacoustical Problem
Authors: Espinosa A. F. , Sierra P. J. , Mickey W. V.
Published: September 2005

Low- and very-low-frequency air-coupled seismic waves were efficiently excited on different occasions by jet fighter planes flying at high altitudes and at Mach numbers greater than 1.2. The experiments presented in this investigation were clearly recorded on a geophone array containing up to 12 short-period vertical component stations, and a singular station recording the transverse and radial type of motion. A higher-mode, seismic, coupled wave from sonic booms has been observed for the first time. Correlation is made between the acoustical signal registered at the microphone stations in Cape Kennedy and the first impulsive onset of the seismic waves recorded at the array setup. The seismic waves coupled from sonic booms are explained as a constructive interference phenomenon in the surficial ground layers. Fourier-transform techniques are applied to some of the seismograms, and some interesting features are delineated.
Symbolic Approach to Dynamical Problems in Plates
Authors: Westbrook D. R.
Published: September 2005

A formal approach is used to obtain two-dimensional differential equations (of infinite order) for dynamical problems in plates. It is assumed that the displacements may be expanded in power series in z, the thickness coordinate. These power series are substituted into the three-dimensional dynamical equations of linear elasticity. The coefficients of powers of z are equated to zero leading to an infinite sequence of differential equations which by formal manipulation are reduced to three differential equations of infinite order in which the midplane displacements are the dependent variables and x, y, t are the independent variables. It is shown how various special theories including the classical theories may be obtained from the general equations by making certain assumptions on the frequency and wavelength of the expected solutions. A short discussion of the solution of an initial value problem by means of the superposition of solutions of the various special theories is also given.
Sound Reflection from a Low-Velocity Bottom
Authors: Winokur Robert S. , Bohn Joyce C.
Published: September 2005

Measurements of ocean-bottom reflectivity were made using explosive sound sources and bottom reflection coefficients determined for grazing angles between 2° and 85°. Theoretical reflection coefficients were computed using a multilayered model of the ocean bottom, in which the lowermost layer is considered to be semi-infinite and solid. The layers are assumed to have plane-parallel interfaces and to be absorbing. Sediment sound-speed measurements made on cores collected in the area, and used in the theoretical computations, indicate the bottom in this region to be a low-velocity sediment interspersed with thin high-velocity layers. Oscillograph records made of the bottom-reflected signals show a phase reversal, with respect to the incident wave at the angles theoretically predicted. Comparisons of theoretical and measured reflection coefficients are made at 1, 2, and 4 kHz, and, in general, the over-all agreement is good. An unusual increase in measured reflection coefficient with frequency is observed at the angle of intromission and can, in part, be explained by the presence of subbottom reflectors.
Identification of the Speaker's Sex from Voiceless Fricatives
Authors: Ingemann Frances
Published: September 2005

A series of experiments was run to study the ability of listeners to determine the sex of the speaker on hearing voiceless fricatives [ɸ,f,θ,s,∫,ç,x,χ,h] spoken in isolation. The accuracy of such identifications corresponded in general to the portion of the vocal tract in front of the place of constriction. Thus, a speaker's sex was more easily identified when he produced [h,χ,x] than when he produced [θ,f,ɸ]. [s] and [∫] also provided for sex identification. Attempts to locate the cues for identification in a portion of the fricative by tape-cutting experiments did not produce positive results.
Multiple Velocity Dispersion in Normal Hydrogen and in Normal Hydrogen-Helium Mixtures
Authors: Valley L. M. , Amme R. C.
Published: September 2005

Velocity dispersion in normal hydrogen and in normal hydrogen-helium mixtures has been investigated at room temperature using an ultrasonic interferometer. Double relaxation theory is in remarkably good agreement with the experimental results. Single-relaxation theory is definitely not in accord with experiment. The relaxation time for the 1–3 transitions is found to be 2.26 × 10−8 sec for hydrogen-hydrogen collisions and 4.39 × 10−8 sec for helium-hydrogen collisions. The respective collision numbers are 321 and 439. The relaxation time increased with increasing energy of transition. Helium-hydrogen collisions appear to be more effective than hydrogen-hydrogen collisions for the 0–2 transitions but not for the higher-energy transitions.
QUIET POWER WHALEBOAT
Authors: Schevill William E.
Published: September 2005

For use in underwater acoustics, an effectively inaudible inexpensive workboat was achieved by a simple arrangement of the propulsion machinery.
Dynamics of an Acoustic Probe for Measuring Pressure Fluctuations on a Hypersonic Re-Entry Vehicle
Authors: Heller Hanno H. , Widnall Sheila E.
Published: September 2005

