74 



ANALOGIES 



The limiting frequencies are given by 



— = and — = 



22 22 



Applying these relations it can be shown that the systems of Fig. 4.11 

 are band pass filters transmitting currents, velocities or volume currents 

 of all frequencies lying between two cutoff frequencies /d and/c2. 



G. Band Elimination Wave Filters. — Electrical, mechanical and acous- 

 tical band elimination wave filters are shown in Fig. 4.12. 



ELECTRICAL 



MECHANICAL 



Fig. 4.12. Band elimination wave filters. 



The impedance of the series arm in the three systems is 



ze\ = 



Zmi — 



Zai = 



1 — cj'^CeiLi 



jcomi 



1 — Op'CMlffll 



jwM 



1 - co^C^iMi 



For a description of the acoustic capacitance Ca\ see Sec. 4.9G 

 The impedance of the shunt arm in the three systems is 



J 



ZE2 = JC0L2 — 



Zm2 = jo}m2 — 



ZA2 = J0iM2 — 



The limiting frequencies are given by 



CoCe2 



J 



<^Cm2 



j 

 wCa2 



^ =: and - = - 4 



22 22 



4.90 

 4.91 

 4.92 



4.93 

 4.94 

 4.95 



