- 30 ILLINOIS STATE ACADEMY OF SCIENCE 



and noting the duration of audible sound under these 

 conditions, the ratio of the efficiencies of rugs to cush- 

 ions may be determined. Naturally, the next step in the 

 investigation was the determination of the absorbing 

 power of the cushions in terms of some more universally 

 accessible and more permanent unit. Viewed from the 

 standpoint of reverberation, it is immaterial whether the 

 sound energy is dissipated as heat, as is the case in true 

 absorption, or escapes from the room through an opening. 

 Experiments in rooms with a large number of windows 

 showed that open windows are also effective in reducing 

 the time of reverberation. The relative efficiencies of 

 cushions and open windows Avere determined in the man- 

 ner indicated above. Assuming that the latter acts as a 

 perfect absorber*, the absorption co-efficients of a large 

 number of materials that are used in the interiors of 

 auditoriums were measured as outlined above, and have 

 been published from time to time in Architectural and 

 Scientific Journals. 



Extending the experiments to a large number of rooms 

 of different volumes, it was shown that the constant pro- 

 duct of absorbing power and time of reverberation is 

 directly proportional to the volume of the room. Using 

 sources of different acoustical powers, the times of re- 

 verberation were found to be proportional to the lo- 

 garithms of the initial intensities. 



In the foregoing, we have gone somewhat in detail 

 into these first experiments merely to illustrate the 

 method by which quantitative sound measurements have 

 been made with apparatus no more complicated than a 

 stop watch and the unaided ear. Pursuing this method 

 through a course of the most careful investigations cov- 

 ering a period of more than twenty years, Professor Sa- 

 bine secured data, and developed a complete theory of 

 auditorium acoustics, which makes the remedy of faulty 

 conditions entirely possible, and, what is practically more 



* Recent experiments show that this assumption is true only In 

 special cases. Theoretical considerations indicate that the fraction of 

 the sound that passes through an opening is not in general unity, and that 

 a portion of the incident sound energy is reflected. The relation between 

 the reflected and the transmitted portions depends upon the dimensions 

 and the shape of the opening as well as upon the wave length of the 

 sound. It is to be said that later work is not based upon this assumption. 



