Page:Popular Science Monthly Volume 92.djvu/143

 Making a Talking Machine

A simple construction within the scope of the amateur B\' Charles Horton

��THE talking machine herein described is of the well-known so-called "hornless" type in which the horn is of rectangular cross-section instead of circular, and is con- cealed within the base of the instrument.

���Details of the turntable and the location of the electric motor for driving it

Contrary to general opinion among experi- menters the talking machine is a very simple instrument and not difficult to make, pro- vided the underlying principles are under- stood and correctly applied.

The chief difficulty, of course, is in making the spring motor.

Sound is understood as that disturbance in the air body which is capable of causing vibration of the ear drum with consequent typical sensation. There are various kinds of sounds, which may be roughly divided into two classes — noises and musical sounds. Noises are unsymmetrical groups of sound waves. Musical sounds, on the other hand, are symmetrical groups of sound waves. A musical note is a group of sound waves occurring in perfect rhythmical order. The rapidity of \'ibration of any sound wave is called the "pitch," and the quality due to the overtones is called the "timber."

The talking machine is a machine for reproducing sounds from permanent me- chanical records of original sounds. The record is made by allowing the original

��sounds to impinge on a flexible diaphragm the resultant movements of this diaphragm being arranged to cause a needle point to trace in a soft substance in motion a wavy line characteristic of the impinging sounds. The reproduction is accomplished by prac- tically the reverse of this process and the tones are amplified by allowing them to pass through a resonant chamber.

From the above it will be readily under- stood why the phonograph is imperfect in its reproduction ; for while it is easy enough to record and reproduce the fundamental notes, some of the complex overtones are of very high pitch and also of very small magnitude and are consequently lost, either not being recorded at all, or not being reproduced, or being lost in the reproducer and resonant chamber. Furthermore, since the pitch of a musical note determines the note, even the slightest variation of the speed of the record changes the pitch of the music. Also the resonant chamber some- times adds typical overtones to the music. Thus the two principal problems to be solved in making a talking machine are,

���FIG.2

��The top plan shows the tiomtable with location of the arm and two needle tills

first, to secure a good reproducer and, second, to secure perfectly uniform speed of the turntable.

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