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1945 Theatre Catalog, 4th Edition, Page 508 (482)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 508
Page 508

1945 Theatre Catalog, 4th Edition, Page 508

equipment be mounted and the conduits run in such a manner that any seepage will not enter the units or penetrate to the wiring.

Projector pedestals should be raised from six to eight inches above the floor and the conduits run along the walls and ceiling rather than under the fioor.

The amplifier rack is mounted on a concrete block about 6 or 8 inches high in order to keep the amplifier equipment above the floor level. The conduit for the inter-apparatus wiring is run along the booth walls or ceiling and not under the booth floor.

Concealing the conduits will greatly approve the appearance of the installation.

If in doubt about seepage, lead-covered cable in rigid conduit with water-tight joints and water-tight outlets will insure against moisture entering the wiring systems.

All wiring outside the projection room should be underground and moistureproofed by one of the approved methods. These runs are usually somewhat longer than in the indoor theatre and it is essential that the size of the wire be selected with a knowledge of the length of the run and the power to be transmitted to insure that the power delivered is adequate and that regulation is within the operating limits of the equipment.

Ramp Wiring

Considerable care must be used in laying out the underground cables from the projection booth to the speaker locations in order to prevent damage to the cable, and to minimize power leakage caused by rain and humidity. Even with the large amounts of audio power available, from the new RCA Drive-in theatre amplifiers, it is essential that the power loss in the feeder lines and speaker connections be kept to a minimum value. Loose underground connections, partially shorted underground connections, water-soaked splices made underground, and watersoaked cable have been the causes of considerable trouble in many drive-in theatres in the past, resulting in interrupted and inferior performance.

An improved underground cable such as impregnated jute parkway cable or tellurium parkway cable could be used between the projection booth and the speakers. The cable is usually buried 12 inches below the surface to protect it against damage from maintenance tools and from the frost. The impregnated jute parkway cable is protected by a non-metallic armor, made of layers of vacuum-impregnated jute with weatherproof compound applied between the layers. These hard layers of impregnated jute protect the cable from mechanical damage and moisture and result in the cable having an unusually long life when buried directly in the ground.

The tellurium parkway cable uses a rubber insulation and tellurium-rubber sheath. It is lighter in weight, easier to handle, more flexible, and more resistant to soil acids and alkalis than the impregnated jute cable. Although the tellurium parkway cable is slightly more expensive than the impregnated jute cable, the extra features of the former type make it preferable.

In-Car Speaker Installation-For incar speaker installations, an underground wiring system from the projection room to and along each of the ramps is necessary to provide power for these units.

It is important that this wiring be properly designed and installed to prevent the entrance of moisture and sound failures.

The wiring should not be less than 12 inches below the surface to avoid damage from maintenance.

Where ground freezes to greater depths, the experience of local reliable contractors should govern the depth of the wiring.

It is recommended that a circuit consisting of two No. 10 conductors be run from the projection room to each ramp for connections to the speaker outlets.

This wiring should be of a type that will not permit the entrance of moisture and will not be affected by any acids or alkalis that may be present in the soil.

The parkway type of cable may be used for this purpose, but the most satisfactory type of wiring is rigid conduit con THE UNDERGROUND TYPE OF SPEAKER. as formerly used in some drive-ins, is sketched in this drawing (courtesy of Moiiogroph and The Sound Track). A concrete reverberation chamber, with a speaker unit inverted over the bowl portion and covered with a grille, is sunk into the parking area. Such speaker, while eliminaiing speaker standards, has some objections which are common to speaker systems which must serve more Than one car.






taining two-conductor lead-covered cable.

There should be no . splices below ground, all splices being made in watertight boxes above ground So that no moisture can enter the splice and also so that it may be readily inspected.

The speaker outlets must be of rugged water-proof construction and securely fastened to a rigid support in the proper location with respect to the position of each car. It is important that the outlets be positioned so that they will not be damaged by the car bumper.

When one circuit is run from the projection room to each ramp, switches may be provided in the projection room to disconnect that circuit from the output of the amplifiers in case of trouble. Thus, whether the difficulty is in the wiring or in one of the speakers on a given ramp, the circuit can be isolated without affecting speakers on the other ramps.

Several different methods have been used

, for Wiring the in-car speakers to the pro jection booth. Here, it will be noted that only one trunk line using No. 10 parkway cable is run down the center of the parking area, and No. 14 feeders are used to feed the speakers on each of the ramps. All of the feeders should be connected to the trunk line above ground. No connections should be made underground. The disadvantage of this method is that if a short circuit develops in the trunk line or in any of the feeder lines, all of the speakers will be affected until the short is located and repaired.

The in-car speaker installation is such that when the car is properly located on the ramp, the in-car speaker will be directly opposite the car window and may be easily reached and easily returned without the patron's leaving his car. It will be noted that one speaker mounting post with twu in-car speakers is positioned to serve two cars. The recommended distance between speaker mounting posts is 18 feet.

In wiring the parking area, a separate No. 10 parkway cable is run from the booth to each ramp and No. 14 parkway cable is used to feed the speakers. Switches in the booth are connected between each trunk line and the output of the amplifier, making it possible to control or isolate sections of the parking area from within the projection booth. If one trunk line develops a short circuit, it will simply be necessary to open the switch in the booth which controls that particular trunk line. This will disconnect the shorted line from the amplifier, and permit operation of all ramps except the one to which the shorted trunk line is connected.

Illumination of Speaker Standards

It has been found desirable by some drive-in theatre owners to illuminate the base of the speaker standards so that the drivers may more easily guide their cars to the correct location on the ramp. Illuminating the base of the speaker standard also greatly reduces the possibility of cars running into the speaker standards and damaging them.

The illumination is provided by a lowwattage lamp mounted on each speaker standard and shaded so that all of the light is reflected to the base of the speaker standard. Electric power must be provided at each speaker standard for these lamps.

1945 Theatre Catalog, 4th Edition, Page 508