THE RING ARMATURE TELEPHONE RECEIVER 



127 



currents. However, with the low effective mass and large effective area of 

 the diaphragm, the constants of the acoustical elements shown in Fig. 12 

 can be adjusted to compensate almost completely for the effects of eddy 

 currents, even up to quite high frequencies. 



(c) Force Factor 



The third element in the block diagram of Fig. 11 is r, the force factor, 

 defined as the force on the armature per unit current flowing in the receiver 



<: 5 

 q: 



Q 



< a 



jo^xa 



IN PHASE COMPOhJENT 

 6 7 8 9 10 



14 15 lexto® 



XIO^ 



400 



800 1200 1600 2000 2400 2800 3200 3600 

 FREQUENCY IN CYCLES PER SECOND 



Fig. 15— Force factor plots of ring armature receiver, (a) Force factor circle, (b) 

 Magnitude and angle of force factor. 



winding. This is a complex quantity whose angle between force and current 

 is designated by the symbol /?. In magnetic receivers like the ring armature 

 receiver, the force factor varies with frequency, both in magnitude and in 

 phase. Fig. 15(a) shows a vector plot of this quantity, and indicates how the 

 terminus of the vector follows an approximately circular path with change 

 in frequency. Figure 15(b) is a chart showing the magnitude of r and the 

 angle /3 as functions of frequency. 



