> Subject: Phonograph Turntable Speeds

> With all the discussion about 78 RPM turntables, does anyone know
> why the RPM rates for the various record sizes were chosen?  For
> example, does 78 RPM represent the best compromise at the time
> using the available technology to achieve reasonable frequency
> response, or was there another reason?

I can shed some light on the 78-RPM speed but the others elude me
at the moment.

From Thomas Edison's early work and on to the Victor Company the speed
was determined as a balance of getting the highest record surface
velocity for a good sound quality that would also give the longest
recording time.  Edison's 2-minute cylinder records were short playing
time for the expense of each record.

Victor settled on the 78-RPM figure so that a 10" record would give
them something around 3 minutes, and thus beat Edison in customer
appeal for that moment.  There were no real standards and various
companies put the RPM figure on the disc records so the governors
of the old spring-operated turntables could be adjusted.

The other limiting factor was the number of grooves you could put on
the record.  The 78s were acoustic records which at first were played
back by acoustical means.  The lateral sound waves in the grooves had
to be wide enough (amplitude wise) to move the needle to produce sound
mechanically.

The Edison 4-minute cylinder record was Edison's answer to the Victor
3-minute recording time, but then Victor released the 12" 78s.  Edison
then developed the first LP from his Diamond Disc flat records.

Edison's long playing record used the vertical hill-and-dale recording
so his long play fine groove records were out many years before
Columbia's and Victor's LPs, but Edison's marketing of just 12 LP
records fell flat and went nowhere, as the company closed in October
of 1929.  The playing time of Edison's LP, at 20 minutes per side,
was only approached when the 12" LP "microgroove" record was developed
in the 50s.

For the answers to many questions regarding the various speeds, sizes,
and record formats, visit the library and see if they have "From
Tinfoil to Stereo" by Reed and Oliver.

Al Sefl