188 BELL SYSTEM TECHNICAL JOURNAL 



Methods for Measuring hiterfering Noises} Lloyd Espexschied. 

 This paper outlines various methods of measuring interference, 

 particularly in radio telephony, which have been found useful in the 

 Bell System. 



Reverberation Time Measurements in Coupled Rooms.'' Carl F. 

 Eyring. The decay of residual sound in simple reverberant enclosures 

 has been the subject of much study. Out of these investigations 

 along with other important developments formulae have emerged 

 which may be used to calculate the reverberation time of enclosed 

 rooms, the one proposed by Sabine being applicable to live rooms, 

 but a more general one being necessary if applied to dead rooms. 

 These formulae may be used in the study of simple enclosures in 

 which the sound is diffuse, the absorbing material is well distributed, 

 and the decay of the residual sound is exponential in time. They 

 may not be applied indiscriminately to complex structures for the 

 author has shown that the curves illustrating the decay of the residual 

 sound intensity level may not be straight under certain conditions 

 for coupled rooms of different natural reverberation times or even 

 for a single room with no sound diffusing scheme and non-uniformly 

 distributed absorption. 



The present paper presents further data on acoustically coupled 

 rooms and offers a theoretical study and formulae applicable to such 

 complex structures. Somewhat similar studies have been made by 

 Buckingham and Davis in the investigation of sound transmission 

 through partitions. But before the coupled room formulae which are 

 based on certain idealizations can be applied in general to auditoriums 

 with various types of balconies and under-balcony spaces, they must 

 be carefully checked by a thorough experimental study of typical 

 theatres. Thus it is expected that empirical formulae, based on 

 theory and experiment, may be evolved for each type of complex 

 structure. 



Recently developed instrumental methods of measuring reverbera- 

 tion time, especially those methods that measure the decay history of 

 the residual sound, give promise of being the tools needed in this 

 study. The results recorded in this paper were made on a meter 

 described by Wente and Bedell in their paper " Chronographic Method 

 of Measuring Reverberation Time" and by the author. This instru- 

 ment plots almost automatically the intensity level of the residual 

 sound measured in db and the time. 



^Proc. I. R. £., November, 1931. 



^ Jour. Acous. Soc. Amer., October, 1931. 



