SINGLE COIL, SINGLE CONE LOUD SPEAKER 



115 



trical circuit of the mechanical system. In this case the driving force 

 applied to the mechanical system must be determined. 



In the example of Fig. 7.1 the damped impedance of the voice coil has 

 been assumed to be a constant resistance. The inductance and the in- 



O .1 



2 ,8 



^.01 

 < s 



.001 



3 4 5 6 7£ 



4 5 6 7 69|o3 



fREQUENCY \U CYCLES PER SECOND 



3 4 5 6 7 89, 



Fig. 7.2. The amplitude frequency characteristics of vibrating pistons, of various diam- 

 eters mounted m an infinite wall, tor one watt output on one side. 



crease in resistance due to skin effect and hysteresis in the iron core at the 

 higher frequencies causes an increase in the impedance at the higher fre- 

 quencies. This, of course, reduces the force available for driving the me- 

 chanical system. The current in the electrical circuit is also influenced 

 by the motional impedance. The motional impedance, in abohms, see 

 Sec. 6.2, is 



(Biy 



■Zem = 7.6 



^here B — flux density in the air gap, in gausses, 



/ = length of the conductor, in centimeters, and 

 'Z'MT = total mechanical impedance, in mechanical ohms. 



1 



■Zmt = rM At j<^m -f 



]<^Cm 



in 



