I N T R O D U C T I O N

General

It is essential to follow these operating instructions strictly, in the order given, in order to obtain satisfactory results and avoid apparatus trouble. Everything in this book should therefore be carefully studied and thoroughly understood. If anything in it is not clear to you, consult our representatives, who will be glad to explain.

Names of the various parts of the apparatus are shown in the illustrations at the end of the book.

Caution

Cases have occurred where persons having some radio experience have experimented with the equipment and made changes and substitutions. Not only is this expressly forbidden in the contract by which the equipment is leased to the theatre (see section on "Replacements"), but. also there will almost certainly be serious ill effects an the quality of reproduction and the life of the equipment.

Page 1

Purpose of the Equipment

The main purpose of the equipment in this application is to reproduce speech or music in connection with moving pictures in a manner so realistic that the effect is practically equivalent to having the speakers or artists present in person, every sound being heard at the same moment that the action accompanying it is seen on the screen. A further use is to accompany feature pictures with specially recorded cued music, known as a synchronized. score, so that every scene has music appropriate to it, and when the scene changes, any corresponding change in the character of the music is accurately and automatically made at the same moment. Hence this application is called synchronous reproduction.

General Principles of the Equipment

Two methods of recording are employed. In one method, the sound record is on a disc similar to a phonograph record, and this is therefore called the disc method. It is used by Vitaphone. In the other method, the sound record is photographed on the film. This is called the film method. It is used by Movietone. A house can be equipped for shoving productions made by either method or both, toe only difference lying in the apparatus used at the projector. The first step in synchronous reproduction is to generate

Page 2

I N T R O D U C T I O N

General Principles of the Equipment

a small electric current whose variations correspond to the sound waves forming the voice or music that was recorded. Depending on which of the two previously mentioned methods of recording was used, this current is obtained as follows:

(1) With the disc method, the current comes from an electrical reproducer playing on a disc record; these records are similar to the best types of phonograph record except that they are much larger and run at about 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 an ordinary film, except that one frame at the beginning is specially marked to give the starting point.

(2) With the film method, the sound record consists of a band about 1/8" 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 it along at constant speed. A narrow bright beam of light from a high-intensity exciting lamp 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 sound track. This 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.

Page 3

I N T R O D U C T I O N

General Principles of the Equipment

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. The current from the amplifiers is converted into sound by means of sound protectors consisting of receivers and horns located at the screen. 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 house. Obviously if the sound is not coming directly from the screen, the illusion is lost.

In the disc method, 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 the fact that the sound record is on the same film with the picture makes synchronism inherent provided that the film is set up 1n 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

Page 4

I N T R O D U C T I O N

General Principles of the Equipment

aperture in the reproducing attachment.

By using two projectors alternately, a continuous program can be run just as with ordinary pictures. 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.

In ordinary moving picture projection, thee 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 and spoiled. All synchronous subjects have therefore to be shown at exactly 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.

Page 5