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Journal of the Acoustical Society of America

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Jan 1947

Volume 19, Issue 1, pp. 1-293

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Image Interference in the Presence of Refraction

Robert W. Young

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 1-7 (1947); (7 pages) | Cited 2 times

Online Publication Date: 17 Jun 2005

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Underwater sound transmission has been studied as a function of range at frequencies of 0.2, 0.6, 1.8, 7.5, and 22.5 kc, under a variety of thermal conditions. At the three lower frequencies, marked interference patterns are observed. These result from the combination of surface reflected sound (as from an image source) and directly transmitted sound. Refraction modifies the interference pattern. When the sound velocity increases with increasing depth, the interference pattern is contracted; when the velocity increases with depth, the pattern is extended. An easily used formula is developed to predict this influence of refraction on the propagation of sound emitted from a point source adjacent to a reflecting plane. The theory is in good agreement with the experimental data obtained with the source at a depth of 14 feet from the surface and the receiver as deep as 300 feet.

Surface Reflection of Short Supersonic Pulses in the Ocean

R. J. Urick and H. L. Saxion

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 8-12 (1947); (5 pages)

Online Publication Date: 17 Jun 2005

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The Acoustical Concomitants of Cavitation and Boiling, Produced by a Hot Wire. I

M. F. M. Osborne and F. H. Holland

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 13-20 (1947); (8 pages) | Cited 2 times

Online Publication Date: 17 Jun 2005

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This paper presents data on the properties of a very simple, low power underwater noise generator—a wire heated by a heavy electric current. The dependence of the sound generated upon frequency, input power, wire size, material, and wire history has been determined. The sound has a very broad frequency distribution. For small wires a large part of the sound is supersonic. About one part in a million of the input electrical energy appears as sound. With increasing electric power the sound power passes through a broad maximum. This paper can also be considered as a study of cavitation noise, the cavities being produced by heat rather than by reduced pressure. Thus a new approach to the problem of cavitation noise is provided. As a study in heat flow, this report provides quantitative data on the acoustical concomitants of boiling.

The Acoustical Concomitants of Cavitation and Boiling, Produced by a Hot Wire. II

M. F. M. Osborne

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 21-29 (1947); (9 pages)

Online Publication Date: 17 Jun 2005

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The properties of an electrically heated wire in various liquids have been investigated in an effort to explain qualitatively the properties of the hot‐wire sound generator of the preceding paper. The sound from the hot wire is primarily a cavitation noise—its properties can all be ascribed to the continuous formation and collapse of vapor cavities. Many of the phenomena of cavitation, including corrosion, have a counterpart in boiling. It is shown that under certain conditions the hot wire has two stable forms of operation for the same input power. In one the wire is relatively cold, and the sound emitted has a broad frequency distribution. In the other the wire is red hot, and for some liquids the sound emitted is a single pure tone a whistle of 1000–2000 cycles/sec. Swishing the wire through the liquid increases the intensity of this whistle.

Absorption of Supersonic Waves in Water near One Megacycle

L. W. Labaw and A. O. Williams, Jr.

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 30-34 (1947); (5 pages)

Online Publication Date: 17 Jun 2005

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Several observers have found that the absorption coefficient for supersonic radiation in water is inversely proportional to the square of the frequency, in the range 3 to 80 megacycles. This agrees with classical theory except in the size of the proportionality constant, but when extrapolated to lower frequencies disagrees sharply with earlier measurements which suggested a strong absorption peak near one megacycle. An experiment is described here which employed a small microphone detector and attempted to measure absorption in a divergent supersonic beam by comparison of the measured and theoretical acoustic pressure curves along the beam axis. The results, between 1.09 and 1.30 mc, are negative in that the computed absorption coefficients fall below the experimental error. However, a fairly reliable upper limit can be set on the coefficient. This limit is consistent with the value predicted by extrapolating the frequency‐squared relationship down to one megacycle. There seems little chance of a strong absorption peak in the near neighborhood of one megacycle.

Two Parabolic Reflector Underwater Transducers

J. R. Reitz and R. E. Mueser

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 35-43 (1947); (9 pages)

Online Publication Date: 17 Jun 2005

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A line source underwater transducer may be used in conjunction with a parabolic cylinder reflector to produce a highly directive sound ray similar to that obtained from a shaded plane source. Poor patterns result from the construction of a unit where the element is at the focus of a parabolic cylinder reflector because the finite size of the element is so great as to block a large proportion of the reflected sound rays. To circumvent this difficulty an ideal surface is derived which will allow placing the line source out of the direct path of the reflected rays. This derivation and the construction and acoustic characteristic of the consequent transducer are discussed.

