Dear simplifier,
The following excerpt from an article that originally appeared in the
"Journal of the Audio Engineering Society" should provide an answer to
your question:
[...]One of the most important innovations in the record industry was
the change of record speeds, in spite of the fact that generally
speaking it matters little what the speed is; it is only important
that it be the same and constant.
Back in the handcranked phonograph days when the same instrument was
used for both recording and reproduction, what was recorded had to be
reproduced at close to the same speed, otherwise, the difference
between recorded and reproduced material would have been too great.
However, within broad limits, the exact speed was unimportant. Several
factors determined what the broad limits were. For better quality, the
crank was turned at a comfortable speed, otherwise jerky motion
resulted. This comfortable speed as found to be about heart-beat rate
-- between 60 and 90 per minute. It is interesting to note that armies
and bands match at this cadence. and speeds in this range are
specified for handcranked farm equipment.
Those who used handcranked phonographs soon learned that if they
turned at a lower speed more time could be recorded on the record. but
lower speeds gave bad sound. At higher speeds. the sound was better
but the recording shorter. They also knew that larger records played
longer than smaller records. The original cylinder records were large
in diameter and almost impractical in size. Spring-wound motors were
necessary before the cylinders could be reduced in size and operated
at speeds first of 120 r/min and, later, at 160 r/min for good sound.
These speeds were beyond the comfortable range for manual operation.
It was soon found that speed is one of the variables of a record
system specification. The other variables are the quality objectives,
the quality of the recording materials, the size of the record, the
length of play and the factor of cost or economics. Change one and all
the others are affected.
With the wind-up phonographs that were used for reproduction only, it
was desirable that the speed be about the same for all records, but it
was not really important since the speed of the player was adjustable.
The same situation existed with the first motor driven units -- the
speed was manually adjusted until the sound was right for the
listener.
In 1925, when electrical recording came into existence, a decision had
to be made as to what speed would be used for recording. At that time,
Victor was operating at 78 r/min, Edison was using 80 r/min for his
disc, while some others were using 82. If Maxfield and Harrison wanted
their system adopted by Victor, then 78 r/min was the speed to use. An
honest and compelling reason was that Victor's 78 r/min was the
predominant speed and it was selected for maximum compatibility
between the old and the new. In fact, 78 r/min was selected, but it
turned out to be 78.2608 r/min because it was necessary to synchronize
the recording turntable to the 60-hertz line and 78.2608 r/min was the
only speed at which it could be done practically with a simple
worm-gear drive. This, however, is not true for spur gears.
The 78,26086957... speed is obtained with a gear ratio of 46 to 1
between the synchronous motor and the recording turntable. This can be
achieved with a one-tooth worm gear mating with a 46-tooth driven
gear. This is the most direct and simple system preferred for
precision work. This speed can also he obtained by a spur-gear train
of two 12-tooth pinions, one intermediate 46-tooth gear and 144-tooth
turntable drive gear. For 78 r/min exactly, the gears are 13-tooth
pinions. 39-tooth intermediate, and a 200-tooth final turntable drive
gear. There is not a practical simple worm gear drive to obtain 78
r/min exactly from a 60-hertz synchronous motor. [...]
Original source:
"Before the Fine Groove and Stereo Record and Other Innovations ....."
by Warren Rex Isom, "Journal of the Audio Engineering Society",
October/November 1977, Vol. 25, Number 10/11
Web sources:
Recording Technology History: Record Speeds, by Steven E. Schoenherr.
http://history.acusd.edu/gen/recording/speeds.html
Beanos: A Record Speed
http://www.beanos.co.uk/bnews/015/index.php
The 78rpm Record Home Page, by Gary Herzenstiel
http://www.geocities.com/SoHo/Museum/8764/
Search terms used:
"78 rpm"
://www.google.de/search?q=%2278+rpm%22&ie=UTF-8&oe=UTF-8&hl=de&meta=
"78 rpm" chosen
://www.google.de/search?q=%2278+rpm%22+chosen&hl=de&lr=&ie=UTF-8&oe=UTF-8&newwindow=1&start=0&sa=N
Hope this is what you were looking for!
Best regards,
Scriptor |
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