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Journal of the Acoustical Society of America

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Jun 1958

Volume 30, Issue 6, pp. 505-583


Attenuation of Sound in Lined Air Ducts

A. J. King

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 505-507 (1958); (3 pages) | Cited 2 times

Online Publication Date: 29 Jun 2005

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Theoretical predictions of the performance of silencers are apt to be difficult and unreliable, so experimental results are often very valuable.
A previous paper contained curves giving the attenuation of sound with frequency in lined ducts of various widths and thicknesses of lining of rock wool. Subsequent experience has shown the need for an extension of these curves to cover thicker linings and splitters, and advantage has been taken of an opportunity to obtain further data on 16‐in. splitters and air channels. New curves including these data are given for a 50% space factor, together with an extrapolation to 32‐in. splitters. Thicknesses greater than 16 in. are unlikely to be used unless frequencies lower than 100 cps are important. For covering very wide frequency bands two‐stage filters are recommended.

Acoustical Design of the Alberta Jubilee Auditoria

T. D. Northwood and E. J. Stevens

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 507-516 (1958); (10 pages)

Online Publication Date: 29 Jun 2005

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Two large auditoria have recently been built by the province of Alberta, Canada, in the cities of Edmonton and Calgary. The main auditoria, which seat 2700 persons, are designed for both concert and large‐scale stage presentations. This paper reports on the design and on the extensive acoustical testing in the laboratory and in the halls themselves. Impedance tube and reverberation chamber data were obtained for materials and components of the auditoria. Reverberation time, pulse tests, and other objective measurements were made in the halls as they approached completion. The project culminated a test concert attended by about 1800 people, including 11 expert observers who afterward participated in a discussion of the acoustical properties of the hall.

Temporary Threshold Shift and Masking for Noise of Uniform Spectrum Level

James D. Miller

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 517-522 (1958); (6 pages)

Online Publication Date: 29 Jun 2005

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This experiment was designed to test the hypothesis that differences in the effective noise level from one critical band to the next can account for the typical audiogram showing the temporary threshold shift which results from an exposure to noise of uniform spectrum level.
For equal masking, or (B+K−β0), the greatest losses were found at the highest frequencies and the smallest losses at the lowest frequencies. However, the hypothesis implied that for equal masking all frequencies would show equal losses.
Further analysis revealed that when the data for temporary threshold shift were plotted against the quantity (B+2.7K−β0), the points for all test‐tone frequencies fell on a common curve.

Temporary Threshold Elevation Produced by Continuous and “Impulsive” Noises

Walter Spieth and William J. Trittipoe

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 523-527 (1958); (5 pages)

Online Publication Date: 29 Jun 2005

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Three experiments compared the amounts of temporary threshold elevation resulting when a given total amount of noise energy was presented to the ear in the form of repeated, short, intense bursts, and in the form of continuous noise (of much lower maximum intensity). Several patterns of noise bursts were tested, as well as continuous noise. One‐millisecond noise bursts and continuous noise, of 20 min duration, were tested most extensively. The most severe impulsive noise tested consisted of 1‐msec bursts every 10 msec for 20 min, with a burst SPL of 127 db or long‐time‐average level of 117 db.
It appeared quite conclusively that 1‐msec bursts of noise have considerably less effect than the equivalent amount of continuous energy on thresholds at 3000, 4000, 6000, and 8000 cps. Noise bursts of 10 msec, 100 msec, and 1 sec length were tested less extensively; it appears that they would cause no more threshold elevation than would the equivalent amount of continuous noise.

Distributed Transducer

Martin Greenspan and Raymond M. Wilmotte

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 528-532 (1958); (5 pages) | Cited 1 time

Online Publication Date: 29 Jun 2005

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The distributed transducer is an array of transducers separated by inactive material having their common characteristic impedance, Z0, and terminated in Z0 at one (the absorber) end. The other end radiates into a load. The input voltages at the successive inputs are delayed so that the speed of the electrical wave, traveling in the direction absorber to load, equals the speed of sound in the transducer material. The elements may or may not be identical and they may or may not be operated near resonance; the acoustic waves arrive at the load in phase in any case. A great variety of frequency‐response characteristics is readily synthesized; particular attention is paid to a flat response over a very broad range. At the same time, the response at the absorber is subject to some control so that the power there dissipated can be minimized.

