Exhibitors Herald World (Oct-Dec 1930)

December 27, 1930 EXHIBITORS HERALD-WORLD 29 \\V SOUND REPRODUCTION THE BLUEBOOK SCHOOL By F. H. RICHARDSON BLUEBOOK SCHOOL QUESTION NO. 55 The question was: "Tell us all you know about the harm that loose connections, dirt, etc., on batteries will do. Also tell us exactly why it is not permissible to use batteries for sound amplification immediately after charging. I AGAIN select the reply of Aubrey D. Hotaling, Orlando, Fla. Hotaling says: "Think I covered the above quite minutely in my answer to Question No. 54, but it may do no harm to again say that for proper performance of any radio or talking picture installation requiring storage batteries, it is essential the battery be kept immaculately clean and free from dust and dirt, and that all connections be free from corrosion and that [Until further notice, all communications to this department should be addressed to F. H. Richardson, 43-28 Thirty-ninth place, Long Island City, N. Y.] they be tight. If this is not done there will be trouble and plenty of it. The horns will tell you so, in no unmistakable terms. The slime on a dirty battery top is a combination of electrolyte and dust, which causes leakage of current between the terminals, and has a tendency to slowly rob the battery of its available power. This leakage will become apparent to the ear in the form of crackling or frying noises in the loudspeaker, commonly known to sound engineers as surface noise "It is not permissible to use a storage battery for this work immediately after a charge. The battery cells will contine to gas for from 30 minutes to an hour after a heavy continuous charge, and the bubbling of the electrolyte will make itself manifest in the loudspeaker. I have heard patrons remark on leaving a sound theatre that the picture was good, but there was quite a lot of static. Of course there was no static in the true sense of that term. They mistook a blundering projectionist's work for it." NEW ADJUSTABLE SIMPLEX SHUTTER THE International Projector Corporation has developed a new shutter in which the blades are adjustable in the matter of width. It is designed for use on the Super-Simplex, or other Simplex models equipped with the rear shutter. Examining the picture herewith presented, you will see that the improvement consists of a narrow vane, which may be rotated within the limits of the slot containing the screws, merely by loosening the aforesaid screws. The effect of such movement will, of course, be either to widen each of the two blades in equal proportion, or else_ to make them both more narrow, depending upon which way the vane is moved. While this shutter is designed primarily for use in place of the regular stock Simplex rear shutter, it also may be substituted for an infront-of-the-lens Simplex shutter by having a machinist bush the hole in the hub to fit the smaller shaft, and by constructing some sort of protective guard to prevent the fingers from coming into accidental contact with the shutter wings when it is in operation. There is no protective rim on this shutter, and while a finger coming into contact with such a shutter probably would not injure the shutter materially, it might make the finger look like a piece of badly chopped hash. Therefore DON'T use this shutter in front of the lens without a suitable protective guard. The reason advanced for putting out this shutter is that the diameter of the light beam varies with different sizes of light source, which does not set forth the real facts. The size of the light beam at the shutter position Simplex adjustable shutter. is dependent entirely upon the size of the reflector or condenser, and its distance from the shutter. It may therefore be readily seen that there would really be considerable difference as between the diameter of a beam from a reflector type of light source using no condenser with a relatively small diameter reflector, and from a Peerless type using a large diameter condenser located relatively close to the shutter. That should be perfectly plain to you all, I think. However, a leading Broadway projectionist with whom I was discussing this shutter said that the variation in beam width made no demands upon shutter blade width. Such an argument has no basis in fact, for the reason that each and every pin point of a condenser or reflecting mirror sends forward to the spot, not a single ray of light, but an actual image of the light source. This image, of course, goes forward in the form of a converging beam. The images sent forward by the center of the condenser or reflector will all enter the aperture, unless the light source be a very large one. The outer zones of the condenser or reflector, however, will send forward images, which will fall partly upon the cooling plate and partly upon the aperture. If you will study this proposition, examining Figure 38, page 168; Figure 38, page 169; and Figure 46, page 181, Volume 1 of your Bluebook, together with the accompanying text, I think you will understand that this Broadway projectionist is in error in his views. However, I was just a bit amused by the reasons advanced for putting out this shutter. I have been demanding the production of exactly this sort of shutter for many years, and for exactly the same reasons — because the diameter of the light beam varies in front of the projection lens. And the proportionate variation is fully as great as it is at the rear of the aperture.