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ARCHITECTURAL ACOUSTICS
321
(f ) Combined Effects of Loudness and Reverberation upon the Reception of Speech in Auditoriums. In the earlier sections of this paper the effects of loudness and reverberation upon speech reception were considered separately. It is obvious that as the time of reverberation in an auditorium is reduced, the average loudness of speech, assuming a constant power rate for the speaker, will be reduced correspondingly. This suggests that there may be an optimal time of reverberation for speech in an auditorium. This would occur when a further reduction in the reverberation would concurrently reduce the loudness to the extent that the impairment occasioned by the diminished loudness would just compensate for the improvement occasioned by the reduction of the reverberation. The manner in which this occurs is indicated by the series of curves which are plotted in Fig. 8. These curves give the calculated values of the percentage articulation in auditoriums of different sizes and times of reverberation, for the probable average loudness of speech of
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Volume Cu. Ft. Cu. rl.
(a) 25,000. 707. (6) / OO.OOD. 2,630. (C) 4 00,000. 11,300. (d) 600.000. 22.600.
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Time of Reverberation Seconds
FIGURE 8.
Group of curves giving the probable percentage articulation in auditoriums of different sizes and with different times of reverberation. These curves indicate that there is an optimal time of reverberation for the hearing of speech in an auditorium of a certain size.