452 KENXELLY AND AFFEL. 



quadrantal points of the circle are 983 and 1065 ~ respectively, or in 

 angular velocity 6176 and 6692 radians per second. Half the differ- 

 ence between these is 258, which represents A, the damping constant. 

 When A is required with greater precision, however, it is better to 

 take a number of frequency points around the circle into account, 

 by means of formulas (20) to (23). 



The resonance curve for this case, giving central maximum cyclic 

 velocities of the diaphragm, against impressed frequency, appears in 

 Figure 15. It is a fairly representative curve for telephonic receivers 

 as a class. The curve of diaphragm velocity is drawn through ob- 

 servation-points with the explorer, while the small circles represent 

 the corresponding points as computed by formula. The motional 

 impedance curve is also drawn through the observations. Theoreti- 

 cally, the ordinates of the two cm"ves should retain a constant ratio. 

 It should be remembered, however, that at frequencies remote from 

 resonance, not only are the amplitudes hard to measure, but the force 

 constant a needs correction. 



The third part of the Table gives the results of the calculated data, 

 in terms of A, m, r and s. The numbers of turns N, in the windings 

 not being known, the value of a/x, which is a characteristic quantity 

 for a receiver, is omitted. 



The equivalent mass factor vi/m was obtained in tests A and B by 

 two different and independent methods ; namely, by the computation 

 of m as in Formula (49) AppendLx I, and through exploration, by Dr. 

 H. O. Taylor, of the amplitudes ■'•'^ over the surface of the diaphragm, 

 in the manner described in Appendix II. The fact that these two 

 values of the mass-factor compare favorably, constitutes a check upon 

 the validity of the amplitude method of determination. 



Influences which Affect the Instrument Constants. 



The telephone receiver is so sensitive to external influences, which 

 effect the motional-impedance circle, that there are numerous ways in 

 which such influences might be exerted and their effects thus revealed. 

 It is proposed here to consider, however, only a few of these influences, 

 and their general effects on certain receivers as deduced from the 

 changes produced in their motional-impedance circles. The influences 

 selected were (1), variations in the screw-clamping of the cap, (2), 



17 Bibliography, No. 17. 



