374 BELL SYSTEM TECHNICAL JOURNAL 



A New Reverberation Time Formula} W. J. Sette. The earliest 

 work relating decay of sound in an auditorium and the acoustic 

 absorption of the surfaces was done by W. C. Sabine who developed the 

 formula which has recently been shown to be applicable to only "live" 

 rooms. More recently Fokker in Holland, Schuster and Waetzmann 

 in Germany and Eyring in this country derived an expression to hold 

 for "dead" rooms also. The assumption of continuous absorption at 

 the auditorium boundaries made in the Sabine formula was replaced by 

 the conception of intermittent absorption, which is more in accord with 

 actual conditions of decay. 



Both of these formulae presuppose in their derivation uniform dis- 

 tribution of energy at each incidence, although Eyring observed that 

 ordered states would necessitate assigning proper weights in computing 

 the average surface absorption. The new formula is based on a similar 

 assumption, but shifts the point of view to another kind of uniform 

 distribution. Instead of each surface receiving a proportional share of 

 the total energy in the room at each reflection, it is assumed that any 

 ray of sound, after repeated reflection will have struck any one surface 

 in proportion to the ratio of the area of that surface to the total room 

 surface. This formulation of the process of decay leads to an alter- 

 native reverberation equation and some further extension of reverbera- 

 tion theory. The new equation is, of course, necessarily specialized 

 and limited to those instances w^here the fundamental assumptions are 

 fulfilled, as is brought out in the body of the paper. 



^ Jour. Acous. Soc. Am., January, 1933. 



