SYSTEM ADAPTATION 



303 



a definite loss in perspective effect if the microphones were placed at 

 a greater distance from the orchestra. This effect is discussed more 

 fully in another paper of this symposium. 



Fig. 2 — Floor plan of Academy of Music, showing location of microphones. 



With the microphones located close to the orchestra their response- 

 frequency characteristics will be essentially those given by the normal 

 field calibration, since relatively little energy is received from the sides 

 and back. For a distant microphone position it would be necessary 

 to use the random incidence response characteristic, which differs from 

 the normal because of the variation in directional selectivity of the 

 microphones as the frequency varies. This difference in response 

 characteristic depends upon the size of the microphone and may 

 amount to as much as 10 db at 10,000 c.p.s. It may be pointed out 

 here that this difference in response is one factor frequently overlooked 

 in the placement of microphones. 



In addition to the three microphones regularly used, a fourth was 

 provided to pick up the voice when a soloist accompanied the orchestra. 

 In this case only the two side channels were used for the orchestra, the 

 voice being transmitted and reproduced over the center channel. The 

 solo microphone was so shielded by a directional baffle that it responded 

 mainly to energy received from a rather small, solid angle. This 

 arrangement permitted independent volume and quality control for 

 the vocal and orchestral music. 



The Concert Hall 

 The music was reproduced before the audience in Constitution Hall 

 in Washington, D. C. This hall has a volume of nearly 1,000,000 



