RECORDING SPEECH VIBRATIONS. 17 



Six such reproducers were prepared with different forms of edge- 

 fixation at B, namely: (1) with vasehne instead of gaskets; (2) with 

 rubber gaskets; (3) with loosely pressed paper gaskets; (4) with dextrine 

 instead of gaskets; (5) with tightly pressed paper gaskets; (6) with no 

 gaskets, but with diaphragm held by direct pressure of the metal ring A. 

 The reproducers in this order represent increasing degrees of tightness of 

 fixation at the edges. 



On the end of one prong of an electric fork of 517 complete vibrations 

 a piece of cork was glued. The fork itself was mounted on a wooden 

 resonator. The fork in vibration produced a loud, smooth tone; by closure 

 of the opening of the resonator the tone became almost inaudible. 



With the fork in vibration but with the resonator closed, the needle 

 of the reproducer was placed on the cork at the end of the prong (figure 8) ; 

 a tone was then heard directly from the reproducer. By opening the 

 resonator the reproducer tone could at any moment be compared with the 

 resonator tone. 



None of the sound boxes reproduced the fork movement as a smooth 

 tone; in every case the sound was more or less .a "sharp, piercing" tone. 

 The degree of "sharpness" was least with the vaseline box; it increased 

 with the boxes in the order given above. We can thus conclude that 

 the correctness with which a tuning-fork movement at the needle is repro- 

 duced by the diaphragm decreases as the stiffness of edge-fixation increases. 

 When used with ordinary gramophone records the reproducers showed 

 likewise that the sharpness of the tone increased with the firmness of the 

 edge-fixation. 



The following conclusions seemed justified: (1) The above gramophone 

 reproducers are incapable of perfectly reproducing the fork vibration; 

 (2) the distortion of the vibration imparted to the needle increases with 

 the firmness of the edge-fixation; (3) the curve of a gramophone record 

 is more truthful than that of the sound from the reproducer. 



Similar conclusions may be drawn concerning the recording sound 

 boxes. These, however, are more carefully constructed. The use of 

 specially selected glass diaphragms (not one in a hundred is found to 

 give the best results) and special methods of fixation render the distor- 

 tion of the vibration much less. 



The motion of the prong of the fork is represented by the simple 

 sinusoid curve, which produces for the ear a simple smooth tone. The 

 " sharper" tone indicates that the diaphragm changes this motion to 

 one that can be represented by a sum of sinusoids. The increase of sharp- 

 ness with increased firmness of edge-fixation indicates that the greater 