Methods of Generating High‐Intensity Sound with Loudspeakers for Environmental Testing of Electronic Components Subjected to Jet and Missile Engine Noise

John K. Hilliard and Walter T. Fiala

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 533-538 (1958); (6 pages)

Online Publication Date: 29 Jun 2005

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This paper discusses several methods for generating high‐intensity sound in the laboratory. Typical characteristics of the two most promising methods—the plane wave tube and the reverberant box—are discussed. A simple formula for the reverberant box is derived. Measurements made on several sound generators commercially built are presented.

Masking of English Words by Prolonged Vowel Sounds

John J. O'Neill and John J. Dreher

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 539-543 (1958); (5 pages)

Online Publication Date: 29 Jun 2005

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One‐hundred and ten monosyllabic words selected from the Thorndike list of 1000 most frequently occurring words in English to represent equally each of 10 vowels were presented to 300 American listeners in an articulation test. Also tested were 72 spondee words, half selected from those in use in audiological tests and half from those in frequent use in air traffic control, further to represent the same vowel sounds. Masking of the stimuli was accomplished by recording separately each of nine prolonged vowels intoned by a trio of male voices. Results indicate that vowels of equal sound pressure levels differ considerably in masking effectiveness, that words containing specific vowel are not masked optimally by the same vowel, and that spondees are masked by prolonged vowels in the same rank as are the monosyllables. Prolonged vowel sounds with relatively high concentrations of energy between 700 and 1000 cps are most effective as masking agents. Rank order correlation of observed masking effectiveness with masking effectiveness predicted by the Strasberg method is 0.52, the Beranek method is 0.59, and by the Pickett‐Kryter method, 0.69. Some observations on resistance of words to masking are made in relation to phonemic transition areas within words.

Ultrasonic Reflectoscope with an Indicator of the Degree of Coupling between Transducer and Object

A. Lutsch

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 544-548 (1958); (5 pages)

Online Publication Date: 29 Jun 2005

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A further development of Firestone's Reflectoscope is described, indicating the degree of coupling between transducer and the test object. It is shown that the distortion of a radio‐frequency pulse—produced by the transducer—is a function of its coupling to the test object. Therefore, the distortion can be used to measure the coupling. The trailing edge of the radio‐frequency pulse is amplified by a time‐selective amplifier, rectified and connected to a galvanometer. Different conditions of coupling are analyzed. Figures are given for a barium titanate transducer working at 500 kcps. References such as back boundaries are no longer necessary in the field of nondestructive testing.

Ultrasonic Absorption in Liquids. I

M. Mokhtar and H. Youssef

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 549-551 (1958); (3 pages)

Online Publication Date: 29 Jun 2005

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The absorption of ultrasonic waves is measured for five nonassociated and five associated liquids at different temperatures extending between their freezing and boiling points. The absorption is measured by an electrodynamic balance specially developed for this purpose and explained in a previous issue. No relaxational processes were detected by varying the temperature. The thermal coefficient of absorption (1/α) (∂α/∂t) is not constant for any liquid, but it varies with temperature. Moreover, its behavior changes from one liquid to another. Such behavior, if plotted on normalized scale of temperature (between freezing and boiling points) instead of ordinary scale, brings all nonassociated liquids to one common line given by (1/α) (∂α/∂t)  =  c1tN½, and all associated liquids to another common line given by (1/α) (∂α/∂t)  =  c2tN+c3, where tN is the normalized temperature. The constants c1, c2, c3 do not depend on the nature of any particular liquid used. Thus these equations may be considered as “reduced equations of absorption.”

