Motion Picture Herald (Nov-Dec 1934)

22 Better Theatres Section December 15, 1934 **Happy New Year! says Balcony Bolivar . . and if you improve your sound it will be a prosperous year as well!" Regular patronage, the difference between profit and loss, depends greatly upon your sound. The C. T. R. Full-Range Sound System is upto-date, moderate in cost, economical to maintain. Matched Unit performance assures natural, clear, true to life reproduction A post card •with your name, seating capacity and dimensions of your theatre will bring you facts and figures promptly, and without obligation. SOUND SYSTEM Sound Division The Cincinnati Time Recorder Company Est. 1896 1739 Central Avenue Cincinnati, Ohio Better Projection at a Saving of 20-30% s yours when you use a GARVER KURRENT CHANGER to change A.C. to D.C. It delivers 15-30 amps, steadily, quietly and dependably, eliminating change-over troubles. No sound interference. Recommended by ^i<^r leading lamp manufacturers $ I ★ For Brilliant Mazda Projection highly concentrated spot or flood lighting have a dependable National Regulator Quiet Operation I 10 or 220 volts ★ Circulars on Request Representatives in Al Principal Cities NOW YOU CAN MAKE THAT PERFECT SPLICE Doesn't scrape 1 It peels off the emulsion. Cannot saturate film. Use with any splicer. PRICE $1.00. Used by exchanges and laboratories. If your dealer cannot supply write us direct. ROSCO FILM CEMENT 367 HUDSON AVENUE, BROOKLYN, N. Y. testalite, or with an a.c. meter. Your local radio man can make the test if you cannot. Third : The difficulty may be due to a loose diaphragm in the loudspeaker. If you have more than one speaker, listen to them separately. If you have but one speaker, does the same trouble appear in the monitor horn? If there is no monitor, then either borrow one or use a pair of head phones. Fourth: In case your system is equipped with a tone control, it may have broken down, thus throwing too much power into the medium and high notes. These are merely suggestions as to the most likely causes of the trouble, if you have described it accurately. REARRANGING GEAR TRAINS FROM Bruce H. Denney, projectionist of the Sobota theatre in San Jacinto, Calif., comes this remarkable letter: "Dear Mr. Richardson, thanks (honestly) for your criticism in the October 20th issue of Better Theatres. Possibly I should have called the effect a "ghost" rather than a travel ghost. The flywheel was out of balance dynamically. The different position may have balanced with some vibration already in the mechanism, but it did cure it. A new flywheel was okey without my tricky adjustment. "But with regard to vibrations in general, many projectionists have fought them. Since my letter to you I have assisted several in rearranging the gear trains of their projectors to transfer little bumps and quivers into time with the shutter cut-off periods, a thing not always easy to accomplish. Sometimes it is difficult to secure the necessary replacement gears, etc., to cure vibrations — lack of necessary funds. "An easy method for determining direction and amount of movement of optical axis is to place a thin sheet of metal containing a pinhole over the projector aperture, so that an image of the hole may be focused upon a piece of cardboard placed in proper position on the stage [or attached to the screen if there is no stage. — F.H.R.]. "In place of the regular rotating shutter, construct one of cardboard having only one opening, and only J^-inch wide. With the projector mechanism at rest, the light on and the pin hole focused on the cardboard, outline the spot of light with a pencil. Start the projector and outline the spot again. Usually it will be found to have been displaced a bit. "Outline this spot and give it some identifying symbol or number, after which rotate the improvised shutter about 10° on its shaft. Start the projector and again outline the spot. Do this while moving the shutter about 10° each time until a complete rotation is made on the shaft. "Some queer geometrical patterns will often be made by the spot outlines. Those that do not concur exactly with the first (rest position) indicate a movement of the optical axis. Such circles as are considerably 'out' with relation to the rest position spot indicate the direction and amount of vibration which, if checked with the flywheel or degree of shutter shaft rotation, will indicate the exact position of the mechanism at the peaks of vibration. "A careful study and analysis of the patterns formed by the spots will indicate the bent shaft, the worn gear or the bound spot in which the vibration has its seat. A pattern that indicates a vertical vibration or movement might be expected to have its seat in the main drive gears or associated shafts. A horizontal pattern would of course indicate a lateral movement that might be associated with the governor or shutter shaft. "Any vibration having its seat in the intermittent movement itself usually occurs during the cut-off period, hence is kept from the screen by the regular shutter. Incidentally, the practice of placing blocks of ^-inch rubber composition material under a very popular sound system base to minimize transmission of noise into the floor, usually permits just a bit too much ghost, halo or what-have-you to reach the screen. In cases of projector vibration, the small screen image at long projection distance suffers much more than its largescreen-image-short-distance brother. "Here is one very common problem and one method of cure: Center frame base of Simplex projector warped by continued and excessive tightening down. Weight sometimes supported by bosses under base and little or no support on machined faces under base. Cutting down boss projections would merely cause base to buckle or sag downward, and on some types of drive the P-331-X pinion (or its equivalent) would be pulled out of proper mesh with the (G-112-G) main driving gear. "This is a very common trouble on older type Simplex projectors. A new base is expensive and not too easy to install. Metal shims about 2.5 inches long by 1 inch wide, piled to proper height under center of the base to serve as a center support, will permit the base to be tightened down to any necessary degree without any tendency to separate gears as above set forth. "As regards my slit azimuth, that name was tacked to it by a machinist at one of the major studios and the name has stuck. By its use a mask may be moved in from either side of the sound aperture to mask out any noisy part of the sound track. In event of a scratch down the exact center of the track, a triangular mask moves down into the light beam until the objectionable sound is removed. True, as you say, the sound volume is more or less reduced, according to the amount of area it is necessary to cover, and the gain must of course be raised to compensate. It works fine on variable density. On variable area the only thing it is possible to do is cut off exactly half the sound track, double the gain and get by on half-wave film pickup. The sound will not be hot, but it will at least be clear, with no machine gun or boiler factory effect. It is necessary to use it only occasionally, but when needed it surely is a life saver !" It is very evident the foregoing letter