BASIC REQUIREMENTS 



243 



centimeter in joules, and T the volume of the hail in cubic centimeters, 

 then it is well known that 



/ = 



1 



ET 



V ' 



(1) 



6 log« 10 



Measurements have shown that when the sound intensity in a free 

 field reaches about 10^^ watts per square centimeter, the average 

 person begins to feel the sound. This maximum value is approxi- 



50 



100 500 1000 5000 



FREQUENCY IN CYCLES PER SECOND 



10,000 



50,000 



Fig. 1 — Limits of audible sound as determined by recent tests. 



mately the same for all frequencies in the important audible range. 

 Any higher intensities, and for some persons somewhat lower inten- 

 sities, become painful and may injure the hearing mechanism. This 

 intensity corresponds to an energy density / of 3 X 10~^ joules. Using 

 this figure as the upper limit to be tolerated by the human ear, then, 

 the maximum power of the sound source must be given by 



£ = 4.1 X 10-8^. 



(2) 



For halls like the Academy of Music in Philadelphia and Carnegie 

 Hall in New York City, in which the volume I^ is approximately 

 2 X 10"* cubic centimeters and the reverberation time about 2 seconds. 



