84 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



10 



c. 



C3 C4 



Figure 14. 



C, 



Curves expressing the reverberation in the large lecture room of the Jefferson 

 Piiysical Laboratory with (lower curve) and without (upper curve) an audience. 

 Tliese curves express in seconds the duration of tlie residual sound in the room 

 after the cessation of sources producing intensities 10"^ times minimum audible 

 intensity for each note. The upper curve describes acoustical conditions wliich 

 are very unsatisfactory, as the hall is to be used for speaking purposes. The lower 

 curve describes acoustically satisfactory conditions. C3 (middle C) 256. 



