bluuebunny/crossref_metadata_2025 huggingface dataset:
Backscattering of Underwater Sound from a Wind-Driven Model Sea Surface
Authors: Medwin Herman , Ball Ernest C. , Carlson John A.
Published: November 2005

Model seas have been generated by adjustable winds over a large anechoic tank. The distribution of heights and slopes and the wave height energy spectrum have been determined for a homogeneous section of this statistically-stationary, anisotropic surface. This known, nearly-Gaussian “sea” has been used to predict the backscattered sound according to several different theoretical “solutions”. The predictions are compared with many thousands of instantaneous values of scattered pressure for sound incidence θ, from normal to 80° and surface roughnesses 0.01<g<60 where (g)12 = 2kσ cosθ, with σ = rms height. Measured mean-square pressures show particularly good agreement with theory when the effect of diffraction is added to the surface spectrum description as developed by Eckart (1953), Marsh (1963), and Wetzel (1966) for g < 1. There is decidedly poorer support for the various statistical approaches used by Eckart, Isakovitch, Cox, and Beckmann in the case of rough surface scatter g≫1. The distribution of amplitudes is found to be Rayleigh, except near normal incidence, where it becomes Gaussian as the roughness decreases to g≪1. [Work supported by Naval Ship Systems Command.]
Frequency Spectra of Forward Scattered Underwater Sound from a Traveling Sinusoidal Surface
Authors: Roderick William I.
Published: November 2005

An experiment has been conducted in a model tank to determine the frequency spectrum of an acoustic signal reflected from a traveling sinusoidal surface. An acoustic signal of 1.85 MHz was transmitted continuously and projected toward the surface (beamwidth 3.5°). A vibration generator produced water gravity waves; wavelength and wave-height measurements were made at the point of reflection. The forward scattered signal was envelope detected and analyzed for spectral content. Frequency information regarding the carrier and sidebands was also obtained. A scattering integral developed in the literature was evaluated for a traveling sinusoidal surface to compare the experimental results. Analytical predictions were made, based on the concept that the surface waves phase modulate the acoustic signal. Important observations are: (1) both amplitude and phase modulation are present, (2) the frequency spectrum is symmetrical about the carrier and can contain only sideband frequencies that are multiples of the surface frequency, i.e., f±nf6, (where f = acoustic frequency, n = 0, 1, 2, 3, ⋯, f6 = surface frequency), (3) the amplitudes of the frequency components are dependent on transmitting and receiving geometry and measured surface characteristics.
Effect of Sediment Shear Waves on Bottom Reflection Losses
Authors: Morris Halcyon E.
Published: November 2005

The question of whether bottom reflection losses calculated with the viscoelastic model for bottom sediments are significantly different from the results from the simpler complex velocity model has been of recent interest. The physical difference in the two models is the generation of shear waves in the viscoelastic model as a result of sediment rigidity and viscosity defined by complex Lamé constants. Results are presented where the same density, compressional velocity and attenuation in the sediment were used in both models. Varying amounts of rigidity were introduced into the sediment layer. Consideration of the shear waves in the viscoelastic model generally results with higher bottom reflection losses than the complex velocity model. The difference is most notable when the sound velocity in water and the compressional velocity in the sediment are nearly the same.
Information Rate, Resolving Power, and High-Resolution Sonar Systems
Authors: Brown D. H.
Published: November 2005

Ultrasonic visualization systems with very high resolution can best be described using concepts similar to those developed in the study of optical imaging systems. Such systems are thus quite naturally called acoustic imaging systems. The concepts of information rate, measured in resolution elements per radian second and resolving power, which is related to the spatial frequency bandwidth of a system, are developed and used as a basis for a historical review of some of the techniques that have been applied to underwater acoustic imaging. Unfortunately, a common characteristic of most systems developed in the past is their limited success. By considering designs that will simultaneously offer high resolving power and information rate, some new techniques that may result in more successful underwater acoustic imaging systems are introduced and discussed.
Atlantic Undersea Test and Evaluation Center (AUTEC)
Authors: Jackson L. L.
Published: November 2005

The Navy's Atlantic Undersea Test and Evaluation Center in the Bahama Islands is one of the largest facilities in the world in which acoustics plays a major role as both a measurement variable and measurement tool. The aims, activities, and purposes of AUTEC will be presented in a 20-min film that will serve as an introduction to the three following papers on the weapons, acoustic, and sonar ranges.
AUTEC Weapons Range
Authors: Oneby William
Published: November 2005

The AUTEC Weapons Range is a three-dimensional tracking facility instrumented to track both in-air and in-water targets. The range presently consists of a 35-mile-long area of the Tongue of the Ocean. The in-air tracking instrumentation is located on shore. The in-water tracking instrumentation includes large hydrophone arrays designed for deep-water operation. The acoustic instrumentation and tracking technique are described.
Directional 420-Hz Sound Source
Authors: Kronengold Morton , Toulis William
Published: November 2005

