bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Air Force Hearing Data
Authors: Gerber Sanford E. , Bien Ann
Published: September 2005

This program was intended to evaluate the effectiveness of the Air Force Hearing Conservation Program in light of several years experience. More than 82 000 audiometric tests on over 58 000 people were transferred to punched cards, processed by a large digital computer, and analyzed. In spite of a large amount of missing, illegible, or otherwise unusable data, it was possible to derive much useful information from the Hearing Data Repository. Benefits from the use of ear protection were not apparent, which leads one to question if people really use ear protection when they should or if they use it properly. The information in the repository on noise exposure, past and present, was not in a form permitting more meaningful interpretations. Further, it was found that the sample used had poorer hearing than a sample of the general population used as a reference, and one would want to derive an Air Force reference. [This program was sponsored by the School of Aerospace Medicine.]
Auditory Sensitivity and Pressure at the Tympanum
Authors: Creelman C. Douglas
Published: September 2005

What is the effect on hearing sensitivity of stress on the eardrum from differential air pressure? A hard earphone casing was fitted to provide small static pressure (up to 10 in. H2O) and measures were made of sensitivity to pure tones at various frequencies. Sensitivity was impaired up to 10 dB at low frequencies by pressure, and the amount of loss varied directly with amount of pressure. High frequencies (presumably above the resonant frequency of the middle ear) showed no loss of sensitivity. There was no reliable difference between effects of positive and negative pressure. The results suggest indirectly that the tensor tympani muscle of the middle ear might serve as a low-frequency noise suppressor. A forced-choice procedure was developed for later tests, which enables rapid estimation of the stimulus energy necessary to achieve a fixed predetermined level of performance. Some characteristics of the procedure are described.
Judgments of the Relative and Absolute Acceptability of Aircraft Noise
Authors: Bishop Dwight E.
Published: September 2005

In exploring the possibility that people can ascribe an absolute scale of acceptability for aircraft noise, subjects from airport neighborhoods judged, in separate tests, the relative and the absolute acceptability of noise produced by actual aircraft flyovers and by recorded flyover signals. The flyover noise judgments were made indoors and outdoors at two locations near the Los Angeles International Airport. Most subjects judged both approach noise and takeoff noise (produced mainly by jet aircraft). Judgments were compared with the maximum perceived noise level occurring during the flyovers. Little difference was observed in acceptability rating scores for approach and takeoff noise or for actual and recorded noise signals. However, a shift in ratings between outdoor and indoor judgments occurred similar in magnitude to that observed in earlier British tests. The relative judgment tests also showed little difference between ratings of takeoff and approach noise or live and recorded signals. However, the results indicated that a larger change in perceived noise level was required for a doubling (or halving) of the acceptability rating than originally assumed in developing the perceived noise level scale. [Work supported by the Systems Research and Development Service, Federal Aviation Agency.]
Sound Transmission by Thin Cylindrical Shells
Authors: Raelson Verner J.
Published: September 2005

An experimental study has been made of the sound field in the interior of a thin circular cylindrical shell exposed to a diffuse wide-band sound field. The sound field was explored point by point and noise reduction, defined as the dB difference between the SPL at a point and the SPL in the diffuse field exterior to the shell, has been investigated as a function of shell geometry.
Free Vibrations of Thin Isotropic Oblate Spheroidal Shells
Authors: Penzes Leslie E. , Burgin George
Published: September 2005

The free-vibration problem of a thin, isotropic, oblate spheroidal shell was solved by Galerkin's method. Membrane theory and harmonic axisymmetric motion were assumed to derive the differential equations of motion. The equations of motion lead to two ordinary differential equations with variable coefficients. The two differential equations can be reduced to one ordinary second-order differential equation with variable coefficients. This eigenvalue problem is solved by Galerkin's method. It was shown that Galerkin's solution for the oblate spheroid yields the exact solution for the sphere as the eccentricity of the oblate spheroid goes to zero. It is shown that two sets of frequencies exist for the oblate spheroidal shell. Galerkin's method converges rapidly for those of the lower set. After the frequencies are determined, the tangential displacements are obtained as solutions of a homogeneous system of equations. For numerical illustration, an oblate spheroidal shell with eccentricity equal to 0.688 was considered.
Study of Acoustic Scattering by Hollow Metallic Spheres
Authors: Diercks K. J. , Hickling Robert
Published: September 2005

Measurements of acoustic backscattering from hollow, air-filled, and flooded metallic spheres are described. Inside diameter/outside diameter ratios of 0.95, 0.8, 0.6, 0.4, and 0.0 were investigated (o.d.=5.00 in.). The ka range was from 1 to 25. Measurements of echo amplitude (reported as target strength) vs frequency and of echo-pulse form at specific frequencies, for both long and short incident-pulse lengths, are shown. Differences in target-strength value obtained with different measurement techniques are discussed. Experimentally obtained amplitudes and echo forms are compared with computed values [see R. Hickling, J. Acoust. Soc. Am. 36, 1124–1137 (1964)]; agreement, in general, is quite good. For the air-filled targets, average target strength is shown to be independent of wall thickness, while with the flooded targets average target strength increases approximately 5 db from the thickest (i.d./o.d.=0.95) walls. [This work was done under contract with the U. S. Office of Naval Research and U. S. Naval Ordnance Test Station.]
Three Experiments on Diffraction from Periodic Surfaces
Authors: Papadakis Emmanuel P.
Published: September 2005

