INDICIAL RESPONSE OF TELEPHONE RECEIVERS 



145 



changes of the constants of the acoustic circuits. The oscillograms indicate 

 a marked improvement as regards oscillations, which is to be expected with 

 increased damping. The time delay is eventually degraded with further 

 increases of damping, however, and the optimum damping is a matter of 

 compromise. 



•20 



•h 15 

 + 10 



+ 5 

 



9-10 

 5 



L 

 ''-15 



-20 

 -25 

 -30 

 -35 



-40 



100 



1,000 

 FREQUENCY (C.RS.) 



Fig. 8 — Three types of hearing aid receivers — frequency response and indicial response 



The effects of a low-frequency cut-off characteristic are shown by curves 

 7,8, and 9, Fig. 7. The absence of a d-c component makes these curves very 

 difficult of interpretation. 



Curve 7, taken with the same receiver as curve 2, except with coupler 

 leakage, shows a loss at low frequencies which is typical of cases where the 

 receiver cap does not make a perfect seal with the ear. The effect on the 

 indicial response is that of a large pulse followed by a few oscillations at the 

 frequency of the leak circuit. 



Curve 8 is a similar condition except taken on a high-quality receiver 



10,000 