The excessive heat development on the exterior structure of hypersonic re-entry vehicles necessitates the use of heat-resistant pressure transducers for the measurement of boundary-layer pressure fluctuations on the vehicle's surface. An appropriate acoustic-probe configuration was developed and tested in wind-tunnel experiments. The frequency response of the probe configuration to flow excitation was studied under subsonic (M = 0.055) and supersonic (M = 2.92) flow conditions and was found to depend both on the probe interior geometry and on the physical characteristics of the flow. In addition, the influence of heat-shield ablation on the frequency response was studied under these same conditions.
Operation of Ultrasonic Light Modulators under Conditions of Random Electrical Excitation
Authors: Minkoff John B.
Published: September 2005

Excitation of an ultrasonic light modulator by random electrical signals will cause a random modulation to be imposed on the emerging light wavefront. A general solution for the resulting light diffraction patterns is obtained, from which the conditions are determined for which the diffracted light-intensity distribution will be a valid representation of the power spectral density of the input electrical noise signal. The necessary experimental conditions for which the variance of the spectral measurements will be small are determined. The percentage of the light-modulator bandwidth over which measurements will be valid is found to be dependent on the product of the spatial-frequency bandwidth of the light modulator and the length of the optical aperture; this effect is evaluated and numerical results are presented. The case in which the input to the ultrasonic light modulator consists of a deterministic signal and noise is also considered. Using these results, the diffracted light levels due to signal and noise are obtained as a function of the input signal and noise power levels.
On the Detection of a Moving Noise Source in a Nonstationary Noise Background
Authors: Tuteur Franz B.
Published: September 2005

This paper considers the detection of signal consisting of broad-band Gaussian noise whose level varies in some predictable manner with time—e.g., the signal received from a passing object. This study differs from previous ones concerned with this problem in that the background noise is explicitly assumed to be nonstationary. The assumed noise model consists, in fact, of a stationary Gaussian noise amplitude modulated by another random process having a relatively very long correlation time. It is shown that the detectability with this noise model is considerably below that obtained previously with a stationary noise model, and the exact dependence on correlation time, fluctuation of the noise level, etc., is obtained.
Electrical Stimulation of Brain Localized without Probes—Theoretical Analysis of a Proposed Method
Authors: Fry William J.
Published: September 2005

A method of electrically stimulating neural elements confined within small volumes of brain at predetermined deep locations without employing probes is considered theoretically. The basic principle of the method is the partial rectification in the focal region of an ultrasonic field of the alternating current that flows in the entire brain, or a major portion thereof, in response to an externally applied electric field of the same frequency. Since the magnitude of the electrical conductivity of the tissue varies with the temperature the adiabatic temperature, changes produced by the acoustic disturbance cause a periodic variation in the conductivity that results in a net unidirectional transfer of charge when the frequenices of the two fields are equal. The condition for stimulation is expressed quantitatively by a relation involving the amplitudes of the electric and acoustic field parameters, the thermal coefficient of electric conductivity of the tissue, the threshold quantity of charge that must be transferred unidirectionally per unit area to result in stimulation, the pulse duration, and a parameter that is determined by the geometric orientation of the electric and ultrasonic field vectors at the acoustic focus. Numerical calculations suggest that stimulation can be produced in the absence of thermal or other mechanisms of damage to the tissue. The values of the charge-stimulation and electrical-conductivity parameters employed in the calculations are derived from available experimental data.
Shifts in Masking with Time
Authors: Bilger Robert C. , Melnick William
Published: September 2005

The time course of masking of a 500-Hz signal was determined for remote masking (noise from 2000 to 4000 Hz) and for direct masking (noise from 200 to 4000 Hz) under conditions of simultaneous and delayed onset of the tracking task. For half the conditions, listeners varied level of the tone against a constant background noise, and in the other half, they varied the noise level to mask a constant level of pure tone. The results showed a downward shift occurred during the first two minutes of tracking for both direct masking and remote masking. The shift in direct masking was influenced by the onset of tracking and the method of control, while the shift in remote masking was independent of these factors.
Observations upon the Relationship of Loudness Discomfort Level and Auditory Fatigue to Sound-Pressure Level and Sensation Level
Authors: Hood J. D.
Published: September 2005

Studies carried out upon subjects with normal hearing have shown that (a) the mean sound-pressure level at which a tone of 1000 Hz is judged to be unpleasantly loud is 100 dB and (b) following sustained stimulation with intensities above 100 dB, there occurs a dramatic increase in the resultant temporary threshold shift. The intensity at which both these events occur is independent of sensation level. It follows that variations in normal threshold of the order of ±10 dB are largely sensorineural in orgin. In addition, the fact that both these unrelated events occur at the same sound-pressure level suggests that it marks a physiological limit of loudness perception. The results lead to the conclusion that the loudness function shows considerable intersubject variability and is dependent upon hearing acuity. Their application to loudness computations and to hearing conservation is discussed.
Masked Tonal Thresholds in the Bottlenosed Porpoise
Authors: Johnson C. Scott
Published: September 2005

