The motion picture projectionist (Nov 1931-Jan 1933)

26 Motion Picture Projectionist November, 1931 10. Disc Recorder Head The size of the groove is determined by the size of the reproducing needle which at present is the same as that evolved for phonograph disc. The depth of the groove is just sufficient so that the needle will stay in it when being moved violently from side to side by the waves in the cut. Since these side to side motions, although very small, may be as rapid as 6,000 times per second, it is obvious that there must be a very close engagement between the needle and the cut. This is obtained by the use of somewhat abrasive materials in the final disc, which grinds the needle to the shape of the cut actually used. These abrasive materials are one of the causes of the hissing noise so frequently heard when discs are used and the elimination of the abrasive material and the use of other materials for the discs is one of the problems which is being extensively studied by many inventors. It appears probable that a solution of this will be reached in the near future. m Fig. 11. Details of Recorder Head From the above it is obvious that while the carefully designed drive is essential in recording, the recorder itself is the most important single element in this work. A picture of the recorder is shown in Figure 10 and an enlarged sketch of the moving parts in Figure 11. From the latter it will be seen that the recorder consists of the following parts: An electro-magnet which is magnetized by means of the coil at the top. In the field of this electro magnet lies a diamond shaped armature. Around each pole of this armature is a small coil through which the sound currents pass thus causing a corresponding motion of the armature in the magnetic field. Attached to the armature is the stylus arm. This stylus arm has cut in it a V shaped slot at the bottom of which are two hard plugs which rest on two knife edges. The stylus arm is kept pressed against these knife edges by means of a "U" shaped spring whose tension is controlled by two knurled screws, one above and one below the stylus arm. At the other end of the stylus arm of the armature is the rubber lining which absorbs most of the energy applied to the arm. At the bottom side of the arm projects the stylus holder which has drilled in it a small hole for holding the stylus. The latter is a small cylindrical sapphire which is ground to the proper shape to cut the groove in the wax. Referring to the Figure 11 it will be noted that at one side of the stylus there is another small projection which has at the end of it another small sapphire. This sapphire is spherical at the end and is so arranged that it supports that part of the weight of the recorder which presses on the wax. It is known as the advance ball. By proper adjusting of the difference in height between the end of this ball and then of the stylus the depth and therefore the normal width of the cut in the wax is controlled. Suction Equipment In addition to the recording machine itself with the various accessory parts mounted upon it, the disc recording equipment comprises a suction equipment, a control box and the motor switches. The suction equipment may be individual for each recording machine as shown in the photograph or a common suction equipment with separate outlets at each machine may be used. The control box contains a switch lamp for showing when the system is in operation, an attenuator for adjusting the sound currents to the proper value relative to the other machines and a meter and resistance for measuring and adjusting the field current of the electro-magnet of the recorder. The operation of recording and the use of these various parts will be discussed later. (To be continued.) Another Letter on the Standard Release Print Editor, Motion Picture Projectionist : I am watching interestedly the comments for and against the Standard Release Print and now feel urged to give my opinion. The Standard Release Print is, I believe, a great step toward perfect presentation, but as yet it has not quite struck the mark under all conditions. The twelve foot numbered start has eliminated any excuse in exchange inspection for having the start mark and the picture out of frame. An evil of utmost decree until lately for the subsequent run houses. Now we must take into consideration the dots. So many projectionists have rebeled against them. Do they ever go to see the show? If they did their interest in watching the picture will cause them to miss the dots. An audience will stand for a good deal of scratches, blotches, and dirt on the film before its attention becomes drawn from the picture to the mutilated film. Then it must be considered that the audience does not know what they are for and is not watching for them. Rebeling operators, ask your audiences about those dots and have them reply, "What dots?" Next comes consideration of the distance between the dots. Therein lies its weakness. Twelve feet is insufficient. Why? The dots and the distance between the start mark correspond, but that does not give the projectionist time to make up for the machine's pickup. Western Electric equipment with a slow pickup and other machines with quick pickup, neither can beat the dots, consequently those projectionists having sound on film forget the advantage formed for them and start right on the pictures, and with the last set of dots, while disc projectionists must run the film down part way increasing the already numerous hazards of synchronism, or some of the still existing film butchers mark a line somewhat ahead of the first set of dots. Why not increase the distance between the dots four and a half feet and give the machine a chance to get up to speed on the twelve foot leader? Then projectionists would start on the beginning. If this were done surely everyone would use it as insurance against faulty changeovers, and then who would need to rehearse his show? With such a step toward success already made, is there any reason for not stepping a little further and attaining success? Clem Williams, Projectionist, Olympic Theatre, Verona, Pa.