ACOUSTIC IMPEDANCE. 



21 



It is evident that the motional-impedance variations, due to ^ary- 

 ing the distant-end orifice of the tube, are greatest on the long curves 

 CC and DD, apparently because the frequencies pertaining to them 

 (921 ~ and 949 ~ respectively) lie nearest to the resonant frequency of 

 the receiver, when loaded with the tube under these conditions. For 

 sensitiveness in the measurement of tube terminal effects in the re- 

 ceiver, the frequency of 850 c^^ was too low, and that of 1000 ~ too 

 high. 



?00 400 600 flOO looo liOO I^VO 1600 



RES-ISTANCE. DYNES PER K.INE 



Figure U. Total ^Mechanic Impedance at Receiver Diaphragm by Inver- 

 sion from Figure 10 and Multiplying by A-. 



The mechanic impedance at the receiver diaphragm, in the various 

 measurements recorded in Figure 10, are presented in Figure 11, after 

 inversion and multiplication l)y A^. These mechanic impedances are 

 vectors, expressible in mechanic resistance and reactance, as dynes 

 per kine, or mechanic absohms, as may be preferred. The origin in 

 Figure 11 is at k. The vector graph A A of Figure 10, becomes con- 

 verted into the vector graph a a of Figure 11, B B into b b, and so on. 



It will be observed that the most sensitive graphs C C and D D of 

 Figure 10 give rise to graphs c c and d d in Figure 11, revealing only 

 small changes in mechanic resistance, but relatively large changes of 

 mechanic reactance, Avith change of tube aperture. On the other 

 hand, <? <? at 1000 ^^ includes more change in mechanic resistance 