Magnetic Throat Microphones of High Sensitivity

Daniel W. Martin

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 43-50 (1947); (8 pages)

Online Publication Date: 17 Jun 2005

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An analysis is made of the problem of intelligence pick‐up from anatomical vibration. Methods for measuring the actual and effective response‐frequency characteristics of the throat are described. Measurements on the variation of effective response among different subjects are discussed in connection with the concept of “oral efficiency.” Design and performance data are given for several magnetic throat microphones of relatively high sensitivity.

A General Theory of Passive Linear Electroacoustic Transducers and the Electroacoustic Reciprocity Theorem. II

Henry Primakoff and Leslie L. Foldy

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 50-58 (1947); (9 pages) | Cited 2 times

Online Publication Date: 17 Jun 2005

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In Part I of this paper, it was shown that the reciprocity theorem for passive linear electroacoustic transducers could be established on the basis of a pair of general linear relations connecting the voltage and current at the electrical terminals of the transducer with the pressure and velocity distribution over the transducer surface provided certain “reciprocity relations” existed among the parameters entering these equations. In Part II it is now shown that on considering a transducer to be comprised of media characterized in the usual manner by appropriate linear constitutive relations between stress, strain, electric and magnetic polarization, charge and current density, and electric and magnetic field intensity, one can establish the validity of the linear relations and the “reciprocity relations” assumed in Part I, provided that certain sufficient conditions are met. These conditions are: (l) That the coefficients in the constitutive relations satisfy certain “symmetry conditions.” (2) That no magnetostrictive media and no static magnetic field are present in the transducer (that is, that the coupling is purely electrostatic or piezoelectric or both), or that no piezoelectric media and no static charge density are present in the transducer (that is, that the coupling is purely electromagnetic or magnetostrictive or both). (3) That the transducer does not radiate electromagnetic waves from its surface.
The validity of the “symmetry conditions” on the coefficients of the constitutive relations is established for frequencies sufficiently low that the harmonic changes in the variables can be regarded as adiabatic in the thermodynamic sense and under certain circumstances at higher frequencies by means of a general argument based on a principle of microscopic reversibility. One may, however, anticipate the possible breakdown of these conditions when appreciable losses due to “relaxation” phenomena in the transducer media are present. The conditions for the validity of the reciprocity theorem derived in this paper are only sufficient, but they may be considerably extended in their generality to include the presence of other phenomena (such as electrostrictive effects) by the application of the same general methods.

Measurement Conditions Influencing the Front‐to‐Back Discrimination of an Underwater Hydrophone

Laymon N. Miller

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 59-62 (1947); (4 pages)

Online Publication Date: 17 Jun 2005

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The “front‐to‐back discrimination” represents the ability of an underwater hydrophone to favor reception of a desired signal originating in front of the hydrophone by discriminating against a usually undesired signal originating behind the hydrophone. Under normal conditions in a confined measurement area, the value of the front‐to‐back discrimination is influenced to a considerable extent by such measurement factors as conditions of the medium, the directionality characteristics of the projector, and the distance separating the projector and the tested hydrophone. It is reported that reverberation appears to mask the true back‐side response of the hydrophone, and that thermal gradients and possibly unusual natural effects oftentimes limit the validity of some underwater measurements. Data are presented to show that a hydrophone measured with highly directional projectors exhibits a higher front‐to‐back discrimination than if measured with non‐directional projectors. It is also shown that the front‐to‐back discrimination appears to decrease with increasing distance between the projector and the tested hydrophone. These effects are attributed to the absence of a strictly free‐field in a bounded volume of water.

Headphone Measurements and Their Interpretation

Daniel W. Martin and Leslie J. Anderson

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 63-70 (1947); (8 pages)

Online Publication Date: 17 Jun 2005

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Methods of acoustical measurement and of data presentation are reviewed, with emphasis on relating headphone data to the requirements of the communications and monitoring fields of application. Data are shown to demonstrate the importance of statistical analyses of the performance of headphones on different wearers. Some effects of presenting too “artificial” an acoustical load to the receiver during measurement are illustrated. An experiment in artificial ear development is described. The requirements for an improved artificial ear are outlined, based in part upon the experimental work.

