106 



KENNELLY-T A YLOR— EXPLORATIONS OVER [April 22, 



The conclusion, therefore, seems warranted that, for this par- 

 ticular steel telephone diaphragm, acoustically excited to frequencies 

 as high as 2,100 ---', the fundamental mode of vibration is the only 

 one that is maintained. If any higher modes of motion were 

 present, they were too faint to be discerned. This does not mean 

 that higher modes of motion could not be produced by any kind of 

 excitation within the above ranges of frequency. The effects of 

 very powerful vibrations were not investigated. 



Since the natural frequency of this diaphragm, with flat clamp- 

 ing, was observed to be Mo = 824---', and since, according to Bessel- 

 Function theory, the natural frequency of the second mode of mo- 

 tion should be 2.09W0, we should naturally expect to find this 

 second mode of motion appearing at and above 1,720'—'. Its non- 

 appearance may have been due to the uniformity of acoustic im- 

 pressed force over the surface, which would tend to favor the first 

 rather than the second mode of forced vibration. 



The vibration-amplitude of the diaphragm was found to vary 

 widely with the pitch of the exciting source. At or near the natural 



TABLE IL^. 



Showing Fundamental Mode of Vibration Maintained for a Range of 



OF Frequencies from 400^ — to 1,800 ■ — '. 



Amplitudes of Vibration in Microns (m) along Radius of Diaphragm No. i. 



Flat-damped. Uo = 704 — '. 



fundamental frequency of the diaphragm, the amplitude of the 

 vibratory response was a maximum. Either above or below this 



