Boxoffice (Jul-Sep 1962)

I sssssssss KEEPING SOUNDHEAD CLEAN A PRIME FACTOR IN TRUE REPRODUCTION 1 Proper Adjustment, Care, Duty of Boothman By WESLEY TROUT V ERY often, out in the field, we have found distorted sound reproduction was due to stabilizer not functioning properly, incorrectly focused or dirty sound lens in the soundhead. Also, undercut constant speed sprocket ... . causing uneven film Wesley Trout travel past the scan ning beam. Some types of soundheads use two flywheels for stabilizer, others use a flywheel-type drum containing a special oil for filtering film travel past the scanning beam. In either type of filtering, the speed of the film must be constant and regular or the sound reproduction will suffer. On one of our trips in the field, we found several situations where the projectionist failed to keep his equipment clean, particularly the soundhead. We found accumulation of dust in all parts of the soundhead — dirt on the stabilizer drum, oil and dirt mixture on the moving parts; gummed up idle rollers and filthy sprockets. The sound reproduction was greatly marred. It was necessary to completely disassemble the equipment and thoroughly clean every component. Dirt on the sprockets and stabilizer drum will cause fuzzy, distorted sound output. And due to improper lubrication, several cases were found that had stabilizer drum shafts not turning freely. IMPROPER ADJUSTMENT AND OILING Too, we found improper adjustment of the guide roller assembly, the rollers grooved and not turning freely, due to dirt accumulation, and not regularly oiled. Only a few drops of high grade oil is necessary, but oiling of the rollers on the shaft is a “must.” Always leave the guide roller assembly open when there is no film in the mechanism. If the roller (soundheads using roller riding the film on the drum) is left closed, flat spot will soon develop on felt rollers, which will cause flutter. We find many cases where the lateral guide roller assembly is not correctly positioned. Every type of soundhead has some type of adjustment for positioning the guide rollers so that the scanning beam from the sound lens is properly positioned on the sound track, using a standard “buzz” track loop for making accurate adjustment of the assembly. TESTING WITHOUT LOOP Now, if such test loop is not available, the adjustment may be made as follows: Thread regular release film in projector and soundhead in the usual manner and start projector. Observe the position of the scanning beam with relation to the sound track. As an aid in observing the edges of the sound track, a flashlight may be directed on the concave side of the film (that side in contact with the rotary stabilizer drum) and the image viewed from the same side of the film. There is seldom any occasion to remove the optical system, but should the occasion arise (sound lens replacement for repairs), in some soundheads the focus of the lens will not be disturbed. However, it should be checked, after reinstalling, with a 7,000 cps test loop for focus, a “buzz” test loop for lateral adjustment, and then overall test with a standard frequency test reel. There are still quite a few old-model soundheads that have a “gate” for holding the film steady where the scanning beam passes through into the photo-electric cell. Needless to state, the proper tension must be maintained at this point and shoes replaced when needed, so the film will lie “flat” and frequency response will not be marred. There are a few Western Electric installations still using a sound gate. For better quality sound reproduction, the more modern soundhead with its kinetic scanner drum (stabilizer) should replace these obsolete soundheads for better frequency response and less upkeep. Repairs for older types of soundheads are hard to get now. With older model soundheads, the “flut ter” caused by uneven film travel is, up to a certain point, kept to a minimum by using a large flywheel for filtering out irregular motion past the light beam. It should be understandable that the motion of the film past the sound gate must be utterly smooth. The slightest jerk will result in “flutter,” which is a tremolo in the sound, and very unpleasant. Moreover, the same result will follow if the film is not held in its proper position, but permitted to move back or forward while in motion past the scanning beam. Here, guide rollers must be perfectly adjusted so that the film will move in a straight line past the light beam. In all makes of soundheads, keep in mind that the sound gate, pad, or dram must be kept scrupulously clean. Particles of lint or film wax or any foreign matter may vibrate with the motion of the film and cause interruption to the light beam. Sometimes these particles become lodged at this point and cut the light beam off or cause noisy sound reproduction. Use a camel hair brush and lintless rag for cleaning sound drum or gate. Clean every day and avoid trouble. MODERN-TYPE REPRODUCERS Before we go into further discussion of reproducers (soundheads) , let us tell you briefly about the modern-type reproducer. In order to obtain high quality sound reproduction, a better means of filtering film travel past the scanning beam was invented. The filtering system now consists of a flywheel which is hollow, and inside it, supported by ball bearings, is a heavy inner flywheel coupled to the outer shell only by means of a suitable liquid. The film is supported at the scanning point by a smooth-faced drum affixed to a freely rotating shaft and on its opposite end the special filtering flywheel arrangement. Now, associated with the film -supporting drum there is usually a freely running auxiliary padded roller to hold the film firmly against the drum. This felt roller should never be allowed to accumulate dirt or other foreign matter as it will scratch the film. Be sure that the guide roller is left open 6 The MODERN THEATRE SECTION