bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibration of a Gaseous Medium in a Parabolical Cavity
Authors: Liu C. K.
Published: September 2005

The normal modes of vibration of a gaseous medium in a parabolical cavity are investigated. The wave equation in parabolical coordinates is solved formally for the most general case in terms of Bessel wavefunctions. The first ten terms of the Bessel wavefunction of order 0, 1, and 2 are computed for arbitrary arguments. As the analytical solution of the wave equation for a cylindrical cavity has been used for computing the frequencies of the standing waves tn the combustion chamber of a liquid-propellant rocket motor, the present analysis may be of value to the development of a rocket motor of more general form.
Portable Instrument for Locating Noise Sources in Mechanical Equipment
Authors: Gilbrech Donald A. , Binder R. C.
Published: September 2005

A portable direction finder utilizing correlation techniques was developed for locating noise sources in mechanical equipment. A description of this instrument and some test results are given. The test results include studies of the direction finding characteristics of the apparatus and a simple method of determining wave fronts.
Message Repetition and Receiver Confirmation of Messages in Noise
Authors: Carterette Edward C.
Published: September 2005

A receiver may be required to decide whether the message he has recorded is or is not the message actually received. The degree of certainty needed for confirmation (the criterion) may be controlled by instructions. A sequence of decisions is generated by repeatedly sending each of a set of messages until the set is confirmed. A simple stochastic model assumes that the probability of confirmation, py, is constant over such a sequence. If N messages are sent, the expected number confirmed after the first n presentations is E(n) = N[1 − (1 − py)n].

Two experimental tests were (1) of the constancy of py by noting whether the equation for E(n) holds, and (2) of the constancy of py's three component probabilities: the probabilities of correct reception, correct confirmation, and incorrect confirmation. Receivers listened under two noise conditions to sets of several hundred messages each. Each message was immediately repeated until confirmed. Estimates of py and of the component probabilities were made from proportions of correct and incorrect responses. The data show that the assumption of constant py yields a very accurate description of the process, and justify the more basic assumption that py's three components are constant over repeated trials. Further, the data are in excellent agreement with predictions from the theory of the total number of communication events required before the entire set of N messages is confirmed, and of the total numbers of correct and incorrect confirmations.
Ultrasonic Velocity in the Liquid-Glass Transition Region
Authors: Litovitz T. A. , Lyon T.
Published: September 2005

Ultrasonic measurements in two associated liquids, glycerol and Arochlor, show that the temperature coefficient of sound velocity in the glassy state is less than in the liquid. No discontinuity in the velocity data is observed at the “transition temperature.” Using ultrasonic waves a “pseudo transition” occurs at temperatures higher than the normal glass transition temperature.
Instrumentation for Study of Propagation of Sound over Ground
Authors: Wiener Francis M. , Goff Kenneth W. , Keast David N.
Published: September 2005

An instrumentation system has been developed to allow continuous determination of the relevant micrometeorological parameters of the atmosphere near the ground in order to relate them to the measured attenuation of an acoustic signal propagated along the ground. Arrays of precision cup anemometers and shielded thermocouples mounted on a 30-ft tower were used to obtain the mean wind and temperature gradients above the ground. To obtain a measure of the atmospheric turbulence, a high-speed wind vane and a bead thermistor were used. The electrical signals obtained from scanning these transducer arrays were fed into a mobile central recording and control facility. Simultaneously, the information provided by the acoustic signal was recorded there by scanning the output of several microphones placed along two test courses each approximately one mile long. The mobile laboratory also contained the necessary equipment for energizing two loudspeakers, one for each test course. This paper discusses the micrometeorological instrumentation in some detail, together with the calibration techniques used. Typical mean wind and temperature profiles as well as turbulence spectra are presented. The relation of the micrometeorological data to the propagation of sound along the ground is discussed elsewhere.
Stroboscopic Interferometer for Vibration Measurement
Authors: Smith E. R. , Edelman S. , Jones E. , Schmidt V. A.
Published: September 2005

This paper describes measurement of vibration amplitude with a Fizeau type interferometer using pulses of monochromatic light of adjustable phase. The interferometer is used to calibrate vibration pickups over the frequency range from 100 to 20 000 cps.
Minor-Lobe Level as a Function of Tolerance on Variations in Individual-Element Sensitivity in Four-Element Line Arrays
Authors: Suchman Daniel F.
Published: September 2005

