PAPERS ON PHYSICS 297 



ACOUSTICAL DESIGN IN BUILDINGS 



F. R. Watson 



Professor of Experimental Physics, 

 University of Illinois 



Acoustical defects in buildings are forced on the at- 

 tention of the public in a considerable number of instances. 

 These defects are sometimes found in auditoriums where 

 speaking or music, or both, are heard at a disadvantage, 

 or again in rooms where sounds from other parts of the 

 building become noticeable in an objectionable way. 



The usual cause of the defects in an auditorium is found 

 in the hard, non-porous walls of the room which reflect 

 a large percentage of the incident sound with a consequent 

 small absorption of the sound energy. This results in an 

 undue prolongation so that successive sounds, as in speak- 

 ing, are thus thrown in competition with each other and a 

 listener has difficulty in following the sequence of a speech. 

 This prolongation of the sound, or reverberation as it is 

 called, may be corrected or avoided by having a suitable 

 amount of sound absorbing material in the room. For 

 music, the defect is not so objectionable, because musical 

 sounds can overlap and yet be acceptable for most cases. 



These principles may be illustrated by describing two 

 auditoriums recently built at the University of Illinois 

 which incorporated acoustical features designed by the 

 writer in co-operation with the architects. In both audi- 

 toriums, the acoustical specifications were detailed in the 

 plans before the rooms were constructed. 



One auditorium is the Concert Hall of the Smith Music 

 Building, for which Professor James M. White was archi- 

 tect with Mr. George E. Wright as associate architect. In 

 this case it was desired to have a room with qualities that 

 would co-ordinate as far as possible in the acceptable pro- 

 duction of music. For this puiT)Ose, as shown by the 

 theory of the subject and illustrated in the cases of audi- 

 toriums already built and found suitable for music, the 

 room was designed with a moderate amount of absorbing 

 material so that the reverberation would be somewhat pro- 