A 24-ft compliant-tube parabolic reflector, with a flextensional transducer at its focus, has yielded acoustic source levels up to 122 dB/bar/yd at 420 Hz in 85 ft of water off Fowey Rocks near Miami, Florida. The projector is part of an ONR supported research program to study underwater sound propagation and related environmental parameters. Modulation signals of continuous-wave pulses, and pseudorandom sequences are transmitted by wire from the Institute of Marine Sciences Laboratory to the transducer, a distance of 12 miles. Bottom-mounted hydrophones are employed at various distances, with the principal sensors on the island of Bimini which lies 45 miles eastward across the Florida Straits. The reflector provides a mainlobe of 28° at the half-power points; the back lobes are down more than 25 dB and the directivity index is 15 dB. The effective mechanical Q of the transducer-reflector combination is 4. At the present depth, the transducer is cavitation limited to an acoustic output of 4 kW.
Human Equilibrium During Acoustic Stimulation by Discrete Frequencies
Authors: Harris C. Stanley , Sommer Henry C.
Published: November 2005

Previous research has demonstrated that high-intensity broad-band noise has adverse effects on human equilibrium. In the present study, an attempt was made to determine whether frequency (Hz) of acoustical stimulation is an important variable in the ability of subjects to balance on narrow rails. Two groups of subjects performed the rail task during exposure to pure tones of 100, 260, 590, 1500, 2500 Hz, and a control condition. One group was presented the tones with equal intensity to both ears (symmetrical exposure) and the other group was presented a higher intensity to the left ear than to the right ear (asymmetrical exposure). A decrement in rail-task performance was obtained only at 590 Hz for the symmetrical exposure group and only at 1500 Hz for the asymmetrical exposure group. The decrement obtained with symmetrical exposure was less than the decrement for asymmetrical exposure. This result supports previous findings that asymmetrical exposure has more adverse effects on human equilibrium than symmetrical exposure. Both frequencies at which decrements were obtained have been found in previous studies to have the lowest thresholds for vestibular stimulation as determined by a slight shifting of the visual field in normal hearing subjects and nystagmus measures in deaf individuals. The results are interpreted as a possible demonstration of the direct effects of noise on the vestibular system.
Olivocochlear Bundle Regulation of Spontaneous and Tone-Evoked Activities of Single Units in Cochlear Nucleus
Authors: Starr A. , Wernick J.
Published: November 2005

132 units were recorded extracellularly in 19 decerebrate unanesthetized cats paralyzed with Flaxedil. Tetanic electrical olivocochlear bundle stimulation at the facial genu (20–200-μA, 0.1-msec pulses, 200/sec) decreased spontaneous discharge rates in 30% of the units, increased it in 18% and had no effect in 52%. Effects of olivocochlear bundle stimulation on tone-evoked responses (Tone bursts, 200 msec in duration, rise and fall times of 25 msec) were analyzed with the units' “best” frequency presented at different intensities. Three types of response modifications occurred. (1) Decrease in discharge rate equivalent to a 5–10-dB shift in the intensity function; (2) increase in discharge rate, and (3) either a decrease or increase in firing rate as a function of tone intensity. The unit's threshold presence of inhibitory surround, and the type of intensity function (montonic or nonmontonic) were correlated with these response modifications. Experiments on animals with cochleas acutely destroyed showed olivocochlear bundle stimulation to still be effective in modifying spontaneous discharges in cochlear nucleus. We conclude that olivocochlear bundle has a direct effect on cochlear nucleus in addition to its well-known receptor effects.
Olivocochlear Bundle: Relationships to Signal Discrimination in Noise.
Authors: Dewson James H.
Published: November 2005

Monkeys, trained to discriminate between human speech sounds presented at 70 dB SPL in 2400-Hz low-pass noise of different intensities, were found significantly impaired in their performance following surgical section of the crossed OCB. There is absolutely no loss in the ability to discriminate between the signals in the absence of noise. The deficit is related to “perceptual” (as opposed to physical) signal-to-noise ratio: high intensity noise per se is insufficient to cause performance decrement if its passband provides inadequate masking of the speech stimuli (e.g., 2400 Hz high pass). The magnitude of the postoperative deficit is apparently related to the extent of destruction of the fibers of the OCB.
Duration and Rise Time of Tone Bursts and the Human Vertex Potentials
Authors: Onishi S. , Davis H.
Published: November 2005

