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Sept., 1937] PROGRESS IN ACOUSTICS 237
with the Rayleigh diffraction theory. • The results are given as follows :
Frequency 100 200 400 800 1200 1600
k 75 56 29 12 6 2.5
For an opening 71 millimeters long, and of different widths as indicated in the table, they obtained, at a frequency of 800 cps. :
Slit width (mm.) 0.1 0.2 0.5 1.0 2.0 3.0
k 300 200 100 64 38 33
The dependence of k upon the frequency is approximately the s. me for rectangular openings as for circular apertures. These results are significant to the acoustical engineer not only in sound insulation but also in the design of sound absorbent materials — the excess of sound energy transmitted through the openings is "absorbed" from the incident sound-waves.
(IV) CONTROL OF REVERBERATION IN A ROOM BY MEANS OF RESONATORS
It is well known that the ancient Greeks attempted to improve the acoustics of their open-air theaters by distributing a large number of bronze vessels, fashioned into resonators, in regularly spaced niches throughout the seating area of the theater. These resonators were carefully tuned to respond to the various notes of musical systems and thereby would emphasize the more important frequency components of speech and music, and would particularly emphasize those notes in music that correspond to the harmonic scale. It is not improbable that these resonators would contribute some value to speech and music, in emphasizing the particular frequency components that are harmonious in music and contribute most to the intelligibility of speech. Somewhat similar resonators, or sound-boxes, are used in old Byzantine and Russian churches. Rschevkin3 has treated theoretically this problem of resonators in rooms, and shows that such a system of resonators in a room increases (1) the effective volume of the room, and (2) the effective absorption of the room. If the damping in the necks of the resonators is small, the volume effect predominates, and the apparent reverberation time in the room is increased especially for frequencies near the natural frequency or frequencies of the resonators. If the absorption in the necks of the resonators is large, the absorption effect predominates, and the apparent reverberation time in the room is diminished for frequencies that are near the natural frequency or frequencies of the resonators. By