6 KENNELLY AND KUROKAWA. 



3 being assumed constant over the entire surface of the diaphragm. 

 This power may be expressed as 



F = i^ iS abwatts (7) 



1 ('^ . 

 Avhere a,-- = I x- dS (rms. kines)- (8) 



or the Acctor mean velocity square i^- is the integrated mean value of 

 .r- over the entire surface. Under these conditions, the acoustic im- 

 pedance of the tube at the disk including both of its sides, will be 



F 

 z = . acoustic absohms Z (9) 



.r 



The mean square ratio ( -^ I = I - I of average to maxinnun central 



velocity or amplitude has been called the mass factor ^ of the dia- 

 phragm denoted by — . 



Tofal Mechanic Impedance on a Diaphragm: When a telephone 

 diaphragm is set in vibration imder an impressed vmf., due to a 

 simple harmonic alternating current in the coils, the maximum cyclic 

 velocity of the diaphragm o^er the poles depends upon the total 

 mechanic impedance to motion. The vector vmf. F may be taken as 

 proportional to the exciting current I rms. absamperes flowing through 

 the coils. ^ 



F = A I rms. dynes Z (10) 



Here A is the vector force factor of the instrument, and ordinarily 

 has a slope ^°, of about —30°, so that the Ainf. F has the same fre- 

 quency as I, and lags in phase l)ehind I by this angle ^°. The total 

 mechanic impedance z' of the diaphragm limits the max. cyclic 

 velocity to 



F F 



.r = -7 = ; — rms. kines Z (11) 



Z Z,/ + z 



F 



or z' = -T total mechanic absohms Z (12) 



X 



2 Bibliography 9, page 477. 



3 Bibliography 7, 8 and 9. 



