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Journal of the Acoustical Society of America

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Apr 1970

Volume 47, Issue 4A, pp. 951-972


Acoustics of Northrop Memorial Auditorium

B. S. Ramakrishna and T. I. Smits

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 951-960 (1970); (10 pages)

Online Publication Date: 03 Aug 2005

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The Northrop Memorial Auditorium is a multipurpose hall with a seating capacity of 4800 in the auditorium and a hundred or more on the stage. It is unique among halls of its size in having, perhaps, the smallest volume per seat (∼210 ft3/seat) and the lowest reverberation time (0.94±0.1 sec). The paper presents the results of measurements on (1) reverberation times, (2) noise levels, (3) sound‐pressure‐level distribution, and (4) intelligibility of speech. By comparison with previous measurements, the acoustical results of some changes made in the auditorium have been assessed. It is hoped that, in turn, these measurements will furnish a reference point in evaluating the outcome of a major remodeling the hall is about to undergo. An attempt is made to relate the physical measurements to the psychoacoustical responses experienced in the hall. The role of sound reinforcement systems in determining the subjective response and hence in choosing a suitable reverberation time for multipurposes halls is discussed briefly.

Sampling Statistics for an Acoustic Mode

Richard Waterhouse

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 961-967 (1970); (7 pages)

Online Publication Date: 03 Aug 2005

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The distribution functions are considered for the random sampling in space of a three‐dimensional acoustic mode. These functions are of interest when it is desired to estimate either the total acoustic energy present in the space, from a finite number of sample values, or the driving point impedance at an arbitrarily chosen point. Expressions are obtained for the probability density and cumulative functions for axial, tangential, and oblique modes set up in a rectangular space containing an ideal elastic fluid. The results are derived theoretically and checked by a numerical sampling procedure. It is found that the distributions are independent of the proportions of the enclosure and of the mode number. They are also the same for hard or soft boundary conditions, or for combinations of these.
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BOND INSPECTION BY DYNAMIC TIME‐AVERAGE INTERFEROMETRIC HOLOGRAPHY OF ULTRASONICALLY EXCITED PLATES

Robert K. Erf, Herbert G. Aas, and James P. Waters

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 968-969 (1970); (2 pages)

Online Publication Date: 03 Aug 2005

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In thin plates, the visualization of ultrasonically excited plates modes by dynamic time‐average interferometric holography can be used to detect some types of material defects. Representative results of a feasibility study, which dramatically demonstrate the potential of the method for nondestructive inspection of the bonds between boron‐epoxy prepreg material and aluminum substrates, are presented. In particular, it is shown that an area of less than 1 cm2 can be easily identified with an excitation frequency on the order of 20–40 KHz.

EASY METHOD FOR MEASURING THE NATURAL FREQUENCY AND DAMPING RATIO OF ELECTROMAGNETIC SEISMIC VIBRATION PICK‐UPS

S. Braun

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 969-970 (1970); (2 pages)

Online Publication Date: 03 Aug 2005

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A method is described for measuring the natural frequency and damping ratio of an electromagnetic seismic transducer. The method is purely electronic and is without any mechanical excitation.

NBS SHOCK TUBE

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 970-970 (1970); (1 page)

Online Publication Date: 03 Aug 2005

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Abstract Unavailable

SOUND IN THE ARTS

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 971-971 (1970); (1 page)

Online Publication Date: 03 Aug 2005

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Abstract Unavailable

PSYCHOACOUSTICAL GLOSSARY

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 971-971 (1970); (1 page)

Online Publication Date: 03 Aug 2005

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Abstract Unavailable

ACOUSTICAL DRAPERY

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 971-972 (1970); (2 pages)

Online Publication Date: 03 Aug 2005

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Abstract Unavailable

ERRATUM

J. Acoust. Soc. Am. Volume 47, Issue 4A, pp. 972-972 (1970); (1 page)

Online Publication Date: 03 Aug 2005

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Abstract Unavailable
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