Three experiments were performed to demonstrate the presence of the first-order diffracted ray from a periodic surface. In these experiments, the incident wave was at grazing incidence and the direction of surface periodicity was in the plane of incidence. The direction of propagation of the first-order diffracted ray agreed with the prediction of Y. P. Lysanov [Akust. Zh. 1 (1954)]. In particular, when λ (wavelength)=L (surface period), the diffracted ray was normal to the periodic surface. One experiment used CW spherical waves in an anechoic chamber with a periodic floor. As the microphone traversed the floor, the pressure dipped once per period. The dips were symmetric and smooth only when λ=L. The other two experiments used pulsed plane waves of ultrasound. In one, the longitudinal ultrasonic waves traveled in a rectangular aluminum block with grooves milled into one face parallel to the beam axis. The opposite, parallel face supported a longitudinal receiving transducer. When λ=L, the plane first-order diffracted wave produced multiple echoes between the grooved surface and the opposite face. In the other ultrasonic experiment, the waves traveled in liquids parallel to the grooved bottom of a tank. An immersion transducer with its axis normal to the grooved surface detected a maximum signal when the ultrasonic frequency f was adjusted to make λ=L. The velocities found by using the relation υ=λf agreed with pulse-echo measurements to 2%–3%
Method for Evaluating Ultrasonic Transducer Loading Effects on Transit-Time Measurements
Authors: Kammer E. W.
Published: September 2005

An ultrasonic measurement technique and data-processing scheme are described in which time intervals are measured between transducer resonance oscillations within the structure of successive unrectified echos rather than between echo leading edges. When plotted against the transducer resonance period, these time intervals determine a family of straight lines which have a single point in common at zero transducer resonance period. It is proposed that the transit time associated with this common point is the true travel time for sound in the medium unperturbed by transducer effects. Longitudinal-mode data are presented for materials ranging in density from tungsten (19) to magnesium (1.74). While the overestimate of the transit time is negligible for tungsten, it becomes increasingly evident with materials of lower density. For example, if quartz transducers, which are resonant in the 5- to 10-Mc/sec range, are bonded to a silica specimen 2 cm thick, the true roundtrip transit time may be overestimated by several percent if loading effects are ignored, whereas the experimental uncertainty of measurement could be less than a few tenths of 1%.
Generation of Transient Acoustic Impulses, Using a Novel Underwater Spark Sound Source
Authors: Warner R. A. , Wright H. A.
Published: September 2005

Investigations of an underwater, impulsive-sound-generating device are described. The device employs electric spark discharge between two volumes of sea water that are separated by a dielectric containing a small aperture. The spark occurs in and adjacent to the aperture, remote from the metal electrodes. Parametric relationships are shown for the pressure-time characteristics of the impulses radiated from single sparks as functions of circuit variables, aperture-electrode geometry variations, and static pressure. Results of input energy level variations up to 5000 J are reported, with corresponding peak-pressure outputs at 1 yd ranging up to 130 dB re 1 dyn/cm2 and pulse durations of 50 μsec. Parallel operation of more than one spark is also described, as are aperture deterioration and failure mechanisms encountered during the investigation. It is concluded that the operating characteristics of the device offers advantages within limits where precisely controlled, transient acoustic impulses of relatively low energy are desired.
Electropneumatic Acoustic Generator
Authors: Fiala Walter T. , Hilliard J. K. , Renkus J. A. , Van Houten John J.
Published: September 2005

Research and development leading to an electropneumatic acoustic generator capable of producing in excess of 6 kW of acoustic power is reviewed. The modulation of pneumatic power by the use of an electrodynamically controlled valve provides a transducer capable of producing either random or complex periodic signals. The development of this valve required considerable investigation of materials and fabrication techniques to establish the necessary compliance and optimized moving-valve structure to obtain a reliable sound generator. The efficiency of this generator with respect to the pneumatic power supply is as high as 17%. The evaluation of the power spectrum, amplitude distribution, and nonlinear characteristics of the transducer is performed in a progressive-wave tube. Current developments include units that produce considerably more acoustic power or extend the useful frequency range of the sound generator.
Direction Pressure-Gradient Microphones for Low Frequencies
Authors: Beavers Bob R.
Published: September 2005

Pressure-gradient microphones of first and higher orders formed by the differential output of pressure sensors can provide directivity at low frequencies in a small package. These directivity patterns are given by the relationship F(θ)=cosn θ, where n represents the order of the gradient. By the inclusion of time delays in the formation of the pressure gradient, uniaxial response and improved directional efficiency can be obtained. For the case of colinear sensors, an analysis is given for the determination of the time delays that give the maximum noise suppression under a uniformly distributed random-noise field. The effect of nonuniform response in the individual sensors has been studied and found to be critical for the lowest frequencies.
Directivity of a Transducer Mounted inside a Thin Shell
Authors: Barger James E.
Published: September 2005

