Direct Drive turntables

J2468, No aversion to measurements here. It's just that I tend to put more trust in our ears.

I find the propensity to associate stylus drag with slippage curious. Although there will always be some amount of slippage with any friction drive (Mark Kelly calls it scrubbing) I do not think that it has much if anything to do with stylus drag.

I believe that an important issue in drive design is delay of torque delivery from the motor. This is akin to what you posted about servo reacting after the fact. A motor connected to a platter via a compliant belt is unable to apply torque to correct short duration speed fluctuations. If the platter decelerates slightly the motor applies more torque to compensate. But the belt simply stretches a little more. The energy ends up being stored in the belt causing a delay before it affects the platter speed. So the correction ends up arriving at the wrong time often making matters worse.

A heavy platter changes but does not solve the problem.
A massive platter will reduce the magnitude of a short term variation but extends it over a longer period of time. A light platter will conversely allow a larger speed variation but it recovers more rapidly. Heavy and light platters sound different but neither solve the problem.

I like your idea of using high speed photography to measure speed variations from stylus drag. But perhaps there is a better way. Rather than use a camera a reference track with a precise, constant tone could be used. This would require two tonearms and a test record with a steady tone and a track with variable modulation. The two tonearm part is easy but I am not sure if a suitable test record could be found.

It is expected that the magnitude of speed variation from stylus drag would be extremely small. To detect and measure the variation would require high precision. It may well be that audible speed variations would be too small to detect with a setup that is not prohibitively expensive. But thanks for the idea. I am interested in pursuing it.

Teres, thank you for a very articulate explanation.

I agree that our ears and our perception are more important than a number on paper. I do believe that with study, we will learn to improve our correlation between measurements and sonic satisfaction. If a measurement does not correlate with perceived sonic satisfaction, then the measuring system needs improvement and such theory does not bar individualism.

In other words, if a measurement not help then throw it out.

Dear Jj2468: +++++ " No aversion to measurements here. It's just that I tend to put more trust in our ears. " +++++

+++++ " I agree that our ears and our perception are more important than a number on paper. " +++++

well, yes and no: in an strict point of view where the target is to achieve a performance with the less " colorations " ( where colorations means: noise, distortions, inaccuracies, etc, etc. ) those two statements are untrue.

I know several audio system owners that are really proud of each one audio system quality performance where they have severe " colorations " because they have an unmatched speaker electrical impedance curve with an amplifier(s) with high output impedance or whatever other " problems " around. That they like it does not means the performance is right because that performance is " wrong ". First step to be confidence with our ears is that we have an in deep experiece/knowledge about music and how it sound or shoul be to sounds, what we like has nothing to see with what is the real thing if we like the " wrong " music presentation.

Problem with measurements is that not many people " understand " it. Many measurements say almost nothing alone and only make sense when we " combine " two or more measurements.
The match between amplifier/speaker impedance as a RIAA eq. deviation are only a few of the measurements examples that alone can tell us part of what we are hearing, normally we have to combine several measurements to more or less understand what's happening.

IMHO today ( in these times. )it is pathetic to read elsewhere that what it counts is only what we hear, it does not matters that what we hear is wrong way wrong!!!!!.
This kind of thinking has a price very high price that all of us ( the high end audio world. ) are paying: mediocrity, that's what we overall have in our home audio systems. This is a fact not an opinion: take a look to almost all the audio links in the audio chain and we can find that in the last 20-30 yyears we don't have almost no improvements or signs that the industry is growing-up in quality performance. We are extremely proud and happy because our SP-10s are wonderful or because the vintage MM/MIs are great alternative, my God!!!!!!!

Shame of us and shame of industry we have ( with exceptions. ).

Regards and enjoy the music,
Raul.

I agree on the post as a whole Raul.
However - "wrong" or "right" will - in the very end - always be up to the individual listeners taste.
There is no absolute here (which is were...) - not in hearing.
Hearing is always a lone and individual one,- and so will be the final judgement about a certain sound systems performance: - individual.
I guess it is indeed rather a matter of different levels of experience.
The seasoned listener to many different systems with a certain technical background will always have a wider foundation - a more solid ground - on which he can make a "judgement".

Dear dertonarm: Agree, so many of us has a lot to learn on the whole subject and try to go up faster in each of us: audio learning curve.

regards and enjoy the music,
Raul.