MINIMUM AUDIBLE INTENSITY OF SOUND. 



439 



times before it is dissipated by absorption and transmission. There 

 are three effects of this multiple reflection ; first, it increases to a large 

 degree the average intensity of sound within the room, second, it sets 



10 



SO 



100 



200 



400 



eoo 



1600 



3200 



6400 



FIGURE 2 



up a stationary wave system with definite regions of maximum and 

 minimum intensity, and third, it reacts on the source to change the 

 amount of energy emitted. 



In a room such as the lecture hall used by Wien for his experiments, 

 the actual average intensity of sound throughout the room under 



