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Journal of the Acoustical Society of America

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Dec 1965

Volume 38, Issue 6, pp. 945-1064

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Evaluation of New Couplers for Circumaural Earphones

K. K. Charan, J. R. Cox, Jr., and Arthur F. Niemoeller

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 945-955 (1965); (11 pages) | Cited 1 time

Online Publication Date: 20 Jul 2005

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An experimental investigation of three couplers, suitable for testing circumaural earphones, was made to determine the limitations on their use. Two of these couplers were modified forms of standard U.S. couplers, the ASA‐type 1 and the NBS‐9A, while the third was a simple flat plate with a hole in which the test microphone is flush mounted. Results presented are based on tests made using the Telephonics TDH‐39 earphone with NAF‐48490‐1 cushion and the Philips model HA‐10 circumaural earphones. Below 2000 Hz, all three couplers are reliable and useful for measuring the responses of circumaural earphones. Above 2000 Hz, small variations in the electroacoustic system, defined by the earphone, cushion, coupler, and measurement microphone, cause large variations in the measured response. Variations in earphone responses are shown to be caused by variations in (1) earphones of a particular type, (2) cushions of a particular type, (3) applied force on the earphone, and (4) placement of the earphone on the coupler. These variations are in addition to the expected variations in the measured responses of different types of earphones when used with different types of cushions and when measured on different types of couplers.

Electropneumatic Acoustic Generator

Walter T. Fiala, J. K. Hilliard, J. A. Renkus, and John J. Van Houten

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 956-964 (1965); (9 pages)

Online Publication Date: 20 Jul 2005

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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 through 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 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.

Transducers for Exciting and Detecting Acoustic Waves in Discharge‐Tube Plasmas

William A. Saxton

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 965-973 (1965); (9 pages)

Online Publication Date: 20 Jul 2005

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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 2½ 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.

Free‐Molecule Propagation in Rarefied Gases

G. M. Sessler

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 974-977 (1965); (4 pages) | Cited 3 times

Online Publication Date: 20 Jul 2005

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Acoustic‐wave propagation in gases is studied for the case where the ratio of the transmitter‐receiver separation s to the mean free path Λ of the gas molecules is sufficiently small so that the propagation constant is independent of Λ (free‐molecule propagation). Experimental results, obtained in air and in argon, are found to be in agreement with the existing theories. Free‐molecule propagation is distinguished from ordinary sound propagation that takes place if s/Λ is sufficiently large in order that the propagation constant is independent of s. The ranges of free‐molecule propagation and sound propagation are found to be approximately s/Λ < 1 and s/Λ > 5, respectively.

Oscillatory Acoustic Transients Radiated by Impulsively Accelerated Bodies

M. C. Junger and William Thompson, Jr.

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 978-986 (1965); (9 pages)

Online Publication Date: 20 Jul 2005

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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

Emmanuel P. Papadakis

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 987-993 (1965); (7 pages)

Online Publication Date: 20 Jul 2005

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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%.

Transient Vibration of Thin Elastic Shells

H. Kraus and A. Kalnins

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 994-1002 (1965); (9 pages) | Cited 1 time

Online Publication Date: 20 Jul 2005

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A complete solution for the response of an arbitrary shell subjected to time‐dependent surface loads is derived by means of the classical method of spectral representation. The solution is expanded in terms of the modes of free vibration, and their orthogonality is proved for an arbitrary shell. As an example, the response of a spherical shell to a suddenly applied uniform normal load is calculated in detail.

Relativistic Perturbed Oscillator

Han‐Shou Liu

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1003-1005 (1965); (3 pages)

Online Publication Date: 20 Jul 2005

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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.

Vibrations of Transversely Isotropic Cylindrical Shells of Finite Length

C. Prasad and R. K. Jain

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1006-1009 (1965); (4 pages) | Cited 1 time

Online Publication Date: 20 Jul 2005

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Flexural, axisymmetric, and torsional vibrations of a transversely isotropic, simply supported, cylindrical shell of finite length are considered. Comparatively simple forms of the equations of motion have been obtained by introducing three auxiliary variables. The solution of these equations is given in terms of Bessel functions. Applying suitable boundary conditions, the frequency equations have been derived. Three‐dimensional theory of elasticity is used in the analysis.

Normal‐Mode Intensity Calculations for a Constant‐Depth Shallow‐Water Channel

H. P. Bucker and Halcyon E. Morris

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1010-1017 (1965); (8 pages) | Cited 2 times

Online Publication Date: 20 Jul 2005

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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−½ 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

Peter Hirsch

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1018-1030 (1965); (13 pages)

Online Publication Date: 20 Jul 2005

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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−¾.

Real‐Time Electronic Spectrograph for Analysis of Acoustic Transients

J. F. Germano, R. Halley, and W. B. Allen

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1031-1034 (1965); (4 pages)

Online Publication Date: 20 Jul 2005

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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

D. Olynyk and T. D. Northwood

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1035-1039 (1965); (5 pages) | Cited 2 times

Online Publication Date: 20 Jul 2005

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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

Allen H. Shiner and Maurice J. Marchello

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1040-1042 (1965); (3 pages)

Online Publication Date: 20 Jul 2005

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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.