Masked thresholds were obtained for a bottlenosed porpoise at 15 frequencies between 5 and 100 kHz, using continuous broad-band noise to mask tonal stimuli. Critical bandwidths were calculated from the ratio of the tonal threshold level to the masking noise level per hertz at each frequency. At 5, 10, 20, 50, and 100 kHz, six different noise levels were used; from the resulting data, a plot of the amount of masking versus the effective noise level was obtained. The data are compared to those from similar experiments with human subjects.
Acoustical Effects of Violin Varnish
Authors: Schelleng John C.
Published: September 2005

Acoustical effects of violin varnish—those of mass, stiffness, and internal friction—are examined qualitatively and quantitatively. Dynamic measurements of Young's modulus, real and imaginary, are made for films of typical oil varnishes on a substrate of cross-grain spruce through aging periods of 1 yr or more and expressed in the practically useful terms of modulus over density. After 112 yr, the hard varnish had a real modulus per unit density of 2.5 × 1010 cm2/sec2 and Q about 23; after 1 yr, the values for the soft varnish were 1.6 × 1010 and 8. A high-grade floor varnish had intermediate values. The imaginary component of the soft one was substantially independent of frequency from 400 to 5600 cps. Exact calculations of added loss and tuning shift, made for a “pseudofiddle” comprising rectangular top and back of orthotropic materials simulating spruce and maple, are believed roughly representative of the violin. Added loss is more apt to be damaging than is detuning of plates. The loss comprises two components: (1) a reduction in sound caused by the reactive parameters of varnish, i.e. mass and stiffness, and effective irrespective of resonance; and (2) one caused by internal friction and greatest at a resonance. With an intermediate varnish, a coat of 0.0127 gm/cm2 (thickness about 0.005 in.) causes “flat” loss of about 1 dB and resonance loss about 3 dB; this is excessive. Varnish loss in the top plate is about three times that in the back; unless the spruce is overly resonant, its varnish should be thin. Top is more subject to detuning than back. Loss due to varnish is best controlled by weighing, with final adjustment of wood thickness after varnishing.
Pressure Fluctuations in a Separated Flow Region
Authors: Fricke F. R. , Stevenson D. C.
Published: September 2005

This paper describes a preliminary experimental investigation of pressure fluctuations in a separated flow behind a thin fence. Methods of determining the position of recombination point, which is closely related to the position of maximum sound-pressure level, are discussed. Noise sources within the flow are identified. Significant and parasitic variables are noted and a dimensional analysis is presented. A similarity relation is also presented, relating sound levels to frequencies and free-stream velocities. Graphs of the variation of power spectral density with frequency, and sound level with distance behind the fence are given for distances up to 50 fence heights behind the fence. It has been found that the frequency spectra alter considerably with distance behind the fence and that the maximum sound level behind a fence is about eight times that in a turbulent boundary layer, with the same free-stream dynamic head.
Acoustic Transients Generated by Antiferroelectric-Ferroelectric Transducers
Authors: Singal S. P. , Carome E. F.
Published: September 2005

A study has been made of the acoustic transients generated in water by transducers made of materials that undergo electric field-forced antiferroelectric-ferroelectric transitions. The amplitude and time profile of the pressure pulses have been examined in detail. It has been seen that finite amplitude signals may easily be generated using such transducers. This behavior indicates that they may be of use as nonresonant generators of high-amplitude acoustic waves.
Vibration Analysis by Holographic Interferometry
Authors: Monahan Michael A. , Bromley Keith
Published: September 2005

Optical holographic interferometry is used to study the vibrational characteristics of a sonar transducer. Experimental methods are described, and photographs of 13 resultant hologram images are included. Each is an interferometric fringe pattern from which the peak-to-peak amplitude of every point on the vibrating surface can be computed. The result of an exact theoretical analysis is stated; the solution for a simplified model is derived; and numerical results are compared.
Rotatory Vibration of a Rigid Circular Die on a Semi-Infinite Elastic Solid
Authors: Paul H. S.
Published: September 2005

The effect of rotatory vibration of a rigid circular die on an elastic half-space has been studied. Two cases are considered: (a) half-space with a circular cylindrical hole in the middle, and (b) half-space made of two materials. The dual-integral equation technique of Noble is utilized to solve the mixed-boundary-value problems.