TELEPHONE DIAPHRAGMS. 463 



The equivalent mass of the diaphragm alone was measured inde- 

 pendently by the loading method. 



It would appear, from the above tests, that the extra mechanical 

 resistance of a circular disk was about 20 dynes/kine for each sq. cm. 

 of disk area, — (ira^). These results, however, can only be regarded 

 as preliminary. 



A few similar measurements, made with circular disk vanes im- 

 mersed in water instead of in air, gave results of roughly 500 dynes/ 

 kine per sq. cm. area of disk, or some 25 times the vibratory resistance 

 of air. In this case it was found that the water not only added 

 mechanical resistance; but also an appreciable extra mass (about 

 0.5 gm. per sq. cm.) to the vibrating system. 



These measurements of extra mechanical resistances are reported, 

 not as definite results, but as indicating the directions in which the 

 motional-impedance circle method may be applied to the analysis of 

 vibrating systems. 



In conclusion, the writers desire to express their acknowledgment 

 to the Research Department of the Western Electric Co. for valuable 

 suggestions, help, and special instrument parts. 



Summary. 



(1) The principal characteristic constants, defining the mechanics 

 of a telephone receiver, are the force-factor a, the equivalent mass m, 

 the equivalent mechanical resistance r and the equivalent elasticity s. 

 They may all be determined from the motional-impedance circle 

 diagram, if one additional independent relation can be secured. 



(2) Out of a number of possible additional independent relations, 

 three are considered in detail; namely, the vibrational exploration 

 method for measuring m, the loading of the diaphragm for obtaining m, 

 and the use of an amplitude measurer for determining the maximum 

 cyclic displacement x^- 



(3) While all three of the above-mentioned methods are capable 

 of giving results, the last named is the recommended method. It 

 consists in applying a simple form of amplitude measurer, to the center 

 of the diaphragm, during motional-impedance tests, and observing 

 the amplitude at resonance. 



(4) With the amplitude measurer, the characteristic constants are 

 derived for several particular types of telephone receiver tested. 



(5) The effects of various influences upon the behavior of a receiver, 

 and on its characteristic constants, are discussed. 



