AN IMPROVED TELEPHONE SET 



261 



frequencies. Furthermore, because of the high receiving efficiency of the new 

 set, the ringer impedance must be high at voice frequencies to keep induced 

 noise from power hne interference to a value no greater and if possible less 

 than with present sets. With the new design these objectives have been 

 realized and five ringers per line or between each wire and ground are per- 

 mitted in place of the usual four. The increased impedance has been accom- 

 plished by the use of a magnetic shunt and the physical arrangement of the 



Fig. 16 — View of Ringer. 



ringer coil winding. Figure 17 shows the impedance frequency characteristic 

 of the new ringer as compared to an earlier type. 



The sound output of the new ringer has been increased by means of 

 resonators that are designed as an integral part of the ringer. These resona- 

 tors are formed aluminum shells mounted beneath the ringer gongs and 

 greatly increase the fundamental gong tones. In previous ringers, resona- 

 tors were added when required to increase the sound output at a particular 

 location. Figure 18 shows the sound output spectrum of the new ringer as 

 compared with the ringer of the former set. It should be noted that the fun- 

 damental frequencies of the two gongs of the new ringer are lower than the 



