A SOUND PROJECTOR SYSTEM 



199 



by moving all resonances out of the working range and by filling the 

 magnet chamber back of the diaphragm with a heavy damping oil. 

 The film used with the disc record, called a synchronized film, differs 

 from ordinary film only in that one frame at the beginning is specially 

 marked to give the starting point. ~ 



■^ — -^lA/W- 



Wypo 



Fig. 3 — Photoelectric cell. 



The film sound record, as has been said, consists of a track of 

 varying density running along one side of the picture. This sound 

 track is 1/10" wide. Differences or changes in intensity of sound 

 are represented by differences in the density of the record, while pitch 



CONDENSER 



►MEGOHMS 



10 

 •MEGOHMS 



I POLARIZING 

 ! BATTERY 



Fig. 4 — Photoelectric cell circuit. 



is represented by the number of changes from dark to light and back 

 again in a given length of track. This sound record is converted 

 into a corresponding electric current by arranging that a narrow high 

 intensity beam of light shall pass through it and fall upon a photo- 

 electric cell. The arrangement is shown in Fig. 2. The light from 