This paper considers the effect of the tolerance placed on amplitude variations of individual elements from their nominal values in symmetrical four-element, uniformly spaced line arrays. The problem of predicting statistically the percentage of acceptable product (i.e., meeting predetermined specifications regarding maximum minor-lobe level) given a manufacturing tolerance for individual-element sensitivity is discussed. Three specific shadings (1-2.0-2.0-1, 1-2.2-2.2-1, and 1-2.5-2.5-1) are investigated and computed results are presented showing the percent of total product with minor lobes in excess of any specified level, as a function of sensitivity tolerance. Finally, families of curves showing minor-lobe level as a function of nominal shading for different tolerances are presented for 1% and 2% defective product.
Sound Absorption at 50 to 500 kc from Transmission Measurements in the Sea
Authors: Murphy S. R. , Garrison G. R. , Potter S.
Published: September 2005

The absorption coefficient of sound in sea water has been obtained by a series of direct transmission measurements at several moderately high frequencies in a sheltered deep water bay in Puget Sound. Advantage was taken of the isothermal and isosaline properties existing during certain seasons of the year in this location. The fluctuations normally encountered in such a measurement were minimized by the utilization of fixed buoys, a radio link for range determination by acoustic travel time, and a method of space averaging. Values obtained, in decibels per kiloyard at a temperature of 10°C and a salinity of 30 parts per thousand, are: 14.4±0.3 at 60 kc, 35.7±0.7 at 142 kc, 57±3 at 272 kc, and 101±3 at 467 kc. Although the frequency dependence of the absorption coefficient given by these measurements follows the normal relaxation law, the magnitudes are lower than those given by Del Grosso by 4 to 10 db/kyd.
Binaural Beats and Binaural Amplitude-Modulated Tones: Successive Comparison of Loudness Fluctuations
Authors: Rutschmann Jacques , Rubinstein Leo
Published: September 2005

An objective psychophysical method for measuring one of the results of binaural (neural) interaction to low-intensity pure tones is presented. Successive comparison of the strength of loudness fluctuations of binaural beats (BB) with loudness fluctuations produced by binaurally presented amplitude-modulated tones is used. The dependency of the percent amplitude modulation (AM) required for a match on stimulus parameters is investigated. At a given frequency level of the tones, the matches are not affected when the frequency difference is changed from 2 to 6 cps. The %AM required for a match increases when sensation level (SL) decreases from 30 to 10 dB. When frequency level is changed, the matches are about the same for 150 and 300 cps, but much less AM is required at 600 cps. The discussion centered on the relationship of the matches to appropriate detection thresholds for AM. Changes in the detection threshold with SL fail to predict the corresponding changes in the matches; e.g., when the SL is lowered, the %AM for detection increases less than the modulation required for the match.
Inferences of Neural Activity Associated with Binaural Acoustic Images
Authors: Toole F. E. , Sayers B. McA.
Published: September 2005

Experimental results relating to the nature of acoustic images arising from binaural, repetitive, wide-band acoustic transients are reported. In addition to the tonal harmonic images that may be identified in certain circumstances, there appear to be two dominant images of impulsive character. The latter images appear to be associated with neural activity arising in specific regions of the cochlea; their lateralization characteristics may be interpreted in terms of inferred temporal features of the basilar-membrane responses in the relevant regions. Implications germane to the physiological mechanisms of binaural interaction are discussed.
Computer Recognition of Spoken Digits Based on Six Nonacoustic Measures
Authors: Hillix W. A. , Fry M. N. , Hershman R. L.
Published: September 2005

Six low-bandwidth measures were used in three types of programs for the automatic recognition of spoken digits. The measures were chosen to be closely related to articulatory rather than to acoustic properties of speech. The first program, without any learning feature, asked specific questions about the values of the six measures; its accuracy ranged from 64% to 97% correct. Two speaker/specific programs, which learned with a sample of two utterances per digit, yielded accuracies averaging 97% when tested on new utterances from the same talker. Performance fell to 88% and 94% when learning was carried out on a pool of four speakers, and to 78% and 86% when a 3-speaker pool provided the learning for classification of a fourth speaker's utterances. It is suggested that such “nonacoustic” measures can be of substantial value in more-general speech-recognition procedures.
Ultrasonic Absorption in MgSO4 Solutions as a Function of Pressure and Dielectric Constant
Authors: Fisher F. H.
Published: September 2005

Measurements in the 100- to 500-kc/sec region have been made of ultrasonic absorption as a function of pressure and dielectric constant for 0.5 M solutions of MgSO4. Relaxation frequencies, reaction rates, and sound velocities are calculated from the results. The magnitude and pressure dependence of the chemical compressibility for aqueous solutions are in good agreement with the four-state dissociation model proposed by M. Eigen and K. Tamm [Z. Elektrochem. 66, 93–107, 107–121 (1962)] to explain ultrasonic absorption at atmospheric pressure. Furthermore, it is pointed out that the effect of pressure on the equilibrium dissociation constant for aqueous solutions at low concentration, predicted with the same four-state model, is shown to be in excellent agreement with electrical-conductivity data as a function of pressure. No explanation of the unusual effects observed for ultrasonic absorption and relaxation frequency at lower dielectric constants can be made at this time.
Experimental Test of the Laval-Raman-Viswanathan Theory of Elasticity
Authors: Swartz Karl D. , Granato A. V.
Published: September 2005

