Turn table speed variation question

Small correction: 5.2 minutes of playing time is 173 revolutions. You dropped the "1". :)

Keep in mind that closed loop speed control systems like used in DD turntables will compensate for changes in load (such as dropping a needle on a record or raising it) and depending on the amount of torque that the motor has- the platter may hold speed even with light pressure of your finger applied to the edge. But closed loop speed control has its own design challenges.
I suspect belt drive became popular because open loop motors w/o controllers is much cheaper to execute and high mass platters do a lot to smooth out the speed variations; not to mention easier to apply isolation and dampening from vibrations. In other words- belt drive offered more bang for the buck. In the end, given the resources and proper design execution, the type of drive system becomes a moot point. I think Peter's website, if successfully populated with data from various types of turntables will reach that conclusion.

Fleib, electronically generated tones can indeed be a very good way to
judge pitch stability. This brings up an interesting issue related to the
previous discussion about the tuning of acoustic instruments, and the
"improvements" in intonation of some modern instruments, and
why these "improvements" are not always a slam-dunk and
often have a clear downside. Some modern instrument manufacturers
attempt to bend the laws of physics and acoustics in an attempt to correct
some of the traditional and naturally occurring pitch issues in acoustic
instruments. A very simple example would be this: the clarinet, being a
cylindrical vs conical (saxophone) woodwind instrument overblows the
twelfth as opposed to the octave. IOW, the first naturally occurring
overtone is an octave and a fifth. For argument's sake, lets assume that
the first (lowest) note on the instrument is a "C". The easy part
is getting the first twelfth ("G") to be fairly well in tune, then you
have to start finding the absolutely correct placement of the tone holes as
you ascend the scale. You may be able to determine a good placement of
the tonehole for the first note after "C" ("D"); but
then, because of the mathematical imperfections of the harmonic series
(and other issues) what might be a good placement of the "D"
tonehole in relation to "C" below it, that D's twelfth
("A") may be too sharp. So, what to do? Leave it that way, or
do you "force" the instrument to sound that "A" lower
in pitch by manipulating other aspects of the design by, perhaps, making
that tonehole's tube slightly taller? Some modern instrument makers strive
to "correct" all these naturally occurring problems and do so
with quite a bit of success. So what is the problem? Most players will tell
you that the more an instrument's natural tendencies have been
manipulated, the more difficult it is to play in tune within an ensemble
comprised of some of these "improved" instruments. These
intruments have less "core" in their sound because the naturally
occurring harmonics are not allowed to manifest themselves and then there
is a less-well defined pitch center. You can't fool Mother Nature! While, on
the surface, all this may seem to have little to do with the issue of pitch
(speed) stability in turntables, it should at the very least highlight how
crucial issues of pitch and intonation are in just one aspect of music
making. So, why should they be any less important in its playback?

****I'm hoping that the thread prompts a discussion of the differences
between various drive types and the distinction between speed accuracy
and speed stability. **** - Peterayer

IMO, we audiophiles don't pay enough attention to pitch issues. No one is
suggesting that we can't enjoy our music if our turntables are not spinning
at the absolutely correct speed with perfect consistency. But, considering
how we agonize over tiny differences in the tonal quality of some of our
gear, it makes no sense to not give as much consideration to pitch. Just to
give an idea of just how sensitive the human ear is to pitch variation:

We are all familiar with the routine of the oboist "giving the A" at
an orchestral concert. More times than not the oboist gives that A by
playing to an electronic tuner that is supposed to be extremely accurate. It
is not uncommon for players tuning to that oboist's A to, pretty
unanimously, feel that the A is slightly high or low; this in spite of the fact
that the electronic tuner is saying that it is dead accurate. The human ear
can tell when the pitch is leaning one way or the other before our
measuring equipment can.

I have never used any technical method for judging my turntables' speed
stability other than an occasional strobe disc, choosing instead to set my
motor controller's frequency by ear and the use of recorded reference
pitches that I then check the tuning of. To the naysayers that feel that
absolutely correct speed accuracy AND stability are not important, I would
say that they are missing out on a significant amount of what the
performances on their LP's have to offer on MUSICAL grounds because of
the very profound effects that inaccurate speed accuracy has on the
musical intent of a recorded performance and the equally profound effect of
poor speed stability on the rhythm and timing of a performance. The same
way that the tuning "A" can be distorted to a degree that the ear
can detect while an electronic tuner can't, the effects of poor speed stability
on the rhythmic feeling of the music can be distorted in ways that are
subtle, and while not obvious in the usual sense, can make the difference
in our emotional reaction to the music.

Halcro
Your DD has stylus drag as well. The only difference is that it is dealt with by the speed servos. Some belt drives have servos, some have self correcting AC motor controllers.
One could argue that the speed correction for the stylus drag in a direct drive is always working - to what effect on the music ??
In Peterayer's example he could correct the stylus drag at the begining of the record, and then any inherent problems of active speed correction are avoided.
In Peterayers example, the speed error after adjusting for stylus drag at the outset, is the VARIATION between maximum and minimum stylus drag incurred by the stylus tracking the record playing. This will be a small %age of 0.003.
In Peterayers video the record does not appear to be flat - the shadows move up and down on the record. Testing by both Bruce Thigpen with his ET tonearms and the Shure white papers on low frequency resonance confirm the existance of stylus "scrubbing" from imperfections in the groove, even apparently flat records, that cause mistracking and WOW. Shure claim resonant peaks of up to 20db, equating to 10 times increases in motion. The timing errors from this artefact would probably dwarf a timing error of a %age of 0.003.
So its all a bit nebulous really. Consistency is probably the greater virtue in terms of speed accuracy once you get a this level.
I would guess many audiophiles cant hear a speed error of that magnitude, but they are more likely to here WOW on a piano or acoustical guitar note. There are many other factors - my perception is that vacuum hold down greatly improves piano stability as does a tangential tracking tonearm - so if you are looking for perfection in timing there may be bigger gains elsewhere than chasing down a %age of 0.003.

Perhaps you would like to make a video of your TW Akustics and add it to the database.

Heh heh......unfortunately the Raven AC-2 or AC-3 is unable to be adjusted to the exact 33.33rpm with its motor controller.
Some would say this is maddening oversight?
It does however seem to maintain a uniform 'loss' of speed...if that makes any sense?
I applaud you on your SME results and your attempts to encourage others to do the same.......however I somehow doubt that many will contribute as it is just so difficult for a turntable to achieve this feat under constant stylus drag....and no-one wants to have his turntable 'publicly' exposed?

Just for the 'record'....hehe....and to comply with Peterayer's request......
HERE is a video of the TT-101 playing a record (single arm and cartridge).
At the beginning and the end....where there is silence.....the arm has not been dropped...or has been raised.