bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the Excitation and Detection of Piezoelectric Surface Waves in Quartz by Means of Surface Electrodes
Authors: Coquin G. A. , Tiersten H. F.
Published: October 2005

The power extracted from a piezoelectric surface wave in quartz by an arrangement of electrodes on the surface is determined by a perturbation technique, which is extremely accurate for low-coupling materials. The mechanical portion of the surface wave is found by neglecting the piezoelectric coupling, which is very small in quartz. The elastic solution then yields both volumetric and surface source terms, which are generated by the piezoelectric coupling and drive the steady-state electrostatic solution. A technique is introduced for reducing the remaining electrostatic problem to Laplace's equation, subject to such boundary conditions that the solution is amenable to conformal mapping techniques for several interesting, and possibly useful, electrode arrangements. Surface waves propagating along the digonal axis for all rotated Y cuts are considered, as well as those propagating in all directions along the surface of an X-cut crystal. A reciprocal relation between the excitation and detection problems is derived, and is used to determine the amplitude of a surface wave generated by the application of an alternating voltage to the surface electrodes when the solution to the detection problem for the same arrangement of electrodes is known.
Trapped-Energy Modes in Quartz Filter Crystals
Authors: Shockley W. , Curran D. R. , Koneval D. J.
Published: October 2005

The behavior of thickness/shear-mode quartz resonators is explained both mathematically and experimentally in terms of lateral standing-wave trapped-energy modes. A cutoff phenomenon, similar to that occurring in optical total internal reflection, results in energy trapping or the restriction of vibratory energy almost exclusively to the electroded region of a resonator, with an energy distribution decreasing exponentially with distance from the electrode edge. Consideration of boundary conditions at the electrode edges of an idealized two-dimensional model yields an expression for the eigenfrequencies of symmetric inharmonic overtone modes (lateral standing waves) that can exist in the electroded region of fundamental- and harmonic-mode resonators. Design formulas for the suppression of these unwanted modes are included. They show that electrode thickness and lateral dimensions can be traded off against one another to obtain a wide range of motional parameters. Previously, unwanted responses were eliminated by restricting the electrode diameter to empirically established values. The present understanding has led to a reduction in resonant resistance and an increase in motional capacitance by at least a factor of four with hf and vhf fundamental- and harmonic-mode filter crystals. Experimental data that verify results predicted by energy-trapping theory are given, and application to design of single- and multi-electrode resonators is considered. Specific examples in the 10- to 180-MHz frequency range are given.
Effect of Temperature on the High-Frequency Component of the Jet Noise
Authors: Krishnappa G.
Published: October 2005

It is known that sound rays are refracted in the atmosphere owing to temperature differences. The effect of temperature differences between the jet and the outside fluid on the high frequency component of a jet noise is discussed by geometrical acoustics approximation and compared with the existing experimental results.
Robust Two-Input Correlators
Authors: Wolff S. S. , Gastwirth J. L.
Published: October 2005

Two-input correlators for the detection of a common-mode signal in two data channels are analyzed in the asymptotic case of a weak signal and long integration time from the standpoint of the effect on their performance of unknown, and possibly non-Gaussian, noise environments. The optimum correlator for a fixed, known noise probability distribution is derived. A natural performance criterion is developed that allows two correlators to be compared. Using this criterion, the existence of ε-maximin robust correlators for quite general classes of noise structures is proved. These correlators have the property that, as the noise distribution is varied, their departure from optimum performance is as small as possible. The mathematical development is applied to the derivation of several maximin robust modifications of the ordinary correlator and the clipper correlator, suggested by the theory of robust statistical tests.
Dynamic Response of Middle-Ear Structures
Authors: Fischler H. , Frei E. H. , Spira D. , Rubinstein M.
Published: October 2005

Automatic tracing of vibrations from several locations on the tympanic membrane and from the stapedial footplate, in human anatomical preparations, was performed by use of a capacitive-probe vibration meter. Normally, the vibrations of the tympanic membrane at the umbo and along the junction with the malleus were in synchrony with those of the stapes. The motion of the eardrum as a whole agreed with that postulated by von Békésy. The direct measurements enabled examination of the ossicular-lever transformation of the middle ear under dynamic conditions. In normal cases, undulation of the lever ratio around the 1.3 value was evidenced. Pathological changes caused an artificial increase of the ratio, due to damping features of the ossicular-lever system; the characteristics of an otosclerotic ear served as an conspicuous example. With the CAT 400B, further increase of the sensitivity of measurements (down to 2 Å amplitude) was possible. Some tests were carried out on patients also. Determination of the acoustic input impedance of the ear is discussed and a possibility of simple conversion of the vibration response of the eardrum into the impedance characteristic is presented. A typical input-impedance curve for a human temporal bone preparation with the unloaded stapes is demonstrated.
Auditory Search for Syllables Embedded within Meaningful Sentences
Authors: Davis Julia
Published: October 2005

