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Journal of the Acoustical Society of America

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Mar 1957

Volume 29, Issue 3, pp. 324-396


Absorption of Sound by Patches of Absorbent Materials

Richard K. Cook

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 324-329 (1957); (6 pages) | Cited 5 times

Online Publication Date: 29 Jun 2005

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Circular patches, or long strips, of sound absorbent material are on the surface of an infinite perfectly reflecting plane. Exact solutions are found for the absorption of perpendicularly incident plane waves, and of randomly incident waves, on a circular piston‐like absorber. An exact solution is found for the absorption of perpendicularly incident plane waves on an infinitely long strip‐piston absorber. The basis of the technique is representation of the total wave field by superposition of an incident plane wave, a specularly reflected plane wave, and a scattered wave. The last‐named is in turn represented by a superposition of plane waves for the strip piston, and by a superposition of cylindrical waves for the circular piston absorber. The superposed wave fields are adjusted to meet the boundary conditions.

Practical Production and Use of Multitones

A. C. Raes

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 329-330 (1957); (2 pages)

Online Publication Date: 29 Jun 2005

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Advantages of multitones over warble tones and random noise are discussed. Three methods for producing multitones with simple apparatus and a tape recorder are described. Satisfactory decay curves have been obtained using only two components. A simple “duotone” generator, continuously adjustable over a single range from 80 to 3500 cps is described.

Some Experiments Related to the Noise from Boundary Layers

Harvey H. Hubbard

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 331-334 (1957); (4 pages)

Online Publication Date: 29 Jun 2005

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This paper presents the main results of several recent experiments relating to the generation of noise in boundary layers. An attempt is made to correlate data obtained from a wind tunnel, a rotating disk, a helicopter rotor, and an aircraft in flight. These data provide evidence as to the mechanism of noise generation in the boundary layer and show how the noise varies as a function of velocity, density, and surface roughness. Some discussion also given with regard to the relative importance of the boundary layer noise and the noise from the power plant in high‐speed jet aircraft.

Effect of a Negative Impedance Source on Loudspeaker Performance

Richard E. Werner

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 335-340 (1957); (6 pages)

Online Publication Date: 29 Jun 2005

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A direct radiator moving coil loudspeaker driven by an amplifier whose output impedance approaches the negative of the blocked voice‐coil impedance can be made to exhibit extended low‐frequency response with reduced distortion. The effect of the system is in some ways analogous to a manyfold increase in loudspeaker efficiency. In a typical case, neutralization of 70% of the blocked voice‐coil impedance completely damps the cone resonance, as well as substantially reducing the nonlinear distortion below resonance. When the amplifier is compensated for the falling radiation resistance at low frequencies, uniform output can be obtained to any arbitrary low frequency, limited only by the ultimate power‐handling capability of the amplifier and speaker. In this system, no additional amplifier power is required at frequencies down to the speaker resonance; additional power is required below that point.

Acoustical Time Regulator

Anton M. Springer

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 341-343 (1957); (3 pages)

Online Publication Date: 29 Jun 2005

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The paper describes a device for altering the speed of reproduction of tape recordings, by mechanical means, without altering the frequency and therefore the pitch.
The playback time can be changed within a range of 50–200% of the recording time. Although there are no technical limits to the range of time‐change, certain loss of quality begins to become apparent if the time‐change is increased beyond ±30%.
The possibilities of application are also discussed.

Elastic Constants of Staurolite

J. Bhimasenachar and G. Venkata Rao

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 343-345 (1957); (3 pages)

Online Publication Date: 29 Jun 2005

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The elastic constants of Staurolite have been determined using the ultrasonic wedge method. The values of the constants are: c11  =  34.3; c22  =  18.5; c33  =  14.7; c44  =  4.6; c55  =  7.0; c66  =  9.2; c23  =  12.8; c31  =  6.1; c12  =  6.7 in units of 1011 dynes/cm2. The value of compressibility is 7.58×10−13 cm2/dyne.

