140 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1951 



3. A flexibility in frequency range, permitting the extension of the fre- 

 quency range to approximately 7000 cps. 



4. A broader superimposed direct current characteristic resulting in 

 greater stability from a mechanical as well as an electrical standpoint. 



5. A lower acoustic impedance, resulting in an improvement of the signal 

 to ambient leakage noise ratio. 



6. A substantial increase in the transmitted bandwidth when the receiver 

 is held at small distances away from the ear. 



Other advantages from a mechanical standpoint are: 



1. A simple mechanical structure of ring-shaped or circular parts. 



2. A low mechanical impedance, permitting the use of large air cavities 

 and elements of low acoustic impedance for response control. 



3. A concave, spherical dome-shaped diaphragm withstanding high tran- 

 sient pressures. 



This work was carried on under the supervision of Messrs. W. C. Jones, 

 F. F. Romanow, and W. L. Tuffnell, from whom many valuable suggestions 

 were received. We also wish to acknowledge the valuable assistance of 

 Messrs. P. Kuhn, L. A. Morrison, R. E. Polk, W. C. Buckland, R. R. Kreisel 

 and R. E. Wirsching during the development of this receiver. 



