THE RING ARMATURE TELEPHONE RECEIVER 



133 



these, the stiffness loss and coupUng loss are the greatest. Considerable 

 progress has been made in the design of this receiver in reducing the stiff- 

 ness loss from 11.3 db for the HAl receiver to 6.9 db. This is due largely to 

 the increased effective area and low acoustic impedance of the diaphragm. 



Receiver Efficiency Limits 



In the analysis above, it is shown that for an ideal receiver having no 

 losses, operating into a 6 cc. chamber, and matched at 1000 cps, the re- 

 sponse approaches an upper limit of 91.7 db vs. (1 dyne per cm^)^ per watt. 

 In other words, this is the limit which the low-frequency response of an 

 idealized receiver approaches when the diaphragm stiffness Sr , the front 

 chamber Vg , and the coil resistance R all approach zero, and the coupling 

 factor k approaches unity. However, in addition to the level limit there exists 

 a frequency range limit which lowers the level of the former limit. The curve 

 labelled ''Locus of Performance Limit" of Figure 16(b) determines both these 

 boundaries. Thus, if any point is selected on this curve, a horizontal and a 

 vertical line through it determine shnultaneously the maximum response 

 level and the highest frequency range obtainable. The calculation of both 



SOURCE 



RESISTANCE 



Ro 



EAR CAVITY 

 COMPLIANCE 



c 



Fig. 17— Network of an ideal receiver having a uniform response over a given band of 

 frequency. 



limits may be based on H. W. Bode's resistance integral theorem.^^ In ac- 

 cordance with this theorem, when an ideal coupling network N, shown in 

 Fig. 17, is used to give the maximum performance between a resistance 

 source Ro and a capacitative load C, we have the general formula 



r 



2a 



do3 = 



2CRo 



(11) 



where e 



- = (i)' 



Eo = the source voltage 



and E = the voltage developed across the load C. 



""Network Analysis and Feedback AmpUfier Design/' H. W. Bode-D. Van Nostran^ 

 Co.— p. 362, 



