Page 281 - The Master Handbook Of Acoustics

256 CHAPTER ELEVEN

in a 8 × 9-ft frame on the floor. Diffraction from the edges of this frame
often result in absorption coefficients greater than unity. In other
words, diffraction of sound makes the sample appear larger than it
really is.
Small cracks around observation windows or back-to-back micro-
phone or electrical service boxes in partitions can destroy the hoped-
for isolation between studios or between studio and control room. The
sound emerging on the other side of the hole or slit is spread in all
directions by diffraction.
In summary, diffraction causes sound, which normally travels rec-
tilinearly, to travel in other directions.

Endnotes

1 Wood, Alexander, Acoustics, New York, Interscience Publishers, Inc. (1941).
2 Olson, Harry F., Elements of Acoustical Engineering, New York, D. Van Nostrand Co. (1940).
3 Muller, C.G., R. Black, and T.E. Davis, The Diffraction Produced by Cylinders and Cubical
Obstacles and by Circular and Square Plates, J. Acous. Soc. Am., 10, 1 (1938) p. 6.
4 Rettinger, M., Acoustic Design and Noise Control, Chemical Publishing Co. (1973).
5 Vanderkooy, John, A Simple Theory of Cabinet Edge Diffraction, J. Audio Eng. Soc., 39, 12
(1991) 923-933.
6 Kessel, R.T., Predicting Far-Field Pressures from Near-Field Loudspeaker Measurements, J.
Audio Eng. Soc., Abstract, Vol. 36, p.1,026 (Dec 1988), preprint 2729.
7 Kaufman, Richard J., With a Little Help from My Friends, AUDIO, 76, 9 (Sept 1992) 42-46.