A NON-DIRECTIONAL MICROPHONE 



419 



If a voltage is in series with Zl it must be multiplied by the ratio 

 of AnjAm. If these transformations are carried out we obtain the 

 following equations. 



a-iAj 



■X-i + 





(iiAo 



+ 



Xo 



[{Jh 





+ JWW/2 



A, 



A2 



+ ^-2 



+ 



-X2 



(as + ^5)^0^, . ,_^ /^4n 

 ^^ + Jo:m4 -j- 



+ r. 



A, 

 A, 



I A. 



V ^4 



J« 



■r2 



X"o 



-t2 = 0, 



^4 = 0, 



Xi 



0. 



These equations can be translated into an equivalent circuit in which 

 the effect of the equalizing tube may be inserted as a shunt enabling 

 the impressed force to enter the case and to reach the diaphragm after 

 passing through numerous circuit elements. 



The voltage generated in the coil due to its motion in an air gap of a 

 permanent magnet is proportional to .to the velocity of the coil. Hence 



ei {Ao) 



the expression should be solved for the expression 



, , , = Z. If / is 



Xo (^-1) 



the length of the wire in the coil, B the flux density in the gap, then the 

 voltage generated in the coil is 



V = BIxo 



Ble, {A,) 



Z (^-1)' 

 and since d = pA^i where p is the pressure we have finally 

 V BlAo 



P z 



The response in db is equal to 



10~^ volts per bar. 



17 = 20 logio 



BlAo 



IO- 



CS) 



