Optimum Reverberation Time for Auditoriums

H E R E is very little published data in regard to the change in reverberation time with frequency in auditoriums which a r c considered near ideal. It is often mentioned by engineers and physicists that to secure the best acoustical results, the reverberation tim-e should be the same for all frequencies in any one room. This specifies t h a t the sensation level shall decay at the same rate for all frequencies of interest. It seems more reasonable, however, to specify that the loudness of all pure tones shall decay at the same rate for all frequencies since it is th« loudness of a tone which takes into consideration not only the energy level but also its ultimate effect upon one's brain. In Fig. 1 * arc plotted data which show the relation between the loudness as judged by a considerable number of otaervers and the sensation level. It will be seen that for frequencies between 700 and 4000 cycles per second these two quantities arc equal to each other so that the two points of view mentioned above demand identical conditions throughout this frequency band. Outside of this band, however, any change in the sensation level gives a greater changc in the loudness, as may be seen. The maximum loudness in which we are interested at present is about 73.* In the figure the curves may be replaced by straight lines which represent fair approximations to the observed data up to this loudness. This family of straight lines may be represented by the expression U - AfSu (1)