Sentence length, syllable position within a sentence, and grammatical class of word in which syllables were embedded were investigated with respect to their effects upon accuracy of syllable identification and response latency in a task of auditory search. Ninety-six university students listened to sentences, which were followed by a syllable that identified the target for search, and determined whether or not the identifying syllable appeared within the sentence preceding it. The time required for search was recorded in milli-seconds. Results indicate a strong negative relationship between accuracy of syllable identification and time required for search. Greatest accuracy and shortest response latencies occurred when syllables were embedded within the shortest sentences of the series (15 to 25 syllables in length), within the final fourth of a sentence, and within nouns, verbs, conjunctions, or prepositions rather than within adjectives and adverbs. Indications are that the task of auditory search requires a rapid, low level, minimal form of language processing and that semantic and syntactic clues are of major importance to successful, rapid processing. Theoretical concepts of selection, recoding, retention, and recall of auditory imputs are discussed in relation to the normal, daily processing of language.
Phoneme Grouping for Speech Recognition
Authors: Reddy D. R.
Published: October 2005

A program for associating a given segment of speech with a phoneme group, such as a vowellike segment, fricativelike segment, etc., is described. Some disadvantages of the presently accepted grouping of phonemes into stops, fricatives, vowels, etc., are discussed. Grouping of phonemes used by Sanskrit grammarians seems to be more appropriate for computer speech recognition. A grouping of phonemes into several nonmutually-exclusive sets that combine the concepts of the presently acceptable grouping and those of the Sanskrit grammarians is proposed. This grouping is more suitable in that it permits algorithmic definitions of vowel-like sounds, etc., in terms of easily obtainable acoustic parameters—namely, intensity and zero crossings. Some results obtained using the suggested algorithm are presented.
Stimulated Brillouin Scattering: Measurement of Hypersonic Velocity in Liquids
Authors: Goldblatt N. R. , Litovitz T. A.
Published: October 2005

Measurements of hypersonic velocity in H2O and CS2 were made, using stimulated Brillouin scattering. These data indicate that this technique can be used to obtain data in agreement with ultrasonic values only if special care is taken to ensure that the output of the laser consists only of a single mode. The technique for accomplishing this is discussed.
Measurement of Acoustic Resistance at Sound-Pressure Levels to 171 dB
Authors: Marino P. A. , Bohn N. , Garrison G. D.
Published: October 2005

Absorbing liners, consisting of arrays of acoustic resonators, are being used successfully to suppress combustion instability in rocket and air-breathing engines. For the design of acoustic liners, information is needed on the variation of acoustic resistance with sound pressure at levels above the linear regime, i.e., approximately 100 dB (re 0.0002 μbar). In the work reported herein, a standard impedance tube driven by a high-intensity sound generator was used, along with an improved data-recording technique, to measure the resistance of Helmholtz-type resonator arrays. Incident sound-pressure levels of 171 dB were obtained, which represents an 11-dB increase in sound level over that reported by another investigator in an earlier, similar experiment. A simple correlation of the nonlinear resistance effects with sound pressure is presented.
On the Zwislocki Acoustic Bridge
Authors: Burke Kenneth S. , Shutts R. Edwin , Milo Anton P.
Published: October 2005

The problems involved in treating data obtained with the Zwislocki acoustic bridge are discussed. The practice of reporting data in arbitrary units is discouraged since these units are not comparable from bridge to bridge. Also, more study of the distribution of responses of nonpathologic ears is urged.
Amplitude Discrimination in Noise
Authors: Henning G. Bruce , Bleiwas Sheila L.
Published: October 2005

The experiment was designed to test a general model of the discrimination process. The discriminability of a given amplitude difference (in decibels) was found to be virtually independent of both the signal-to-noise ratio and the frequency of the tones to be discriminated, provided that the ratio of signal energy to noise-power density is sufficiently great. These findings lend support to a general model of the discrimination process suggested by Henning [G. B. Henning, J. Acoust. Soc. Am. 40, 1250(A)(1966)].
Preparation of Bismuth Surfaces for Ultrasonic Attenuation Measurements
Authors: Augeri R. , Freedman S. J.
Published: October 2005

A combined electropolishing-grinding technique is described, which produces plane, single, crystal surfaces on bismuth that yield significantly lower values for the acoustic attenuation above 30 Mc/sec than do standard techniques. The frequency dependence of the excess attenuation introduced by standard surface-grinding techniques has been measured and the results compared to various theories of attenuation in polycrystalline material.
Further Measurements on the Effect of Ice Cover on Shallow-Water Ambient Sea Noise
Authors: Payne F. A.
Published: October 2005

Shallow-water ambient-noise measurements have been made under open water and ice cover conditions at Prince Edward Island. Through the use of improved equipment, measurements were made that covered a greater range in frequency (3–3200 cps) and noise levels than previously reported for this area.
Reply to “Comments on ‘Parametric Solution of the Dispersion Relation for Guided Sound Propagation in Shallow Water’” [I. Tolstoy, J. Acoust. Soc. Am. 41, 1376(L) (1967)]
Authors: Pierce Allan D.
Published: October 2005

