Turntable speed accuracy

What is the best way to verify results?

It depends on what results you're trying to verify.

With regard to general speed accuracy, a good strobe like the KAB or the Timeline both work well.

With regard to stylus drag or other very short-term transient events, my ears are far more sensitive than such tools, which lack a sampling rate capable of measuring variations which occur over mere nano-seconds. YMMV.

What is the most speed-accurate drive method?

A car on cruise control, which will transport you to the venue of your choice to hear real music. All TT drive methods are compromised, each in its own ways, so there's no answer to this overly simplified question.

And is speed accuracy really the most important consideration for proper turntable design or are there some compromises with certain drive types that make others still viable?

Whaaat? That's like asking if a red car is best or should we shovel snow or plow it. ;)

1. Is speed accuracy really the most important consideration for proper TT design?

It depends on the sensibilities of the listener. Some posters on this thread and very many TT designers seem oblivious to speed variations that drive me up the wall. I in turn am only just able to hear speed variations that drive my partner out of the room, screaming. OTOH, neither of us has absolute pitch to the extent necessary to identify a TT that's running 1% fast or slow but effectively resists stylus drag, yet my mother's absolute pitch can. What's important depends on who's listening.

2. Are there some compromises with certain drive types that make others still viable?

There are compromises with all drive types. Which ones are viable depends on the effects they have and how audible those effects are to you. Nothing about one design makes any other design more or less viable. Independent phenomena must be judged on their own merits.

Peter,

Sorry for the hyperbole.

Our own TT's speed stability did go through two periods where it drove us nuts. We heard the first problem yet no commercial strobe showed it. Paul built a custom, higher resolution strobe and we captured many hours of data to demonstrate the problem to Teres. The data helped Teres identify a problem in their motors but it took them three months of testing and measurement to confirm that the redesign/rebuild actually fixed the problem. The other problem was subtler and was addressed by our own experimentation with better belt materials and implementations.

That Aries was a touch soft on transients but much better than most BD's we've heard. In our experience many (mostly less costly) BD's are unlistenably bad due mostly to poor belt materials, as others have said.

OTOH, concluding that idler wheel/rim drive designs are inherently better than BD's would be going too far. We've had such a design in our system, made by Teres, and it was audibly inferior to our carefully worked out BD. Implementation is always critical and individual cases may trump general rules.

what do you mean with this? that Paul and you listened to two TTs bis a bis with similar tonearm/cartridges at the same sessions/comparisons?

Fair question, Raul.

One TT, one tonearm, one cartridge, everything identical except the drive systems. We were comparing our tweaked BD to the (then new) Teres rim drive. Switching from one drive to the other took < 30 seconds so it was easy to compare, far easier than comparing cartridges or tonearms.

Result: we kept our BD.

FWIW, most who made the same comparison on their tables preferred the rim drive. However, those people weren't using our belt tweak because we hadn't published it yet, so their BD wasn't performing like ours. The two people to whom I provided tweaked belts also preferred the BD to the rim drive.

Implementation, implementation, implementation. :)

***

Tdaudio,
The main problem turned out to be intermittent failures in the motor brushes. Very difficult to diagnose. After months of experimentation/verification, Teres found that gold brushes eliminated the problem and performed for the long haul. Ours is still working fine, quite a few years on.

Secondarily, Teres tightened the correction threshhold of the motor controller by one order of magnitude. Our platter speed now drifts from 33.33 (45) rpm just 10% as much as it used to before the controller alters voltage to the (DC) motor.

This improvement was visible with a good strobe if you watched for some time, but not really audible to me. One would need absolute pitch sensitivity to hear it.

I suggested him to try driving the Teres platter with a Technics SL-M3 direct-drive turntable via VHS tape.

Sounds like an interesting idea, he gets the speed lock of the DD plus the high mass and resonance sinking of the Teres platter, plinth and bearing.

He might get better results with the drive tape we developed. Compared with VHS tape it's less slippery, less elastic and much more resistant to stretching or misforming in any direction. Far better performeer than VHS tape on our TT. Check out this thread.