32 



ILLINOIS STATE ACADEMY OP SCIENCE 



possible. The wind pressure for the organ is supplied by 

 an organ blower driven by an electric motor placed just 

 outside the Sound Chamber The acoustic insulation be- 

 tween the blower and the organ is so good, that although 

 there is a direct air passage between the two, the noise 



■flOLK- 6t>ICH 



PLAN 



Figure 3. 



from the blower is entirely inaudible in the Sound Cliam- 

 ber. The organ is operated from four different key- 

 boards, one in each of the Test Rooms and one in the 

 Sound Chamber. By means of a specially designed stop- 

 watch chronometer, the duration of audible sound in the 

 larger room, and as heard in the smaller rooms through 