Tolstoy's claims to a previous parametric solution are considered. It is shown that, although Tolstoy never explicitly derived nor mentioned the existence of a parametric solution for the Pekeris waveguide, results in his early papers may be used to derive two such solutions. The resulting solutions, however, would appear in a less useful form than that given by the author.
Characteristics of Long-Range Atmospheric Infrasonic Propagation
Authors: Richie W. C. , Chick D. R.
Published: October 2005

A surface explosion of 500 tons of TNT at the Suffield Experimental Station Alberta, Canada, was monitored with a solion infrasonic microphone at a horizontal distance of 299 km to the southwest. The frequency response of the infrasonic microphone extended from 0.01–50 Hz. Statistical analysis using the power spectra and deterministic analysis using the amplitude spectra show a primary signal component at 0.26 Hz. Additional examination of the autocorrelation function and the power spectra indicates that atmospheric turbulence modulated the infrasonic wave as it propagated to the monitoring site. It is also suggested that his modulation could provide a measure of the atmospheric turbulence along the propagation path.
Transversal Motion in Transformer Laminations as a Cause of Noise
Authors: Hasson Sol , Shulman Yechiel
Published: October 2005

Transversal (out-of-plane) motion of transformer laminations has been noted by investigators of transformer noise, but it can be explained readily neither by electromagnetic forces between poles nor by magnetostriction. A new approach to the theory of transversal vibration is presented that suggests a cause of this type of lamination vibration and noise, namely, any magnetic path that causes magnetic flux to cross an air gap provides a force mechanism resulting in significant out-of-plane motion. This approach is particularly applicable to ballast transformers, in which air gaps, lamination slots, or leakage flux are commonly used. The theory furnishes expressions for the expected values of lamination displacement and velocity. A comparison with experimental data for one set of parameters is given.
Influence of Compressor Action on Speech Intelligibility
Authors: Caraway Betty J. , Carhart Raymond
Published: October 2005

The effects of compressor action, which reduces the long-term dynamic range of speech, on intelligibility of monosyllabic words presented in quiet was investigated. Three ratios of change in input level to change in output level were used, namely, 1- to 1-dB, 2- to 1-dB, and 3- to 1-dB. Peak powers of the speech signals were adjusted for these three conditions of reproduction so as to achieve presentations of 0, 8, 16, and 24 dB sensation level. The interphonemic dynamic range of the speech signal was the variable under study. Performance of the normal hearers, patients with labyrinthine hydrops, labyrinthine otosclerosis, and presbycusis improved only slightly during either condition of compression. Moreover, the subjects with hearing loss did not achieve any greater benefit from compressor action than did normals. These results warrant the conclusion that neither the 2- to 1-dB nor the 3- to 1-dB compression ratio offered any important advantage over 1- to 1-dB reproduction when comparison was made only in terms of intelligibility at a given sensation level of the output signal.
Machine-Aided Formant Determination for Speech Synthesis
Authors: Strong William J.
Published: October 2005

A semi-automatic analysis-synthesis scheme that can be viewed as a “manual formant vocoder” is described. A human operator makes decisions about formant positions on processed speech data. The parameters which result from the operator decisions are used to control a four-pole parallel synthesizer. Speech processed by the system had an error rate of 4.2% for vowels and 16.9% for consonants.
Parameter of Nonlinearity in Fluids. III. Values of Sound Velocity in Liquid Metals
Authors: Coppens Alan B. , Beyer Robert T. , Ballou Joseph
Published: October 2005

The speed of sound is reported for liquid metals (mercury, indium, bismuth, sodium, and tin) as a function of pressure (0 to 150 atm) and temperature (up to 100°K above the melting point). The result and data are used to obtain expressions for the derivatives of the sound speed with respect to temperature and pressure. These coefficients are then used to determine the parameter of nonlinearity in terms of the ratio B/A of the first two coefficients of the adiabatic expansion of pressure in terms of the density.
Pressure Correlation for a Cylinder in a Diffuse Sound Field
Authors: Wenzel Alan R.
Published: October 2005

A theoretical calculation is given of the surface-pressure correlation function for a rigid, infinitely long cylinder in a three-dimensional diffuse sound field (i.e., a sound field in which waves having all frequencies impinge on the cylinder from all directions). The analysis includes the effects of scattering of the sound waves by the cylinder. A general expression is derived that gives surface pressure spatial correlation as a function of both circumferential and longitudinal separation for any arbitrary distribution of sound amplitude versus frequency. With the aid of a computer, numerical results are obtained for the case of a narrow-band acoustic noise field. These results show a decrease in spatial correlation with increasing circumferential and longitudinal separation , as well as with increasing frequency. The results also indicate that scattering by the cylinder affects the spatial correlation only slightly in the longitudinal direction, but that it affects it considerably in the circumferential direction.
Frequency Dependence of Reverberation in the Ocean
Authors: Anderson Victor C.
Published: October 2005

