The motion picture projectionist (Oct 1927-Sept 1928)

May, 1928 The Motion Picture Projectionist TS PROJECTOR {SIMPLEX MACHINE aSSH 2-A REPRODUCER ASSEMBLY WPERGEARBOX SHAFT UNIVERSAL JOWTS LOWER GEAR BOX MOTOR COHTROt BOX Disc-and Film-Equipped Projector passes on leaving the projector head. Disc Records The disc records employed are similar to the best types of phonograph record except that they are much larger and run at about one-half standard speed; this enables each record to play throughout a whole reel. The film used with the disc record, called a synchronized film, is similar to any ordinary film, except that one frame at the beginning is specially marked to give the starting point. Film Record With the film method (Movietone) the sound record consists of a band about Y% in. wide, called the sound track, which runs down one side of the film and consists of microscopic lines. The spacing of these lines at each point depends on the pitch of the sound which was recorded at that moment. The difference in density of the lines depends on the loudness of the sound — that is, the greater the contrast between light and dark lines, the louder the sound. Such a film is called a sound film, and is otherwise similar to an ordinary film. After leaving the lower sprocket of the projector head, the sound film enters the reproducing attachment where it passes over a sprocket that moves along at constant speed. A narrow beam of light from a high-intensity exciting light is focused on the sound track of the film through a system of lenses and an aperture plate. The light which has passed through the moving film will then vary in intensity according to the variations of the lines recorded on the soundtrack. The light falls on a photoelectric cell, which produces a small electric current whose variations correspond to the light, and therefore to the sound which was recorded. Amplification The small current from the electrical reproducer or the photoelectric cell passes along to one or more vacuum tube amplifiers similar in principle to those used in the audio-frequency stages of radio sets ; these amplifiers deliver a greatly magnified copy of this current. Sound Projectors The current from the amplifiers is converted into sound by means of sound projectors consisting of receivers and horns located on the screen. The numbers of horns used, and their exact location, depend on the size and acoustic properties of the theatre. Usually a special type of screen is employed, which reflects light well and enables a good picture to be obtained, but is practically transparent to sound waves. The horns are placed immediately behind the screen so that a perfect illusion that the voice or music is coming from the speakers and artists seen on the screen is obtained in all parts of the theatre. Obviously, if the sound is not coming directly from the screen, the illusion is lost. The horns used in all these systems can be mounted in such a manner that they are removable whenever the stage is used for purposes other than pictures. This can be done either by flying them or mounting them on towers that are easily and quickly movable. Synchronism In the disc method (Vitaphone), perfect synchronism between sound and picture is assured by having the projector and the turntable carrying the record both driven by the same motor ; hence if the film and record are started together they must necessarily keep in step throughout the remainder of the reel. In the film method (Movietone), the fact that the sound record is on the same film with the picture makes synchronism inherent provided that the film is set up in the attachment with the proper loops to ensure that when a picture is at the picture aperture in the projector head, the accompanying portion of the sound track will be at the light aperture in the reproducing attachment. The Fader By using two projectors alternately, a continuous program can be run just as with ordinary pictures. A device called the "fader" is employed in making the transition from one machine to the other, which can be effected with no break in the music or voice. All that is necessary for this purpose is to turn the fader knob when the incoming machine is started. Auxiliary fader positions permit of making the change from any projector position. At the end of each record or sound film, the music overlaps the opening notes of ■ the next, so that with proper operation the audience is unaware of any change being made. The volume of sound heard in the theatre is also controlled by the fader. Speed Regulation The film reproduction attachment is driven through gears and universal jointstoward the forward end of the motor, while the turntable is similarly driven from the rear end. In ordinary picture projection, the film is usually shown at a faster speed than it was taken. However, this cannot be done with a synchronized film or a sound film, as the pitch would be changed and this would cause the voice or music to be distorted or spoiled. All synchronous subjects have therefore to be shown at exac-tly the same speed they were made, which is 90 feet per minute. This speed is maintained automatically by means of a special type of motor and an electrical governing system contained in the motor control box. To permit of running films other than synchronized numbers in the usual manner, means are provided on the motor control box for regulating the speed within the usual range employed in projection. Mechanical Filter In all mechanical equipment using gears, etc., vibrations and speed fluctuations are produced. Even when the most accurate manufacturing processes have reduced such disturbances to a point where they would be quite negligible in any ordinary mechanism, their effect might, in the case of apparatus for sound reproduction, be noticeable to the listener as a kind of. "flutter" or tremolo. This effect is completely eliminated in both the disc and film reproducing attachments, by means of special spring drive systems for the turntable and the film sprocket, respectively. This important refinement is called a mechanical filter. Other Systems Non-synchronous reproduction is esserr-tially similar to synchronous disc reproduction, already described, with the difference that since the record does not have to be synchronized with the film, it is not necessary to drive projector and turntable by the same motor ; therefore the turntable need not be in the projection room but can be in any part of the theatre which permits a view of the screen. Voice amplification systems for theatres, and announcing systems, are not within the province of the projectionist. {To Be Continued) #T A SIMPLIFIED SECTIONAL VIEW. AFILM AS IT PASSES THRU* THE CAMERA. B.-*AEO"LIGHT TUBE. C.-SLOT THRU' WHICH LIGHT STRIKES ON FILM.