Direct Drive vs. Idler Drive vs. Belt drive

Alex are you kidding? I would wager $1000 that you can't hear the difference between a cheap belt drive and an SP10 in regards to wow and flutter. Not only can you hear rumble but it also distorts everything else you woofers are doing. And, since when have you made that comparison in a scientific fashion. Let me answer for you. Never.

Lewn, I do not own a Clearaudio Turntable because I do not care for their designs but they are very well made. Way better than say VPI. I do own one of their cartridges and it is well made and quite delightful.
I do not have to have direct communication with either. I only need to see what they are doing, knowing that both are trying to attack the state of the art in their own way. Anyone can make a direct drive table. The motors are readily available. Even VPI managed to come out with one. Belt drives are not that simple. There are complexities under the surface that take careful engineering. It is how ever and this is not IMHO, the most elegant way to make a high performance turntable and the vast majority of turntable manufacturers feel the same way. The vast majority of audiophiles with expensive systems also feel the same way. There are a few new DD turntables that I have yet to hear but the basic problem remains, an oscillating magnetic device directly under an exquisitely sensitive magnetic device who's job is to resolve magnetic oscillation.
Magnetic field strength drops off with the square of the distance. Every centimetre increase in distance between the motor and the cartridge decreases the motors influence over the cartridge by a factor of 10 increasing exponentially. I believe I would prefer an idler wheel drive table over a direct drive (haven't made that comparison) even though I would have to shelve my subwoofers. 
This is why Howard Johnson's made 28 flavors. Some people would rather look at a turntable than listen to it.      

mijostin  I would offer the counter view. It is far harder to build an acceptable DD than BD for the reasons I noted earlier in this thread

Further with respect to the distance from the source, as you say the inverse square law applies. Double the distance and the field strength falls to 1/4 of the original. The 10 times per cm factor you sight applies only if the reference field source is originally 3.16mm away from the cartridge, a physical impossibility. 

Also one would think that a ID would experience this interference issue since the motor is similarly close to the platter. 



I

Mijostyn.

Correction to my earlier calc, for those of you looking at my numbers.
The original distance would be 4.63mm, where plus 10mm gives a 10 fold reduction in field strength. Still a physical impossibility. Apologies, for my typo. 

Cheers. 

Once one hears a great idler or direct drive, it would be very heard to go back to belt drive.  I have not heard a belt drive under 10 grand that can deliver the punch and very organic sound of the idler drive or the very accurate sound of the direct drive.  They really make music sound like music.  Under 10 grand if you want a decent belt drive table and can live with MM cartridges, the older B & O tables actually are not bad and can outperform many other belt drives.