274 



BELL SYSTEM TECHNICAL JOURNAL 



a -15 



200 



500 1000 2000 



FREQUENCY IN CYCLES PER SECOND 



10,000 



Fig. 8 — Output-frequency characteristic of high frequency receiver as measured in 



a small room. 



Fig. 



100 500 1000 



FREQUENCY IN CYCLES PER SECOND 



5000 10,000 20,000 



9 — Output-frequency characteristic of combined low and high frequency re- 

 ceivers as measured in a large room. 



100 500 1000 



FREQUENCY IN CYCLES PER SECOND 



5000 10.000 20.000 



Fig. 10 — Output-frequency characteristic of moving coil microphone. 