Directivity patterns of a cylindrical transducer excited so as to generate a directive acoustic field have been computed, both with and without a concentric thin cylindrical shell around the transducer. The effect of the shell is observed as an increase of several minor-lobe amplitudes and a decrease of the directivity index. The largest beam-pattern distortion is found to occur at frequencies near shell-resonance frequencies, which are associated with membrane (extensional) strain in the shell rather than bending strain. The transmission loss for the major lobe, defined as TL=−10 log [(major-lobe intensity with shell)/(major-lobe intensity without shell)] is also presented. It is found that the transmission loss suffered by the major lobe on transmission through the concentric shell is less than the transmission loss suffered by a plane wave at the same frequency on transmission through a flat plate of the same material and thickness as the shell material. [Work performed under subcontract to the Raytheon Company, Submarine Signal Division, Newport, Rhode Island.]
Noise Control in Air-Handling Systems
Authors: Sanders Guy
Published: September 2005

This summary paper describes the measures that can be taken to reduce the noises in air-handling systems. Noise control applicable to heating and air-conditioning systems, forced-draft fan installations, as well as gas-turbine and jet-engine facilities is described. In addition, techniques useful in the reduction of noises produced by high-pressure venting, air compressors, and internal-combustion engines are explained. Considerations peculiar to each of the abovementioned air-handling systems are discussed.
Effect of Noise at One Ear on the Detection of Signals at the Other Ear
Authors: Mulligan B. E. , Wilbanks W. A.
Published: September 2005

Detection of a tonal signal in noise at one ear improves in proportion to the level of correlated noise in the “off” ear up to the point of equal noise levels in the two ears. A given level of correlated noise at the “off” ear produces a nearly constant improvement in detection over monaural masking independent of the signal-to-noise ratio in the ear receiving the signal. A given level of uncorrelated noise at the “off” ear, however, has the opposite effect. It produces a nearly constant decrease in detection over the monaural condition for various signal-to-noise ratios in the “on” ear.
Interaural Noise Correlation and Monaural Signal Detection
Authors: Whitmore John K. , Wilbanks W. A.
Published: September 2005

Data are presented on the effects of interaural noise correlation on detection for monaural tonal signals of 250, 500, 1200, 3000, and 4000 cps. Correlations of +1.00, +0.90, +0.75, +0.50, +0.25, and zero were obtained by mixing correlated and uncorrelated noise in the channels to the two ears. For signals of 250 and 500 cps (200 msec), masking-level differences (MLD's) on the order of 9 dB were obtained (NoSm vs NuSm). These MLD's diminished rapidly as the interaural noise correlation was decreased from unity. These findings are in agreement with earlier studies. At 1200 cps the MLD was about 4 dB. Again, detection dropped quite rapidly as the correlation was decreased from unity. No appreciable MLD's were obtained for signals of 3000 and 4000 cps. Although the evidence is not compelling, the data suggest that at low frequencies purely monaural detection (NmSm) is, if anything, slightly superior to NuSm.
Some Parameters of Contralateral Masking
Authors: Zwislocki J. , Damianopoulos E. D. , Buining E. , Glantz J.
Published: September 2005

A masking tone presented to one ear produces a threshold shift in the contralateral ear within a narrow frequency range surrounding the frequency of the masker. This is true when sound transmission across the head is effectively eliminated. The effect has been studied as a function of sensation level and duration of the masking tone for various frequency differences between the masking and the masked tones. Interaural sound transmission was minimized by using insert phones. In view of the large number of parameter values, von Békésy's tracking method has been found suitable for the investigation. The obtained data are interpreted in terms of neural excitation and inhibition patterns.
Antiphasic Versus Monaural Detection as a Function of Duration
Authors: Green David M.
Published: September 2005

The detectability of a 250-cps gated sinusoid partially masked by continuous noise was measured in three detection situations: (1) a simple monaural condition (SmNm), (2) the signal in one ear, the noise in phase in both ears (SmN0), and (3) the signal in both ears but out of phase by 180° at one ear, the noise in phase in both ears (SπN0). The three signal durations were used: 1/100, 1/10, and 1 sec. The shape of the psychometric function (i.e., the percentage correct in two-alternative forced-choice versus the signal-to-noise ratio in decibels) is essentially the same for all conditions and durations except for displacement by a constant number of decibels. The signal is about 10 dB easier to hear in the SmN0 condition than the SmNm condition and about 17 dB more detectable in the SπN0 condition than the SmNm condition at all durations. [This research was supported in part by National Institutes of Health, U. S. Department of Health, Education, and Welfare, and by the National Science Foundation.]
Effect of Bandwidth of Masking Noise on Detection of Homophasic and Antiphasic Tonal Signals
Authors: Bourbon Walter T. , Jeffress Lloyd A.
Published: September 2005