In a review of available data for some cubic materials, Raman and Krishnamurti [Proc. Indian Acad. Sci. 42, 51–70; 43, 111–130 (1955)] found that the behavior of these crystals cannot be expressed in terms of the three classical elastic constants, but can be expressed in terms of the four elastic constants prescribed by the theories of Laval and of Raman and Viswanathan. We have observed that dynamic measurements can be used to measure the four constants and that, when data of the accuracy achievable with dynamic measurements are used, the discrepancy claimed by Raman and Krishnamurti disappears. Thus, we find no evidence for the four-constant theory.
Scattering of a Plane Acoustical Wave by a Spherical Obstacle
Authors: Cohen Donald S. , Handelman George H.
Published: September 2005

The long-time behavior of the scattered field produced by a plane acoustical pulse stalking a spherical obstacle is investigated. Incident pulses are taken that represent a unit step in potential (or equivalently delta function pulse in pressure), an arbitrary potential pulse of finite duration, and an arbitrary pressure pulse of finite duration. Both hard and soft spheres are considered. In addition, a pulse consisting of a unit step in velocity impinging on a hard sphere is examined. In each case, the time rate of decay to the steady state is established. This is seen to be controlled by the zeroes of certain naturally occurring special polynomials that arise because of the spherical geometry and are independent of the shape of the incident pulse.
Backward-Wave Transmission of Stress Pulses in Elastic Cylinders and Plates
Authors: Meitzler Allen H.
Published: September 2005

The propagation characteristics of longitudinal modes are described by the Pochhammer frequency equation in the case of elastic cylinders and the Rayleigh-Lamb frequency equation in the case of elastic plates. The longitudinal modes in both geometries are closely analogous. In both cases, the second branch of the mode spectrum determined by the roots of the applicable frequency equation shows a region in which phase and group velocities have opposite signs. Wave motions having phase and group velocities of opposite sign occur in certain guided-electromagnetic-wave motions and are often referred to as backward-wave motions. This paper reports experimental observations of stress pulses traveling in backward elastic-wave motions in cylinders and plates. Also included in the paper is a detailed description of how the distribution of the energy flux density changes as the wave motion corresponding to the second branch of roots goes from the region of forward-wave motion to the region of backward-wave motion.
Axially Symmetric Vibrations of a Finite, Isotropic Cylinder
Authors: Kumar Ram
Published: September 2005

Vibrations corresponding to the different propagation constants for the same frequency parameter have been superimposed to satisfy the boundary conditions approximately at the flat surfaces of the cylinder for the frequency-parameter range where the Pocchammer-Chree frequency equation yields two real and one imaginary root. Taking the Poisson's ratio as 0.31, the thickness/diameter ratios (in the range of 1.0328–5.5630) for which resonance will occur at any particular frequency parameter have been calculated and shown graphically. The corresponding vibration patterns have been drawn for three particular cases for ka = 4.0 and the residual stresses calculated as a test for the validity of the approximation.
Predicting the Effective Dynamic Coupling Coefficient of the Flextensional Transducer (Preliminary Design Considerations)
Authors: Royster L. H.
Published: September 2005

Expressions for the effective dynamic coupling coefficient of the flextensional transducer have been approximated. The approximate solutions are illustrated and compared with experimental data.
Balance Technique for the Measurement of Very Low Ultrasonic Power Outputs
Authors: Kossoff G.
Published: September 2005

A method of measuring the acoustic output of ultrasonic-pulse-detection equipment is described. The apparatus consists of a sensitive analytical balance and either an absorbing or a reflecting target. The sensitivity of the technique is 0.08 or 0.04 mW, respectively.
Equivalent Circuit of a Tube or Spring
Authors: Bauer B. B.
Published: September 2005

In the equivalent circuit analysis of acoustical structures, invariably the question arises on how to represent distributed-constant members with lumped-parameter electrical components, to a given degree of accuracy. For a tube (or spring), a T-type configuration, with the arms consisting of inductors each equivalent to 12 the total inertance and the center leg, a capacitor equivalent to the total acoustical capacitance predicts the 14-wavelength resonance frequency within a 10% error. For shorter wavelengths, an equivalent circuit of equal quality is obtained by treating the tube as n equal segments where n is the number of 14-wavelengths of the highest frequency of interest approximating the length of the tube. When n is doubled, the error is reduced to within about 3%.
Soil Compliance as a Function of Moisture and Dry Density
Authors: Johnson L. E. , Niemoeller Arthur F.
Published: September 2005

Measurements of the compliance of class A-6 soil as a function of moisture and dry density are presented. These measurements show that a recently published model, a three-dimensional surface relating compliance to moisture and density, is invalid.
Equations of Motion of Spherical Shells
Authors: Jahanshahi A.
Published: September 2005