Data on acoustic reverberation, collected at 12 stations in the Pacific Ocean, are presented to show gross characteristics of the volume reverberation as a function of depth at two frequencies, 10 and 25 kHz. The experimental equipment consisted of a cable-connected, horizontally directional echo-ranging instrument package, operating in conjunction with a shipboard digital data recorder. Of interest are the comparisons of relative scattering coefficients measured simultaneously at two frequencies. These comparisons indicate significant changes of scatterer composition with depth.
Shallow-Water Propagation under Downward-Refraction Conditions
Authors: Cole Bernard F. , Podeszwa Eugene M.
Published: October 2005

The important features of shallow-water sound transmission under downward-refraction conditions are interpreted in terms of ray theory and are discussed relative to some specific 30-f (fathom) propagation-loss results. The propagation results are shown to depend directly upon the velocity profile and the bottom loss. A bottom-loss value of 1.3 dB per bounce was inferred from the measurements and is shown to compare favorably with theoretical values computed from bottom-impedance information. Observed pulse shapes are then compared with theoretical pulse shapes synthesized from the combined ray and bottom-loss models. In addition, the computed propagation-loss values for the various paths are presented as a function of source angle in order to illustrate the vertical directivity introduced by the environment. Finally, the effect of this vertical directivity on shallow-water propagation measurements is demonstrated by comparing propagation-loss results for directional and explosive sources.
Angular Distribution of Lower Room Modes
Authors: Donato R. J.
Published: October 2005

The angular distribution of the lower frequency modes in a rectangular room is calculated for various room dimensions. Applying the results to reverberation-room measurements, it is shown that a sample placed with its surface normal to a long dimension of the room experiences the most diffuse field. Various methods are proposed to modify the existing techniques of absorption measurement, where it usually happens that the sample is placed with its surface normal to the shortest axis, thus experiencing the least diffuse field.
Mechanistic Aspects of Hearing
Authors: Corliss Edith L. R.
Published: October 2005

The results of a number of apparently diverse experiments on human hearing can be summarized via a simple model. Two mechanisms are required: One element emits unit responses whose number is proportional to the instantaneous amplitude of a sound. The other is a selector mechanism, analogous to a resonant circuit, that integrates the responses. Correspondingly, just two parameters are involved: the threshold of hearing and the “Q” of the selector mechanism. The system of equations representing the model makes it possible to derive the necessary parameters from the results of a number of different types of experiments. The theory of the selector mechanism is based upon a recent study of the limits of performance of a system capable of storing oscillatory energy reversibly, but the remainder of the theoretical description makes use of ordinary communication theory. The discrimination ability of the normal ear is shown to be proportional to the one-fourth power of the level above threshold, and to relate closely to the sensation of loudness. Many features of the behavior of normal and impaired ears can be predicted by application of familiar network theory to the parameters derived from the model. The properties of the model may be used as criteria in the choice of experiments to develop explicit data on the way the ear performs its function.
Additivity of Masking
Authors: Green David M.
Published: October 2005

Suppose, in separate experiments, the level of noise and the level of a sinusoid are adjusted so that each produces the same amount of masking of a gated sinusoidal signal. If now the noise and sine-wave masker are combined, how much must the level of the signal be increased to achieve the same level of masking effectiveness as before? Few conditions require only a 3 dB increment of the signal. It is argued that an increment greater than 3 dB implies that the processing of the signal when masked by noise and when masked by a sine wave are different.
Visualization of Quasilongitudinal and Quasitransverse Elastic Waves
Authors: Staudte Juergen H. , Cook Bill D.
Published: October 2005

An optical method that permits the visualization of the deviation of energy flux from the wave normal of elastic waves in transparent crystals is described. Both the wavefronts and the direction of energy flux are simultaneously rendered visible by spatial filtering (Schlieren technique).
Brief Comment on the Hydraulic Analogy of an Acoustic Wave in a Pipe
Authors: Solomon L. P. , Cuadra Elizabeth
Published: October 2005

A plane acoustic wave encountering a small area change in a pipe gives rise to transmitted and reflected waves; an analogous problem occurs in shallow-water theory when an incident wave encounters a small area change in a channel. Experiments with a hydraulic analog, in which photographs obtained from motion pictures of the unsteady phenomena are used to obtain wave heights, agree with the theoretically predicted transmitted-wave heights using shallow-water theory. The value of the hydraulic analog as a flow-visualization tool in research and as a teaching aid in fluid mechanics and acoustics is reconfirmed.
EFFECTIVENESS OF TWO-PARTICLE IMPACT DAMPERS
Authors: Masri S. F.
Published: October 2005

The exact solution for steady-state motion of an undamped harmonic oscillator in a state of resonance equiped with a two-particle single-container impact damper is derived analytically. The response of this damper is compared to that of a single-particle impact damper.
Transient Radiation Loading on Spherical Sonar Arrays
Authors: Junger M. C. , Garrelick J. M.
Published: October 2005

