^iiQ 



SOME PROPERTIES OF VIBRATING TELEPHONE 

 DIAPHRAGMS. 



By a. E. KENNELLY, S.D., A.M., and H. O. TAYLOR, Ph.D. 



{Read April 14, 1916.) 



This investigation was conducted by the Research Division of 

 the Electrical Engineering Department, of the Massachusetts Insti- 

 tute of Technology, during the years 1915-16, under an appropria- 

 tion from the American Telephone and Telegraph Company. The 

 experimental work was carried on at Pierce Hall, Harvard Univer- 

 sity. It constitutes a continuation of the researches reported by the 

 same authors in the paper read last year before the American Philo- 

 sophical Society,^ and in the paper by Kennelly and Affel, read 

 last year before the American Academy of Arts and Sciences,^ 

 dealing with the motional-impedance circle of telephone receivers. 



It is now well established that the motional-impedance circle 

 of a telephone receiver; i. e., the circular locus of that part of a 

 receiver's impedance which is due to the motion of the diaphragm, 

 enables the characteristic constants A, m, r and ^' of the instrument 

 to be determined experimentally. Its diameter, OD, Fig. 4, is 

 depressed below the resistance axis OA (resistance component of 

 impedance), through a certain angle, AOD, which is designated by 

 /^i° + 1^2^ ■ Here j3-^^ is regarded as the angle of lag of the pull on 

 the diaphragm behind the alternating current in the coils giving rise 

 thereto ; while ^80° is regarded as the angle of lag of the E.M.F. in- 

 duced in the coils, behind the velocity of the diaphragm's vibrational 

 motion producing it. 



The researches here reported have been two-fold namely : 



1 " Explorations over the Vibrating Surfaces of Telephonic Diaphragms 

 under Simple, Impressed Tones," by A. E. Kennelly and H. O. Taylor, Proc. 

 Am. Philos. Soc, Vol. LIV., April 22, 1915. 



2 Bibliography, 10. 



415 



PROC. AMER. PHIL. SOC, VOL LV, Z, JULY ID, I916. 



