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FIG. 1. — “Penthouse” stereophonic sound reproducers now being marketed by Kinevox (left), Magnasync (center) and Westrex (right).
Units are mounted on standard theatre projectors, between upper film magazine and regular head of projector, as shown above.
'Penthouse'' 4-track Sound Reproducers
Auxiliary sound heads solve problem of reproducing 4-channel magnetic sound from composite CinemaScope prints.
By RALPH LAWTON
The final step in the fabrication of Twentieth CentruryFox CinemaScope for the screen was the development of a successful method of putting the system’s four sound tracks on the picture film, thereby eliminating need for a separate film for the sound. Actually, two steps were involved: 1) working out a suitable method for putting the magnetic sound tracks on the picture film, and 2), developing equipment for reproducing the four tracks by standard 35mm theatre projectors.
The four-track system was developed by Earl I. Sponable, director of research for TCF studios. The new method, Sponable says, means a considerable saving in the inspection, processing and shipping of CinemaScope films, in addition to lowering projection booth costs, and eliminating millions of feet of film stock which otherwise would be required for separate sound tracks.
To gain the necessary space on 35mm film for the additional tracks, TCF engineers narrowed the width of the sprocket holes in 35mm film from .110 to .078 of an inch, and at the same time also whittled down the size of the sprocket teeth to corresponding dimensions. (See Fig. 2.) Making this step possible was the use of acetate film, which now replaces the old nitrate film for CinemaScope prints. Nitrate film shrank in laboratory processing; the new acetate film is stable.
In all, many months of engineering work went into this phase of the system’s development. Both Eastman Kodak Company and Technicolor Corp. had to provide special film stock; new gears for projectors and cameras had to be made and installed; and many changes had to be worked out in laboratory practice.
The second step had as its aim to make it as easy as possible for the average theatre owner to convert his equip¬ ment to reproduce the sound from the fourtrack Cinema¬ Scope prints. For this, TCF engineers conceived an auxiliary
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FIG. 2 — How the four magnetic tracks for stereophonic sound are arranged on CinemaScope film. Narrowed sprocket holes make possible the additional tracks without reducing picture area.
FIG. 3 — Film path and mechanical layout of one model of “penthouse” magnetic sound head.
sound head which they termed a “penthouse” and installed the prototype between the upper film magazine and the reg¬ ular head of a standard 35mm projector. Leading equip¬ ment manufacturers were asked to manufacture the “pent¬ house” sound head for exhibitors. Today, such firms as ( Continued on Page 502!)
478
American Cinematographer
October, 1953