Tone bursts with linear rise times of 3 or 30 msec and plateaus from 0 to 300 msec were presented at four intensities to five adult subjects. With a 30-msec rise, the amplitude (N1 to P1 and latency (N1 peak) were unaffected by increasing the plateau from 0 to 300 msec. With a 3-msec rise and 30-msec plateau, the amplitudes were slightly increased at all intensities over the 30-msec rise time. With a 3-msec rise and plateaus of 10, 3, and 0 msec (a tone pip), amplitudes were significantly reduced. The latency was slightly prolonged (re 65 and 85 dB) at 45 dB (ISO), significantly prolonged at 25 dB. In another experiment, rise and fall times were varied with a 2.5-sec plateau. Only small differences in amplitude and latency appeared for rise times of 50 msec or less. The increase of latency was one-sixth of the rise time for plateaus at 85 and 65 dB and one-third of the rise time at 45 dB. The same relations hold for the OFF responses although amplitudes were smaller one-third and latencies shorter than for corresponding ON responses. [Work supported by National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Motion Sensing with Liquid-Filled Systems
Authors: Evertson Dale W.
Published: November 2005

Several variables influence hydroacoustic element properties. The dynamics of a motion-sensing system using such elements can be modified more easily than that of a system using mechanical elements, whereas transduction is less difficult using mechanical elements. Examples of hydroacoustics systems for measurement of earthquake motion will be described. Experiences with a hydroacoustic system using a polarized-cathode solion transducer will be discussed.
Seismic Space-Time Processing
Authors: Backus Milo M.
Published: November 2005

Frequency filtering and spatial filtering have been usefully applied for many years to the problem of extraction of signals from noise in active seismic exploration and in passive earthquake surveillance. Because broadband (octave or more) transients are of interest in both areas, frequency dependent spatial filtering has been frequently used. In some cases, interfering noise is spatially nonrandom, and “optimum” space-time filters are used to advantage. Essentially similar spatial response is usually obtained independent of the “optimization” criteria (e.g., least squares, maximum likelihood). Similar techniques may be used to employ arrays with complex inter-element signal relationships (such as combinations of horizontal and vertical motion seismometers). Although useful coherent properties of signal and noise can be exploited with an assumption of space stationarity, time stationarity, or space-time stationarity, in many cases use of space-time varying optimization is worthwhile and is being increasingly employed. Some of the current approaches to tracking down useful statistical space-time properties of signal and noise and their exploitation in seismic information extraction will be discussed.
Distribution Theory in Vocal Tract Analysis
Authors: Selvaggi Jerry A. , De Clerk Joseph L.
Published: November 2005

Solution of Webster's horn equation is accomplished in a discrete manner by means of distribution on theory. In the process of applying distribution theory exact solutions result. In the past, numerical integration was utilized. Given output formant frequencies, area functions can be calculated, or conversely, formant frequencies can be calculated from vocal tract area data. The results can be converted to an analog, which describes the behavior of the vocal tract. By quantizing the vocal tract an exact solution to Webster's horn equation results, whose reciprocals turn out to be transfer functions of transmission line theory under certain boundary conditions. Radiation impedance has been absorbed in the quantized vocal tract sections. Actual area functions of the vocal tract are determined by midsagittal cinefluorographic tracings and dental casts of the mouth. Acoustic data are synchronized with the cinefluorographic data by means of a digital code that provides registration between articulatory events and formant tracks. Determining vocal tract analogs by physiological data is more desirable than using formant information alone since consonants as well as vowels can be included in the analog. In addition, by referring to data that change every 8.33 msec a better insight is gained concerning articulatory movement. This technique is more realistic since it uses dynamic data which more nearly typifies the transient characteristics of speech than the usual steady-state analysis.
Vocoder Filter Design: Practical Considerations
Authors: Golden Roger M.
Published: November 2005

Successful digital computer simulation of a spectrum channel vocoder, [R. M. Golden, J. Acoust. Soc. Am. 35, 805(A) (1963) has also led to new filter design procedures for vocoder bandpass filters. These procedures yield designs that result in improved performance of the spectrum channel vocoder. The procedures are accomlished by computer aided design programs. The programs permit the examination and modification of the time and frequency response characteristics of the various bandpass and low-pass filters required by a spectrum channel vocoder. Such examination readily shows why the Bessel (or Linear Phase) designs are to be preferred over filter designs such as Butter-worth and Elliptic. In addition to choice of prototype filter design, consideration must also be given to filter resolving power (i.e., passband and stop-band characteristics) and to the frequency cross-over point of contiguous filters. This latter consideration accounts for the fact that performance of some vocoders has been improved by the simple device of shifting the phase of alternate channels by 180°. For many vocoder configurations, equalization of filter group delay characteristics is necessary between various channels. This factor is important for those vocoder designs using increasing bandwidth filters for the higher frequency channels. Equal bandwidth filters combined in pairs or triplets achieve both equalization and the desired increase in bandwidth.
Effects of Signal Probability on the Listening Band
Authors: Sorkin Robert D.
Published: November 2005