Transient surface pressures generated by a piston set in a spherical baffle or sonar array are obtained in analytical form for velocity steps and CW pulses. Neither the wave-harmonic series, which converges poorly at early times, nor geometric acoustics, which predicts zero pressure on passive elements, is applicable. A technique successfully used for CW impedance calculations was adapted to transient situations. On passive elements, the pressure is computed from Watson's “creeping-wave” formulation, which fails on the active element; there, the pressure is approximated by ignoring baffle curvature. The required Laplace integrals are available in the literature. Numerical results are presented. [Sponsored by Naval Ship Systems Command, under Computer Applications, Inc. subcontract.]
Aperture Corrections for Sound-Absorption Measurements with Light Scattering
Authors: Danielmeyer H. G.
Published: October 2005

Even small collection angles in the receiving optics can appreciably broaden, distort, and shift Brillouin lines observed in a light-scattering experiment, thereby causing errors in both sound absorption and sound velocity. A general expression for the observed lineshape is derived for a Lorentzian scattering line in terms of the distribution of thermal phonons and the shape of the collection aperture. Relaxational effects are also considered. For a square aperture, a closed-form solution is obtained and discussed. Applicable correction formulas for the true linewidth and lineshift are derived. To first approximation, Brillouin line is the sum of two arctan functions.
On a Method of Generating Ultrasonic Circularly Polarized Waves
Authors: Plicque F. , Feupier J. , Zarembovitch A.
Published: October 2005

In the present paper, we suggest a device that is able to produce circularly polarized ultrasonic waves by transposing the optical arrangement known as Fresnel's parallelepiped into the acoustic domain. A plane elastic transverse wave is propagated in an isotropic solid medium and then reflected at a plane air-solid interface. This wave is linearly polarized at 45° to the plane of incidence and so results in two components of equal amplitude, which are in phase. After reflection at an appropriate angle, the two transverse waves are in phase quadrature and the reflected wave is circularly polarized. This result is essentially independent of frequency.
Digital Analysis of Acoustic Reflectivity in the Tyrrhenian Abyssal Plain
Authors: Hastrup Ole F.
Published: October 2005

Acoustic bottom-reflectivity experiments with explosive sources made in the Tyrrhenian abyssal plain have been analyzed in detail using digital-analysis techniques. The reflection losses are computed and reported as functions of both angle of incidence and frequency. The impulse response is also computed for different angles of incidence, and it shows a large number of reflections from deep interfaces. Theoretical loss and impulse response have been computed from acoustical parameters measured on cores taken in the same area, and these agree well with the experimental data.
Coupling through a Small Aperture in a Waveguide
Authors: Van Bladel J.
Published: October 2005

The problem of the waveguide coupled to an external load through a small aperture is expressed in terms of an integral equation. Solution of the latter yields an equivalent circuit for the load as seen from the waveguide. Holes in terminal planes and sidewall are considered separately. Some attention is also given to multiple-hole coupling.
Vibrations of a Dissipative Composite Lumped-Distributed System
Authors: Herman H. , Pappas M.
Published: October 2005

Generalized functions and Laplace transformation are employed to obtain a solution for the vibrations of a composite lumped-distributed dissipative system consisting of a cantilever beam with a mass-spring-dashpot attached at some point along its length. The solution obtained contains the steady-state solution in closed form. The natural modes of vibration comprising the transient solution are found to be periodically self-similar and orthogonal in the sense that motion started in a given mode will be confined to that mode. Except for special cases, the natural modes will have no nodes. Curves are presented showing the behavior of the natural frequencies and decay constants as functions of the various parameters as well as the shapes of some associated modes. When the lumped elements are attached at the end of the beam, it is found that, for large values of the spring constant, increasing the dashpot strength may cause an increase in the natural frequency.
Natural Frequencies and Strain Distribution in a Ring-Stiffened Thick Cylindrical Shell
Authors: Patel Jayant S. , Neubert V. H.
Published: October 2005

The natural frequencies and strain distribution at resonance in a freely supported circular cylindrical shell reinforced by equally spaced thin deep ring stiffeners is presented. In this approximate solution, the basic assumption admits the existence of all the strains and, by the process of systematic elimination, it is shown to be important to retain the transverse shear strain γτθ. The analytical results are compared with the experiment, and good agreement between the two is obtained.
Errors Obtained in Spectral-Density Analysis with Sweeping Filter and Remaining Ripple When Using Equalizer-Analyzer System for Random-Vibration Test
Authors: Reveman Anders
Published: October 2005