An Acoustic Constant of Enclosed Spaces Correlatable with Their Apparent Liveness

J. P. Maxfield and W. J. Albersheim

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 71-79 (1947); (9 pages)

Online Publication Date: 17 Jun 2005

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Normal Frequency Spacing Statistics

Richard H. Bolt

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 79-90 (1947); (12 pages) | Cited 2 times

Online Publication Date: 17 Jun 2005

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Factors Governing the Intelligibility of Speech Sounds

N. R. French and J. C. Steinberg

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 90-119 (1947); (30 pages) | Cited 96 times

Online Publication Date: 17 Jun 2005

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The characteristics of speech, hearing, and noise are discussed in relation to the recognition of speech sounds by the ear. It is shown that the intelligibility of these sounds is related to a quantity called articulation index which can be computed from the intensities of speech and unwanted sounds received by the ear, both as a function of frequency. Relationships developed for this purpose are presented. Results calculated from these relations are compared with the results of tests of the subjective effects on intelligibility of varying the intensity of the received speech, altering its normal intensity‐frequency relations and adding noise.

Effects of Distortion on the Intelligibility of Speech at High Altitudes

G. A. Miller and S. Mitchell

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 120-125 (1947); (6 pages)

Online Publication Date: 17 Jun 2005

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Premodulation Clipping in AM Voice Communication

K. D. Kryter, J. C. R. Licklider, and S. S. Stevens

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 125-131 (1947); (7 pages)

Online Publication Date: 17 Jun 2005

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Articulation tests were conducted to assess the advantages of premodulating clipping in A M voice transmitters. The results show that a saving of as much as 14 decibels in carrier power can be achieved, without loss in intelligibility, if the speech wave is first subjected to 24 decibels of peak clipping and then reamplified by 24 decibels in order to obtain 100‐percent peak modulation. Three obvious advantages result from this procedure: (1) the effective range of a given transmitter is increased, (2) overmodulation is permanently prevented, and (3) interference to communications on adjacent frequency channels is eliminated. Realization of this third advantage requires the introduction of a low‐pass filter between the clipper and the point of modulation. Excessive amounts of premodulation clipping should be avoided whenever speech quality is an important consideration and whenever the microphone picks up large amounts of ambient noise. On the other hand, when communication is impaired by ambient noise and atmospheric static at the receiver location, large amounts of premodulation clipping serve to maximize intelligibility.

Diffraction of Sound around a Circular Disk

Henry Primakoff, Martin J. Klein, Joseph B. Keller, and E. L. Carstensen

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 132-142 (1947); (11 pages)

Online Publication Date: 17 Jun 2005

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The sound field behind a circular disk in the presence of a point source of sound on its axis, is computed approximately. The calculation is based on the reduction of the Kirchhoff surface integral to a line integral by the Maggi Transformation. The predictions of the Kirchhoff theory are compared with a more accurate calculation which makes use of the Green's function. The theory is compared with accurate measurements of the sound field, and satisfactory qualitative and quantitative agreement is found.

On the Diffraction of a Progressive Sound Wave by the Human Head

Francis M. Wiener

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 143-146 (1947); (4 pages)

Online Publication Date: 17 Jun 2005

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An earlier paper described the distribution of sound pressure in the auditory canals of a number of subjects in a plane progressive sound field. At a given frequency, the ratio of the sound pressures at the eardrum and at the entrance to the ear canal was found to be greater than unity and essentially independent of the orientation of the observer with respect to the sound source, as might be expected from theory. With this ratio known, it is possible to determine, with relative ease, the sound pressures at the eardrum as a function of azimuth from pressure measurements near the entrance to the auditory canal. By positioning a probe microphone at the entrance to the ear canal and comparing the sound pressures there with the free‐field pressures at the subject's location an estimate of the obstacle effect of head and pinna is arrived at. Adding the known pressure increase in the auditory canal yields a measure of the total obstacle effect of the human head and auditory canal. The subjects were placed in front of a loudspeaker in a room essentially free from acoustic wall reflections. The measurements of the sound pressure at the entrance of the left auditory canal and in the free field in the absence of the subject were carried out by means of a small probe microphone in the frequency range extending from 200–6000 c.p.s. A range of azimuths of 360 degrees was covered in 45‐degree steps. If it is assumed that the two auditory canals are alike and that the head is symmetrical about the median plane, the ratio of the sound pressures at the left and right eardrums can be readily computed from these data. This ratio is of importance in the mechanism of binaural localization. The average for six male subjects was compared with the values obtained by Sivian and White from threshold measurements and was found to be in fair agreement.