A two-interval detection procedure was used to study the effects of signal probability on the listening band. The signal was chosen randomly on each trial from a set of three 100-msec, equal amplitude, phase-coherent sinusoid segments of 650, 750, or 850 Hz. The relative likelihood of a specific frequency signal being present on a trail was varied over three experimental conditions: (1) P(650) = P(750) = P(850) = 0.33; (2) P(650) = P(850) = 0.17, P(750) = 0.66; and (3) P(750) = 1.0. Performance was assessed under constant noise level and two signal levels (10 log E/No = 10.4 and 12.2 dB). Plots of P(C)-vs-signal frequency indicate a small but consistent difference between the three experimental conditions. The effective listening band appears to be sharper under conditions in which the center frequency signal has a higher presentation probability. Analysis of the one trial sequential probabilities fails to support an interpretation of the results in terms of a simple sequential model. The observers appear to be using correct-trial information in order to improve their ability to detect the midfrequency signal, even when the preceding correct-trial was on a high (or low) signal.
TSD Applied to Footfalls in Buildings
Authors: Watters B. G.
Published: November 2005

We have studied the acceptability of intruding footfalls in buildings, and found that “just-detectable” signals cause significant annoyance. Consequently, we have considered how well the theory of signal detectability (TDS) predicts the perception of footfall sounds modified by low-pass filtering and reverberation, and partially masked by random noise. The “heel click” portion of a footfall signature, often the acoustically important part, has been simulated by a short series of periodic, filtered Dirac impulses. The signal replication caused by multiple echoes in rooms was progressively introduced. The first complication was a series of three of the above impulses, spaced by 10 msec and heard anechoically. The next was a reverberant signal, generated by producing single clicks in a 12-sec RT room, picking these up with a microphone and reproducing them as unidirectional reverberant pulse trains in the anechoic chamber. Finally, the subjects were placed directly in the reverberant room. All the above signals are recognizable as (synthetic) footfalls. We will discuss whether the memory which permits the subject to recognize these waveforms is adequate to enable him to perform cross correlation in the detection process, as for the SKE and SKEP models. [This work was supported by the Armstrong Cork Company.]
Nonuniform Spherical Radiation Through Thick Shells
Authors: Yeh G. C. K. , Molloy C. T.
Published: November 2005

The work previously done on uniform radiation through thick spherical shells has been extended to cover arbitrary, nonuniform radiation. A spherical transducer is surrounded by a fluid medium that is in turn surrounded by a thick viscoelastic shell. The shell is immersed in a fluid medium of infinite extent. Functions have been derived that define the pressure field due to the transducer that is driven sinusoidally with a prescribed radial velocity amplitude over its surface. The inverse problem is also solved, namely: to find the radial velocity distribution on the transducer which will produce a prescribed pressure field. These results have been used to study the effect of the shell upon the directivity pattern of the transducer and the effect of the shell upon the transducer velocity pattern when it is producing a prescribed pressure field. The insertion loss due to the shell has also been examined. Numerical calculations illustrating these effects are presented.
Radiation of Pistons and Rings on Oblate and Prolate Spheroidal Baffles
Authors: Blizard Marvin A. , Dillon James F.
Published: November 2005

The radiation impedance, self and mutual, and nearfield pressure of finite pistons and rings on oblate and prolate spheroidal baffles have been computed for several combinations of radiator size, ratio of height-to-diameter (α), and of the frequency parameter h(h = Kd/2), where K is the wavenumber and d is the interfocal distance of the spheroid). These results were obtained by substituting numerical values of the oblate and prolate spheroidal wave-functions (recently computed at NRL by Hanish et al.) in the infinite series solutions of Nimura and Watanabe. For the oblate case, 0.1⩽h⩽12.0 and 0⩽α⩽0.8944 (Nimura and Watanabe gave results for 0.01⩽h⩽4.0 and α=0). For the prolate case, 0.1⩽h⩽10.0 and 1.005⩽α⩽10.0 (Nimura and Watanabe gave results for 0.06⩽h⩽6.0 and α=1.8). These calculations provide a compilation of numerical values for impedance and nearfield pressure in ranges of h, α, and radiator size, heretofore never obtained from an exact infinite-series solution.
Numerical Approach to Pattern Synthesis
Authors: Little D. F.
Published: November 2005

In the past, many methods of synthesizing patterns of radiated energy have been advanced for special situations. Modern computing techniques make possible a direct approach applicable to arrays of general geometry and to general modes of excitation. Furthermore, prescribed patterns are not constrained to special mathematical forms. For application of the method, it is necessary to obtain experimentally or analytically a transformation matrix—probably nonsquare—which connects boundary values on the array with farfield pressures. The problem is solved by generating the generalized inverse of the matrix. A description and analysis of the method as well as the following results are included in the discussion: (1) side-lobe reduction of a pattern from a band aperture on a sphere was accomplished without substantial changes in output power or radiation impedances; (2) a pattern with a 90° beamwidth and no side lobes was synthesized from a line array; (3) a pattern with a 15° beamwidth and “back radiation” 20 dB down was computed using two columns of cylinders and taking account of individual element patterns.
Special Relationships between the Farfield and the Radiation Impedance
Authors: Sherman Charles H.
Published: November 2005

