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Journal of the Acoustical Society of America

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Apr 1941

Volume 12, Issue 4, pp. 481-531


A New Microphone Providing Uniform Directivity over an Extended Frequency Range

R. N. Marshall and W. R. Harry

J. Acoust. Soc. Am. Volume 12, Issue 4, pp. 481-498 (1941); (18 pages)

Online Publication Date: 16 Jun 2005

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A new microphone is described which consists of a moving coil pressure element combined with an improved ribbon pressure gradient element to give a cardioid directional characteristic. The theory of operation is reviewed, and consideration is then given to variations in directivity caused by diffraction, separation of the elements, and disparities in their phase and response characteristics. It is then shown how these variations are largely eliminated by equalization in the electrical circuit so that the resulting directivity is practically independent of frequency throughout the range from 70 to 8000 cycles. The use of a moving coil pressure element makes high efficiency possible, while the design of an unusually rugged ribbon element provides a marked reduction in noise due to air currents. Several useful directional patterns in addition to the cardioid pattern are provided in the new microphone, and the theory and merits of these patterns are presented. Finally some of the results which were obtained in field trials of the new microphone are di‐cussed.

Room Noise Spectra at Subscribers' Telephone Locations

Daniel F. Hoth

J. Acoust. Soc. Am. Volume 12, Issue 4, pp. 499-504 (1941); (6 pages) | Cited 3 times

Online Publication Date: 16 Jun 2005

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Abstract Unavailable

Ultrasonic Absorption in Water

Francis E. Fox and George D. Rock

J. Acoust. Soc. Am. Volume 12, Issue 4, pp. 505-510 (1941); (6 pages) | Cited 1 time

Online Publication Date: 16 Jun 2005

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The coefficient of absorption (2αν−2) of ultrasonic waves was measured by a radiation pressure method at frequencies from 7 to 50 Mc. The average value is given for each frequency. These cluster closely around 43.1 × 10−17, and there is no indication of a drop in 2αν−2. Errors entering into absorption measurements are discussed.

The Propagation of Sound in Cylindrical Tubes

Nathaniel Rochester

J. Acoust. Soc. Am. Volume 12, Issue 4, pp. 511-513 (1941); (3 pages)

Online Publication Date: 16 Jun 2005

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The theory of the propagation of sound in cylindrical tubes is presented. Formulas are developed for the calculation of the attenuation factor for the first mode (“plane” waves), and these formulas take into account both the resistive and reactive components of the tube wall impedance. The nature of the higher modes of sound propagation in the tube is illustrated.

On the Absorbing Power of an Opening Adjacent to an Absorbent Room

Sadao Kawashima

J. Acoust. Soc. Am. Volume 12, Issue 4, pp. 514-516 (1941); (3 pages)

Online Publication Date: 16 Jun 2005

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Abstract Unavailable

The Intensive Difference Limen in Audition

Forrest L. Dimmick and Ruth M. Olson

J. Acoust. Soc. Am. Volume 12, Issue 4, pp. 517-525 (1941); (9 pages)

Online Publication Date: 16 Jun 2005

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In spite of its interest for acoustics, the intensive difference limen for sound has not been determined over a comprehensive range of frequency and amplitude. In the present experiment we have determined the difference limens for discrete intensive discrimination at five frequencies ranging from 128 cycles to 1000 cycles with intensities from 0.02 bars r.m.s. pressure to 3.4 bars (−65 db to −15 db). Both the physical conditions and the psychological judgment have been carefully controlled. The data yield a value for Δ db of 2.4 db in the middle range of intensities (−35 db to −15 db or 35 SL to 70 SL.)

Elementary Quantity of Sound Perception

Samuel Lifshitz

J. Acoust. Soc. Am. Volume 12, Issue 4, pp. 526-528 (1941); (3 pages)

Online Publication Date: 16 Jun 2005

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Abstract Unavailable

The Mode of Vibration of a Clarinet Reed

C. S. McGinnis and C. Gallagher

J. Acoust. Soc. Am. Volume 12, Issue 4, pp. 529-531 (1941); (3 pages)

Online Publication Date: 16 Jun 2005

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Theoretical explanations of the action of the vibrating clarinet reed have been based upon the assumption of the partial closing of the aperture under the reed. This assumption is not supported by experimental evidence. The motion of the reed was observed stroboscopically, with the tone produced by an artificial embouchure. The actual frequency of the reed has been determined and other details in the mode of vibration observed.
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