This paper deals with some problems of equalizing and analyzing the acceleration density spectrum obtained when performing a random-vibration test with specified tolerances. A peak-notch pair in the spectrum, as obtained from a single-degree-of-freedom resonance within the specimen or fixture, is considered as being the most severe part of the spectrum to equalize or analyze. This pair is characterized in the error estimation with parameters for the peak-notch amplitude ratio and the peak-notch frequency ratio. The influence of the analyzing filter shape outside the passband is such that an equivalent bandwidth-increase factor can, within certain limits, be expressed as a linear function of the 12-/3-dB shape factor. Diagrams are given that show the errors due to bandwidth and shape of the filter used for the analysis as a function of the peak-notch pair to be analyzed. In the case of the equalizing-analyzing system, the filter shape was not found to have any evident influence on the accuracy of the equalization, only the 3-dB bandwidth of each filter. The phase angles between adjacent filters are also of minor importance, as the filters in severe parts of the spectrum act rather independently. Diagrams are given that show the accuracy of the equalization as a function of the peak-notch pair to be equalized. For a sweeping analyzer, the maximum sweep rate of 0.2 bandwidths per averaging time is recommended.
Dynamic Bulk Moduli of Several Solids Impacted by Weak Shockwaves
Authors: Coleburn N. L.
Published: October 2005

The bulk compressibility of several solids was measured using attenuated underwater shockwaves. Attenuation was such as to deliver an approximate sonic pulse to the test specimens. Measurements were made of the wave-attenuation and the wave-transit time in several metals, plastics, and chemical compounds. High-speed smear-camera shadowgraphs were used for the measurements.
Geometric Theory of Ray Tracing
Authors: Eby Edward S.
Published: October 2005

A temporal metric tensor is defined by combining the sound-speed function with the spatial metric tensor for a Riemannian space. Fermat's principle implies that spatial rays are temporal geodesics. Ray equations generalized to Riemannian spaces are shown to be temporal geodesic equations expressed in spatial terms. This geometric derivation leads to the consideration of geodesic deviation and its relation to three-dimensional spreading loss. Previous results [E. S. Eby, “Frenet Formulation of Three-Dimensional Ray Tracing,” J. Acoust. Soc. Amer. 42, 1287–1297 (1967)] are generalized to Riemannian spaces, and tensor expressions are derived for ray curvature and torsion.
Theoretical Investigation of a Double Family of Normal Modes in an Underwater Acoustic Surface Duct
Authors: Pedersen M. A. , Gordon D. F.
Published: October 2005

This article investigates an underwater surface duct model that requires two distinct families of normal modes for the representation of the acoustic field in the image-interference region. Each family contains an infinite number of modes. In the image-interference region, the propagation losses of mode and ray theory give almost identical results, with the mode approach being limited at short ranges by the large number of modes required and by the necessity for extreme computational accuracy in determining the contributions of individual modes. By means of phase velocity, the first and second family of modes are associated with ray groups that, respectively, do or do not reflect from the ocean surface. A new method of identifying mode number by phase changes in the mode depth function is presented. The fallacy of the incoherent addition of modes at close range is illustrated. Mathematical techniques for determining eigenvalues are discussed in detail. The analysis of a number of limiting cases leads to explicit approximations that provide guides to the general theory that can be expressed only in complicated forms.
Intensity Equations in Ray Acoustics. III. Exact Two-Dimensional Formulation
Authors: Uginčius Peter
Published: October 2005

An exact formulation is presented for calculating intensity in ray acoustics for planar rays in a stationary medium in which the index of refraction can be an arbitrary function of two space variables. This is done by specializing the general three-dimensional equations to the two-dimensional case. The results clarify the approximations used in an earlier version [P. Uginčius, J. Acoust. Soc. Amer. 45, 193–205 (1969). See also Erratum, 45, 1572 (1969)].
Low-Frequency Sound-Propagation Anomaly
Authors: Oncley P. B.
Published: October 2005

In the propagation of sound near a porous ground plane, an excess attenuation in the vicinity of 300–500 Hz has been noted by various investigators. This attenuation can be explained in terms of interference between direct and reflected sound if allowance is made for phase lag on reflection, following the analyses of Rudnick and Ingard.
Acoustical Criteria for Auditoriums and Their Relation to Model Techniques
Authors: Jordan Vilhelm Lassen
Published: October 2005

The first step in using model technique as a design tool is to establish a quantitative criterion (besides reverberation time). “Early to reverberant energy,” “steepness,” and “initial reverberation time” or “early decay time” (EDT) must be considered the most relevant factors, from aspects such as: (1) simplicity of measurement, (2) correlation with subjective assessments, and (3) possibility of comparing values obtained in scaled models with values obtained in full-size halls. Measured values of EDT may be applied either by calculating the inversion index, i.e., the average value in the audience area of a hall divided by the average value in the stage area, or by comparing values of EDT measured in different locations of a model (or a hall) with values of average reverberation time. These techniques have been applied in a number of 1:10 scale models and, also, in some completed halls.
Model Techniques in Architectural Acoustics
Authors: Veneklasen Paul S.
Published: October 2005

Sound sources, microphones, detection, and display are described for the modeling methods for both the steady-state and transient types of testing. The methods have been refined for excellent precision for determining diffracted sound levels around complicated building structures, and for studying echograms within proposed auditorium designs so as to optimize envelopmental sound. Examples and quantitative results are presented for many types of applications.
On the Energy Transported with a Sound Pulse
Authors: Young Robert W.
Published: October 2005