Some new relationships between the sound pressure at certain points in the farfield and the radiation impedance for certain acoustic sources have been derived from the Helmholtz integral formula. Under special conditions these relationships reduce to exact analytical solutions of problems that can otherwise only be solved numerically. For example, for a cylinder of arbitrary cross sectional shape with the ends vibrating uniformly and the sides motionless the farfield pressure in the direction of the cylinder axis is simply related to the radiation impedance. Such relationships provide helpful checkpoints for evaluating the success of some of the elaborate numerical methods which are currently being developed for attacking previously unsolved acoustic radiation problems with large digital computers. In certain cases, they can also provide new methods for determining radiation impedance from farfield calculations or possibly from farfield measurements. [Work supported by U. S. Navy Underwater Sound Laboratory.]
Numerical Methods for the Computation of Acoustic Radiation Functions
Authors: Martin G. E.
Published: November 2005

During the last decade, the large scale digital computer has become available to almost all scientists. The speed and accuracy of such machines has led some people to use mathematical methods that are not always appropriate. The primary purpose of this paper is to discuss some numerical methods for the improvement of the convergence of series encountered in acoustical theories. This paper is restricted to general comments and a discussion of one special case, namely the mutual mechanical impedance between circular pistons in an infinite plane rigid baffle, which has been represented by Pritchard as a double or single series of Bessel function products. If the separation of the two pistons is large as compared with the diameter of the pistons, the series can be represented to sufficient accuracy by its partial sum of a very few terms. On the other hand, if the separation is only slightly greater than the diameter, a large number of terms must be included in the partial sum. Methods for reducing the numerical computations and/or improving the accuracy of results have been studied. An integral method has been used with excellent success.
Wave Propagation across an Interface between Solid and Fluid Bounded Media
Authors: Miller G. K. , Hixson E. L.
Published: November 2005

Stress-wave propagation conditions across a plane interface between a cylindrical solid rod and confined fluid column are determined. This is done by expressing the displacement and stress fields as infinite sums over the eigenvalues found from dispersion relations resulting from the appropriate wave equations and transverse boundary conditions. To obtain numerical results, these sums are truncated and the interface boundary conditions are imposed at enough points along a radius to solve for amplitude coefficients in the truncated series. The number of terms can be increased to satisfy the boundary conditions everywhere to an arbitrary degree of accuracy. For the case of nylon to water, fields are calculated in both media from which intensity, power flow, and transmission loss are determined. New information is obtained about the stress and displacement fields as a function of frequency, axial and radial position. An end resonance similar to that of a free bar is found at which practically no energy couples to the water. [Research supported in part by the Office of Naval Research, The Link Foundation, and Department of Defense's Joint Services Electronics Program.]
Intelligibility of Individual Consonant Sounds Distorted by Infinite Peak Clipping
Authors: Joseph Maurice E.
Published: November 2005

Previous experiments on infinite peak clipping, using whole-word intelligibility as criterion, have shown that speech may retain high intelligibility when relative amplitude information in the waveform is eliminated. To determine whether this effect holds true for all speech sounds or whether individual phonemes are affected to a different degree, in the present experiment 10 listeners phonetically transcribed infinite-peak-clipped nonsense words tape recorded by three talkers. The test materials were based upon a corpus of six plosive and six fricative consonants, voiced and voiceless, combined with five vowels in VCV utterances. Eight syllable types containing the twelve consonants provided a controlled context with equal response alternatives for each stimulus. A differential effect of clipping was evident: dental fricatives were severely degraded in intelligibility, while plosives and alveolar fricatives tended to remain relatively unaffected. Intelligibility of voiced versus voiceless sounds was not differentially affected by clipping. Confusion matrices revealed that most errors occurred within the same voicing or manner-of-articulation category.
Selecting an Intelligibility Test for Communication System Evaluation
Authors: Williams Carl E. , Hecker Michael H. L.
Published: November 2005

A variety of intelligibility tests are available for evaluating speech-communication systems. These tests have certain advantages and limitations that must be considered in terms of the particular requirements of a given evaluation task. Because any single test provides only some of the desirable features found among all tests, the selection of a test is often a compromise. To facilitate an optimal selection, it is suggested that four generalized requirements be rank ordered according to their importance in a given evaluation task: (a) the need to diagnose specific system shortcomings, (b) the need to discriminate among highly intelligible systems. (c) the need to use speech material that provides a representative sampling of the sounds occurring in everyday speech, and (d) the need for rapid test administration and scoring. Suggestions are made for the development of a new test that would hopefully incorporate more desirable features and thus reduce the present restrictions encountered in the selection of a test.
Speech Sounds in Atypical Environments
Authors: Speakman Jerry D.
Published: November 2005

