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CINEMATOGRAPHIC ANNUAL
100 42 30
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60 40 20
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1.0 20 3.0 4.0 5.0 6.0 7.0 3.0 9.0
Re,i/e>rb<era tion Seconds FIGURE 4.
Curves showing the interfering effect of reverberation upon the hearing of speech. The lower curve represents the most probable fit with the observed data. The upper curve has been corrected for loudness, and corresponds to a loudness of 70 db.
pendent upon the amount of absorption in the room. Assuming the power of the speaker's voice to remain constant,1 the resulting intensity of the speech would be almost inversely proportional to the total amount of absorption in the auditoriums, or directly proportional to the time of reverberation. It was found experimentally that the average loudness of the speakers' voices used in these tests, in an auditorium having a volume of 8,440 cubic meters (300,000 cubic feet) and a time of reverberation of 1.50 seconds, was about 48 db. Using this datum, and the loudness-articulation data given in Fig. 3, it is possible to correct the lower curve in Fig. U for variation of loudness. The upper curve in Fig. U was obtained by applying such a correction so as to give the percentage articulation for a uniform loudness level of 70 db, which is the loudness level for optimal hearing. This curve has been extrapolated to a time of reverberation of .50 second, as indicated by the dotted portion of the curve. Such an extrapolation is warranted by articu
xThis assumption seems more plausible than the alternative one that the speaker maintains a constant loudness level. It seems likely, however, that neither assumption is correct. A speaker generally attempts to raise his voice to the loudness level required for satisfactory hearing, but is limited by the physical characteristics of his speech apparatus.