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1945 Theatre Catalog, 4th Edition, Page 503 (477)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 503
Page 503

1945 Theatre Catalog, 4th Edition, Page 503

Netes on Equipment for Drive-Inl'heatres

Individual Loudspeakers Main Deviation From Apparatus Used In Enclosed Cinemas

The careful selection of equipment is of prime importance to insure highest entertainment values. In terms of equipment, drive-in theatres are divided into two general groups: (1) theatres up to (BOO-car capacity and (2) theatres over 600ecar capacity.

When selecting the projection and sound equipment, it is important that many factors be considered to insure sufficient illumination on the screen and sufficient power to operate the speakers at the required volume level without distortion.

Although standard theatre projection equipment may be used in most cases, it is important that the equipment be such as to provide an adequate source of light, high efficiency of light transmission to the screen, and rock-steady projection.

For reproduction of sound, standard theatre sound heads are suitable, but amplifiers of considerably more power must be employed, especially where the individual speakers are permanently installed on the field, or where in-car speakers are used.


The drive-in theatre screen has an area of approximately three to five times that of the screens used in large enclosed theatres. The average size of the screen used in an enclosed theatre seating 2,500 is approximately 24 feet wide, with an over-all area of 432 square feet. To illuminate this entire area and this screen to the intensity recommended by the Society of Motion Picture Engineers, it is necessary to use either a Suprex type of lamp, using 8-mm. Suprex positive carbons, operating at their maximum current carrying rating of 65 to 70 amperes, or to use the super-high intensity lamp, using 13.6-mm. carbons operating at 125 amperes. Using the same types of lamps in a driVe-in theatre with a screen 40 feet wide, and with an over-all area of 1,200 square feet, the intensity of light on the screen would be only one-third as great; and used in a drive-in theatre with a screen 52 feet wide, and having an overall area of 2,028 square feet, the intensity of light on the screen would be approximately one-fifth as great as in the enclosed theatre using a screen 24 feet wide. If insufficient light is used on the drive-in theatre screen, operation cannot start until it is completely dark, thereby further limiting the available showing time with a resultant decrease in revenue. It can be seen, therefore, that it is extremely important that a drive-in theatre be provided with a powerful light source, together with the necessary projection equipment to transfer the maximum amount of light to the screen.

Fortunately a large screen does not require so great an intensity of light as small ones for good visual acuity, be l945--THEATRE


cause, for example, it is easier to read large print than it is to read small print under the same lighting conditions. It is for this reason that a standard theatre arc lamp operating at from 65 to 76 amperes will give satisfactory illumination on large drive-in theatre screens, provided that the projectors, lenses, and operating conditions are such as to result

in maximum eniciency of light transmis- '

sion to the screen.


Projectors are available today in both the singleoshutter and double-shutter type. The double-shutter type allows the transmission to the screen of approximately 20 per cent more of the available light than the singlevshutter type and is, therefore, preferred in all drive-in theatres.

In laying out the projection room, it must be borne in mind that the projection angle must be up instead of down. The projectors should be mounted on special reverse incline concrete or metal bases.


Either a motor-generator or copperoxide rectifiers are recommended for furnishing current to the arc lamps, however, generators apparently are a much more favored arc lamp power source.

The motor-generator selected should be one designed especially for operation with Suprex type of arc lamps. It should

i be rated at 70 to 75 amperes for continu ous operation without over-heating, and double this value for five minute periods so that change-overs may be made without any decrease in screen illumination.

Copper-oxide rectifiers selected for drive-in theatres should be designed for continuous operation at 70 amperes without over-heating. It is important that the rectifiers be operated below their maximum current rating, and be adequately ventilated at all times, otherwise they will become excessively hot and de teriorate rapidly.


The long projection distances and unusually large screens required by drivein theatres justify that careful attention be given the selection of the best optics available for illumination and picture definition. .

The use of fast, long focal-length projection lenses would permit the construction of the booth at the back of the parking area. This would mean that more space would be available for cars and it would also mean that the booth could be constructed above the ground level. thereby eliminating the danger of flooding during rainy periods.

But projection lenses with a speed of f/2 have the greatest advantage of transmitting to the screen the greatest

percentage of light available from modern projection arc lamps. As the speed of the lens is decreased, the efficiency of light transmission decreases very rapidly. As an example, when an arc lamp is being used with an optical system capable of filling an f/2 projection lens, approximately twice as much light will be transmitted to the screen as would be if a projection lens, with an optical speed of f/3 were used with the same are lamp. It can, therefore, be seen that the speed of the projection lens is extremely important.

Accordingly, for the best projection results, the use of f/2 projection lenses is suggested. While this type of lens has been available in focal lengths up to five inches, it is desirable to lay out the theatre so that the projection room be within the range of the screen permitting the use of these lenses. The high speed of the f/2 will transmit the full cone of illumination supplied by the optics of the light source and place on the screen all the light science has thus far made available for this purpose. The longer focal lengths make the problem of crisp definition less severe so that a less involved formula makes these lenses exceptionally transparent to the passage of light.

Projection lenses of the coated type are much to be preferred, because of their greater efficiency and freedom from refiections and glare. Coating the lenses results in increased light-transmission efficiency of approximately 20 to 30 per cent, and in a definite improvement in picture definition and color fidelity when projecting color pictures.


Most of the drive-in theatres already constructed have used a 30x 40-foot screen and have had about 10 ramps. This size screen has proved very satisfactory for this number of ramps. If additional ramps are required, the screen width should be increased five feet for each additional ramp. It is important that the screen be high enough above the ground so that cars parked on the ramps directly in front of the projection room will not be in the line of projection.

The distance of the bottom of the screen above the ground varies from 16 to 26 feet.

In localities with a great variation of weather conditions, it is advisable to paint the screen once each season.

Plastic screen paint, which will permit an even higher quality of projection, will shortly be made available. This paint will be impervious to weather conditions to which drive-in theatres are subjected and will be of a type which can be easily restored by use of a chemical cleaner.


The success of the drive-in theatre is dependent to an important degree on the

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1945 Theatre Catalog, 4th Edition, Page 503