Maintaining Your 16mm Projector
By: Ed "Movieeman" DeLorean
Chapter One -- The Sound Sytem
What follows will be a broad informative discussion of the mechanics of maintaining the sound system of the typical 16mm film projector. Photos and descriptions will detail the system in the Eastman Model 25 and it's successors, but the principles should be just as applicable to other high quality 16mm projectors.
An optical sound track on film intercepts a beam of light which is directed onto the face of a photocell. The variations in the amount of light allowed through the sound track cause a variation in the amount of light falling on the cell which varies the electrical output of the cell. The output is amplified and reproduced as an audio signal.
Older film used a "variable density" track. The density of the track varied and this caused the light beam to be modulated. The newer and better type of track is a "variable area" which modulates the light reaching the photocell by variation of the total opaque area of the track. In either system during a period of silence the sound track area/density is unmodulated.
Here is a diagram showing the typical components of the sound system in a 16mm projector. On the next page we'll discuss the adjustments that are possible to make to each component to obtain optimum sound quality.