Plinth mass vs. Foundation mass

Slaw is correct.

Concrete slabs are the best place to start for isolation.

Elevated joist floors tend to be vulnerable to many vibrations and resonances. IT will depend upon construction quality to a large extent. Generally, a higher level will be more subject to these factors than a lower one in any particular building/home.

The other big mistake people make is placing a table at the top of a tall cabinet or stand. Elevation above the floor is generally the enemy of turntables in that external vibrations via the floor are amplified at greater height requiring more cost and work to isolate well. Keeping it low to the ground is best.

I am very fortunate that for the first time ever, in my current home (moved in in 1998) I was able to place my system in a basement level directly on the concrete foundation. That makes all the difference! This is the first time that I have had a near perfectly isolated table and the sonic benefits are clearly evident compared to all homes prior. It is truly a vinyl lover's dream situation that can be hard to replicate otherwise.

The coupling between the platter and the tonearm must be exact. If the platter is moving with respect to the arm, the cartridge will interpret that as a signal and a coloration is thus introduced.

Thus the plinth should be utterly rigid and devoid of vibration. Mass is good but its better if its non-resonant, so long as rigid coupling between the elements is maintained.

However the above requirements are met is not so important as the fact that they are indeed met.

Thank you, gentlemen.

My listening room has a suspended joist floor (crawl space,
floor about 30" above the dirt). Turntable will go near
an outer wall, next to the concrete foundation.

Table is an SP-10 with original obsidian plinth. SME-V arm,
but I haven't mounted the arm yet. Old Clearaudio Accurate
cart.

I had thought to put the turntable on a rather heavy little
table of some sort, on the rug, on the floor. I could
easily try some sort of soft pad/coupling between the
turntable and the table. This would be my starting point.

Another thought that came into my head is that, since the
TT is not set up yet, I could sell the whole obsidian
plinth setup and buy something even bigger and heavier,
something that would also accomodate the SME V-12 12" arm.

I guess I've been bitten by this damn bug.