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The Projection Booths. Leaving the sound room, we went downstairs to one of the projection booths - Able,
to be exact, on the extreme right. The projectors are built especially for Cinerama. Though the arc-house and
the basic casting are standard projection equipment, the interior of the head is drastically modified. For
example, the frame size on standard 35mm sound film measures 0.631 by 0.868 inches. Cinerama's frame is
half again as high - with six perforations per frame instead of the usual four - and runs to the sprocket hole
edges on both sides (since the optical sound track is eliminated). The resulting frame is slightly taller than it is
wide - that is, 1.119 by 1.000 inches.

Further, there are the "jiggilos" on each side of the aperture to dodge out the sharp vertical lines which would
otherwise appear between the three screen panels. These comb-like metal strips are cam-operated, moving
up and down once per frame and remaining stationary while the shutter is closed. Jiggilos on adjacent profjectors
are 180 degrees out of phase. Because they generate considerable frictional heat in the aperture, which is
already subject to arc heat, Cinerama projector apertures are water-cooled.

Oversize Reels. We have mentioned the 8000-foot reels used in the Cinerama process. Because the ordi-
nary projector motor would not be strong enough to tum a full reel of this size, an auxiliary torque motor turns
the takeup reel. And to counteract its inertia, the feed reel is equipped with a brake. All this film does not
constitute a fire hazard, however, since Eastman safety film is used. Because human vision is more sensitive
to flicker in the peripheral area of the retina which Cinerama covers, the projectors are operated at 26 frames
per second instead of the conventional24. Combined with the taller frame, this results in a film speed of 146.3
feet per minute compared to the standard 90 for conventional 35mm sound projection.

Sound System Backstage. After loading his projector and trimming his arc carbons, each projectionists flips
a control switch from "local" to "remote", which turns over subsequent control of his machine to the console
operator. Next stop on our tour was backstage, behind the great curved screen. As we stepped out of a rear
door onto the stage, the boards vibrated beneath our feet under the impact of the low-frequency "drivers."
There are six banks of speakers behind the screen - one for the prolog projector, five for the Cinerama se-
quences. Each consists of two 18-inch, low-frequency reproducers ("woofers") and two exponential high-
frequency horns ("tweeters"). All are Alteo-Lansing equipment.
In the auditorium there are nine additional banks consisting of one woofer and one tweeter each. These are
distributed as a left wall and right wall bank on each audience level, as well as a rear wall bank behind the
audience on each level. The booster and power amplifiers (Aiteo-Lansing models 126 and 247-B, respectively)
for the stage speakers are located on the stage as close as possible to the speaker banks to avoid power and
fidelity losses. Amplifiers for the side speakers are installed in the side projection booths (A and C) downstairs.
The rear speaker amplifier is the centre booth (B) and also serves as a standby amplifier for the composite
track.

For audiophiles interested in the amplifier tube layout, the preamp for each channel (located in the sound
room) contains a 1620 and 6SJ7; these are coupled into the booster stage (near the speaker) which consists of
a pair of 1620's driving a pair of 6l6's in tum driving a pair of 807's in the power amplifier. The output
transformer is the size of a small doghouse and the power rating for each channel is 75 watts, giving Cinerama
a potential power output of nearly 600 watts! Needless to say, it has never been opened up- the building might
fall down!

Faster Tape Speed. Another factor contributing to Cinerama's high fidelity sound (which faithfully reproduces
frequencies from 30 to 15,000 cycles per second) is the linear operating speed of its magnetic tracks. While
home tape recorders get along on tape speeds of 3 3/4 or 7 1/2 inches per second, and hi-fi or broadcast
equipment generally runs at 15 i.p.s., it will be noted that 146.3 feet per minute (which is the film speed) comes
out 29 1/4 inches per second.
Reprinted from "International Projectionist ". May 1954

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: EDITORS NOTE :
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• Sorry about the lack of reading in this issue. We are currently a little thin on articles to print. •
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