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

I must be doing something right, if both Geoff and Clearthink are angry at me. Clearthink even used his signature triplicate warning system.  (I mustn't "limit, restrict, or discourage...")   Did you think that Geoff is some shrinking violet who needs to be defended lest he walk away in tears?  Here's the thing, Geoff:  Have you considered that we are riding on an enormous ball that is circling the sun at 67,000 mph, while also rotating about its own axis at about 1,000 mph, at the equator?  My point is that the earth is our platform and everything is subject to those seismic vibrations with which you are so obsessed.  Relatively speaking we are all in a sort of spaceship that is subject to the seismic forces.  Therefore, relatively speaking there is no net motion due to seismic forces of a turntable with respect to a tonearm or cartridge or vice-versa.I'm surprised at you for getting so hot so quickly, but perhaps I struck a nerve.

You didn’t strike a nerve, pal, you struck out.

@fsonicsmith 
Nothing is wrong with Aluminum; to the contrary, it is a superb material for almost anything mechanical (there is a reason supercars are built from it). It rings because it is very stiff, and that is usually a good thing, but because it is very stiff (and light), it is very easily damped. So if you dampen Aluminum, you get the best of both worlds; stiffness yet well damped composite. Steel or cast iron is a different matter. It is stiff, but weighty and therefore hard to damped, usually not a good material for anything audio (unless you are building a bell).  

That has been my experience as well sciencecop. FWIW Brass seems to dampen aluminum very effectively in combination with soundcoat material (1/16" thick sheets).