Unusual breathing environments such as those containing helium are being considered for future manned space systems. In the study reported herein, the physical acoustic characteristics of speech generation were investigated for helium concentrations of 0%–70% at pressures from sea level to 258 mm Hg. An electromechanical-acoustical model of the vocal tract for the sustained phonetic vowel sounds of [i] (eat), [o] (lost), and [u] (boot) was utilized to determine the shift in formant frequency and the change in acoustic power radiated relative to that for normal air. For comparison purposes, the relative acoustic powers were calculated for the sss and th fricatives, some simple ideal acoustic generators and moving voice coil-type loudspeakers; in addition, loudspeaker directivity characteristics and power output were experimentally measured. Previously noted impaired communication capability in these environments can be attributed to speech spectrum changes due to the nonuniform power reduction of vowels and consonants and changes in formant frequency and directivity.
Volume-Scattering Observations in Puget Sound and Nearby Waters
Authors: Moose P. H.
Published: November 2005

In March of 1967, observations of volume scattering at 28.5 kHz were made in Puget Sound and nearby waters. Both day and nighttime measurements were taken in eight sequences, spaced over several days, at each of four stations. Pulse width of 1, 3 and 10 msec were transmitted, the shorter pulses having a greater ability for resolving organisms. The observed return consisted of a continuous envelope of reverberation, plus individual echoes from single scatterers. A nighttime upward migration of the scattering layer was observed at most stations. At two stations the average volume scattering coefficient (Sv) attained a value of −46 dB (re: yd2/cubic yd) at a depth of 100–200 ft. The average value of target strength for the 395 individual targets observed was −40 dB, and the extreme values were −85 and −29 dB.
Some Applications of Meteorology to Underwater Ambient Noise Studies in Block Island Sound
Authors: Huff Llyod C. , Williams Robert G.
Published: November 2005

Turbulent atmospheric boundary-layer theory is applied to wind observations made over a shallow-water embayment to explain variations in ambient noise levels. Broad-band ambient-noise data for sea states up to 3 obtained at a fixed receiving site are presented for a shallow water acoustic test range in Block Island Sound. Hourly wind-speed averages are analyzed by means of spectra and covariance functions in order to compare the frequency composition of the acoustic and meteorological data. The power spectrum computed from the record of ambient noise pressure level as a function of time has significant peaks centered on frequencies of 0.04 and 0.10. Similar peaks at the corresponding frequencies are present in the spectra of wind speeds. The results of this experiment suggest that for wind speed fluctuations of less than 0.33 nonlinear effects of the wind are relatively unimportant in the generation of ambient noise.
On the Vibration of an Elastic Plate on an Elastic Foundation
Authors: Yen David H. Y. , Tang S. C.
Published: November 2005

This paper is a study of the vibration of an elastic plate under a time-harmonic point force. The plate is infinite in extent and rests on an elastic foundation. This study is made on the basis of the improved (Timoshenko) plate theory. The mathematical problem is to seek a fundamental solution of the time-reduced plate equation of the improved plate theory. Such a fundamental solution is constructed by the distributional Fourier transform method. From the explicit expressions of the fundamental solution is examined in detail the behavior of the fundamental singularity as a function of the vibration frequency and the foundation stiffness. Also, it is found that several types of plate resonance may occur depending upon the combination of the vibration frequency and the foundation stiffness. The paper is concluded with a discussion on how to construct integral representations for steady-state vibrations (Green's functions) for finite plates. [Research supported in part by the National Science Foundation.]
Behavior of Complex Propagation Roots in Thick and Thin Cylindrical Shells
Authors: Frymoyer Edward M.
Published: November 2005

On the basis of linear elasticity analysis, the set of modes, which may exist in an infinitely long cylindrical shell, have real, pure imaginary, and complex propagation numbers. Previous investigations, except for a recent paper by McNiven et al. [J. Acoust. Soc. Am. 40, 1073–1976 (1966)], have concentrated almost entirely on the real branches, but the complex and imaginary branches are important when general boundary conditions of a finite shell are considered. The complex branches of the mode dispersion curves for elastic curves in an isotropic cylindrical shell occur at lower frequencies than in a solid cylinder of the same dimensions. The modes describe the end distortion displacement component in the characteristic vibrations of a finite cylinder. The change from thin to thick shell behavior is traced. The complex branch intersects on the imaginary plane for thin shells and on the real plane for thick shells. The exact transition from thin to thick shell behavior is a function of Poisson's ratio. For a Poisson's ratio of 0.3, it occurs at a thickness/mean radius ratio of 0.65 for the axially symmetric case. The results of approximate analysis based on thin-shell theory (Flügge) and thick-shell theory (Mirsky-Herrmann) are compared to three-dimensional linear elasticity analysis. For thin shells, the approximate analysis reproduces the full low-order three-dimensional branches in detail. [This investigation was performed at the Ordnance Research Laboratory under U. S. Naval contract with the Naval Ordnance Systems Command (NOSC) and the Office of Naval Research (ONR).]
Vibration of Cellular Shells
Authors: Hayek Sabih I. , Patel Manu C.
Published: November 2005

