RECORDING AND REPRODUCING OF MUSIC AND SPEECH 503 



knowledge of mechanical wave transmission systems. The result is, 

 therefore, that mechanical transmission systems can be designed more 

 successfully if they are viewed as analogs of electric circuits. 



While there are mechanical analogs for nearly every form of electrical 

 circuit imaginable, there is one particular class of electrical circuits 



m, ^2 



g N 



C,^ 



Fig. 6 — Electrical equivalent of system shown in Fig. 5 with its ternunation 



whose study has led to ideas of the utmost value in guiding the course 

 of the present development. This class of circuits consists of infinitely 

 repeated similar sections of one or more lumped capacity and induc- 

 tance elements in series and shunt and are commonly known as filters. 

 The study of filters began with the work of Campbell and a recognition 



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a 4= 



Fig. 7 — Electrical equivalent of the spider section 



of their importance as frequency selective systems in telephone re- 

 peaters, carrier systems, radio, signalling systems, etc., led to their 

 intensive study. In the available literature is to be found a fairly com- 

 plete statement of their properties and details of their design.^ 



6 Campbell, G. A., "On Loaded Lines in Telephonic Transmission," Phil. Mas.-, 

 March 1903. 



Campbell, G. A., U. S. Patents L227,113; 1,227,114; "Physical Theory of the 

 Electric Wave Filter," Bell System Technical Journal, November 1922. 



Zobel, O. J., "Theory and Design of Uniform and Composite Electric Wave Filters," 

 Bell System Technical Journal, January 1923. 



Peters, L. J., "Theory of Electric Wave Filters Built up of Coupled Circuit Ele- 

 ments," Trans. A. I. E. E., May 1923. 



Carson, J. R. and Zobel, O. J., "Transient Oscillations in Electric Wave Filters," 

 Bell System Technical Journal, July 1923. 



Zobel, O. J., "Transmission Characteristics of Electric Wave Filters," Bell System 

 Technical Journal, October 1924. 



Johnson, K. S., and Shea, T. E., "Mutual Inductance in Wave Filters with an In- 

 troduction on Filter Design," Bell System Techincal Journal, January 1925. 



Johnson, K. S., "Tansmission Circuits for Telephonic Communication," D. \ an 

 Nostrand, 1925. 