A set of five equations of motion for deep spherical shells, which include the effects of transverse shear deformations and rotatory inertia, is given. Certain unsatisfactory features of the existing system of equations of motion for deep spherical shells, which claim to include the effects of transverse shear deformations and rotatory inertia, are pointed out.
Nature of the Sonic-Room Problem
Authors: Hubbard Harvey H.
Published: September 2005

Significant factors of the sonic-boom problem are shown to be numerous and to involve a variety of scientific and engineering disciplines. Special mention is made of the rôles of aircraft design, aircraft operations, and the effects of sonic booms on other aircraft, people, buildings, etc. The material of this paper is introductory to the more detailed discussions that follow.
Relativistic Perturbed Oscillator
Authors: Liu Han-Shou
Published: September 2005

This paper concerns the use of a canonical transformation in finding a solution to the problem of the relativistic perturbed oscillator. The transformation is performed so that the final solution is obtained in a certain desired form. The ultimate nature of the relativistic perturbed oscillation is revealed.
Normal-Mode Intensity Calculations for a Constant-Depth Shallow-Water Channel
Authors: Bucker H. P. , Morris Halcyon E.
Published: September 2005

Normal-mode theory is used to calculate the propagation of sound at moderate-to-long ranges in a realistic, constant-depth, shallow-water channel. The channel is made up of two isovelocity water layers lying over a layered, viscoelastic, solid bottom. The equations for the sound intensity are written in rather simple form by using Brekhovskikh's formulation in which the effect of the channel bottom enters the equations as a single reflection coefficient. Because the bottom sediments absorb some sound energy at each bottom reflection, each of the modes has art exponential attenuation as well as the usual r−12 spreading loss. In this paper, these mode-attenuation constants are calculated exactly—i.e., to any desired accuracy—by an iterative process. Reasonable agreement is shown between calculated values of propagation loss and some experimental values from a recent sea test by the U.S. Navy Electronics Laboratory. The introduction of a directional source into the calculations is briefly discussed.
Acoustic Field of a Pulsed Source in the Underwater Sound Channel
Authors: Hirsch Peter
Published: September 2005

The peak amplitudes of solar signals are estimated by considering a particular mathematical model for the acoustic-speed versus depth profile of the ocean and for the explosion waveform. The sound speed is assumed to vary as c2 = c02(1−α2s2)−1 where c0 is the speed at the channel axis, s is the vertical distance from the axis, and α specifies the width of the channel. The source waveform is assumed to be a short sinusoidal wavetrain. It is found that the range dependence of the direct arrival in the received pressure amplitude is the product of two terms. The first is the expected cylindrical-spreading loss. The second term oscillates with range. The amplitude of the oscillation depends on the source waveform and the range; for a 233-cps, 8-msec pulse at 100 NM (nautical miles), the amplitude is about 14 dB. The distance between successive maxima of the oscillation depends on α and c0, but is independent of range and source waveform. For values of the parameters that fit a typical North Atlantic profile, the distance between maxima is about 6 NM. The amplitude at successive maxima is found to decrease as r−34.
Real-Time Electronic Spectrograph for Analysis of Acoustic Transients
Authors: Germano J. F. , Halley R. , Allen W. B.
Published: September 2005

A real-time electronic spectrograph that produces a time-versus-frequency display on a cathode-ray storage tube is described. A DELTIC (DElay Line TIme Compressor) is used to obtain high-frequency multiplication ratios and, thereby, essentially real-time analysis with a swept-filter heterodyne analyzer. The device examines the time-frequency structure of a stored sample. The resulting output displays the complete content of the store in one recirculation per bandwidth. The entire sample is thus analyzed in a fraction of a second. Pulses, tones, and noise transients were used to test the capabilities of the analyzer with respect to time resolution, frequency resolution, response to noise, and processing gain. Results of these tests and other illustrative examples of the analyzer output are presented, which show that (1) frequencies separated by one bandwidth or more can be resolved, (2) pulses shorter than the filter-buildup time are lengthened whereas pulses longer than the buildup time retain their original length, and (3) the device does not respond to level changes of white noise at the input.
Subjective Judgments of Footstep-Noise Transmission through Floors
Authors: Olynyk D. , Northwood T. D.
Published: September 2005

The current procedure for assessing impact transmission through floors involves comparing the spectra of transmitted noise produced by a standard tapping machine. An obvious weakness in the method is that it does not really simulate footsteps. One is more interested, however, in how well the method rank-orders floor structures as compared with the impressions of an apartment dweller listening to his upstairs neighbor. This project was intended to provide a partial answer to this complex question. Subjective comparisons were made of the “loudnesses” of footsteps on a concrete slab floor with various added structures. Comparison with FHA ratings indicates that the ratings exaggerate the differences between floors in the most unacceptable range, but that there is a reasonable degree of correlation among the important range of floors. A variation of the FHA procedure that improves the correlation is also reported.
Effect of Humidity on Sound-Transmission Loss
Authors: Shiner Allen H. , Marchello Maurice J.
Published: September 2005

