RECORDING AND REPRODUCING OE MUSIC AND SPEECH 511 



of the needle arm. For example, in the spider section , Fig. 15, the 

 mass is driven directly by the force from the needle-arm compliance, 

 there being a small series compliance in the connection owing to 

 bending of connecting rod. The diaphragm is connected through the 



Fig. 11 — Detailed drawing of the mechanical filter of an electromagnetic recorder. 

 (Lettering same as in Fig. 12) 



compliance of the prongs of the spider. The equivalent circuits are 

 shown in F"igs. 7 and 16. 



The equations of this network may be obtained from the equations 

 for the needle arm by placing Ci equal to zero, taking a unity ratio 

 transformer, and substituting nii for ;wi, c^ for Ca, fs for Cz and Zd for Zs. 



Another type of network which occurs frequently in the building 

 of mechanical vibrating systems is represented diagrammatically in 

 Fig. 8. This is clearly a particular case of Fig. 7 with d made infinite. 



By combining Fig. 6 representing the needle arm, Fig. 7, repre- 

 senting the spider section and Fig. 4 representing the diaphragm, 

 air-chamber and horn, the comijlete reproducer may be l)uilt up. 

 The resultant network is shown in F'ig. IG. Since methods are avail- 

 able in the theory of electric wave filters to determine the proper 



