Direct Drive turntables

Mapman, Spinning a platter at an average speed of 33.3333 is very easy. In fact it is fairly easy to get the accuracy to 4 or even 5 decimal points (not that it matters much). The problem is making it constant at a microscopic level, or at least to a level below audibility. This part is very difficult and in some ways at least as difficult than rocket science.

Isolation from the motor is all about constant speed. Motors vibrate primarily because the torque they deliver is not constant. The uneven torque translates into speed instability and speed instability (even tiny amounts) translates into degraded sound.

My experience with turntable drive systems has convinced me that speed stability is one of the most important, and challenging parts of turntable design. I have to admit that this finding was surprising to me so I understand your skepticism.

All,
I currently use a highly modified Rockport Sirius I TT with a 50# stainless steel platter and constrained layer damping driven by an external motor, oversized power supply, aramid fiber belt. The motor uses a flywheel, the platter a vaccuum draw down. I have experimented extensively with the vaccuum on and off and with an ancillary Lurne record clamp used in conjunction with the vaccuum hold down. In my system, I have concluded that the vaccuum hold down always results in better sound, even with flat records; however I doubt that the reason has anything to do with record slip/stylus drag. I say that because the sound even with the vaccuum engaged further benefits from the use of the Lurne clamp. I would note that Andy Payor bonds a proprietary material to the top surface of the stainless steel platter which he feels better interfaces the record with the platter and that the vaccuum is necessary to maximize the coupling. Prior to the Rockport, I owned both a Goldmund Reference (belt) and a Goldmund Studio (DD). I will note that the tables sounded very different with the same arm (T3F) and cartridge; however, I will not try to ascribe these differences to the differring drives mechanisms. Too many other design choices were different. I will note that the reference was not superior in all ways to the Studio and that both benefitted significantly from the use of the Lurne clamp in place of the Goldmund Reference clamp. I will say that my empirical conclusions based on many years of listening tend in many areas to align with those of Dertonarm, but that I also have great respect for Raul who has visited my home and listened to my system in its current configuration.

It never ceases to amaze me how many audio nuts propound theories without data. And when folks ask for data usually the answer is it's too complex to measure or we measure the wrong thing. Or, it's so obvious that no testing is necessary.

Are you really saying that none of you physics guys can figure a way to measure a) slippage due to stylus drag and its effect on dd versus bd, b) the similar effects of a vacuum and spindle clamp, and c) the constancy and behavior of the hypothesis that belt drive slippage averages a high mass platter even in the instance of variable amounts of stylus drag? Last, nobody has attempted to measure human sensitivity to pitch (speed) variation relative to the duration of measurement? If I were a manufacturer, I could turn a kitchen daisy wheel at exactly 33.3 if you gave me enough time to manipulate it.

FWIW, I vote that agon creates a science first forum where opinions must be backed by data (or references thereto).

FWIW, I vote that agon creates a science first forum where opinions must be backed by data (or references thereto).

there are lots of forums where 'prove it' is dominant. in those forums few focus on listening, and it's interesting how the 'sceintists' rarely if ever post about listening experiences. they focus on why this or that cannot be true because of their expertise. and pretty quick 'listeners' find another forum.

it is a personal decision whether to trust one's ears. i'm not passing judgement on anyone else's way of looking at things. but having to 'prove it' with data is not my idea of a good time. it's fun to compare perspectives on the basis of listening to music. and if it's not (or when it's not) fun then i'm gone, i deal with facts 6 days and 55 hours a week.

i'm not anti-data. measurements have a place in their service of the art (music). i think the balance of posting perspectives here on AudiogoN is healthy. if someone gets off track there is feedback questioning that perspective. do we sometimes ignore science? i would hope so.

that said, if someone wants to do a bunch of measurements and present them no one is stopping them. knock yourself out.

I agree with Raul in this case and he makes some salient points about 'evidence' or lack thereof vs theoretical postulations.
I also think it 'big' of him to recant as I seem to recall that up to a year or so ago he was a keen supporter of clamps?
What Daniel claims is 'theoretically' correct (and obvious)........if there IS slippage between record and mat/platter it puts the subject "beyond any serious discussion from my point of view".....however Daniel fails to provide evidence of ANY slippage let alone extent or magnitude?

There are many turntable manufacturers who specifically discourage the use of clamps on their designs (Linn, Rega, Raven).
There are also designers who advocate vacuum hold-down as well as clamps (Rockport, Continuum) whilst others recommend clamps but not vacuum hold-down (Walker).
I have heard all these designs and if 'clamping' and 'bonding' were essential to prevent 'slippage' of the record, then you would think its effects would be obvious in the resulting sound differences and ALL great turntables would have in common, their use of vacuum hod-down and clamping?
In my experience this is not the case.
For 30 years I have had a Rega Planar 3 followed by a Raven AC-3 and neither turntable sounds better with a clamp.
As Raul confirms.......one doesn't need to 'calculate' the effects of clamps vs no clamps? One need only listen.
Those turntables specifically designed with vacuum hold-down and clamps will no doubt sound poorly without them but those designed with the opposite philosophy will not necessarily sound better with their addition?

As usual in this hobby, 'absolute statements' rarely withstand scrutiny?