A test program was recently instituted by the United States Gypsum Company—Research Center, with the cooperation of the Riverbank Acoustical Laboratories, to determine the effect of ambient humidity on the sound-transmission loss of a double-leaf gypsum-board partition system. The results of this test series were quite explicit. As the humidity was increased, a degree of freedom was introduced that allowed for lateral movement of the gypsum core and paper. These two skins were then able to perform independently of one another, causing the eventual shift of control frequency from 2800 to 350 cps—i.e., from coincidence to resonance control. In addition, these test data reveal that, at some frequencies, a difference of as much as 6 dB occurs between the high and low humidity levels, while at others the differential is 0 dB. These differences clearly indicate the need for standardization of the humidity conditions at the present commercial testing laboratories.
Hypersonic Absorption and Velocity from Measurement of Light Scattering: Dichloromethane
Authors: Hanes G. R. , Turner R. , Piercy J. E.
Published: September 2005

Apparatus used to determine hypersonic velocity and absorption in liquids by spectroscopic analysis of light scattered from a single-frequency laser beam is described. A measurement on dichloromethane is presented, the acoustic parameters are derived, and the significance of their relation to ultrasonic measurements and to the theory of relaxation mechanisms is discussed.
Fresnel-Zone and Plane-Wave Impedances on Very Large Pistons
Authors: Junger M. C. , Thompson William
Published: September 2005

The radiation-loading distribution over a large, rigid, circular piston embodies fluctuations associated with Freznel zone interference patterns. These fluctuations do not vanish as the ka of the piston tends to infinity, thus leading to the paradoxical conclusion that an infinite, rigid, plane piston does not radiate plane waves. It is shown that plane-wave radiation and a uniform, ρc impedance can be predicted by accounting for the transients occurring at the beginning of a CW pulse. These transients produce a ρc impedance in regions of the piston not yet reached by a diffraction wave that starts from the piston edge at the beginning of the pulse. By allowing the piston diameter and, hence, the envelopment time to become arbitrarily large, the plane-wave radiation loading prevails over an arbitrarily large region of the piston.
Statistics of Sound Multipaths
Authors: Martin J. J.
Published: September 2005

This analysis determines the expected number of multipaths and their angular density between sound source and target for reflections from a one-dimensional not-too-rough boundary with random normal distribution of slopes. Generalization to two-dimensional, nonisotropic roughness and to multiple reflections is possible.
Method for the Reduction of the Harmonic Content of High-Intensity Acoustic Pulses
Authors: McDaniel Oliver H. , Prout James H.
Published: September 2005

A method has been devised for reducing the level of specific harmonics from underwater sound sources by introducing an out-of-phase harmonic signal at the electrical input to the system. Experimental results show that a significant reduction in harmonic level can be obtained by this method.
Refraction of Injected Sound by a Very Cold Nitrogen Jet
Authors: Grande E.
Published: September 2005

A pure-tone “point” source of sound was placed within the potential core of a nitrogen jet at −180°C, and the distortion of its sound field by the jet temperature and velocity fields was measured. The sound was found to be refracted inward—a focusing effect—to yield a maximum intensity along the jet axis; the maximum increased with frequency and decreased with jet velocity. Polar directional plots of the self-noise of the cold jet (“jet noise”) exhibited a similar shape, quite unlike the usual heart-shaped pattern for warmer jets.
Transducers for Exciting and Detecting Acoustic Waves in Discharge-Tube Plasmas
Authors: Saxton William A.
Published: September 2005

Transducers used for the excitation and/or detection of acoustic waves in laboratory plasmas must be compact and dimensionally compatible with the structure that contains the plasma; and, they must be made of materials that do not outgas in high-vacuum environments, and are capable of withstanding temperatures of 500°C. This paper considers such requirements and establishes the important acoustic and constructional specifications for transducers that are housed in long, cylindrical glass discharge tubes with diameters of approximately 212 in. After pointing out the limitations of conventional designs, details of satisfactory moving-armature and solid dielectric-type transducers are presented, along with brief descriptions of their measured performance. Although the moving-armature refit has had the greatest use to date, the solid dielectric version promises to be quite useful as a microphone in detecting plasma sound waves. Therefore, an explanation of techniques for building such a device is included, with particular emphasis on methods for coating the stationary electrode with a dielectric material.
Oscillatory Acoustic Transients Radiated by Impulsively Accelerated Bodies
Authors: Junger M. C. , Thompson William
Published: September 2005

