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INTERNATIONAL PROJECTIONIST
VOLUME V
NUMBER 2
APRIL 1933
W. E. EXTENDED FREQUENCY RANGE EQUIPMENT
A. C. Schroeder
MEMBER OF I. A. LOCAL UNION 150, LOS ANGELES, CALIFORNIA
WE hear much about "perfect" sound projection, but every projectionist knows that there are too many variables in the visual and sound reproduction chain to permit of perfect projection. Perfect visual projection has not yet been attained, and the combination process is only just now beginning to reflect the vast amount of development work which has been poured into the refining process. Sound projection need not be perfect to be acceptable, of course, but it must be what might be termed "pretty good."
Every advance made in the art makes the task of everybody in the field just so much more difficult, for once given improved quality, Mr. Cash Customer attunes his ears to that level and will be content with nothing less.
In this connection, the results of an examination by the writer of the new Erpi equipment installed in Grauman's Chinese Theatre in Hollywood, should prove of interest. Projectionists undoubtedly would like to know more about the new-type sound gates which
are used, about why the change from the old-style gates was made, and in a comparison of results obtained. The projectors under consideration previously were equipped with the so-called roller gates.
As most projectionists know, it is extremely difficult to pull the film past the exciter lamp beam at a perfectly itjiijorni rate of speed. The film, instead of moving at a steady rate of speed moves at a varying rate, and in very bad cases it probably simulates an intermittent motion. This nonuniform film movement is due to the fact that motion is imparted to the film by the teeth of a sprocket. As each tooth engages a hole in the film and commences to pull, the speed of the film is slightly accelerated ; and an instant later the movement of the film is slightly retarded. This varying motion of the film causes a form of "flutter," or raspy sound. Due to the size of the striations on the film at the high freciuencies, these "highs" are very much mf)re, affected by the varying speed than are the lower frequen
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cies. This defect is most pronounced in extended frequency range .systems. To overcome this deficiency work was begun on the sound gates, with the result now to be described.
Film Travel Path
In the roller gate there is reall}' m; "gate," as we think of it in the usual sense. The film passes over a series of rollers and eventually over the Movietone sprocket, and it is kept under tension all the way. On leaving the lower sprocket of the Simplex head the film passes over a large roller about 1^ inches in diameter. This roller has a good deal of tension placed on it by a spring, tending to keep it from turning, "^i'he film is kept in contact with this roller by a pad roller that bears directly against the film, holding the film tightly against the large roller. This causes the film to adhere to the latter sufficiently to force it to turn and thus keeps the film under tension as it passes through the rest of the rollers on its path past the light beam.
I'his large tension roller is shown