TRANSIENT RESPONSE 



141 



exerted by the electrical system is of consequence. However, there is 

 very little difference between Class " A " and feedback operation. 



When a loud speaker operates from a high impedance vacuum tube 

 amplifier, the internal mechanical resistance of the loud speaker is the 

 major factor influencing the transient response. Figure 7.17 shows 

 response of a 12-inch (10-inch diameter cone) loud speaker to a unit force 

 for various values of mechanical resistance. In order to correlate the 



2 30 



X 



©40 



z 

 <0.5 



Fig. 7.17. The unit force response of a loud speaker coupled to a generator of very high 

 resistance for different values of the internal mechanical resistance. The impedance fre- 

 quency characteristics indicate the degree of internal damping. 



response with actual systems, the impedance frequency characteristic for 

 each system is also shown. These characteristics are for a loud speaker 

 coupled to a generator with very high internal impedance. For this type 

 of operation it is customary to provide a large mechanical resistance rus-, 

 the second and third conditions of Fig. 7.17. 



Figures 7.16 and 7.17 show that the " hangover " in properly designed 

 and operated loud speakers is very small. Of course, the systems are im- 

 proved as the fundamental resonance frequency is lowered. In some of 

 the small receivers employing i-elatively high impedance power amplifiers 

 driving loud speakers having the fundamental resonance above 100 cycles, 



