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1945 Theatre Catalog, 4th Edition, Page 507 (481)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 507
Page 507

1945 Theatre Catalog, 4th Edition, Page 507

trouble was experienced in the past with the failure of one speaker unit causing a sound outrage over the entire field. At one location, it was reported that pranksters would deliberately cause a shortcircuit by sticking a pin through the speaker attached to the in-car speaker in their car, thereby short-circuiting a complete section of the field, and, in some cases, the entire field. Oftentimes, considerable difiiculty and time was experienced in locating and correcting this trouble. Using this RCA method of connecting speakers, a short-circuited cord can only affect the two speakers connected to their respective terminal box. This not only allows the rest of the speakers in the parking area to continue operating normally, but it also positively indicates the location of the trouble so that it may be quickly corrected.

In-Car Speakers Equipped With Hearing Device-To enable the hard-ofehearing to enjoy outdoor theatre entertainment, many drive-in theatre operators are providing in-car speakers with a special plug-in jack for the easy attachment of hearing aids.

For this purpose, there are available well-knOWn devices, consisting of attractive, individual lorgnette receivers, which may be either of the air or bone conduction type.

Theatres which have advertised this feature report regular and steadily ine creasing patronage from those who are handicapped by impaired hearing.


To provide sound of better quality and greater volume for with broadcast type or individual speakers, the new and improved amplifier equipment consists of a pre-amplifier (which may be mounted on the front wall), driver stages and a series of up-to-date power amplifiers, the number of which depends upon the number of individual loud-speaker outlets.

The pre-amplifier is fed directly from the photocell through high impedance coaxial cable. Included in the amplifier case is the volume or fader control and the sound change-over switch. One such amplifier is associated with each machine. In the main amplifier, the driver amplifier includes facilities for equalization of the sound characteristics. The feed-back circuit which serves this purpose also reduces distortion and permits parallel operation of amplifiers where required.

The driver amplifier feeds a bank of power stages, each of which is selected to provide ample power output for an optimum number of loudspeaker outlets operated in parallel, and suitable switch facilities are provided which will permit emergency interchange of power source to the various groups of speakers in case of failure of one or more of the power stages.

Complete emergency operation can be assured through installation of dual preamplifier and driver amplifiers with suitable controls to permit transfer from an inoperative unit to standby equipment. The exciter lamp power unit also includes an emergency feature.

A special switching arrangement provides dexibility between amplifiers and loudspeakers so that only those actually required need be in operation as the others can be cut out in any section of


the theatre.

The amount of power necessary to operate an in-car speaker at the volume level required by most people is approximately 0.2 watt. This is a very small amount of power and only a very small amplifier would be required if it were necessary to operate only one speaker unit. However, inasmuch as an in-car speaker is required for each car parked in the theatre, an amplifier must be provided which is powerful enough to furnish at least 0.2 watt to each speaker. This means that a theatre with a capacity for handling 400 cars requires an amplifier output of at least 400 times 0.2 watt; and a theatre with a capacity for handling 600 cars requires an amplifier with a power output of at least 600 times 0.2 watt, or 120 watts.

One of the problems which was encountered when a standard theatre amplifier was used for drive-in theatre operation was the necessity for the operator to be continually adjusting the amplifier volume control to maintain the proper average speaker volume level when the number of speakers in use was increased or decreased.

RCA, for example, has sound systems designed especially for drive-in theatres, which overcome these difiiculties. In designing these systems careful thought was given to all of the factors involved in the reproduction of sound in a drive-in theatre, such as adequate power for operating a large number of speakers, correct frequency range for use with individual speakers, adequate emergency facilities, and economical operation.

An exclusive feature of the RCA amplifiers is that it is unnecessary for the projectionist to be continually changing the amplifier volume control in order to maintain the proper average speaker volume level, as the theatre fills up and more speakers are placed in use, or when the show is nearly over and the number of speakers in use progressively decreases.

New circuits recently developed by RCA automatically compensate for speaker-load changes on the amplifier so that, once the volume has been adjusted to the proper level, it will remain practically constant, regardless of the numberof speakers in use.


Proiecfion Booth Installation

The installation of the projection equipment in a drive-in theatre booth differs very little from an enclosed theatre booth installation. Perhaps the most important rule to follow is to mount the equipment above the floor level, so that it will not be damaged in the event the booth becomes fiooded.

The installation of projection and sound equipment in the projection room of drive-in theatres is, in general, made in the same manner as in the regular indoor theatre. However, since the floor of the projection room is below ground level, some seepage may occur even though the structure is carefully waterproofed.

It is essential, therefore, that all of the

WIRING ALL RAMPS SEPARATELY is the second system. Shown in this Radio Corporation of America drawing is the general plan for controlling, from the control swiIch panel in the proiecvion booth, Ihe speakers of any porIiculor tier of stalls, any group of tiers, or all of them. In both cases, No. l0, two-wire parkway cable is used between control panel and the Iier, with the tier itself wired with No. 14, two-wire parkway cable.






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1945 Theatre Catalog, 4th Edition, Page 507