THE RING ARMATURE TELEPHONE RECEIVER 



119 



250 



750 1000 2000 



FREQUENCY IN CYCLES PER SECOND 



3000 



4000 



Fig. 6 — Available power response-frequency characteristics of Ul receiver, measured 

 withe a source impedance of 128 ohms, on human ears as passive couplers. 



60 



S75 



a. 



m -5 

 Q O 

 ? cr 



LU 

 LU CL 



in 



Z ^ 



70 



65 



55 



750 



.N^- PRESENT STANDARD 

 / RECEIVER (HA1) 



4000 



1000 1500 2000 3000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 7— Available power response-frequency characteristics, with receivers raised i 

 inch from normal position on coupler. 



noise is predominantly low frequency noise not only because typical room 

 noise characteristically decreases with increase in frequency,io b^t also 

 because the leakage path has an acoustic impedance which rises with fre- 



lo^Room Noise Spectra at Subscribers' Telephone Locations," D. F. Hoth, Journal 

 of Acoustical Society of America, Vol. 12, April 1941. 



