International projectionist (Jan-Dec 1953)

the film down through the gate), and finally over the holdback sprocket. Deficiencies in Early Models The performance of this soundhead left much to be desired. Although the free-turning impedance roller was intended to smooth out irregularities in the motion of the film, it actually caused more flutter than it eliminated. The reasons are not difficult to find. In the first place, the film was held in the curved sound gate so tightly by the clock-spring steel tension pads that any damping effect that the impedance roller and its flywheel could possibly exert was effectively nullified. Second, the length of film from scanning point to sound sprocket was so great that uneven shrinkage of the film unavoidably resulted in fluttery sound. It will be noted that the most satisfactory of the old-time soundheads were so designed that the distance between the sound sprocket and the point of scanning in the sound gate was as short as possible. Third, excessive tension on the film in the soundgate created a condition whereby the taut loop of film passing around the impedance roller acted very much like a bouncing spring, imparting irregularities to the movement of the film. The last pair of these soundheads in the writer's State were replaced with modern reproducers a couple of years ago. With the development of the "rotary stabilizer," soundhead design changed radically. The soundgate was replaced by a free-turning scanning drum; and the sound sprocket ceased to act directly upon the film at the point of scanning. Soundhead Design Changes The scanning drum of the modern soundhead is a cylinder over which the film passes with a lateral displacement sufficient to permit the scanning beam to pass through the soundtrack without being cut off by the solid drum. The surface of the drum is highly polished to prevent scratching the film. Any dirt or emulsion which may happen to accumulate on the drum should be removed with an orangewood stick, not with any metallic object that might scratch the surface. The scanning-drum shaft carries a flywheel at its opposite end. This, a self-damping flywheel of special construction, is the rotary stabilizer. Now, the scanning drum is driven only by the film which is pulled down at the rate of 90 feet per minute by the sound sprocket. But after the freeturning scanner attains normal speed, HI SPOTLIGHTS BY STRONG DOMINATE NEVADA RESORTS The regard held for the proper lighting of the pretentious stage and floor shows presented by Las Vegas, Nev., hotels is evidenced by a picture of a modern and completely equipped control room. The Sahara, Sands, and Flamingo hotels and the Desert Inn have provided for an abundance of exceedingly bright, flickerless light by adopting high-intensity arc spotlights with automatic arc controls. Control room space has been conserved by using adjustable, self-regulating transformers with these spots, rather than spotlights that require heavy rotating equipment. A trim of carbons burns 80 minutes. Using a two-element, variable-focal-length objective lens system, together with a silvered glass reflector, these hotels can produce a sharp-edged spot from head spot to flood. The horizontal masking controls can be angled 45 degrees in each direction. Fast-operating, 6-slide color boomerangs permit the embellishment of any act by the use of light of any color. Pembrex Theatre Supply Co., Los Angeles, directed the intsallations. A brochure describing this equipment may be had without cost from Strong Electric Corp., 14 City Park Ave., Toledo 2, Ohio. it continues to revolve, not by the direct pull of the sound sprocket on the film but by the "filtered torque" of a small film-loop which automatically forms between the kinetic scanner and the sprocket. Any small irregularities in the rotation of the sound sprocket, therefore, are absorbed by this small loop, or slackness in the film, and cannot affect the rotation of the scanner which moves the film at a constant speed through the scanning beam. Function of Film Loop At first thought, this seems very confusing— the film, pulled by the sound sprocket, makes the scanner revolve; yet the scanner moves the film through the scanning beam! The film, however, is not taut between sound sprocket and scanning drum: a "slackness," or small loop, has formed of its own accord. And while sufficient pulling power is transmitted through the loop to keep the scanner revolving, the very fact that there is a slackness in the film between sprocket and scanner is insurance against irregularities of movement being transmitted to the film at the scanning point. To make certain that it is the revolving drum, and not the sound sprocket, that effects transit of the film at the point of scanning, the film is pressed firmly against the drum by a guide-roller and pressure-pad assembly. So important is the condition and adjustment of this assembly to proper operation of the soundhead that the projectionist should inspect it frequently and lubricate it according to the manufacturer's instructions. Neutralizes Disturbing Factors Unlike an ordinary flywheel, the ro tary stabilizer neutralizes all forces which tend to disturb the constant speed of the kinetic scanner. The flywheel which is attached directly to the scanner shaft is a hollow drum — something like a scaled, empty can of rugged construction. Inside this can is a smaller, solid flywheel. The heavy, inner flywheel is not fastened to the scanner shaft, however, but is free-turning, mounted on ball-bearings. The small space between the inner surface of the outer flywheel and the outer surface of the inner flywheel is occupied by oil of proper viscosity. A film of oil is thus the only mechanical connection between the two flywheels of the rotary stabilizer. The friction provided by the vis INTERNATIONAL PROJECTIONIST March 1953 i