Asymmetrical Vibrations of Cones

Piero Giorgio Bordoni

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 146-155 (1947); (10 pages)

Online Publication Date: 17 Jun 2005

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Abstract Unavailable

Acoustic Wave Fronts from a “Piston” Source

A. O. Williams, Jr.

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 156-161 (1947); (6 pages) | Cited 2 times

Online Publication Date: 17 Jun 2005

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Some properties of wave fronts or constant‐phase surfaces in the acoustic field of a piston‐like source are deduced from an approximate expression for the velocity potential. The calculations are limited to certain ranges of frequencies, piston sizes, and distances from the source, of chief interest in supersonics. The results comprise for plane pistons (a) a determination of the place where the wave fronts reverse their curvature from converging to diverging shape; (b) a calculation of the radius of curvature of the fronts at moderately large distances from the source; (c) an approximate theoretical equation for the shape of the wave fronts, which permits plotting the paraxial portion of these surfaces at medium and large distances. For a concave piston, calculations similar to those of (a) are made. A few comparisons with experimental results are given under (a), (b), and (c). Agreement is qualitative to semi‐quantitative.

A Curvature Meter for Use in Disk Recording

Ludwig W. Sepmeyer

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 161-164 (1947); (4 pages)

Online Publication Date: 17 Jun 2005

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A limiting factor in the reproduction of disk recordings with a modern reproducer is the tracing distortion arising from the finite size of the reproducing stylus. The sharpest groove modulation which can be reproduced is that having a radius of curvature slightly larger than the tip radius of the reproducing stylus. It is, therefore, desirable to monitor the cutting of disk records with a meter whose indication is based upon this curvature limitation, rather than with a conventional volume indicator. When using a volume indicator alone, overmodulation by as much as 20 db is possible. The theory and construction of such a curvature meter are discussed in this paper.

Improved Theory of the Light Pattern Method for the Modulation Measurement in Groove Recording

J. Hornbostel

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 165-169 (1947); (5 pages)

Online Publication Date: 17 Jun 2005

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A formula is derived that is applicable to the evaluation of light pattern measurements when non‐parallel light is used. It is shown that deviation from parallelism encountered in the laboratory may cause Buchmann and Meyer's simplified formula to be in error by several db. Numerical examples are given, and the results are extended to vertical and loop recordings.

Sound Embossing at the High Frequencies

Milton Morse

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 169-172 (1947); (4 pages)

Online Publication Date: 17 Jun 2005

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Abstract Unavailable

Wire Recorder Wow

Arthur W. Sear

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 172-178 (1947); (7 pages)

Online Publication Date: 17 Jun 2005

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Short Duration Auditory Fatigue as a Method of Classifying Hearing Impairment

Mark B. Gardner

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 178-190 (1947); (13 pages)

Online Publication Date: 17 Jun 2005

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Earlier studies have classified deafness cases into two general groups, those having functional disorders of the middle ear and those having impairments resulting from atrophy of the nerve fibers terminating along the basilar membrane (conductive and nerve deafness types, respectively). Such classifications have been made using bone conduction threshold measurements and unilateral loudness balance results as the basis for differentiation. Bone conduction results, however, are often subject to considerable error while the unilateral loudness balance technique can only be applied to individuals having one normal and one impaired ear. These limitations introduce a need for a completely independent monaural method of classifying deafness types. This is particularly true for the selection of candidates suitable for the fenestration operation for the restoration of hearing in otosclerosis (immobilized stapes). The present paper is concerned with an investigation of short time auditory fatigue as a method of obtaining an impairment analysis. In this study, it was found that the fatigue of the conductively deafened observer was similar to the normal observer except the onset of fatigue was shifted by the amount of the threshold loss. For the nerve deafened observer, on the other hand, the onset of fatigue was found to occur at normal intensity levels. The occurrence of excessive fatigue in one of the nerve type impairment cases investigated appears to offer additional information on the nature of the lesion.

Investigations on Acoustic Resonators

H. Samulon

J. Acoust. Soc. Am. Volume 19, Issue 1, pp. 191-193 (1947); (3 pages)

Online Publication Date: 17 Jun 2005

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The following paper contains investigations into the resonance sharpness of acoustic resonators. Experimental and theoretical results are compared and found in good accordance.
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