A method is presented for determining the natural frequencies of an elastic cellular shell of finite length. The shell is made of two concentric shells, with equally spaced ring stiffeners placed in between. For the sake of formulation, the shell is replaced by an equivalent multilayered solid-wall shell, the layers being homogeneous and anisotropic. The equations of motion are obtained by Hamilton's principle. The natural frequencies are computed for various shell geometries and mode numbers.
Response of a Conical Shell to a Turbulent Boundary Layer Pressure Field
Authors: Chandiramani K. L.
Published: November 2005

A thin truncated conical shell can be looked upon as a series of cylinders of varying diameters. This point of view, in conjunction with some well-known vibration properties of rectangular flat plates, circular flat plates, and cylinders, yields an approximate description of the vibration properties of conical shells. Comparison with available experimental results is encouraging. The same approximate approach is used in a slightly different form for estimating the vibration response of a conical shell to a turbulent boundary-layer pressure field. Response is found to increase gradually from the smaller end of the conical shell to the larger end.
Vibrations of an Oval Ring
Authors: Brigham G. A.
Published: November 2005

Love's equations of a curved rod in flexure are applied to an oval ring having symmetry about an X axis and a Y axis. The original set of equations is then reduced by successive approximations to one relating the normal deflection and the applied forces. For an oval shape similar to that used by Marguerre and later by Romano and Kempner, the deflection may be expressed as a series of Mathieu functions, which are the normal modes. An ellipse may be approximated by this method if the ratio of minor to major axis ⩾23. Comparison is made between the predicted and measured deflections and natural frequencies of a 1-in. thick aluminum oval module of axis ratio ≐ 12 which are commonly used in the construction of flextensional transducers. The model is restricted to an eccentricity parameter less than unity.
Existence and Uniqueness of Solutions of Integral Equations for Acoustic Radiation and Diffraction Problems
Authors: Noble Ben
Published: November 2005

Although a radiation or diffraction problem may have a unique solution, certain formulations of the problem may result in integral equations that do not have solutions, or whose solutions are not unique. Typically, when considering the exterior problem, trouble may occur at frequencies corresponding to resonance in the interior of the body. This paper summarizes our present state of knowledge concerning existence and uniqueness. The implications in connection with approximate numerical solution of the integral equations are examined. Methods are discussed for obtaining integral equations that always have unique solutions. The theoretical advantages and disadvantages of various methods will be compared.
Approximate Numerical Representation of the Helmholtz Integral Operator
Authors: Pohler R. F.
Published: November 2005

The discussion is concerned with numerical aspects of solving the Helmholtz integral equation of acoustics. The various numerical techniques which are used are interpreted in terms of an abstract vector space. From this point of view, the system of algebraic equations which approximates the integral equation corresponds to a representation of the integral operator in terms of a set of basis functions which spans part of the vector space. The special properties of the integral operator for separable geometries are reviewed, and the rôle of the associated eigenfunctions as a basis set is discussed. The influence of the given boundary conditions on the choice of the basis set is considered. Numerical examples which compare results using different basis functions are given.
Distribution of Damage in Random Fatigue
Authors: Pulgrano I. , Bernstein M.
Published: November 2005

The rate at which Palmgren-Miner damage accumulates under narrow-band random stress oscillations is well known. Not as well known, however, is the portion of the total damage that is attributable to peaks lying within a given stress range. It is of interest to know whether it is the relatively infrequent high-level stress peaks or the much more frequent peaks at low levels that contributes most to the total damage. A simple extension of previous work permits the development of a damage distribution function, which gives the relative contribution of peaks in any stress range to the total damage. The results indicate that most of the damage is produced by peaks lying in a stress band that is about 2σ wide. For 2024-T3 aluminum, which is considered as a particular case, the damage-producing band is centered on about 2.7σ and it contains about 23% of the total number of peaks.
Shock Expansion Tube as a Potentially Useful Tool for Sonic Boom Simulation
Authors: Dahlke H. E. , Kantarges G. T. , Van Houten J. J.
Published: November 2005

Considering the emphasis being placed on studies of community reaction to sonic-boom phenomena, the simulation of these pressure transients has increased in economic and scientific importance. The expansion of shock waves produced by burst diaphragm techniques similar to those used in the shock tube provides waveforms that approximates the subjective pressure experienced during the onset of a sonic boom. Conventional shock-tube analysis, combined with Whitham's theory concerning the gas dynamics of a nonuniform channel, provides the basis for predicting the pressure time history of the waves generated in the expansion tube. Two shock tubes in a unique arrangement are attached to one acoustic horn. When the two burst diaphragms are subsequently punctured by an electrodynamically driven plunger, a pressure signature is generated which closely resembles the waveform subjectively experienced by an observer of a sonic boom. Experimental data are presented indicating the wide range of pressure amplitudes and pulse durations achievable utilizing this tool. [Work supported by the National Aeronautics and Space Administration, Langley Research Center.]
Sensitivity of Auditory-Nerve Fibers to Tonal Stimuli
Authors: Kiang N. Y. S. , Marr E. M. , Demont D.
Published: November 2005

