A VOICE AND EAR 



311 



mission,^ and the other, a deskstand type receiver. Measurements of 

 the response characteristics of these two types of receiver have been 

 made on male human ears as described in the Appendix. The results 

 obtained, together with similar measurements on the same receivers on 

 the artificial ear, are shown in Figs. 15 and 16. Over most of the 

 frequency range rather good agreement is found between the human 

 ear and artificial ear measurements, the discrepancies in most cases 

 being relatively unimportant. 



Electrical impedance measurements were made on two commercial 

 types of receiver whose impedances at resonance are relatively sensitive 

 to changes in acoustic load. These measurements were made with 



(r < 



5000 10,000 



Fig. 15 — Response-frequency characteristic of moving coil receiver on ears. 



500 1000 



FREQUENCY IN CYCLES PER SECOND 



the receiver in free air and when held to the human ear and to the 

 artificial ear. The results are shown in Table III. The values of 



TABLE III 



Electric.\l Impedanxe Data for Different Types of Receivers 



WITH Various Loads 



'"Master Reference System for Telephone Transmission," W. H. Martin and 

 C. H. G. Gray, Bell System Technical Journal, July, 1929. 