Definitions of Fourier pressure spectrum level and integrated band pressure level are proposed for engineering description of the spectra of sonic booms and explosive sounds, and relations to specific energy spectral density are demonstrated.
Use of Acoustical Holography for the Imaging of Sources of Radiated Acoustic Energy
Authors: Greene David C.
Published: October 2005

It is experimentally demonstrated that scanned-receiver acoustical holography is useful for mapping or “imaging” those parts of a complex vibrator responsible for the energy radiated to the far field.
Methods for Evaluating the Performance of Small Acoustic Filters
Authors: Gatley William S. , Cohen Raymond
Published: October 2005

Experimental methods are needed for determining the characteristics of small acoustic filters used in systems with pulsating gas flows. These characteristics could then be used to predict the performance of proposed filter designs in a particular system, according to plane-wave acoustic theory. Dependence on trial-and-error experimentation in solving noise-control problems would thus be minimized. A literature survey revealed only a few earlier attempts to evaluate the acoustic performance of small filters and filter elements. Three methods for determining reflection and transmission factors are described, evaluated, and compared. A method employing a standing-wave tube of unique design is recommended for determination of reflection factors. Transmission factors are obtained from reflection factors and pressure measurements at the filter inlet and outlet. Use of an anechoic termination simplifies the calculations and increases accuracy; design and evaluation of such a termination is described.
Extremal Statistics of Combined Random Sinusoids
Authors: Lyon Richard H.
Published: October 2005

The statistics of sums of independent random variables are well represented by a simple approximate method in some important instances. This approximate method, based on saddle-point integration of the moment generating function, is particularly useful to large values of the random variable. The method is applied to estimating the density of a sum of sinusoids with random phases and amplitudes at large values of the sum.
Asymmetries in Cylindrical Waveguides
Authors: Forristall G. Z. , Ingram J. D.
Published: October 2005

Cylindrical geometries with axial symmetry are often used to model physical systems. Although such a model materially simplifies calculations, it may ignore significant effects arising from small asymmetries in the system. In order to demonstrate this and to examine the nature of such effects, a model was analyzed consisting of a cylindrical waveguide with perfectly reflecting walls and an isolated point source displaced small distance from the axis of the hole. The subsequent analysis shows two distinct types of arrivals associated with the geometry. Both of these produce strikingly large asymmetries in the motion of the system. These effects are clearly displayed in the closed-form solutions obtained for the problem and the light that they shed on the nature of the reflection process at a cylindrical interface may well be of significant value for ray-theory methods in diffraction.
Effect of a Shear Layer on Plane Waves of Sound in a Fluid
Authors: Graham E. W. , Graham B. B.
Published: October 2005

Available theory indicates that plane waves of sound are reflected and refracted at an interface of relative motion (a velocity discontinuity) between two regions of fluid. If the relative velocity is sufficiently great, three types of reflection occur, ordinary, total, and amplified, depending on the incident wave angle. In the amplification regime, theory predicts resonances. Here the velocity discontinuity replaced by a transition layer of finite thickness separating the two fluid regions. This layer is approximated by two equal velocity discontinuities (Model I) and by a linear velocity profile shear layer (Model II). For one example in the regime of ordinary reflection, the effects of thickness are negligible for thicknesses up to 1/10 of the incident wavelength. For the chosen examples in amplified reflection, extreme reductions in transmission and reflection coefficients occur for a thickness as little as 1/50 of a wavelength. The two models approach (at unequal rates) total reflection and zero transmission at larger thicknesses. These effects are produced by layers of fluid traveling at or near the apparent wave speed parallel to the shear layer. Such layers tend to “insulate” the two fluid regions from each other.
Vibrations of Fluid-Filled Spherical Shells
Authors: Engin Ali E.
Published: October 2005

Utilizing linear shell theory, which includes both membrane and bending effects, the differential equations for the axisymmetric, nontorsional motion of a fluid-filled thin spherical shell are obtained by means of Hamilton's principle. The motion of the fluid is assumed to be governed by the linear wave equation. It is shown that appropriate limiting cases of the frequency equation of a fluid-filled shell agree with those of the simpler models previously investigated. A description of some of the salient features of the frequency spectrum of such a fluid-shell system is also given in view of the frequency spectra of the limiting cases.
Bubble Dynamics in a Non-Newtonian Fluid Subject to Periodically Varying Pressures
Authors: Chan K. S. , Yang Wen-Jei
Published: October 2005

This paper investigates the vibration characteristics of a small insoluble gas bubble in quiescent blood subject to harmonic pressure fluctuations close to the natural frequency. Pressure fluctuations of about 0.05, 0.1, and 0.2 of the mean pressure are studied. Results are obtained for the pressure variation of the blood in the vicinity of the bubble and for the changes of the mean radius and surface acceleration of the bubble. The resonance curves are calculated. It is disclosed that the effect of viscosity on the response is rather important in blood.
Helmholtz Oscillations in Pulsating-Combustion Chambers
Authors: Moseley P. E. , Porter J. W.
Published: October 2005