Radiation Load on Arrays of Small Pistons

W. J. Toulis

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 346-348 (1957); (3 pages)

Online Publication Date: 29 Jun 2005

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The radiation load on a piston in an array is examined, preliminarily, through the correspondence of a piston in an infinitely long tube and in a conical horn to arrays on an infinite plane surface and on a rigid sphere, respectively. The evaluation of the velocity potential for the two arrays suggests that the average radiation load on an array consists of two terms. The principal term arises from a uniform distribution of the total source strength over both active and inactive areas of the array. The secondary term corresponds to the free space load for one of the pistons but reduced in magnitude by a factor proportional to the average separation between adjacent pistons.

Some Measurements of the Impedance at the Eardrum

J. Zwislocki

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 349-356 (1957); (8 pages) | Cited 2 times

Online Publication Date: 29 Jun 2005

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Three methods are described for measuring the impedance at the eardrum. Two methods are psycho‐physical and one is purely physical. Although the physical method seems to be more appropriate for this kind of measurement, all three methods yield comparable results. The final results agree with some of the measurements made in the past on the reactance at the eardrum up to 1000 cps. They disagree on reactance above 1000 cps and on resistance. The new data seem to fit the general picture of sound conduction in the ear better than did values obtained earlier. They could lead to corrections in the coupler cavities used for miniature earphones and in calculations the sound attenuation afforded by some ear protectors.

Auditory Adaptation

James F. Jerger

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 357-363 (1957); (7 pages) | Cited 1 time

Online Publication Date: 29 Jun 2005

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The apparent decline in the ear's response under sustained stimulation, phenomenon which has been variously labeled “auditory fatigue,” “perstimulatory fatigue,” and “auditory adaptation,” was measured for pure tones over a wide range of frequencies and intensities by the median‐plane‐localization method.
For a given intensity, increasing the frequency from 125 to 1000 cps increased both the initial rate and maximum amount of adaptation. Above 1000 cps further increases frequency did not appreciably change the adaptation curves.
For a given frequency, increasing the intensity of the sustained stimulus also increased both initial rate and maximum amount of adaptation. The function relating adaptation, in db; to stimulus intensity was, in general, negatively accelerated.
The duration of sustained stimulation at which adaptation reached maximum value was related to both frequency and intensity.

On Presenting the Output of a Mechanical Speech Recognizer

D. B. Fry and P. Denes

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 364-367 (1957); (4 pages)

Online Publication Date: 29 Jun 2005

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The output of a mechanical speech recognizer consists of a series of units which are closely correlated with the phoneme sequence which forms the speech input to the system. This output has to be transformed and presented to the human “reader,” usually in one of two ways, either by using it to reconstruct audible speech sequences or by presenting it in a sequence of visible characters. In both cases, the success of the recognizer will depend greatly on the degree to which good use can be made of the reader's existing linguistic knowledge, and methods of assessing its success must take this fact into account. This paper will present the results of experiments designed to compare methods of presenting the output and also methods of measuring the performance of the recognizer in terms of the ease with which the “reader” can reconstruct the input.

Confirmation of the Normal Threshold for Speech on C.I.D. Auditory Test W‐2

John F. Corso

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 368-370 (1957); (3 pages)

Online Publication Date: 29 Jun 2005

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The present study was undertaken to determine the threshold for speech intelligibility for normal ears on the Central Institute for the Deaf (C.I.D.) Auditory Test W‐2. Data were collected on both right and left ears of 139 subjects, ages 18 to 24 years inclusive, showing negative otological findings, a maximal pure tone hearing loss of 5 db at 500, 1000, or 2000 cps, and a history of minimal noise exposure. The obtained mean threshold for speech, for all ears combined (N = 278), was 18.55 db re 0.0002 dyne/cm2, with a standard deviation of 4.46 db. These results confirm the normal value for the threshold of intelligibility for the spondaic words of C.I.D. Auditory Test W‐2.

Method of “Single Descent” in Group Audiometry

W. Dixon Ward

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 371-376 (1957); (6 pages)

Online Publication Date: 29 Jun 2005

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Various methods for determining threshold in a group testing situation were compared. No significant differences in reliability were found between the method of adjustment (either direct or indirect) and the method of “single descent,” in which the listener presses a button “just when the beeps disappear.” However, the method of single descent is independent of individual differences in adjustment time and requires less apparatus. Thresholds determined by single descent were affected only slightly by rate of descent, starting level and practice factors. A comparison between single descent and the standard clinical technique showed the thresholds to be valid. Field performance of the method, in a 10‐man group audiometer, has fulfilled expectations from the pilot studies.