When a submerged solid body is subjected to a translational velocity step, it radiates oscillatory, transient acoustic pressures, whose natural period is proportional to the travel time of a sound pulse around the accelerated solid. Transient velocities displaying more-complicated distributions over the radiating surface give rise to acoustic-wave harmonics that, with the exception of the breathing mode, are also oscillatory, and characterized by one or more “natural” frequencies proportional to the ratio of the sound velocity to the characteristic dimension of the radiator. These pressures are analogous to room reverberation attenuated by radiation damping but their phase velocities and attenuation are reminiscent of creeping waves. If the initial velocity impulse is modified by subsequent gradual accelerations (or decelerations) as embodied, for example, in an exponentially decaying or “pulsed CW” velocity, the “reverberant” oscillatory-sound field is superimposed on an acoustic field whose time history is identical with that of the motion of the radiating surface. The phenomenon of oscillatory transients radiated by nonoscillatory motions of submerged bodies appears to be characteristic of any finite solid geometry. The effect of these reverberant transients on the radiation and radiation loading of spherical sources generating CW pulses is analyzed. Finally, the effect of these transients on the performance of large arrays is explored. It is shown that, at the beginning of a CW pulse, radiation impedance is uniform over the array, the difference with the CW impedance that fluctuates strongly over the array surface being accounted for by the transient. Consequently, arrays in which circuits of individual elements have been adjusted for fluctuations in CW radiation impedance will display a non-uniform response at the beginning of the pulse, which may result in fatigue failures.
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 [Soviet Phys.—Acoust. 1, 60–72 (1955)]. In particular, when λ (wave-length) = 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 that had 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 v=λf agreed with pulse-echo measurements to 2%–3%.
Acoustic Relations of the Human Vertex Potential
Authors: Davis Hallowell , Zerlin Stanley
Published: September 2005

The average amplitude of the slow, diffuse, nonspecific electrical response of the human cortex, called the V potential, evoked by tone pips or by tactile stimuli to thumb and forefinger, follows a power law with exponent about 0.24 (re sound pressure). The variability of the responses is great, across both trials and subjects. If auditory or tactile stimuli are judged equally strong, across frequency or modality, the V potentials tend to be equal. Both the latency and the amplitude of the V potential are independent of the rise time of a tone burst, at least up to 100 msec. The amplitude also remains nearly constant as the duration of the plateau of a burst, with rise and fall times of 5 msec, is varied from 2 to 320 msec. An off response that closely resembles the on response in waveform, latency, and amplitude appears at the end of any burst that is long enough, but an off response that follows an on response by 1 sec or less is much reduced in amplitude, and so is an on response that too closely follows an off response. The V potential is a response to change in stimulation either on or off.
Auditory Threshold Location and Uncertainty as a Function of Tone Parameters and Fatigue
Authors: Silbiger Herman R. , Elliott D. N.
Published: September 2005

The relationship of auditory threshold location for various pulsed and continuous tones was investigated, using a Békésy audiometer. It was found that for periods from 250 to 750 msec an increase repetition rate results in a decrease in threshold, independent of the duty cycle. This relationship was maintained after a TTS6–10 (temporary threshold shift) of 20 dB. The pen-excursion size, however, was found to be a function of the pulse length, during TTS6–10, with the longer pulse giving the greatest reduction in pen-excursion size (PES); continuous tones yield the highest thresholds and the greatest reduction in pen-excursions size, with under normal conditions and under TTS6–10. It therefore appears that threshold location and pen-excursion size may be independently manipulated. The differences in threshold location are thought to be owing to an increase in the ability to make tone present-absent decisions during interruptions, while the decreases in pen-excursion size during TTS may be owing to the perception of the increased rate of loudness growth.
Earphone versus Sound-Field Threshold Sound-Pressure Levels for Spondee Words
Authors: Tillman Tom W. , Johnson Robert M. , Olsen Wayne O.
Published: September 2005

This experiment sought to establish the difference between earphone and sound-field measures of spondee threshold SPL (sound-pressure level). Recorded spondee words were delivered to both a conventional and an insert-type earphone as well as to a single loudspeaker that generated the signal in the sound field. Monaural spondee threshold SPL's were established for both normal hearing and hypoacousic subjects under the three listening conditions. The intensity level of the spondee words under the three conditions was expressed as the SPL of an “equivalent” speech spectrum noise. For both groups of subjects, the mean sound-field threshold SPL was about 7.5 dB lower than that measured under the conventional earphone and approximately 12.5 dB lower than that established under the insert-type earphone. These results tend to confirm the reality of the “missing 6 dB.” Further, they indicate that the difference between minimum audible pressure (MAP) and minimum audible field (MAF) is a product of both diffraction and “closed-ear” effects. The latter effect appears to vary as a function of the volume of air enclosed by the pressure transducer.
Interaural Time and Intensity Difference and the MLD
Authors: Zerlin Stanley
Published: September 2005