Langford and Jeffress [J. Acoust. Soc. Am. 36, 1455–1458 (1964)] report evidence that the bandwidth involved in masking an antiphasic signal, N0 Sπ, is considerably wider than that involved in monaural or homophasic masking. The present paper describes a study of the effect of narrowing the noise band used for masking a 500-cps tonal signal from 100–3000 cps to about 10 cps in width. The same band of noise was employed for both the diotic conditions N0 S0 and the antiphasic N0 Sπ. In the former case, no improvement in detection occurred until the bandwidth was less than about 150 cps, but in the latter substantially increased MLD's were found for bandwidths as great as 300 cps. The rate of improvement of detection under the antiphasic condition was much more rapid as the bandwidth was narrowed than was the case for the diotic condition. The findings support von Békésy's idea that some kind of neural “funneling” assists in narrowing the band of frequencies involved in monaural detection. In antiphasic detection, the bandwidth may depend solely on the mechanical filtering provided by the cochlea without assistance from neural funneling. [Work supported under a grant from the National Aeronautics and Space Administration.]
Masking-Level Differences and the Form of the Psychometric Function
Authors: Egan James P. , Lindner William A. , McFadden Dennis
Published: September 2005

Psychometric functions were determined for various interaural conditions; these functions show the relation between the detectability and the energy of the signal. The signal was presented in one of two temporal intervals against a continuous noise. The relation between d′ and signal energy E is approximately d′=m(E/N0)k, where m and k are constants for a particular function; 0⩽d′<4. The data indicate that k is constant for a particular observer and that m depends upon interaural conditions. Therefore, MLD=(10/k)log(mi/m0), where mi is the constant for condition i, and m0 corresponds to a reference condition. Consequently, an MLD is independent of the d′ chosen for determination of that MLD. Also, the form of the psychometric function is independent of the interaural condition. This result indicates that “release from masking” may be considered equivalent to a decrease in the noise at the input, rather than reduction in the amount of uncertainty for the observer concerning the parameters of the input. [Work supported by the U. S. Air Force Office of Scientific Research.]
Propagation of Plane Compressional Waves at Finite Amplitude in Real Fluids
Authors: Bow Y. F. , Hiedemann E. A.
Published: September 2005

The primary objective of this paper is to formulate a theory describing the distortion of a plane, initially sinusoidal, compressional wave of finite amplitude traveling through a real (nonlinear and dissipative) fluid medium that is initially undisturbed. Based on the hydrodynamical equations, a suitable nonlinear differential equation for this problem is derived by neglecting the variation of one of the “Riemann's invariants.” An approximate solution to this differential equation is obtained by assuming the existence of an implicit functional relation between the particle velocity u, space coordinate x and time t. The numerical result of this solution is in fairly good agreement with the experimental measurements and compatible with previous theories. From the existence theorem of implicit functions, a single condition is obtained, by which the general behavior of sound propagation in a dissipative medium can be more easily understood. [Work supported by the U. S. Office of Naval Research.]
Lossless Propagation of One-Dimensional, Finite-Amplitude Sound Waves
Authors: Banta Edwin D.
Published: September 2005

Lossless propagation of one-dimensional, finite-amplitude sound waves exhibits a new mathematical technique for solving the finite-amplitude-wave problem. It involves expanding the wave equation's solution in a Taylor series about the boundary, followed by use of the differential equation to replace the Taylor-series derivatives by derivatives of the boundary function. This leads to a result that is formally identical with the Lagrange expansion formula and, thereby, to stability criteria. Two examples are included, one of which reproduces a classical result, while the other one illustrates the commencement of asymmetries in a propagating, finite-amplitude wave.
Interference of Finite-Amplitude Ultrasonic Waves in Solids
Authors: Gauster W. B. , Breazeale M. A.
Published: September 2005

A unique application of the pulse-overlap methods of McSkimin [J. Acoust. Soc. Am. 22, 413–418 (1950)] and of Williams and Lamb [J. Acoust. Soc. Am. 30, 308–313 (1958)] has been made to the observation of second-harmonic generation of ultrasonic waves in solids [M. A. Breazeale and D. O. Thompson, Appl. Phys. Letters 3, 77–78 (1963)]. In this application, the dependence of the second-harmonic amplitude on the square of the fundamental amplitude produces unusual interference effects. The applicability of the method to measurement of the nonlinear distortion of finite-amplitude waves is discussed [Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation.]
Numerical Results from a Successive Diffraction Theory for Diffraction of Light by Ultrasonic Waves
Authors: Hargrove L. E.
Published: September 2005

Numerical results have been obtained from a successive diffraction theory for diffraction of light by ultrasonic waves of arbitrary waveform. [L. E. Hargrove, J. Acoust. Soc. Am. 36, 323–326 (1964)]. These are presented for the special case of ultrasonic waveforms of the finite-amplitude type (odd symmetry) and for a range of parameters wherein elementary diffraction theory is almost valid. Estimates are made of errors that would result if elementary diffraction theory [e.g.. B. D. Cook, J. Acoust. Soc. Am. 32, 336–338 (1960); 37, 172(L) (1965)] were used to calculate ultrasonic waveforms from light-diffraction spectra resulting from conditions under which elementary theory is not adequate.
Damping Constants and the Definition of Models for Cavitation Bubbles
Authors: Flynn H. G.
Published: September 2005