Elastic Strain Produced by Sudden Application of Pressure to One End of a Cylindrical Bar. I. Theory

Robert Folk, George Fox, C. A. Shook, and C. W. Curtis

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 552-558 (1958); (7 pages) | Cited 4 times

Online Publication Date: 29 Jun 2005

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A double transform method is used to solve the problem of determining the elastic strain in a semi‐infinite cylindrical bar with a stress free lateral surface, subject to the end conditions that the stress applied normally to the end is uniform and has a step function time dependence and that the radial displacement at the end is always zero. The exact solution appears as a sum of Fourier integrals whose integrands have the form of Pochhammer‐Chree waves. These integrals cannot be evaluated in general by simple means, but asymptotic solutions have been obtained which are valid for large distances of travel. The theoretical predictions are compared with the results of experiment in a companion report.

Elastic Strain Produced by Sudden Application of Pressure to One End of a Cylindrical Bar. II. Experimental Observations

George Fox and C. W. Curtis

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 559-563 (1958); (5 pages) | Cited 2 times

Online Publication Date: 29 Jun 2005

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Measurements are presented which show that the elastic strain produced in a cylindrical bar by step‐function end‐loading corresponds closely to predictions of the theory presented in Part I. In particular, even at large distances from the end of the bar, there is an observable strain moving faster than the bar velocity determined by Young's modulus. The theoretical shape for the head of the pulse conforms to experiment, and the head is followed by oscillations having the correct periods and amplitudes. Second‐mode oscillations appear at the times predicted and with the expected periods and amplitudes.

On the Attenuation of Finite Amplitude Waves in a Liquid

Isadore Rudnick

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 564-567 (1958); (4 pages) | Cited 1 time

Online Publication Date: 29 Jun 2005

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An expression is obtained for the rate of attenuation of large amplitude waves of stable form propagated in a liquid whose attenuation varies as the square of the frequency. Calculations are presented for several liquids and comparison made with recent published data.

Vibration of Axially Loaded Beams Carrying Distributed Masses

Hugh L. Cox

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 568-571 (1958); (4 pages)

Online Publication Date: 29 Jun 2005

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The lowest two natural frequencies of flexural vibration are obtained, by the use of energy methods, for uniform axially loaded beams which rest on elastic foundations and which carry masses that may be distributed symmetrically along portions of the spans of the beams. The ends of the beams may be either pinned or clamped. Simple formulas for the lowest two frequencies are given so that one may compute rapidly a desired frequency and determine the effects of the various parameters which influence that frequency.

Averaging Time and Data‐Reduction Time for Random Vibration Spectra. II.

Charles T. Morrow

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 572-578 (1958); (7 pages)

Online Publication Date: 29 Jun 2005

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In Part I, formulas were given for uncertainty when a power‐spectral‐density plot is estimated from a short sample of random vibration. The relation between this problem and the time required to obtain the spectrum was investigated for the sweeping of a simple analyzer through the frequency band. Other methods of obtaining the spectrum are now discussed.

Note on the Backscattering of Sound from the Sea Surface

Elroy O. LaCasce, Jr.

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 578-580 (1958); (3 pages)

Online Publication Date: 29 Jun 2005

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Experimental observations of backscattering from the sea surface are compared with computations based on an idealized surface. The scattering at angles near normal incidence is related to the theory of scattering from a sinusoidal surface. Scattering patterns for superposed sinusoids indicate the effect of ripples on backscattering.
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Caravelle Takeoff Noise Study

Laymon N. Miller and Leo L. Beranek

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 581-581 (1958); (1 page)

Online Publication Date: 29 Jun 2005

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Abstract Unavailable

Unreleased Velar Plosives after Back‐Rounded Vowels

Pierre Delattre

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 581-582 (1958); (2 pages)

Online Publication Date: 29 Jun 2005

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Abstract Unavailable

Simple Demonstration of the Presence of Second Harmonic in Progressive Ultrasonic Waves of Finite Amplitude

K. L. Zankel and E. A. Hiedemann

J. Acoust. Soc. Am. Volume 30, Issue 6, pp. 582-583 (1958); (2 pages) | Cited 1 time

Online Publication Date: 29 Jun 2005

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