16 



THE STUDY OF SPEECH CURVES. 



" records " are accurate copies of the wax original. To turn the gramophone 

 record into sound its groove is made to pass under the needle point of 

 a "reproducer" whose construction is similar to that of the recorder. 



A photomicrograph from a phonograph record (matrix) showing the 

 varying width and depth of the speech groove is given in figure 5. Being 

 from the matrix, the figure shows the groove as a raised ridge. The pho- 

 tomicrograph, figure 6, shows the groove of constant depth but changing 

 position on a gramophone disc. 



Sound box 



Cork ^g 



■^m.'MW/MM//WM/M///////fi/>. 



} m^ . WMMM MMMMMm,^VJM 



n Conta 



Resonator 



FiQ. 7. — Gramophone reproducer or sound box, section. 

 FiQ. 8. — Sound box repeating motion of a fork. 



Some experiments made on gramophone sound boxes indicate the 

 necessity of changing the prevalent view of such vibrating diaphragms. 

 They indicate also the reasons for the phonograph or the gramophone 

 twang to the records. 



For these experiments the ordinary gramophone reproducing sound 

 boxes with certain modifications were used. Part of the useless projecting 

 metaUic rim was cut away so that the mica diaphragm could be seen to 

 its full extent. A section through such a reproducer is given in figure 7. 

 The mica diaphragm E is connected at the center to the arm G, which 

 holds the needle K. The arm G is held by a Ught spring at H. Around 

 the edge of the diaphragm are the two rubber washers (or gaskets) tightly 

 pressed by the metal ring A to the body of the box CD. The tube F is 

 for connection to the trumpet. The needle K runs in the groove on the 

 gramophone disc and transmits the vibratory movement to the diaphragm. 