Masking‐Level Differences as a Function of Interaural Disparities in Intensity of Signal and of Noise

James P. Egan

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1043-1049 (1965); (7 pages) | Cited 8 times

Online Publication Date: 20 Jul 2005

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A marked release from masking, or masking‐level difference (MLD), results when a monaural signal is presented with perfectly correlated (in‐phase) binaural noise, N0—Sm, rather than with monaural noise, Nm—Sm. When the noise in the nonsignal ear is introduced at a lower level than that in the signal ear, a smaller MLD results. In one experiment, MLD's were determined as a function of the intensity of the noise in the nonsignal ear with the interaural conditions of N0, Nπ, and NU as parameters; for N0, there is some release from masking even when the noise in the nonsignal ear is as much as 40 dB down from that in the signal ear. The following considerations led to a second experiment. A release from masking results when a sinusoid is presented monaurally Sm rather than binaurally and in phase S0 with perfectly correlated noise N0. With N0‐S0, when the sinusoid in one ear is reduced in intensity, rather than being removed entirely, a smaller MLD than for N0‐Sm should result. Therefore, MLD's were determined as a function of the ratio of the energies of the left‐ and right‐ear sinusoids with correlated noise N0. In all experiments, the signal (500 cps, 0.25 sec) was presented to the listener in one or the other of two temporal intervals, against a background of white noise. Psychometric functions were determined for each condition, and MLD's were estimated from these functions.

Learning to Identify Complex Sounds: Prompting versus Confirmation

Norman A. Sidley, Eugene Winograd, and Erwin W. Bedarf

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1050-1052 (1965); (3 pages)

Online Publication Date: 20 Jul 2005

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Three groups of subjects were taught to identify, by label, complex sounds. With temporal overlap controlled, confirmation and prompting training procedures were compared. Despite recent emphasis on the superiority of prompting procedures, no significant difference in the efficacy of the two methods was observed.

Release from Masking for Speech

Peter B. Weston, James D. Miller, and Ira J. Hirsh

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1053-1054 (1965); (2 pages)

Online Publication Date: 20 Jul 2005

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Intelligibility scores were obtained from 12 listeners for monosyllabic words presented monaurally with noises at one or both ears. Release from masking previously reported by Licklider [J. Acoust. Soc. Am. 20, 150–159(1948)] was confirmed, but sizable differences between right and left ears in the amount of release were not found. However, one listener consistently had about 5% more release for speech at the right than the left ear.
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Effect of Filter Type on Energy‐Detection Models for Auditory Signal Detection

M. V. Mathews and Sheila M. Pfafflin

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1055-1056 (1965); (2 pages)

Online Publication Date: 20 Jul 2005

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Two different assumptions about the shape of the filter in energy‐detection models for auditory signal detection are investigated. It is shown that, when the mean square output of the filters is equated, the variance calculated for the model whose filter consists of a single resonant circuit is half that of a model whose filter has a rectangular passband. Some implications of this result are discussed.

Acoustic Bridge for the Measurement of Liquid Quantity

Thomas L. Ward

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1056-1057 (1965); (2 pages)

Online Publication Date: 20 Jul 2005

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Liquid quantity measurement in aerospace vehicles during free fall is complicated by the fact that liquid in a partially emptied tank will cluster in globules distributed through the tank. The liquid quantity can be determined indirectly by measuring the volume of a gas occupying the “empty” volume of the tank. The volume flow from a low‐frequency acoustic source is divided by two fixed acoustic resistances. A portion flows into the unknown volume and a portion flows into a reference volume. The differential pressure between these volumes can be used as a measure of the unknown volume.

Hypersonic Absorption and Velocity from Measurement of Light Scattering: Dichloromethane

G. R. Hanes, R. Turner, and J. E. Piercy

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1057-1059 (1965); (3 pages) | Cited 2 times

Online Publication Date: 20 Jul 2005

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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

M. C. Junger and William Thompson, Jr.

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1059-1060 (1965); (2 pages)

Online Publication Date: 20 Jul 2005

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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.

Errata: Stability Criteria for Longitudinal Pressure Oscillations in a Rocket Motor [J. Acoust. Soc. Am. 37, 872–878 (1965)]

S. N. B. Murthy and J. R. Osborn

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1060-1060 (1965); (1 page)

Online Publication Date: 20 Jul 2005

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Propagation of Low‐Frequency CW Sound Signals in the Deep Ocean

Albert N. Guthrie and John D. Shaffer

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1060-1061 (1965); (2 pages)

Online Publication Date: 20 Jul 2005

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The acoustic pressure field of a low‐frequency CW source, towed at slow speed at a depth of 25 m, was measured as a function of range by a stationary hydrophone 460 m below the surface for ranges between 64 to 122 km. Frequencies of 10.04 and 13.89 cps were used. Reversed radial runs were made to test range dependence and repeatability of modal‐interference patterns that were observed in previous experiments. Range dependence and repeatability of the patterns were verified for both frequencies, and a computed theoretical curve for 10.04 cps over a limited range interval closely resembled an experimental curve consisting of an average of three separate runs made over that range interval.

Analysis of Sea Water from the Tongue of the Ocean

W. L. Konrad

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1061-1061 (1965); (1 page)

Online Publication Date: 20 Jul 2005

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The chemical analysis of sea water sampled in the Tongue of the Ocean is presented as a function of depth. Water temperature and sound velocity are also tabulated for each depth. The results are quite typical of the Caribbean, with the exception of somewhat larger percentages of bicarbonate and calcium ions.

Statistics of Sound Multipaths

J. J. Martin

J. Acoust. Soc. Am. Volume 38, Issue 6, pp. 1061-1062 (1965); (2 pages)

Online Publication Date: 20 Jul 2005

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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.
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