There's been a lot of discussion in MMD this month about the origin
and/or derivation of standard turntable speeds, with many logical
opinions expressed.  Mine was not among them, however, and has to do
with gear reductions.

Common synchronous motors run at 1800 RPM from 60 Hz electrical power.
45 RPM and 33-1/3 RPM speeds are simple to reduce from 1800 RPM.
33-1/3 RPM also reduces easily from 1200 RPM, which was the speed of
the 3-phase synchronous motors used by Western Electric for recording
Vitaphone discs.

The earliest Vitaphone shorts and the first feature, Don Juan, released
in 1926, established 33-1/3 RPM as the speed for the 16-inch discs.
The reels of film and associated soundtrack discs were only about ten
minutes in length.

The 35 mm film was running at 90 feet per minute, with sprockets turning
4 times per foot (16 frames) and the shutter shaft turning at 1440 RPM
or once per frame -- all simple ratios to motors driving them at either
1200 or 1800 RPM.  The Vitaphone system was soon adapted to become the
standard for radio transcriptions in both vertical and lateral formats,
using a 2-mil jewel stylus instead of a steel needle, with a running
time of about 15 minutes per side.

The 78 RPM speed (actually 78.26) apparently derived earlier from the
use of non-synchronous disc lathe motors in the days before electrical
recording, and was reduced from the nominal speed of an induction
motor, about 1720 RPM.

Richard Simonton

 [ I've never seen a turntable with direct gear-reduction drive from
 [ an electric motor.  How is the motor hum and gear noise isolated
 [ from the turntable?  Rubber couplings?  I suppose Vitaphone used
 [ a horizontal drive shaft to a worm and worm gear under the turntable.
 [ I've heard that some Victor recording turntables, even into the
 [ 1930s, were powered by falling weights like an old barrel organ,
 [ because of hum problems when using electric drive.  (I'm thinking of
 [ the horrible hum from the motors in many orchestrions.)  -- Robbie