Two simple models—the stable cavity and the transient cavity—have been proposed as suitable representations of physical bubbles found in acoustic cavitation. Heretofore, both models have suffered from a lack of precision in their definitions. A mathematical formulation of equations of motion for a cavity has been used to study the damping of free oscillations of cavities owing to heat conduction, viscosity, and acoustic radiation. It was found that the thermal-damping constant of a cavity is a function of amplitude at the start of a cycle and that this function has a maximum. This maximum marks a transition between stable and transient cavities; for stable cavities, the thermal-damping constant increases with amplitude, while for transient cavities it decreases with amplitude. The results of this calculation suggest a fundamental definition for stable and transient cavities and a criterion for the range of their usefulness as models for physical bubbles. [Work supported by Acoustics Programs (Code 468), U. S. Office of Naval Research.]
Influence of Ocean Bottom on Explosion Bubble-Pulse Period
Authors: Epstein David
Published: September 2005

Preliminary investigation of a theoretical deduction concerning modification of an explosive waveform, due to detonation in proximity to the surface and bottom of the sea, respectively, attributed to Friedman, and presented in Underwater Explosions, by Coles, is discussed. The Friedman formulas have been verified in the surface case, but some doubt as to their applicability to bottom firings exists. Few data on “bottom firing” are readily available, but some data, suitable for analysis, have been published in an article by Ewing and Worzel. These data have been analyzed and, contrary to the Friedman formula, the predicted modification does not occur. A possible explanation of this result is that, at least in these instances, the bottom seems to behave as a liquid layer, thereby permitting uninhibited expansion of the explosion gas bubble. Recent evidence seems to reinforce this conclusion; analysis of bottom sediments near the boundary frequently indicates high porosity; consequently, the existence of this “almost liquid state” may be responsible for sharply reducing the expected increase in the bubble-pulse period.
Maxima and Minima in the Spectrum of an Underwater Charge
Authors: Weinstein Marvin S. , Christian Ermine A.
Published: September 2005

The position of the maxima in the spectrum generated by an underwater explosive charge has been considered to occur at integral multiples of the inverse of the bubble-pulse period. The spectrum of the shock wave, represented by a decaying exponential, includes a frequency-dependent phase shift, while the bubble pulse, represented by a double exponential, has a phase-invariant spectrum. When this is considered, the positions of the maxima and minima are given, to a first approximation, by tanωnτ=ωnT, where τ is the bubble pulse period and T the shock-wave decay constant. The shift from integral values increases with the order and is asymptotic to 1/(4τ). In the actual case, where the shock wave has a finite rise time, the asymptotic limit is removed and the shift continues to increase with increasing order. For low-order maxima, the over-all effect is small for shallow detonations, but becomes appreciable as the depth increases. Theoretical predictions are compared with experimental data. [Work supported by the U. S. Office of Naval Research and Advanced Research Projects Administration.]
Physical Model for Airblast Generation by Underwater Explosions
Authors: Carbonell Jaime R. , Malme Charles I. , Dyer Ira
Published: September 2005

The technique for calculating airblast pressure signatures from deep underwater explosions presented earlier [J. Acoust. Soc. Am. 36, 1033(A) (1964)] requires detailed knowledge of the interface motion. An experimental study recently completed showed disagreement with linear continuous theory—the decay of the interface velocity following its abrupt rise is position-dependent and of the order of 20 times longer than that of the underwater pulse. A physical model that explains these discrepancies is presented. It is based on the existence of one or more delaminated layers of water just below the interface, originated by reflected negative underwater pressure pulses. Quantitative predictions based on this model are in good agreement with interface-velocity data, photographic evidence, and airblast pressures recorded from deep explosions. For shallow explosions, a different mechanism applies; the “bow shock wave” originated by the supersonically rising dome and plume is the dominant feature in airblast generation. [Research supported by the U. S. Naval Ordnance Laboratory.]
Effect of Thevenin Equivalent Internal Impedance on Velocity Control and Acoustic Power of Planar Broadside Arrays
Authors: Porter David T.
Published: September 2005

A Thevenin equivalent circuit for array elements, which has an input force in series with a radiation impedance and an internal impedance ZI, is discussed. The arrays considered are 80-element, close-packed, unshaded arrays, with many different ka and ZI. Four limitations to input voltage are discussed: velocity, transducer voltage, available power, and cavitation. Velocity-limited acoustic power is maximum for infinite |ZI| (equal velocities) and worst for RI=0 and XI between −XSELF and −2XSELF. Cavitation-limited acoustic power is maximum for ZI=0, when about 3 dB more power is obtained than with equal velocities and, with steered arrays, more than 3 dB. A velocity control factor UCF=|Z12|/|ZI+ZSELF| is presented, where Z12 is the mutual impedance between nearest-neighboring pistons. Velocity-limited acoustic power decreased as UCF increased.
Theory of Spatial Processing
Authors: Stocklin Philip L.
Published: September 2005

