436 KENNELLY AND AFFEL. 



(1) In the case of static-deflection measurements, the forces are 

 appHed at the center of the diaphragm; whereas in a vibrating tele- 

 phone diaphragm, the forces are apphed over a considerable area 

 of the surface, and with a different distribution of surface curvature, 

 thus producing a different resultant effect. 



(2) In the case of static-deflection measurements, the deflections are 

 observed to increase with the time of application, especially with thin 

 diaphragms. Consequently, the elastic constant, as deduced from 

 static deflections, is likely to be less than would develop with rapid 

 alternations of the impressed force. 



Diaphragms numbers 2 and 6, in Table I, were submitted to a gen- 

 eral analysis to be later described, by which the effective values of s 

 were found to be respectively 77.6 and 36.7 megadynes per cm., values 

 which are roughly twice as great as those given in the Table. It is 

 believed, therefore, that the values of s obtained by static deflection, 

 are much less than those which are effectively developed with im- 

 pressed alternating forces. 



Method of Direct Determixation of m. 



It is shown in AppendLx II, that it is possible to determine the 

 equivalent mass vi, of a diaphragm, in terms of its total mass M, in 

 active vibration, by exploring the vibration amplitude over the sur- 

 face, when the diaphragm is actuated by a simple harmonic vibro- 

 motive force. ^ This method is theoretically capable of supplying 

 the missing fourth equation, and, therefore, of determining, with the 

 above mentioned data, all four constants, a, m, r, and s. This method 

 has been developed, and actually carried out, in a number of instances 

 for small diaphragms generally, and in two instances for the case of 

 telephone-receiver diaphragms, operated electromagnetically. 



While the method appears to be practically satisfactory, and its use 

 throws much light upon the behavior of vibrating diaphragms; yet it 

 is open to two objections, for the purpose here considered, namely: 



(1) The technique of the exploration is both tedious and delicate. 



(2) The telephone receiver must be screwed into a specially con- 

 structed amplitude-exploring apparatus, in which the upper surface of 

 the diaphragm is left exposed; so that the telephone-receiver cap has 

 to be removed, thereby altering, to some extent, the receiver character- 

 istics. 



This method is, therefore, not recommended for practical use. 



7 Bibliography, No. 17. 