Masking-level differences (MLD) for a 600-cps low-pass transient were explored as a function of (1) interaural time difference (Δt; (2) interaural intensity difference (ΔI); and (3) combinations of Δt and ΔI. Masking-level difference here is the difference between two levels of coherent noise (N0), one required to mask a given condition of click, the other to mask a binaural in-phase click (S0). (1) MLD increases with signal Δt in a manner similar to that for interaural phase differences of the tonal frequency within the filtered transient. Furthermore, for larger values of Δt, where the transients no longer overlap in time, the MLD decreases in a manner suggesting temporal integration of two brief signals. (2) As signal ΔI increases, MLD approaches limiting value of about 7 dB, for signal monaural (Sm) condition. An interaural intensity difference of 24 dB yields an MLD of 6 dB, still a decibel or so short of the monaural value. (3) When ΔI is combined with Δt greater than 0.4 msec, the MLD decreases ΔI increases, no matter whether the louder signal is leading or lagging in time.
Speed of Sound in n-Amyl Alcohol as a Function of Temperature and Pressure
Authors: Bradley David L.
Published: September 2005

An empirical equation relating sound velocity to temperature and pressure ia given for n-amyl alcohol together with the coefficients for the equation. The change in velocity with the addition of CH2 groups is shown for five primary alcohols.
Attenuation of Sound over Snow-Covered Fields
Authors: Tillotson J. G.
Published: September 2005

Preliminary measurements of the attenuation of sound propagated over a field covered with a new fall of snow are presented, for frequencies in the audio band. At 800 cps, the characteristic impedance of fresh snow has been determined as Z2 = /ρ1c1 = 1.83 − i0.27. The complex propagation constant K2 = α + iβ = 0.10 +i0.27 has been measured as well. The attenuation measurements have been made at different source heights above the snow field. Where complete data are available, reasonable correlation exists between theory and experiment.
Circumferential Waves on Solid Cylinders
Authors: Grace O. D. , Goodman R. R.
Published: September 2005

A mathematical investigation of the velocity and attenuation for waves traveling around a solid cylinder immersed in water is reported. In the limit of large cylinders approximate results are given for both velocity and attenuation. The method used is an extension of the theory of Viktorov [Soviet Phys.—Acoust. 4, 131 136 (1958)].
Experimental Studies in Underwater Directional Communication
Authors: Bauer B. B. , Torick E. L.
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 under water 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 were 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.
Calibration and Analysis of Underwater Earphones by Loudness-Balance Method
Authors: Bauer B. B. , Torick E. L.
Published: September 2005

Recent experiments in underwater directional communication necessitated the use of earphones with uniform response characteristics. Two earphones from headset P-120-PQC-1 were calibrated underwater by the loudness-balance method at 50 dB above 1000-cps threshold sound-pressure level (SPL). A 25-dB range in response was observed in the frequency interval of 200–3000 cps, with principal resonance at 600 cps. Equalization was provided, after considering the 50-phon loudness contour, resulting in uniform response over the interval of 200–2500 cps. The experiment sheds some light on the role of tympanic versus bone-conduction modes in underwater listening, and suggests a receiver design with uniform frequency response and 40-times greater efficiency than the P-120-PQC-1.
Reciprocity Calibration in a Tube with Active-Impedance Termination
Authors: Beatty Louis G.
Published: September 2005

A new application of the reciprocity principle has been developed for calibrating electroacoustic transducers in a dosed vessel at static pressures to 8500 psi and frequencies from 100 to 1500 Hz. The necessary plane progressive wavefield is provided by sound propagation in the longitudinal mode within a sound channel terminated at both ends with active impedances. The technique is particularly well suited to the calibration of underwater-sound transducers because the high static pressure under which many of them must operate, as well as their size, mechanical construction, and operating frequency, often prevents the use of more conventional methods. The case of a rigid-walled, water-filled tube is analyzed theoretically. Results of measurements made by this method in a practical high-pressure calibration chamber are shown.
Sonar Transducer Calibration in a High-Pressure Tube
Authors: Beatty Louis G. , Bobber Robert J. , Phillips David L.
Published: September 2005

A unique tube facility for the calibration of sonar transducers under hydrostatic pressures to 8500 psi is described. The pressure vessel consists of the modified liner from a 16-in. gun. The liner is 50 ft long and has an inside diameter of 15 in. An active-impedance principle is applied to establish plane progressive waves within the tube. Resonant transducers can be calibrated in the frequency range 100–1500 Hz; nonresonant, hard transducers can be calibrated in the range 40–1500 Hz.
Pseudorandom Signal-Correlation Methods of Underwater Acoustic Research II. Instrumentation
Authors: Allen W. B. , Stewart James L. , Zarnowitz R. M. , Brandon M. K.
Published: September 2005