Starting from the uniform spatial sampling theorem, a nonuniform spatial sampling theorem is developed for single-frequency acoustic fields. Using these two theorems, it is shown that, if a processing operation is known which maximizes a criterion C for the outputs of one array of spatial sampling points, then the equivalent processing operation, which maximizes C for the outputs of a different array of spatial sampling points, can be found using the uniform and nonuniform spatial sampling functions. The utility of this result is to permit direct computation of the processing operation maximizing C for a point array of unusual or complicated shape, starting from a point array for which the processing operation maximizing C is simple. Examples include a demonstration of superdirectivity as the equivalent processing operation for usual pattern formation of half-wavelength spaced point arrays, a qualitative comparison of surface versus volumetric array processing, and connection with recent work of Cron and Marsh.
Study of Underwater Horns—Single-Loading Exponential and Pseudohemispherical Horns
Authors: Muster Douglas , Christensen A.
Published: September 2005

Single-loading, axisymmetric exponential, and pseudohemispherical horns were tested under water by pulse techniques over the frequency range from 1000 to 22 000 cps. The sound source was a piezoelectric bender-type transducer in the shape of a circular disk. Both impedance and radiation measurements were made. The results are discussed in terms of the separate and joint effects of horn geometry, modes of radiation, back radiation, and the pistonlike action of the transducer. A theory is proposed to predict the behavior of the horns. Separate predictions of cutoff frequency, impedance, and radiation characteristics were made for each type of horn. The predicted behavior and the measured results are compared and found to be in reasonable agreement over the frequency range above. Planned extensions of the current work are discussed. [This work is supported by the U. S. Office of Naval Research.]
Experimental Studies in Underwater Directional Communication
Authors: Bauer B. B. , Torick E.
Published: September 2005

Previously, a scheme was suggested for sensing directional perception underwater by receiving sound with two back-to-back cardioid pattern receptors connected to earphones via a crosscoupling network that restores normal interaural delays [J. Acoust. Soc. Am. 36, 1041(A) (1964)]. To test this scheme, two experiments were performed: (1) Observers under water used calibrated earphones while the experimenter topside adjusted relative voltages to the crosscoupling network to simulate the bicardioid receptor array. The observers underwater sensed direction with an accuracy comparable to that obtained with previous in-the-air experiments. (2) Two miniature hydrophone transducers were mounted 10 cm apart and interconnected with a symmetrical phase-shift network to produce an array with a polar pattern equivalent to two back-to-back cardioid transducers, over a frequency range of 200–2500 cps. With this array in variable orientation relative to an underwater projector and with topside observers listening through earphones equipped with a crosscoupling network, the orientation of the array was readily ascertainable. [Work supported by U. S. Navy Mine Defense Laboratory.]
Use of Abbreviated Series to Describe Non-Gaussian Random Signals
Authors: Himelblau H. , Bockemohle L. P.
Published: September 2005

In a previous paper [J. Acoust. Soc. Am. 34, 732(A) (1962)], the abbreviated Gram-Charlier and Edgeworth series were used to determine probability density and distribution curves for non-Gaussian random signals as a function of the coefficients of skewness and kurtosis. Certain mathematical results were obtained that made it impossible to compare these curves directly with physically realizable random signals; e.g., negative values of probability density were obtained, the probability of exceeding the maximum possible instantaneous value of the signal was not always zero, etc. Subsequent modification of the equations have overcome these difficulties. Probability density and distribution curves are presented that may be used with physically realizable random signals.
Statistical Basis for Objective Measurement of Speech Levels
Authors: Brady Paul T.
Published: September 2005

First-order probability distributions of speech amplitudes are studied to obtain a suitable 1-dimensional measure of speech level. The logarithm of the level of the long-term syllabic waveform is found to be approximately uniformly distributed above a threshold. The average peak level (APL) is obtained by taking the time average of the log of the syllabic waveform and deriving from it the peak of the log-uniform distribution that would have produced the same average. It is shown that changes in the over-all speech level are ideally more linearly reflected by the APL than by certain other level indicators, such as root mean square or average voltages. The digital speech-level meter is described as an instrumentation of the technique used to obtain the APL. Measurements made with this meter are easily obtained and very repeatable. Although the results so far are promising, much work is yet needed to fully determine the applications of the device.
Matching Speech Cineradiography with Pseudospeech
Authors: Truby H. M.
Published: September 2005

