CONDENSER AND CARBON MICROPHONES 



57 



diaphragm a resonant frequency of 5700 cycles per second. The 

 method employed in making the determination of the resonant 

 frequency is substantially the same as that used in connection with the 

 assembly of the condenser microphone, with the exception that the 



Pier. 7_Westeni Electric Company's 387-type carbon microphone. 



DIAPHRAGM 



FINAL 

 STRETCHING 

 RING 



DAMPING 

 PLATE GROOVE 



INITIAL 

 STRETCHING -• 

 RING 



Fig. 8— Cross-sectional view of the 387-type carbon microphone. 



frequency at which the ma.ximum output occurs is usually determined 

 by ear rather than by the coupler method previously described. 

 In order to insure a uniformly low contact resistance the portions of 

 the diaphragm which are in contact with the granular carbon are 

 covered with a film of gold deposited by cathode sputtering. 



