Direct drive vs belt vs rim vs idler arm

Dover,
As 'stylus drag' must vary with the modulation of the grooves responding to the complexity and dynamics of the musical performance.......it would not, I think, be a constant?
If you merely adjust your speed-controller to hold the Timeline constant with the cartridge tracking........it would be interesting to see where the Timeline 'mark' would be at the end of a whole side of a powerful symphony such as The Royal Ballet, The Three Cornered Hat, Pines of Rome or Witches Brew?

Yes I agree, thats pretty much what I proposed for testing to quantify the variation between that minimum and maximum drag levels and the impact of a piece of music in total...I think you misread my syntax ( no pun intended ). ("how consistant" , ie I meant range of variation. )

I am wondering that every Turntable discussion is based on speed only. Like Dev wrote, it is the beginning and it is important. But is that all?
A little more knowledge should be available I think, we have the year 2013 now and serious High End has 5 digits or more and a lot of owners want to spend that money

- Quality and Influence from the Bearing
- Quality and Influence from the Chassis
- Quality and Influence from the Belt
- Quality and Influence from the Platter
- Influence from Suspension and how it was solved
- Why are some platters so heavy
- Direct Drive works with continuous correction, what is the sonic result
- Platter weight from DD and their sonic attributes
- Weight in general and why
- Is a polished frame good for sonics
- Idler Drive has direct contact to Platter and Spindle
- Advantages / Disadvantages
- Speed correction or not
- What material is used and is it stable over the years
- suspension for Idlers, necessary or not
- sonic results from contact motor to platter
- isolation from internal vibrations in general
- is reliability important or not
- do Fangroups replace knowledge
- are facts welcome or do they disturb dreaming
- why are no turntable manufacturers found in such discussions
- is analog the last resort for "I-do-what-I-want-and-who-cares-Design"
- what is a stable Design
- why can a unit change Performance when your wife opens the window
- what is sonic feedback

and so on and on

Hi Dover, one thing to quickly recalculate is that the record spins 0.5556 revolutions per second. (Inverse of 1.8) So the speed error would be 0.008% if it takes 7200 seconds to lose/gain one rotation.
What I believe is that we will hear a difference in PRAT if speed is off before we hear sour notes (tonal pitch); at least most of us. If speed is off by 0.1%, then concert A would be off by 0.44Hz. I do not think that I could tell the difference even if I had a tuning fork to my ear. But I now know that I can sense the pace of the music by small changes in speed. An orchestra, for example, tunes to the oboe. If the oboe is off a Hertz or two, it doesn't matter because the whole orchestra will be matched to it; but the tempo of the music doesn't change- can't do that with a recording.

Your tt platter is a flywheel. Like any good flywheel design, the bulk of the mass is on the outer edge (Think 2001 A Space Odyssey). The moment of inertial equations illustrate the effectiveness of having the bulk of the mass at the outer edge. A uniform mass flywheel is I=1/2mr^2, but when the mass is concentrated at the outer edge it is I=mr^2. The moment of inertia is doubled. Therefore, a "hollow" flywheel half the mass of a solid flywheel has the same moment of inertia. And the moment of inertia is directly related to the amount of torque it takes to accelerate the platter- double "I" and torque must double to get the same amount of acceleration. Conversely, double "I" and the impact of stylus drag change on platter speed drops by half.