ANALOGIES 75 



Applying these relations it can be shown that the systems of Fig. 4.12 

 are band elimination filters transmitting currents, velocities or volume 

 currents of all frequencies between zero and the cutoff frequency /d and 

 between the cutoff frequency /c2 and infinity. 



4.11. Summary of Electrical, Mechanical and Acoustical Analogies. 

 — A large number of equivalent electrical, mechanical and acoustical sys- 

 tems have been discussed in this chapter. The analogies between the 

 elements in the three systems are obtained by a comparison of the coeffi- 

 cients occurring in the differential equations of the forced oscillations in 

 the three systems. For every symbol used in the electrical system there 

 is a corresponding symbol in the equations for the mechanical or acoustical 

 system. Furthermore, the corresponding symbol for each of the systems 

 appears in exactly the same place in all the corresponding equations of 

 the three systems. This is the essence of the electrical equivalent of a 

 mechanical or acoustical system. 



Table 4.1 lists the quantities, units, symbols and dimensions of the 

 analogous quantities in the electrical, mechanical and acoustical systems. 



Three fundamental dimensions are necessary to form a complete me- 

 chanical dimension system. Table 4.1 uses mass M, length L and time 

 T. In the case of the electrical units dielectric constants and permeability 

 are assumed to be dimensionless. 



