ABSTRACTS OF TECHNICAL PAPERS 213 



energy below this frequency is completely suppressed. These results 

 indicate that the sound absorption coefficient of materials placed in an 

 auditorium for reducing the reverberation time should be high for 

 tones of low frequency and low for those of high frequency. Most 

 porous materials commonly used for this purpose have absorption 

 characteristics quite the reverse. Rooms that have been treated with 

 a rather large amount of such materials are therefore often unsatis- 

 factory for speaking purposes, although the adjustment for reverber- 

 ation time may have been carried out according to accepted standards. 



