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your Achilles heel?
% Like Achilles' heel, your booth equipment is the vulnerable spot in your theatre.
that is why so many motion picture theatres throughout the country subscribe to Altec Service. They not only gain the services of an expert engineer to keep their sound and projection equipment in perfect running condition-but, should & sudden breakdown occur, they know that the Altec Service man will be on the spot in record time to repair or replace the broken part.
There is an Altec Service plan especially suited to your booth equipment. We will be glad to give you more information — no obligation.
250 WEST 57TH ST. NEW YORK 19.
DESIGN OF SUB-STANDARD SOUND PROJECTORS
{Continued from page 16)
which the pins or sockets are embedded in soft rubber, to which the cable sheathing is vulcanized, making the cable and plug a single unit. These, however, are not entirely trouble-free, chiefly due to the pins being made of soft material and not making sufficiently good contact with the sockets. Another fault of this type of plug is the difficulty of repair should the cable fail.
The ideal mobile projector should be constructed without the use of flexible cables or plugs. Let the stand contain the electrical controls, making contact with the projectors through spring contacts; the latter would need careful design, but given this most of the worries oi the mobile projectionist would be at an end.
A vital requirement of any mobile projector is silent running. The principal sources of noise are:
1. -The motor.
2. The cooling system.
3. The intermittent motion.
4. Gear drives.
5. Transformer and other A.C. hums.
6. The amplification of such noises by large unsupported surfaces.
The only way to reduce motor noise is by reducing the speed of the motor, which in its turn necessitates a heavier and bulkier motor; there is obviously a limit to which such improvements can be carried. Some improvement can be effected by careful balancing of the motor windings.
High-speed fans must be avoided. Lowspeed turbine fans are reasonably silent, but are again bulky, proper design of air ducts and the avoidance of sharp bends should help.
In the silencing of the intermittent motion, probably the chief factors are the avoidance of abrupt acceleration and deceleration, and the absence of play in the working parts, which, of course, entails a high standard of workmanship. Gear noise can also be reduced by good design and workmanship — the use of coarse-pitch non-metallic spiral gears, as far as possible running at low speed and properly meshed. Transformer hum can be minimized by sound design and construction.
In conclusion, I have been asked to say a word on the conversion of silent sub-standard projectors to sound. My advice can be. contained in one word: Don't. If you must, remember that the motor was not intended to drive a soundhead, nor to maintain the speed constancy necessary for sound, so provide another motor which should drive the projector from the sound head, and not I'ice versa. Chain drives must be avoided
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INTERNATIONAL PROJECTIONIST