THEORY or THE HOWLING TELEi'IIOXE 



31 



These factors are usLiall\- complicated functions of tlie frequency 

 while St likewise depends on the kind and amount of agitation. In 

 the case of a system of a single degree of freedom which may be 

 regarded as a first approximation to this case 



S=mco'^-'rjur-{-s 



(0) 



where co is 27r times the frequency. When referring to the movements 

 of a diaphragm, the quantity m represents the mass, r the mechanical 

 resistance, and 5 the elastic constant. The stiffness factor S divided 

 by jo3 is usually called the mechanical impedance. 



Measurements have shown that for the transmitters and the 



£00 



(oOO 800 



FREaUENCY 



1000 



lEOO 



1400 



Fig. 2 



receivers used in the experiments described below, the following 



constants represent approximately the two stiffness factors in the 

 region of resonance 



5i?=-.93co2+230>+3X107 (6') 



5r=-4.5a;2+2000/co + 2Xl0s (6") 



An important constant which enters into the determination of the 

 unilateral mutual impedance ^1/ is the force factor of the receiver 

 which will be designated by Z. It is defined as the force in dynes 

 acting upon the diaphragm i)er unit of current. For the receivers 

 used in this investigation, its values in magnitude and phase are shown 

 for various frequencies in F\g. 2. These were determined by the 

 method outlined by Wegel.^ In the region of the resonant frequency 

 its value in absolute units can be approximateh' represented by 



Z = 5.3Xl0n'24^- (") 



' Theory of rckphoiic Recei\xTs— Wegcl, K. L., Jour, of .\. I. E. E., Oct. 192 L 



