38 



BELL SYSTEM TECHNICAL JOURNAL 



If a value of c equal to 2.7, which is approximately equal to the 

 square root of the ratio of mechanical impedances of the two dia- 

 phragms, then the solution for reversed DC supply becomes 



/=1001 cycles 



/j=47.3 



r = 236 ohms 



7 = 39 mils 



i = 10 mils 

 e = 7.16 volts 

 z = 3.9 microns 

 10.5 microns 



y 



It is thus seen that changing the ratio arm has increased the howling 

 intensity, but the increase for the various elements is greatly different. 

 The frequency is slightly lowered, the values of h and / have been 



L 



k=300 



T 



R 





Fig. 8 



reduced by 26% and 14% respectively, while the values of y, z, T, 

 i and e have been increased 400%c. 105%, 57%, 22% and 30% respect- 

 ively. 



If the circuit of Fig. 7 is modified as shown in Fig. 8, the induct- 

 ance L being very large, then the condition for howling becomes 



cSr-\—St 



and 



/= r 



24 



300+ r 



(21) 



(22) 



