International projectionist (Jan-Dec 1936)

12 INTERNATIONAL PROJECTIONIST September 1936 INTERMITTENT SPROCKET PICTURE GATE LOWER FEED SPROCKET PROJECTOR MECHANISM SOUND REPRODUCER FIGURE 1 Showing path of film travel in Standard soundhead. The film passes from the intermittent sprocket around the drum (kinetic scanner) and then over the projector lower feed sprocket (see Fig. 2) soundhead features: the path of film travel, the "Kinetic scanner," the absence of gears or sprockets, and the adjoining parallel strips of film running from the film chute down to and around the scanner and on up to' the projector lower feed sprocket — which features demand close inspection. The most important element herein is the kinetic scanner, it being a fundamental requisite for good sound reproduction that the film pass the scanning point at a uniform speed. Many projectionists are familiar with rotatingdrum film-scanners, of course, but the details anent the application of the principle in this instance are of interest. The kinetic scanner is used in both the Standard and Heavy Duty soundheads. Erpi's kinetic scanner is an inertiacontrolled scanning drum which is mounted on precision ball bearings to reduce friction to a minimum. Extra precautions have been taken to effectively seal the ball bearings against the entrance of dust, since this would interfere with the smooth rotation of the scanning drum and introduce disturbances, in the reproduced sound. The initial lubrication should last for an indefinite period. Constant speed of the scanning drum is maintained by means of the specially designed double flywheel: one flywheel is integral with the scanning drum which effectively prevents high-frequency oscillations of the film; the other is free floating and is coupled to the first one by means of a mechanical filter which effectively suppresses slow oscillations. The kinetic scanner is so stabilized that a sudden change in film speed or a disturbance in the film loop, such as the passage of a film splice, has no appreciable effect on its uniformity of rotation. During the acceleration period of the scanning drum the two flywheels are coupled together by means of a centrifugal clutch. The film is guided by a pivoted guide roller onto the drum of the kinetic scanner around which it is wrapped (Fig. 1). The extremely low friction of the kinetic scanner allows the film to rotate it without being subjected to appreciable tension, resulting in the formation of an elastic film loop between the scanning drum and the feed sprocket which introduces a compliance between sprocket and drum and prevents the sprocket tcoth impulses from being transmitted to the scanning point. The film chute can be readily dismantled for cleaning. Film scratching and abuse is eliminated by the use of highly-polished film guides. The pivoted guide roller, supported between bronze bearings lubricated through covered oil cups, is provided with chromium-plated flanges to resist wear and positions the center of the sound track at the center of the optical system. Its adjustment is accomplished by a slotted knob which is accessible through an opening in the closed door. It is thus seen that no film sprocket or sprocket drive mechanisms are employed in the sound reproducer, as has been the practice heretofore. This results in a much less expensive and simpler construction. The location of the lower film magazine is such that the usual projection angles are readily attained. The writer was particularly interested in two features of this head: (1) the increased amount of film therein, and (2) the possibility of flutter occasioned by the rather long adjoining parallel film strips (Fig. 1). Erpi has given assurances that the design of this head not only does not induce more flutter than earlier heads but actually effects a sharp reduction thereof. Erpi offered to confirm these assurances by a practical demonstration, an invitation which will be accepted by the writer at an early date and reported upon subsequently. The answer as to whether there is too much free-running film in this head will be forthcoming after the design is used under practical operating conditions. Incidentally, all Mirrorphonic unit-combinations, from M-l to M-5, meet the requirements of the National Board of Fire Underwriters. The exciter lamp is mounted in a separate holder external to the sound reproducer. To eliminate adjustments and to facilitate replacement, a new k\\\\\\\\\\\\\<W^^^^ ~nm~ &::a FIGURE 3 A total reflecting prism is located within the scanning drum to deflect the light which has passed through the sound track out at right angles into the photoelectric cell type of lamp provided with a pre-focus skirt on its base is employed. This permits the use of a low-cost automobiletype of pre-focus socket, obtainable from any commercial dealer. The lens tube assembly, hermatically sealed, differs from earlier designs in that it images the incandescent filament of the exciter lamp as a concentrated line of light directly on the sound track of the film by means of cylindrical lenses without the use of a mechanical slit. The assembly may be adjusted with the com FIGURE 2 Halftone presentation of the Standard soundhead (see Fig. 1)