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Journal of the Acoustical Society of America

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Nov 1947

Volume 19, Issue 6, pp. 943-996

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The Influence of Body-Baffle Effects on the Performance of Hearing Aids

R. H. Nichols, Jr., R. J. Marquis, W. G. Wiklund, A. S. Filler, C. V. Hudgins, and G. E. Peterson

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 943-951 (1947); (9 pages)

Online Publication Date: 17 Jun 2005

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The effect of the wearer's person as an acoustic baffle on the response of a hearing aid, under free-field and diffuse-field conditions, has been studied with a number of hearing aids and wearers. A characteristic effect is found for each model of hearing aid when it is worn at center-chest position in free field. The character of the effect does not appear to be strongly correlated with the size and shape of the wearer. In a sound field of “random” direction of incidence, the body-baffle effect appears to be negligible. Within the limits of linear amplification of a hearing aid, one of the most pronounced of the body-baffle effects had little or no influence on the intelligibility of speech, as determined with four hard-of-hearing subjects.

Cones as Underwater Transducer Reflectors

Roland E. Mueser

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 952-955 (1947); (4 pages)

Online Publication Date: 17 Jun 2005

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Two conical reflectors have been constructed and used in conjunction with complete 90 tones. The result is a directional transducer in place of the non‐directional pancake pattern resulting from a line source radiator. The change in peak sensitivity by focusing the beam is approximately equivalent to the change in directivity index.

A Precision Ultrasonic Interferometer for Liquids and some Velocities in Heavy Water

D. R. McMillan, Jr. and R. T. Lagemann

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 956-960 (1947); (5 pages) | Cited 5 times

Online Publication Date: 17 Jun 2005

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An acoustic interferometer of improved design and the associated electronic circuit for measurement of ultrasonic velocities in liquids are described. A beat frequency oscillator is used to generate the ultrasonic waves in the liquid, and a vacuum‐tube voltmeter is employed as a detector of nodal positions. In order to secure adequate stability an electronically stabilized power supply is used. Measurements of velocities in acetone, benzene, and distilled water are compared with earlier workers and new measurements for heavy water at 5°, 10°, and 15°C are tabulated.

Self‐Reciprocity Calibration of Electroacoustic Transducers

Edwin L. Carstensen

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 961-965 (1947); (5 pages) | Cited 1 time

Online Publication Date: 17 Jun 2005

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By an extension of the reciprocity principle for the absolute measurement of sound, it is demonstrated that a calibration may be obtained on a single transducer without the aid of auxiliary transducers. Measurements using the technique are described and shown to give satisfactory agreement with conventional calibrations.

A Recorder of Difference of Level

James M. Lawther and John G. King

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 966-971 (1947); (6 pages)

Online Publication Date: 17 Jun 2005

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Modifications have been made on a Sound Apparatus Company level recorder to permit its application to the measurement of difference in level between two sounds. The modified circuit explained with reference to simplified diagrams; anti‐hunting devices are briefly noted; and the methods of pre‐setting the instrument for level and differential operation are discussed.

The Application of Helmholtz Resonators to Sound‐Absorbing Structures

Vilhelm L. Jordan

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 972-981 (1947); (10 pages)

Online Publication Date: 17 Jun 2005

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This paper intends to set forth some of the more important facts about sound‐absorbing structures of the kind whose absorption may be explained as primarily due to resonance phenomena of the same kind as that occurring in Helmholtz resonators. It is believed that this kind of absorption has not been met with the general interest which it deserves, neither from the theoretical nor from the practical point of view. The theory is developed here only for the simple case of a single resonator. Special attention has been given to the question of the resistance of the resonator. It is pointed out, that the formula commonly used for the resistance of an aperture is not applicable in the case of resonance absorption, the actual values of the resistance being 3–6 times higher than the calculation predicts in the cases considered. Some examples of the practical applications of resonance‐absorbing structures are mentioned.

The Measuring of Impact Sound Transmission through Floors

Fritz Ingerslev, A. Kjerbye Nielsen, and S. Falck Larsen

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 981-987 (1947); (7 pages)

Online Publication Date: 17 Jun 2005

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Construction and Design of Parmly Sound Laboratory and Anechoic Chamber

Peter J. Mills

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 988-992 (1947); (5 pages) | Cited 1 time

Online Publication Date: 17 Jun 2005

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A description is given of the construction details of the Sound Laboratory recently completed by the Parmly Foundation at Technology Center, Chicago. The function of the laboratory is to carry out research in the prevention and alleviation of deafness. The chief feature of the laboratory is an echo free or “anechoic” chamber. The 40‐ton chamber of concrete, steel, wood, and sheet‐rock construction is suspended on Neoprene pads to have a natural frequency of about four and one‐half cycles per second. Continuous ventilation through ducts of high sound attenuation, 90 db at 128 c.p.s., is provided. The inner surfaces are designed to have 99 percent absorption or better at 115 cycles per second or above. The Harvard treatment of wedge‐shaped Fiberglas is used. The chamber is housed in a concrete block wing, the walls of which are lined with Fiberglas sheets. Costs in terms of man hours are given.

Performance of the Anechoic Room of the Parmly Sound Laboratory

H. C. Hardy, F. G. Tyzzer, and H. H. Hall

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 992-995 (1947); (4 pages) | Cited 3 times

Online Publication Date: 17 Jun 2005

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The performance of the anechoic room of the Parmly Sound Laboratory has been measured to determine the characteristics of rooms of small volume with wedge‐covered walls. The inverse square law holds to within ±1 db to 6.5 feet from 60 to 24,000 c.p.s., although the theoretical cut‐off frequency of the room is 115 c.p.s. At 100 c.p.s., the radiation resistance of a loudspeaker placed near the walls was found to be 18 percent above the free‐field value, and the radiation reactance was approximately 5 percent above the free‐field value. The differences disappeared two feet from the wall. The wall transmission has been measured as a function of frequency, and the wedges themselves are found to act similarly to a thin plate in optics, having a maximum transmission at 110 c.p.s.
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Electronic Musical Instruments

B. F. Miessner

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 996-996 (1947); (1 page)

Online Publication Date: 17 Jun 2005

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Abstract Unavailable

Acoustical Society News

Wallace Waterfall

J. Acoust. Soc. Am. Volume 19, Issue 6, pp. 996-996 (1947); (1 page)

Online Publication Date: 17 Jun 2005

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Abstract Unavailable
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