The product of “speech synthesis” is, at best, pseudospeech, and since the neurophysiological processes operative in perception in general are little understood, the perception of pseudospeech remains particularly enigmatic. In the perception of natural speech, the ultimate cues have been postulated (Liberman) to depend upon proprioceptive stimuli arising from articulatory gestures and upon perceived differences and similarities to correspond more closely to articulatory than to acoustic features. The visual inspection of speech articulation possible with high-speed, x-ray motion-picture photography suggests the attempted fitting of pseudospeech continua to “corresponding” speech-articulation sequences, not only in the specific interest of improving the acoustic quality of simulated speech, with especial reference to timing phenomena, but also in the consequent general increase of knowledge about speech analysis, and as a contrivance for acoustically matching sustained articulation instants. Acoustically simulated “steady-state isolated vowels” and corresponding slides of typical articulatory instants are presented as an introduction to a demonstration of high-speed cineradiography of vowels uttered in isolation augmented with matching pseudospeech continua.
Acoustical Modeling in Architectural Acoustics
Authors: Veneklasen Paul S. , Ortega Jose C. , Christoff Jerry P. , Little John , Morse Bonard
Published: September 2005

It is imperative to investigate the acoustical properties of roms with the aid of models prior to construction. Two sound sources have been developed to facilitate these investigations. An air jet utilizing four intersection jets provides a nondirectional random noise, over a frequency range of 2400 cps to over 100 kcps for the study of the steady-state properties of rooms. A repeating spark generates an acoustical pulse having a rise time of less than 2 μsec and a duration of 20 μsec, providing a source for the study of the reflection of pulses within a room. These sources, with a 14-in.-diam microphone, are used in 1/50 scale models. Results utilizing these acoustical tools are illustrated by data on the absorption of direct sound over a sloping audience surface, reflection of sound from a canopy, side-wall reflections, and the acoustical performance of an orchestra enclosure.
Sound-System Correction of a Church having Severe Focussed Echoes
Authors: Boner Charles R.
Published: September 2005

This paper describes the procedure by which the acoustics of a church having severe focussed echoes was corrected by a sound-reinforcing system employing passive narrow-band LC networks. The church, seating 1600, is circular in planform, and its ceiling geometry approximates a paraboloid of revolution, with maximum height being 80 ft. Before correction, speech was heard with great difficulty, with the virtual sources appearing to move from point to point as the pastor changed his position on the rostrum. Sound from different members of the choir was focussed at different locations in the pews. Two concentric rings of double-baffled loudspeakers were installed, with the speaker axes being vertical. Eighteen sections of narrow-band networks were used in controlling room-ring modes and feedback modes.
Model Experiments on Sound Transmission from Engine Room to Accommodation in Motorships
Authors: Janssen J. H.
Published: September 2005

Sound transmission, both airborne and structureborne, from engine room to accommodation was investigated on board a 14 000-ton deadweight shelterdeck Dieselmotor vessel, with accommodation around the casing near midship. Typical ship noise in cabins is shown not to originate in engine-room airborne noise. This is in agreement with data obtained by other workers. As mathematical models for sound radiation by decks and bulk-heads did not explain the experimental facts satisfactorily and further experiments on board were impossible, a 1:10 scale model was built. It consists of one side of the casing with two decks, stiffeners, deck beams, etc. made from steel plate. A model cabin is mounted between the decks. Airborne-sound transmission in model and prototype turned out to be very similar. Consequently, structureborne-sound transmission was investigated. Agreement again is satisfactory. The model is now in use for studying resiliently mounting exhausts and other piping. [This research was carried out under contract with the Studiecentrum TNO voor Scheepsbouw en Navigatie (Netherlands' Research Center TNO for Shipbuilding and Navigation).]
Compressibility Effects in the Problem of Body Impact on a Free Surface
Authors: Ogilvie T. Francis
Published: September 2005

When a blunt body impacts on a free surface, the compressibility of the water must be included in the calculation of hydrodynamic reactions; otherwise, infinite pressures will be produced at the instant of impact. It is shown that, for a short period after impact, the wave equation and the usual high-frequency free-surface boundary conditions are applicable to the problem. The boundary condition on the impacting body is replaced by a simpler condition on the plane of the undisturbed free surface. For a 2-dimensional body, it is shown that the mathematical problem is equivalent to a solved problem of supersonic flow over an airfoil.
Attenuation-Loss Measurements in the SOFAR Channel
Authors: Sussman B. , MacDonald R. B. , Kanabis W. G.
Published: September 2005

An experiment was performed with the object of determining whether the attenuation suffered by an acoustic wave in the deep sound channel is affected by the presence of a steeply sloping bottom near the receiving hydrophone. The question was raised because Thorp and Urick, in separate experiments of a similar nature, obtained results that were far apart. The receiving hydrophone in Thorp's experiment was located on Plantagenet Bank, while in Urick's experiment the hydrophone was in the open ocean. In the current tests, signals from SOFAR shots were received on two systems, in one of which the receiving hydrophone was bottom-mounted on Plantagenet Bank, while in the other it was suspended over the side of a ship located far from shore. Both hydrophones were at approximately the depth of the channel axis. Results were obtained for frequencies in the range 112–898 cps. The results obtained are compared also with those of other tests done in the Mediterranean and Pacific.
Statistics of Sound Multipaths
Authors: Martin J. J.
Published: September 2005

