VPI TNT Turntables

Flywheel speed?

I'm not an engineer.  Why don't you buy or borrow a VPI flywheel and try it yourself?  I'm not the only one to observe this; see analogluvr above.  As all TNTs (I think) came with a speed controller of some sort, anyone who has added a flywheel has done it for a reason.  If it didn't add additional audible stability and benefit we would have heard complaints well before now.

I have always thought that the flywheel, like a heavy (and rim-weighted) platter, is the more important component as instantaneous speed accuracy is more important (to me) than average speed stability over one or a small number of revolutions.

I have what I call a 3.5 model. Heavy platter, squash balls from bladders from springs, SME-V, no flywheel and a SDS. I keep the tripod set-up as I believe it evens out bearing wear. The sound is weighty and full but not ponderous as some report. This is the only TNT I’ve heard so I can’t compare it to anything. I do have a Trans-FI air bearing linear tonearm on a different VPI and it competes easily with some of the best at a fraction of the cost. You might look into that is you feel the need to replace whatever comes on the table. It is about $1,000 last time I checked and the designer, Vic, is really great in his customer support.
http://i3.photobucket.com/albums/y57/WntrMute2/photo-11a_zpsjvdghrdy.jpg

I'm not questioning whether it makes a difference, everyone would seem to agree that it does.  I'm interested in finding out WHY it makes a difference.

The reason posited by most is the increased inertia that a flywheel provides improves stability, but the math doesn't support that assertion.  For a solid disk of even density, the formula for rotational inertia is Ir=(m*r^2)/2 where m is mass and r is the radius (note that there is no speed component in the formula).  So for a 20 lb, 12" platter the result is 360 and for a 12lb 3" flywheel it is 13.5 or ~27x smaller.  Now, adding a periphery ring to the platter would definitely help more as the mass is concentrated at the largest diameter (although the mass is smaller compared to the platter).  I just don't see where a smaller, lighter flywheel has that much of an impact at least on inertia, angular momentum or kinetic energy.

FYI, a properly designed speed controller will provide excellent instantaneous speed stability, but long term speed accuracy is improved with feedback.

Like I said, I’m no engineer, but:

Lets assume that the platter speed is affected by the stylus drag, which itself varies according to the music being played. As there is no equivalent drag on the flywheel, small as it may be, it can contribute to a more stable platter speed.

Also, my flywheel has a diameter of 5".  

"a properly designed speed controller will provide excellent instantaneous speed stability" Yes, perhaps, but not excellent enough, since the instantaneous speed stability is clearly improved by adding a flywheel or a periphery ring.

Fellows,

I am no engineer (though I did stay at a Holiday Inn Express) but I have experienced how greater mass/weight has more inertia and would be much harder to change the speed than would one with less mass/weight.  For example, picture changing the speed on a playground merry-go-round that is empty, vs. one that is totally weighted down by a full load of equally distributed passengers.  It will take much more effort to slow down or speed up the heavier one.  The flywheel effect in cars and trucks is another example of the heavier, more massive one continuing to spin at a more stable rate, while the lightweight one will lose rpm more quickly.  I have noticed this too when sharpening tools on a blade sharpening wheel.  It takes much more force to affect the speed of the heavier wheel.  It seems to me that the heavier more massive turntable motor flywheel would be more stable and would be less susceptible to external forces, like fluctuations in power supply, intermittent friction, etc.  I am sure I'm wrong, please explain why.