102 DRIVING SYSTEMS 



The electromotive force, in abvolts, developed by the motion of the con- 

 ductor is 



e = Blx 6.2 



where x = velocity, in centimeters, per second. 

 From equations 6.1 and 6.2 



- = {Biy^ 6.3 



e 



-. = Zem 6A 



I 



where Zem = electrical impedance, in abohms, due to motion. 

 The mechanical impedance of the vibrating system is 



Jm ^ . 



-r = Zm 6.5 



X 



where Zm = mechanical impedance, in mechanical ohms, the total mechani- 

 cal impedance at the conductor including the mass reactance 

 of the voice coil. 

 The electrical impedance due to motion (termed motional impedance) 



from equations 6.3, 6.4 and 6.5 is 



Zem = D.o 



Zm 



The motional impedance of a transducer is the vector difference between 

 its normal and blocked electrical impedance. 



The normal impedance of a transducer is the electrical impedance meas- 

 ured at the input to the transducer when the output is connected to its 

 normal load. 



The blocked impedance of a transducer is the electrical impedance meas- 

 ured at the input when the mechanical system is blocked, that is, in the 

 absence of motion. 



The motional impedance may be represented as in series with the blocked 

 impedance of the conductor. 



The dynamic driving system is almost universally used for all types or 

 direct radiator and horn types of loud speakers. 



6.3. Electromagnetic Driving System. — A magnetic driving system 

 is a driving system in which the mechanical forces result from magnetic 

 reactions. There are two general types of magnetic driving systems, 

 namely: the reed armature type and the balanced armature type. 



