TELEPHONE DIAPHRAGMS. 



441 



presented in Table III, it will be seen that the effect of loading the 

 diaphragm, with masses up to nearly 2.5 gms., did not seriously affect 

 the equivalent mass m of the diaphragm, as deduced from the observa- 

 tions recorded in Column VII. On the other hand, similar loads, 

 applied to other diaphragms, have been followed by changes in equiva- 

 lent mass, with corresponding vitiations of results. ^^ 



It has also been found, in certain cases, that while the addition of a 

 load to the center of the diaphragm changed the equivalent mass of 

 the diaphragm considered by itself, the addition of further loads, 

 seemed to leave the equivalent mass of the diaphragm with the first 

 load practically unchanged. Consequently, if say three different 

 increasing loads are added in succession, the solutions of simultaneous 

 equations, using the unloaded and any loaded case, will not be con- 

 sistent; whereas solutions of simultaneous equations using different 

 loaded conditions may be consistent. 



The following case may illustrate the preceding remark. A tele- 

 phone receiver with an active diaphragm weight of 4.94 gm. and 0.399 

 mm. thick, over japan, was tested by the motional-impedance circle, 

 first unloaded, and then with three successively increasing brass loads 

 of 0.615, 0.978, and 2.998 gms. The resonant angular velocities in 

 these four cases were respectively (1) 7570, (2) 6568, (3) 5990, and (4) 

 4289 radians per second. From these data, we obtain the following 

 results, using formula (5), entered with various pairs of observations: — 



TABLE IV. 



11 Dr. Jone.s reports having obtained satisfactory results with the loading 

 method, in various cases when the total added mass was not greater than 0.3 

 gm. 