Spike discharges were recorded from auditory-nerve fibers in anesthetized cats. “Thresholds” for tone bursts at the characteristic frequency (CF) were determined by audiovisual detection of spikes synchronized to the bursts. “Thresholds” for continuous tones were determined from the spike rate versus stimulus level function. Both sets of thresholds give comparable graphs of threshold versus CF. When thresholds are expressed as peak-to-peak stapes displacement the points roughly describe a curve that declines 40 dB per decade of frequency. Thus, fibers with low CF tend to be less sensitive than fibers with higher CF's. For individual cats, the spread of thresholds for units with similar CF is approximately 20 dB. These findings have implications for models of excitatory mechanisms in the cochlea. In addition, they fail to support the concept that (aside from frequency-dependent differences) separate populations of auditory-nerve fibers exist with large threshold differences. [Work supported by NIH grants, the Joint Services Electronics Program, and a NASA grant.]
Spontaneous Firing Characteristics of a Computer Model of the Peripheral Auditory System
Authors: Lummis Robert C. , Lundry Elizabeth A.
Published: November 2005

A model of the peripheral auditory system was programmed on a digital computer. The components of the model simulate the mechanical response of the middle ear and basilar membrane, and the hypothesized behavior of the hair cell and the first order neuron. In the model, the hair cell releases excitatory quanta at random times at an average rate that is a function of basilar membrane deflection. These quanta produce excitatory postynaptic potentials that add linearly in the neuron and cause firing when a threshold is exceeded. The threshold varies to simulate refractory effects. A number of parameters in the model were varied and the statistics of the resulting spontaneous firing were compared with physiological data published by Kiang et al. The choice of parameter values is most severely restricted by the requirement that the mode of the firing interval histogram be independent of the firing rate.
Structural Organization of Response Properties of Single Units in Primary Auditory Cortex of Cats
Authors: Abeles M. , Daly R. L. , Goldstein M. H. , McIntosh J. S.
Published: November 2005

Single unit data from AI of immobilized unanesthetized cats were analyzed to investigate correlations between gross aspects of the arrangement of cells and coding of simple acoustic stimuli (clicks, noise bursts, tone bursts from 500 Hz to 50 kHz at moderate intensities). Twenty electrode tracks with 160 well-isolated units were located in histological sections. Angles between these tracks and anatomcial columns ranged between 1° and 63°. Consecutive units within each track having some specific common response property were identified as runs for that property. A runs test analysis indicated that for tone bursts and for clicks responsive units were clustered within the tracks. When runs of units with common sensitive frequency ranges were analyzed, long runs were found more frequently in the tracks closely aligned with the anatomical columns. However, there was no evidence that runs of responsiveness to tone bursts, to clicks, or to noise bursts were highly organized in the direction of the columns. [Work supported in part by the Public Health Service, U. S. Department of Health, Education and Welfare, and by the U. S. Air Force Office of Scientific Research.]
Kinematic Considerations for Deriving Laryngeal Cartilage Motions from Laryngoscopic Photographs
Authors: Broad David J.
Published: November 2005

The motions of the laryngeal cartilages, though taking place in three dimensions, are sufficiently constrained by the laryngeal joints to permit their derivation from two-dimensional projections such as those provided by laryngoscopic photographs. To accomplish this, equations relating the degrees of freedom of the cartilage system to dimensions measurable in the laryngoscopic view are developed and solved. The degrees of freedom are taken to be the tilt of the thyroid cartilage, the rotation of the cricoid cartilage relative to the thyroid, the rocking motion of the arytenoid cartilages on the cricoid, and the gliding motion of the arytenoid cartilages on the cricoid. The measurable dimensions selected are the medial-lateral distance between the vocal process and apex of the arytenoid cartilage, the lateral displacement of the apex, the anterior-posterior distance between the vocal process and apex, and the length of the membranous part of the local folds. The selection of these dimensions in this same order facilitates a simple solution to the equations. To implement the results still requires the estimation of certain anatomical constants.
Application of Some Acoustic Measures for the Evaluation of Laryngeal Dysfunction
Authors: Koike Yasuo
Published: November 2005

Perturbation of pitch period and fluctuation amplitude of voice were studied both on normal subjects and on patients with laryngeal diseases. Sound was extracted during vowel phonation by a contact micropohone through the skin and pretracheal tissues. Special attention was paid to the initial period of phonation; the data from this period were compared with those of steady periods of phonation. The investigations indicate marked perturbation of pitch and considerable fluctuation of amplitude exist in the initial period. These findings are closely related to the type of initiation. Fundamental frequency also affected the pitch perturbation and amplitude fluctuation. Pathologic cases showed different values according to the degree and nature of the laryngeal involvement in the disease process. The potential and limitatation of applying these measures for screening and evaluating laryngeal disorders are discussed.