The motion picture projectionist (Nov 1931-Jan 1933)

40 Motion Picture Projectionist December, 1931 Greater SAFETY Here is a Sound Screen that challenges the field on every point that involves perfect projection. It is acoustically correct and free from sound aberration and visionary distortion. It is the final result of scientific application of all fundamental requirements for a better Sound Screen from every angle. Approved by E. R. P. L FEATURES 1. Fireproof. 2. Free from distorts o n of sight or sound. 3. Acoustically perfected. 4. Eliminates "sound pockets." 5. No glare — restful to the eyes. 6. Easy to clean — lasts longer. Sold by National Theatre Supply Company, at all Branches. V/ISIBESTONE J THE PERFECT FIREPROOF SOUND SCREEN KEASBEY & MATTISON COMPANY AMBLER, PENNA. ask the fellow who uses one! he'll tell you HOFFMANN SOOVS RHEOSTATS are perfect!! Every PERFECTION RHEOSTAT has satisfied its owner. Breakdowns, service-calls and trouble are unknown to Perfection users. THE ONLY UNION MADE RHEOSTAT Recognized as the Highest Standard everywhere. Now equipped with solderless, adjustable lugs to take wire sizes from No. 4 to 4/0 without any additional cost. We build rheostats for special requirements. Communicate with us Direct. There is no obligation. Sold by all Branches of National Theatre Supply Co., Sam Kaplan, New York, Continental Theatre Accessories, and by your dealer. 11 OFFM ANN SOONS Electrical and Engineering Corporation 387 FIRST AVENUE, NEW YORK Contracting Electrical Engineers — Moving Picture Theatre Electrical Specialists a little above the average of such apparatus in quality. To enumerate, it must be: 1 — Reliable. 2 — Quiet running and free from vibration. 3 — It must not drop off in voltage and consequently in amperes when additional load is put on. 4 — It must be decidedly free of voltage ripples. Such ripples are likely to cause disturbing noises. Reliability is a factor often overlooked until the owner has had a dark house. The larger circuits generally provide for this by the installation of duplicate sets either of which will run the show. This gives full protection. Other than this, apparatus is often provided so that, if the generator fails, recourse can be had to A.C. through a choke coil or other device. Of course such a picture is very unsatisfactory after running on direct current, and the proper solution in every case is to use the best generator that can be bought and give it good care. It must be remembered that the generators are usually given pretty severe service, operating in many places for long hours every day at a point near full load with shots of severe overload. Suggestions for Installation Quite often the owner or architect does not give the generating set the attention it deserves when the house is being designed. It may be placed in a location where even a slight noise is telegraphed to the audience either through the air or through the supporting beams. Sometimes elaborate precautions are taken to support the unit on cork, rubber, or springs, only to bolt it down against the beams of the floor, thus entirely neutralizing the benefits hoped to be derived from the cork, rubber, or springs. The set is generally so well balanced mechanically that no bolts should be required. Even the fastening of the pipe conduit rigidly to the set and leading it into the concrete will carry considerable disturbance into the house. The generating unit consists of parts of considerable weight, some of which rotate at high speed and are bound to cause some noise and vibration. In addition there are magnetic and brush noises that must be damped down to the lowest possible point. The building of these sets has become a very much specialized art, yet there are some theatre owners who will accept a unit built up at random out of any kind of commercial motor and generator so long as it will deliver current regardless of regulation, noise or efficiency. A very noticeable fault in many multiple sets is the falling off in voltage, and consequently current, when the second arc goes on. This dropaway is not always, to be sure, en