Date:         Fri, 16 Apr 2004 21:18:17 -0400
Reply-To:     Association for Recorded Sound Discussion List
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Sender:       Association for Recorded Sound Discussion List
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From:         "Steven C. Barr" <[log in to unmask]>
Subject:      Re: Rumble when playing cylinders
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----- Original Message -----
From: "Art Shifrin" <[log in to unmask]>
>>>>>Mechanically adjusting for improved concentricity is often not as
simple as one would hope.  The physical distortions of the tubes are not
uniform: a setting for one end is not necessarily optimal for the center or
other end.  Theoretically, adjustments for portions of the cylinders should
be made individually (in whatever increments you deem desireable: every
1/2", 1" etc of grooves) & the file then assemble edited.  I do this
comparably for disks when changing the arm's tangent (for disks  with
extremely disparate radii of inner and outer most grooves).
<<<<<
Wouldn't any rumble created by eccentricity be either at a frequency equal
to the rotational speed or
the first harmonic (double) of that (unless the record was "out of round" in
a complex pattern)?
Thus, if you had a filter with a very steep curve, that could effectively
filter out that frequency
(or frequencies, in the case of harmonics) while not affecting others, the
noise would be removed.
>>>>>Another effective technique for dealing with cylinders' tubular
eccentricites is to run them at 1/2 speed and then double the pitch for
playback.
<<<<<
How would this affect the signal...or are you assuming that 1/2 speed would
be too low to be picked up?
Since cylinders (IIRC) run at 120 or 160 rpm, half of this is still an
audible frequency.  This raises
an interesting point...a flattened cylinder should create a spurious signal
at twice the rotational
speed...or, in the case of 160 rpm, 320 Hz...which is above middle C! Or am
I making a mistake here?
>>>>>I don't know if anyone's undertaken to make for themselves, or to offer
them to others, but it'd be smart to have a machinist precisely (accurate to
.0001")  mill a suitably configured cylinder that'd be analagous to a test
record or alignment tape.  It'd be made out of something soft that would
retain its shape but not jeopardize styli & their cantelevers, i.e. teflon.
It wouldn't necessarily have to be grooved, but would provide a baseline of
measurement determining how much rumble's generated from any playback
mechanism versus that emnating from a particular record.
<<<<<
But wouldn't this just create a standard of "no physical
distortion"...which, since it means "no
rumble," would simply be a flat-line waveform, which in turn is created by
zero signal? Or are
you trying to get the "zero" for a specific playback device for comparison
purposes?
>>>>>Also, it's important to not assume that any given groove is "vertical".
As with all mechanical devices, tolerances are involved.  IF a groove
induces a stylus to meaningfully oscillate at some angle other than true
perpendicular (+ or - the theoretical standard), then unnecesary low and
high frequency noises will occur. This is remedied by continually adjusting
the phase relationship of the stereo cartridge being used to track the
grooves.  I call the process "vectoring". It's extremely beneficial for ALL
monaural grooves.
<<<<<
I would guess what you mean here is "...if any movement other than vertical
causes the pickup to
generate a signal..."...right? This could depend on a myriad of
things...including the fact that
vertically-cut grooves can often vary in width proportional to the depth of
the cut, so that a
stylus NOT dead-centered in the groove (which is most likely the case unless
some mechanical means
of centering, like Edison's feedscrew-driven reproducers, is used) could
pick up the horizontal
variations of one groove wall. In fact, the old "record player" I was using
to play 78's
(mostly lateral-cut) seemed to be able to play h&d discs this way, which
enabled me to hear
for the first time some vertical 12" transcriptions I had bought about 30
years ago!
Steven C. Barr