An investigation has been made of the conditions under which liquid-fueled pulsating-combustion chambers operate as Helmholtz resonators. The experimental apparatus consists of a vertical, cylindrical combustion chamber that is partially filled with a liquid fuel and completely closed except for a single, sharp-edge orifice in the top end. A manifold chamber and an exhaust pipe are mounted above the orifice. The pulsating-combustion process operates on air drawn intermittently from a steady flow of air that is supplied through the manifold. Measurements have been made of chamber pressure as a function of time for various chamber configurations and exhaust-pipe lengths. Results show that the mode of operation is either anharmonic or harmonic, depending on whether the exhaust-pipe length is smaller or larger, respectively, than a critical transition length. The transition to harmonic operation is accompanied by a sudden jump in both frequency and pressure amplitude. Theoretical double-cavity resonator frequencies agree well with experimental frequencies for the harmonic mode of operation but are larger than frequencies for anharmonic operation by factors of about two or greater. The harmonic mode of operation appears to be governed by a Helmholtz-type mechanism, whereas the anharmonic mode is governed predominantly by heat-transfer processes.
Application of the Fast Fourier Transform to Linear, Distributed System Response Calculations
Authors: White Pritchard H.
Published: October 2005

The calculation of the response of a distributed system to a homogeneous random field involves the calculation of an integral of the form ∫S(x − x′, ω)G(x0, x,ω)G*(x0,x′,ω)dxdx′, where S(x − x′, ω) is the cross spectrum of the random field, and G(x0, x,ω) is the system response function. Transformation to the spectral domain, (k − ω space), simplifies the integration and allows considerable savings in computational time. The fast Fourier transform technique can be readily applied to the problem, reducing the required time by more than an order of magnitude. An example of transducer resolution in boundary layer-turbulence is presented.
Effect of Frequency and Space Averaging on the Transmission Responses of Multimode Media
Authors: Schroeder M. R.
Published: October 2005

Expressions for the standard deviation of the amplitude response of a multimode transmission medium to signals with nonzero bandwidth are derived. In the “statistical” case (normal modes overlapping frequency and negligible coherent transmission), the standard deviation is found to be approximately 5.57 (1 + 3.3⋅τW)−12 dB, where τ is the decay-time constant of the energy of the normal modes and W is the bandwidth of the excitation signal. For spatial averaging, the standard deviation of the response fluctuation in decibels is approximately 5.57 (1 + 3.3X/λ)−12 dB, where X is the length of the (linear) averaging interval and λ is the wavelength of the excitation signal. For excitation signals with finite bandwidth W, the response fluctuations are given by 5.57[(1 + 3.3τW)(1 − 3.3X/λ)]−12 dB, where λ is the average wavelength. These results are applicable to fluctuation problems in multipath transmission, random vibrations, concert hall acoustics, and power measurements in reverberation chambers.
Dynamic Stress and Displacements in a Two-Material Cable System Subjected to Longitudinal Excitation
Authors: Goeller Jacques E. , Laura Patricio A.
Published: October 2005

This paper deals with the analysis of the dynamic stresses and displacements in a cable subjected to longitudinal excitation simulating ocean-wave motion. The cable is considered to be made up of two segments of different materials and different physical dimensions. External damping due to fluid action and internal damping due to viscoelastic material properties are considered. The payload mass attached to the end of the cable is considered to be attached to a rigid foundation by an elastic spring and dashpot. This model covers a large number of possible oceanographic applications ranging from salvage recovery of objects immersed in the ocean sediments to suspension of instrumentation packages from buoy systems. Numerical results are presented for a hypothetical system consisting of the payload attached to a steel-nylon elastic cable exposed to sinusoidal excitation at the upper end. Forcing frequencies approaching the second natural frequency are shown to cause forces in the steel portion which are significantly higher than those predicted by a single degree of freedom discrete system. It is further shown that external damping reduces the amplitude response of the payload; but can cause an increase in the cable stress in the steel segment when compared to the undamped case.
Image Fusion, Broadening, and Displacement in Sound Location
Authors: Gardner Mark B.
Published: October 2005

The fusion or blending of two or more spatially separated complex signals (such as speech or music) into an apparent single image requires that the common origin signals be alike in quality and follow each other in rather close sequence (within about 50 msec). If both the quality and arrival-time conditions are fully met, complete fusion appears to occur and a single image is heard coming from a single location. If these conditions are only partially met, then only partial fusion or image broadening results. The degree of broadening may be relatively small, or it may be sufficient for the image to appear to fill the intervening space between the physical boundaries of the real sources. For certain combinations of parameters, the creation of a single image either inside or outside these boundaries (image displacement) may occur. The present paper describes a number of arrangements that may be used to achieve each of these effects. The techniques employed date from as early as the mid-nineteenth century to the modern filter and computer techniques of recent years.