[Jukebox-list] RE: Seeburg's "promise"

[David Breneman]

--- Steve Wahl <steve at pro-ns.net> wrote:

> The inner grooves of a 12" 33 are at the same diameter as a 7" 45,
> right?  Have the inner grooves of LP's always been a compromise, or
> did they work around this?

No, physics is physics.  :-)  That's one of the reasons RCA
didn't like the LP concept.  They didn't think Goldmark's
group had done their homework on surface speed and pinch
effect.  The RCA engineers established that intermodulation
distortion became objectionable at 10%.  At a peak recording
level of 14 cm/sec you could have a maximum of 275 grooves per
inch and in order to keep distortion below 10%, the surface
velocity needed to be no less than 11.5 inches/sec.  At 33-1/3
RPM, that resulted in a groove diameter of *no less than*
6.6 inches.  Thus, a 33-1/3 RPM record, in order to contain
5.5 minutes of program material, would have ot be 8-1/2"
in diameter so that, after 5-1/2 minutes, the minimum groove
diamter of 6.6 inches would be obtained.  I don't have any
LPs here at work, but it would be interesting to see how
many adhere to the 6.6" minimum groove diameter.  Columbia's
7" 33 singles certainly didn't, except in the lead-in groove!

> My experience (in the 80s) was also that LPs seemed to have a
> better
> sound than 45s -- quieter, less surface noise, less distortion.  It
> felt like maybe the manufacturers paid closer attention
> Quality-control wise to the LPs, but maybe I was finding out the
> difference between plastic/styrene/whatever and vinyl?

Manufacturers certainly didn't treat the 45 format very
well in later years.  The recording level increased past
14 cm/sec to make the records louder, and that increased
distortion in the inner grooves.  Quality control also was
much lower than for LPs.  And, Columbia's introduction of
polystyrene 45s, which were quieter than vinyl for the
first dozen or so plays, then got progressively more
crackly, was another detriment to the format.


David Breneman         david_breneman at yahoo.com

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