Tonearm mount to the plinth vs arm board vs rotating arm board vs isolated tower

Thanks for all the information.
 I am considering a direct mount tonearm.
is there a sonic difference between Reed 3p and 2a

Yes.

The mounting of the platter bearing in the plinth will be thus coupled as rigidly as possible to the mounting of the tonearm. If it is not, any vibration at all can be interpreted by the pickup (arm and cartridge) as a coloration.

That's the advice you get from 'amateurs'....🤪
HERE is the 'reality' from Mark Doehmann, responsible for the designs of the Continuum Caliburn and Criterion turntables as well as his own Doehmann Helix 1 and Helix 2 turntables.....all of which are carefully designed with the tonearm mounting bases ISOLATED from the bearing and plinth 👍

I've heard the Doehmann Helix in a system with which I am very familiar.  It indeed seems to be a fabulous turntable, perhaps the best belt-drive I have ever heard.  My friend has since sold it because he needs to downsize and decided to go all digital.  I could have bought it for a "nice" price, but even the nice price was a bit much for my blood.  As to the independent mounting of the tonearm, I don't recall that it was evident.  How did he make it look integrated with the turntable and yet isolate it?  By the way, smart guys (Atma-sphere, Richard, and Mark) can differ in opinion, which does not make the persons on the other side of the argument "amateurs".  If you wanted to make a list of competent designers who line up on one side or the other of this particular proposition, I daresay the "couplers" might have a larger contingent.  But you and I have been over this before, and I have no beef with your preference, nor do I wish to argue about it all over again.  Peace.

That’s the advice you get from ’amateurs’....🤪
HERE is the ’reality’ from Mark Doehmann, responsible for the designs of the Continuum Caliburn and Criterion turntables as well as his own Doehmann Helix 1 and Helix 2 turntables.....all of which are carefully designed with the tonearm mounting bases ISOLATED from the bearing and plinth 👍

Sorry Halcro, you fail to understand that both can be true.

Here is the brief from Dohmann...

The new ’table retains a somewhat simplified version of the unique "floating" armboard technology originally found in Mark Döhmann’s earlier designs, which physically isolates the board while maintaining (it is claimed) positional stability.

So Dohmann claims to provide BOTH isolation AND postitional stability.
I have not personally deconstructed the Dohmann but I understand that it uses a series of interlocking plates and composite materials to provide both isolation and maintain positional stability of the arm relative to the platter.

We are after all trying to measure a micro groove with the stylus - the stylus mounted on the armboard, the groove is mounted on the platter.
Any lack of rigidity between the platter and armboard will result in inaccurate measurment of the record groove. Its that simple.

If you want to perform an experiment - try measuring the height of your house whilst bouncing on a trampoline - you could post a video on you tube with and without the trampoline and we can then give you some feedback.