PAPERS PRESENTED AT GENERAL SESSIONS 31 



useful, enables the architect to provide in advance of con- 

 struction for acoustic conditions, with the same assur- 

 ance as he provides for lighting and ventilation. Finally, 

 the progress of the investigation developed an extremely 

 useful means of making acoustical measurements, which 

 may be called the Sound Chamber method. Having es- 

 tablished the relation existing between the time of re- 

 verberation, the absorbing power and the volume of the 

 room, and the acoustical power of the source, it is pos- 

 sible to compute the intensity in terms of minimuni audi- 

 ble intensity at any time after the source has ceased. The 

 only other physical factor upon which this time depends, 

 the acnity of hearing of the observer, enters into the 

 problem in such a way that the results are independent 

 of its absolute value. Hence, although this threshold 

 intensity may vary widely with the pitch of the sound, 

 and be markedly different for different individuals, yet 

 measurements made by different observers prove to be 

 quite consistent. 



The Laboratory at Geneva was built primarily for the 

 purpose of applying this method of acoustical measure- 

 ments to the study of the transmission of sound through 

 building constructions. Figure 3 shows the arrangement 

 for measuring the transmission of sound by standard 

 types of partitions as well as by any other construction 

 or material. The Sound Chamber is an empty room 

 27 X 19 X 19 feet, with walls of brick, eighteen inches in 

 thickness. As shown, there is no stnictural connection 

 between this room and the rest of the building. The ar- 

 rangements for excluding sound from without is such 

 that obseiwations requiring complete silence in the room 

 can be made while others are at work in the building. 

 Openings into three smaller rooms called Test Chambers 

 are made in the walls of the Sound Chamber. In these 

 openings, which are of different sizes, the largest being 

 6x8 feet, the partitions to be studied are built. Heavy 

 steel doors can be closed over these openings, so that it 

 is possible to restore the room to standard conditions 

 whenever control experiments are necessary. 



The source of sound is a complete organ of seventy- 

 two pipes, voiced so as to give as nearly pure tones as 