A discussion presented of a correlation signal-processing system for studying the distortion of underwater acoustic signals, and some of the preliminary observations obtained with this equipment are given. The system uses a 100-cps-bandwidth pseudorandom signal and both 5- and 25-sec averaging times; this gives a simultaneous time resolution of 0.01 sec and frequency resolutions of 0.2 and 0.04 cps. DElay Line TIme Compressors (DELTICs) provide a high search rate in time (range). A difference-frequency correlator, employing a bank of 11 bandpass filters as averagers, provides search over ±1- and ±0.2-cps Doppler frequency shifts, respectively. The effects have been observed of clipper normalization in the presence of multipaths and the degradation of the correlation owing to reflections at high angles from a violently moving ocean surface.
Signal Detection by Arrays with Arbitrary Processors and Detectors
Authors: Usher Theron
Published: September 2005

The signal-detection characteristics of local arrays of transducers that are used to detect the presence of a plane-wave random signal in an isotropic noise background are analyzed for the situation in which the transducers are followed by identical nonlinear processors. The resulting signals are summed and detected by a square-law device with a low-pass filter. The performance of this system is compared to that for a system with linear processors and a square-law detector. Also analyzed are the signal detection characteristics of an array with linear processors and a non square-law detector. The performance is also compared to that for the linear system with a square-law detector. Results indicate that, for maximum output signal-to-noise (S/N) ratio, the system with linear processors and a square-law detector is optimum for both situations considered above. The degradation in performance caused by deviations from the optimum is not great, however. On an output-signal basis, defined by the difference between “on target” and “off target” output, the linear processor provides an optimum system, if there is a choice of processor function. However, no optimum exists when the processor is linear and there is a choice of detector function.
Examination of Binaural Interaction
Authors: Deatherage Bruce H.
Published: September 2005

The study of binarual interaction may be conveniently divided into three areas: anatomy, physiology, and psychology. These areas, while furnishing large amounts of data, have not yet provided enough information to make possible a complete theory of binarual interaction. Several partial theories are discussed, two experiments are reported, the results of the experiments set in perspective, and the problems of the construction of a full theory of binarual interaction are presented. A Bibliography is appended.
Reflection of Sound Waves from Transition Layers
Authors: Gupta Ravindra N.
Published: September 2005

The problem of reflection of plane waves from transition layers in fluid media with an arbitrary, variation of velocity and density is discussed as an extension of a recent paper by the author [Geophysics 30, 122–132 (1965)]. Numerical results are given for some cases of interest. It is found that the reflection coefficient is very insensitive to the precise manner in which the elastic parameters vary within the transition zone as long as both velocity and density terminate at the same values.
Uniqueness of Mean-Square Approximate Systems
Authors: Bogdanoff J. L.
Published: September 2005

A proof is given, in a form readily available to the engineer, of the uniqueness of mean-square approximate systems. The proof is based upon the fact that weighted mean-square error can be expressed as a simple quadratic form in normal coordinates of sample systems.
Method of Computation of Damped Resonance Frequencies for a System of Equal Masses, Equal Spring Constants, and Equal Viscous-Damping Coefficients
Authors: Raynor S. , Frank E.
Published: September 2005

A method of computation of natural frequencies for a closed, coupled, damped-vibrational system of equal masses, springs, and dashpots is devised, based on a known method applicable to an equivalent undamped system. It is shown that the higher oscillatory modes are completely suppressed. The analysis is extended to a viscoelastic continuum exhibiting similar behavior.
Sound Scattering by Elastic Cylindrical Shells
Authors: Doolittle R. D. , Überall H.
Published: September 2005

We present the solution for the scattered field corresponding to a plane sound wave incident upon an infinite elastic circular-cylindrical concentric shell, imbedded in a fluid and enclosing another fluid. The results are shown to contain the known special cases of fluid and elastic solid cylinders. Furthermore, limiting expressions for long wavelengths are obtained in special cases.
Underwater Sound Propagation in the Straits of Florida
Authors: Steinberg John C. , Birdsall T. G.
Published: September 2005

In a fixed-system study of relationships between variations in underwater sound transmission across the Straits of Florida and variations in environmental factors, an unexpected degree of phase stability was observed. The phase of the received wave, referenced to the phase of the transmitted wave, varied less than 100° during intervals of 12–1 h. Intervals of 1–4 h occurred in which the phase varied less than 360°. In other intervals, the phase drifted in positive or negative directions at maximum rates of 5°–15°/min. The over-all behavior had a pronounced diurnal period. The observations were made during a 4-day continuous test employing 420-Hz CW (continuous wave) transmission. Results for individual arrivals by different paths, obtained in subsequent transmission employing pseudorandom sequences, were consistent with the CW observations.