66 



ANALOGIES 



The reactance of a capacitance is inversely proportional to the frequency. 

 Therefore, the current transmission will increase with increase in frequency 

 as shown in Fig. 4.5H. 



The impedance of the compliance of the mechanical system of Fig. 4.6F 

 is inversely proportional to the frequency. Therefore, at low frequencies 

 the compliance will remain comparatively stationary and there will be 

 very little velocity transmission. At high frequencies the motion of the 



— nm^l — 



M 



ELECTRICAL 



VvJv.VV' 



N O 



MECHAhJICAL ACOUSTICAL 



FREQUENCY 



P 



RESPONSE CHARACTERISTICS 



Fig. 4.6. A line in series with the following: A an inductance. E a capacitance. 7 an 

 inductance and a capacitance in series. M an inductance and a capacitance in parallel. 

 The mechanical equivalents are shown in 5, F, J and N. The acoustical equivalents are 

 shown in C, G, K and 0. The transmission-frequency characteristics are shown in D, H, 

 L and P. 



compliance corresponds to the input velocity. Therefore, the velocity 

 transmission characteristic will be shown in Fig. 4.6//. 



There is no simple acoustical system which is equivalent to an electrical 

 capacitance in series with a line. The equivalent shown in Fig. 6G con- 

 sists of a stiffness controlled diaphragm, that is, the mass of the diaphragm 

 is small and the stiffness of the suspension high so that the frequency range 

 under consideration is well below the natural resonant frequency of the 

 diaphragm and suspension. The acoustic capacitance of this system is 



