502 



BELL SYSTEM TECHNICAL JOURNAL 



In the design of the recording and reproducing systems each part of 

 the system has been made as nearly perfect as possible. Errors of one 

 part have not been designed to compensate for inverse errors in another 

 part. Although this method is the more difficult, its flexibility, par- 



Fig. 4 — Electrical equivalent of mechanical system shown in Fig. 3 



ticularly as regards the commercial possibilities of future impro\e- 

 ments justifies the extra effort.^ There is, therefore, no distortion in 

 the record whose purpose is to compensate for errors in the reproducing 

 equipment; the only intended distortion in the record being that re- 



Fig. 5 — Schematic mechanical arrangement of needle arm transformer 



quired by the inherent limitations mentioned above. See Figs. 2, 14 

 and 20. 



General Basis of Design 



An interesting feature of the development of the mechanical and 

 electromechanical portions of the recording and reproducing system is 

 their quantitative design as mechanical analogs of electric circuits. 

 Both the recording and reproducing systems are good examples of the 

 use of this type of analogy. 



The economic need for the solution of many of the problems con- 

 nected with electric wave transmission over long distances coupled with 

 the consequent development of accurate electric measuring apparatus 

 has led to a rather complete theoretical and practical knowledge of 

 electrical wave transmission. The advance has been so great that the 

 knowledge of electric systems has surpassed our pre\'ious engineering 



^ Green, I. W. and Maxfield, J. P., "Public Address Systems," Tras. A. I. E. E., 

 Vol. 42, 1923, p. 64. 



