316 



TABLE 310.— ARCHITECTURAL ACOUSTICS (concluded) 



0.020 



0.018 



0.016 



01 0.014 



0.012 



a. O.OIO 

 HI 



z 



2 0.00& 



< 



D 

 Z 

 UJ0.0O6 



0.OO4 



0.002 



io 



ZO 30 40 50 60 



RELATIVE HUMIDITY IN PER CENT 



80 



90 



Fig. 3. — Attenuation coefficient m per foot as a function of humidity. 



TABLE 310A.— OPTIMUM REVERBERATION TIME (FIGS. 4 AND 5) 



The following figures give the recommendations of Knudsen and Harris for optimum 

 reverberation time for different types of rooms as a function of room volume. The optimum 

 times for speech rooms, motion-picture theaters, and school auditoriums are given by a 

 single line ; the optimum time for music by a broad band. The optimum reverberation time 

 is not the same for all kinds of music. For example, slow organ and choral music require 

 more reverberation than does a brilliant allegro composition played on woodwinds, piano, 

 or harpsicord. 



The optimum reverberation time vs. frequency characteristic for a room can be obtained 

 from these charts in the following manner : After having specified the volume and purpose 

 of the room, determine the optimum reverberation time at 512 cycles from the upper chart. 

 Then, to obtain optimum reverberation time at any other frequencies multiply the 512-cycle 

 value by the appropriate ratio R which is given in the lower chart. Note that R is unity 

 for frequencies above 500 cycles, and is given by a band for frequencies below 500 cycles. 

 The ratio R for large rooms may have any value within the indicated band ; preferred 

 ratios for small rooms are given by the lower part of the band. 



{continued) 



SMITHSONIAN PHYSICAL TABLES 



