RECORDING AND REPRODUCING OE MUSIC AND SPEECH 509 



The last fixe cciuations in each case gi\'e the complete sokition of 

 the network. By analogy between the two sets of equations, 

 therefore, the air-chamber corresponding in the electrical case to a 



shunt capacity, c? is spoken of as a shunt compliance, Ci= ** 



together with a transformer inserted before the horn, which has an 

 equivalent turns ratio equal to the ratio of the areas of the diaphragm 

 and horn openings. 



Taking up now the somewhat different illustration of the needle arm, 

 the following symbols are needed (Figs. 5, 6, 15, 16) : 



/i = Distance from pivot point to end of needle; 

 4 = Distance from pivot point to center of "spider" (Fig. 15); 

 / = Moment of inertia of needle arm; 



Wi = Apparent or equivalent mass of arm as measured from the 

 center of the spider 



~ /•;- ' 



Ci = Compliance of needle point; 



C2 = Compliance of bearing to turning of the needle arm, as meas- 

 ured from end of arm at the spider; 



C3 = Compliance of end of needle arm attached to spider; 



5i = Displacement of tip of needle; 



5-2 = Displacement of end of arm at the spider; 



53 = Displacement of spider; 



Si = Mechanical impedance of spider and remainder of structure = 

 X^ector ratio of applied force to resultant velocity; 



d = Angular displacement of needle arm; 

 F = Applied force at needle point. 



We have the three force equations: 



Si — lv 



, =F (6) 



(It- Ci Ci Ci ^ ' 



c, ^■'' dt -^ ^^^ 



