Tiir.ORY 01' II Hi iioirj.ixc; 'ir.iJiriioMi 45 



where 





VR VI vtQr yp 



The unilateral nuilual impedance 71/ is given by 



IhZ 



M = 



iV Sin h-r cos — 



a a 



The condition for sustained howling becomes 



IZ - - - . O)/ , _ <j)l , „ . , 



TfTT^h^N sm — hP cos— . (54) 



If the two diaphragms work directly into the connecting tube as 

 pistons, then Qj^ = QT = q = Q and Vr=Vt = and the expressions 

 for M and 6" become ^ 



, ^ _ IhZ Q acop 



[SRST-{,ao:p)-Q^\ s'm—-\-{SR-\-ST)Qawp cos" 



(55) 



{SRST—{a(j:QY\ sin — + (acopQ) {Sr-}- St) cos— 



S = "" -. (56) 



Or sm — hawp C' cos— 

 a a 



The method ol sohuion is the same as that given for the simpler 

 cases, although it is e\'ident that the actual work of calculation is 

 more involved. 



It is seen that in such a system the intensity and frequency depend 

 upon a large number of quantities, namely : Sr and Sr, the diaphragm 

 stiffness factors; (2i2 and Qt the effective areas of the two diaphragms; 

 Vr and Vt the volumes of air entrapped between the diaphragm 

 and the opening into connection tube; the length / and the cross 

 section q of the connecting tube; the pressure a, the density s, and the 

 velocity of sound a for the gas in the connecting tube; the resistance 

 T, direct current / and modulation factor h of the transmitter; and 



'These two equations were given ])y 11. \V. Nichols in essentially this form in 

 the Physical Review.^Vol. 10, p. 171; 1917. 



