Upgrade from TW Acustic Raven AC-3 to what?

Hi Mosin, to add inertia and by doing so increasing speed stability of the moving system is indeed a wise decision. However - this added "dynamic mass" is not "seen" by the stylus assembly as it is only a dynamic (sic) part of the moving system. The platter of your TT still remains at a static net mass of 12.5 kg (which still is pretty much for an idler drive and already in a serious league).
So for the model I have set up we do need the bare net mass of the platter.
The added inertia helps to stabilize the speed - but it does not help the platter in its fight against tracking-born vibrations. Its only the pure static mass underneath the record - i.e. the platter itself - which matters in this case.

Nevertheless its always a smart move to increase inherent speed stability by added inertia - even in an idler drive ( which once again shows indeed, that there are many ways leading to Rome - but in the very end they all merge at the Capitol (or the Via Appia.... in case you want it to be a triumphal march....).

Keep up the good work.
Enjoy the journey,
D.

Audiophiles "opinions":
"I wrote it the right way, so it was copied the wrong
way right. I mean the right way wrong." :-)

Dertonearm, The billiard experiment you cite is an interesting analogy. It seems to me that when the billiard ball encounters the billiard table, it is first of all sitting on the felt cover. The outcome of the experiment would seem to depend on how much of the kinetic energy of the ball is absorbed by the felt/stone entity vs how much is reflected back into the ball. That has a lot to do with what happens right at the interface of the ball and the felt/stone. Different kinds of felt might affect the outcome, for example. Billiard table stone is usually slate. Slate from different locales around the world has very different hardness. Hardness or density would affect what portion of the energy is absorbed vs reflected. In other words, it's not only about mass. High turntable platter mass would be good though to sink the absorbed stylus energy as heat rather than to reflect it back into the cartridge, if the platter material were of a nature to absorb enerby from vinyl rather than to reflect it. So platter composition would have something to do with this phenomenon as well.

There is also the question of whether ideally one wants to absorb the energy imparted by the cartridge or to reflect it back to the cartridge. In this aspect, the billiard ball analogy may fail. I cannot argue with your listening experiments, as you cite them to Mosin, but I am guessing you were using a belt-driven tt at the time. So there is another question of whether the drive system makes a difference. I have no basis to form my opinion on that except to say that I hear more solid base lines from upper mid-level direct-drive tables than from similar quality belt-drive tables, when the latter have platters of much higher mass.

Lewm, on the "billiard analogy" ALL other factors (level, felt/fabric, size etc.) are the very same - the only difference being the mass underneath the felt. Be it slate, granite or (seldom...) other hard stone. Check out billiard tables - the huge difference in prices of different models by the same manufacturer is direct related to mass (mass underneath the felt...) and usually the published thickness of the stone platter underneath the felt is the "price factor" per se.
So - lets just predict that it is the larger mass only which makes the difference (and this too is the technical fact..).
The larger the difference in mass between two singular bodies - one (the smaller) moving on the other - the less energy is absorbed/withdrawn from the smaller moving mass by the larger mass underneath. Resulting in more inherent energy "staying" with the moving corpus and is used for movement = longer distance running.
In billiard - which I was into in my youth - this is common sense and knowledge. At least in Snooker and Karambolage - not sure about Pool....

So - let just take that fact for granted.
Of course the inner damping of the platter does add to the overall result, as does the clever sequence of different speed of sonic distribution in different materials, but the total mass has a paramount impact.
Take the platter of the vintage Basis Debut Gold.
Its not that heavy (but still above 20 lbs I think) and it is very well damped despite its vacuum suction.
However, its lower bass performance - while being very good - can NOT compete with the low register performance of platters twice its weight.
I too wished it would be otherwise.
My new turntable thus features a very complex platter with a total weight of 135 lbs (static net weight ...... but there will be 2 inertia units going with it.... so the dynamic mass will be , well - immense).
Not because I like heavy cylinders, but because I know what I need to do to achieve what I want.
The drive system does make a difference, but to a much lesser extend that widely assumed.
It does make a sometimes huge difference with poor (cheap) motors and/or light platters.
I already had a great argument with the idler-drive and direct drive fraction here on Audiogon some months back.
I know why I use the drive I am using and I am getting the results I wanted and which others won't believe.
For the model set up in my earlier post there is only one thing that matters - brute mass.
The other points mentioned do matter too - and a few more.
Enjoy the journey,
D.

Dertonearm, I am thoroughly enjoying this discussion, and I do thank you for your patience with my recalcitrance. I feel like this is a Socratic search for truth, not an argument. So.... you wrote, "The larger the difference in mass between two singular bodies - one (the smaller) moving on the other - the less energy is absorbed/withdrawn from the smaller moving mass by the larger mass underneath." I think this statement is incorrect for a ball rolling on a flat inert surface, provided it is a given that the surface does not deform due to the pure weight of the ball. (We could agree that a ball won't roll very far in mud.)

I know your conclusion re what type of tt is best is based on extensive listening and even more extensive trial and error experiments that I cannot come near to replicating. So I would not dare say you are wrong in that regard. I am just commenting on the why of it.