This analysis determines expected number of multipaths and their density between sound source and target versus beam-position angles for 1- and 2-dimensional boundary roughness randomly distributed. This applies to both single and multiple bounces between the medium's boundaries and to constant sound speed and sound-speed gradient.
Propagation of Underwater Explosive Shockwaves at Long Range
Authors: Stockhausen J. H.
Published: September 2005

The results of some recent measurements of pressure pulses at ranges up to 90 000 ft from 1.8-lb TNT charges detonated underwater are compared with the predictions of three methods of determining pulse shape previously reported by E. L. Peterson, and by Arons, Yennie, and Cotter. Two methods involve only attenuation, the third also incorporating finite-amplitude effects. Using rise time as a criterion, the best agreement is obtained when finite-amplitude effects are considered.
Analysis of Underwater Acoustic Backscattering from a Random Surface
Authors: LeBlanc Lester R. , Hill R. F.
Published: September 2005

This paper is essentially a continuation of work presented earlier [J. Acoust. Soc. Am. 36, 1987(A) (1964)]. A mathematical model is hypothesized that yields the backscattered power as a function of incident angle, transducer-beam pattern, frequency, and the waveheight spatial-correlation function. This model considers the surface to be composed of differential facets with dipole beam patterns. The average backscattered power is obtained by squaring the spatial integration of the time-varying signal and averaging in the statistical domain. Curves are presented that compare results from model tank experiments with the analytical results. [This investigation is supported by the Acoustics Program, U. S. Office of Naval Research, and the U. S. Naval Underwater Ordnance Station, Newport, R. I.]
Deep-Scattering-Layer Observations off Southern and Baja California
Authors: Barham E. G. , Batzler W. E.
Published: September 2005

In coastal waters off San Diego, October 1962, large populations of a physonect siphonophore were observed from TRIESTE at the depths of an extremely strong scattering layer. Peak scattering coefficients of −50 dB were measured from a surface ship. Similar measurements in deep oceanic waters off Southern California recorded slightly deeper layers, but net hauls indicate few siphonophores were present, the best correlation being with bathypelagic fishes. Off Cape San Lucas, February 1965, visual observations from a diving saucer showed the presence of a population of lantern fishes to correspond with the depths of the main component of a scattering layer. Observations were made while the layer was at the surface, at its daytime depth, and while the layer was migrating. A deeper, weak component and a shallow, diffuse layer of scattering were correlated with two species of physonect siphonophores. It appears that these two types of organisms are the major causes of the scattering-layer phenomenon, the siphonophores being more restricted in time and space. Visual observations suggest that squid and fish schools are responsible for large acoustic reflecting features frequently recorded on echo sounders. Motion picture films documenting these observations are shown.
Frequency Discrimination of Random-Amplitude Tones
Authors: Henning G. Bruce
Published: September 2005

The ability of human observers to discriminate frequencies of tones between 1000 and 15 000 cps was measured in a temporal 2-alternative forced-choice discrimination experiment. On each trial, one of the test tones, selected at random, was attenuated by a random amount ranging from 8 to 20 dB in 2-dB steps. (The amplitude of the unattenuated tone was 77 dB SPL.) Comparing the results of this experiment with those of previous experiments in which fixed-amplitude tones were used, there appears to be little difference between the observers' abilities to discriminate frequencies of fixed- and random-amplitude tones at 1000 cps. Discrimination with random-amplitude tones becomes relatively poorer, however, as frequency is increased. The classical data show a frequency “jnd” of 40 cps at 10 000 cps; in the present experiment, with random-amplitude signals, the observers were unable to achieve 75% correct responses until ▵F was 300 cps. [This paper reports some of the work to be reported in Defence Research Medical Laboratories Research Paper 597. The research was supported in part by the Public Health Service, U. S. Department of Health, Education, and Welfare.]
Frequency-Discrimination Ability of Presbycusics
Authors: Voots Richard J. , Reger Scott N. , Majerus Diane
Published: September 2005

Forty elderly subjects were tested individually for frequency-discrimination ability, using a relatively simple automated testing procedure. These subjects were selected on the basis of audiological criteria as exhibiting typical presbycusic hearing deficits. A comparison group of 40 young adults, audiologically normal, were administered the same test. Test frequencies were 500, 1000, 2000, and 4000 Hz at approximately 40 SL. Statistical tests of the performance of the two groups confirm previous reports of a loss of frequency-discrimination ability in the aged. Additional statistical analyses were made on the aged-group data relating age to frequency discrimination and frequency discrimination at each test frequency to hearing loss at that frequency. Of these 8 comparisons, only one, that relating frequency discrimination performance at 4000 Hz to age, was found statistically significant at the 0.01 level. Examination of these comparisons suggests that, though hearing loss and frequency-discrimination loss are probably both closely related to age, the change in frequency-discrimination ability is not necessarily a direct result of the reduced hearing sensitivity associated with presbycusis. [This work was supported in part by the National Institute of Neurological Diseases and Blindness, Public Health Service, U. S. Department of Health, Education, and Welfare.]