Reflection of Plane Sound Waves from a Sinusoidal Surface

John G. Parker

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 377-380 (1957); (4 pages)

Online Publication Date: 29 Jun 2005

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The problem of calculating the specular component of the sound field reflected from a sinusoidal pressure release surface is discussed. The incident field is assumed to be plane and directed normally to the surface. Basically, the problem consists of obtaining the solution to a nonlinear differential equation derived in an earlier paper. This was done numerically and the results compared with existing experimental data on sound reflection from two differently formed surfaces. In one case agreement between calculated and measured values is quite good while in the second case there is considerable discrepancy. A possible explanation of this discrepancy is given.

Formulation of Wave Propagation in Infinite Media by Normal Coordinates with an Application to Diffraction

M. A. Biot and I. Tolstoy

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 381-391 (1957); (11 pages) | Cited 19 times

Online Publication Date: 29 Jun 2005

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In the theories of acoustical and electromagnetic vibrations of enclosures, as well as in field theory and electrodynamics, one quite commonly uses normal modes as generalized coordinates in Hilbert space. Here the method is extended to unlimited or partially limited mechanical media, essentially by first solving the problem for an enclosure and going to a limit while expanding all or some of the boundaries to infinity. This leads to a very useful technique, of somewhat more generality than analogous procedures used in field theory. Thus it is applicable to all non‐dissipative mechanical continua, for any boundary conditions, irrespective of the order or number of differential operators describing the continua and regardless of whether the coordinate systems are separable or not.
A general orthonormality condition valid in all such cases together with the necessary rules for dealing with divergent normalizing coefficients are easily obtained by limiting procedures. An equally general formulation for arbitrary sources is obtained from the principle of virtual work. The method is illustrated by simple examples, for the case of a point source representing the instantaneous injection of a unit volume, i.e., an idealized, infinitely rapid, explosion. It is shown that in the problem of diffraction by a rigid wedge or corner one is led very quickly to an explicit solution in closed form, involving elementary functions only. Some physical implications of this solution are mentioned briefly. The advantages of the normal coordinates method are discussed when thus used in propagation or diffraction problems in unlimited or partially limited mechanical continua. Obvious advantages are its generality, its flexibility in dealing with arbitrary sources, and the fact that it leads directly to the progressive transient solution.
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Note on Acoustic Radiation Pressure

Jobu Awatani

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 392-392 (1957); (1 page)

Online Publication Date: 29 Jun 2005

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A method of obtaining the acoustic radiation force (i.e., the process of integrating the force on every surface element of the object placed in sound waves) is criticized. This process yields the sum of the contribution of the true radiation pressure and that of the mean pressure. Though there is no effect in plane progressive waves, the mean pressure has a considerable effect on the result obtained in plane standing waves or progressive spherical waves.

On the Fundamental Qualities of Speech in Communication

Y. Ochiai and T. Fukumura

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 392-393 (1957); (2 pages)

Online Publication Date: 29 Jun 2005

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Auditory Threshold

Robert R. McPherson and Theodore G. Birdsall

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 393-394 (1957); (2 pages)

Online Publication Date: 29 Jun 2005

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Improved Barium Titanate Composition

D. Schofield and R. F. Brown

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 394-395 (1957); (2 pages)

Online Publication Date: 29 Jun 2005

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Comments on “Mechanical Mechanism of Destructive Effects of Sound on Tissue”

Floyd Dunn

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 395-396 (1957); (2 pages)

Online Publication Date: 29 Jun 2005

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A recently proposed theory to explain some of the nonthermal, non‐cavitation effects of intense high‐frequency sound on living tissue is discussed in the light of more recent experiments. It is concluded that the assumption of the theory that the observed effects are caused by uni‐directional forces (proportional to the square of the particle velocity amplitude) of the acoustic field which create sufficiently great displacements in structural members of the tissue to produce elastic failure, is not supported by experimental results.

Erratum: Equivalent Circuit for Spherical Radiation in a Solid [J. Acoust. Soc. Am. 28, 724 (1956)]

V. Salmon

J. Acoust. Soc. Am. Volume 29, Issue 3, pp. 396-396 (1957); (1 page)

Online Publication Date: 29 Jun 2005

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