A Copernican View of the Turntable System

Hi Dgob,
Unless you have the turntable and armpods located on a solid wall-hung shelf.....structure-borne feedback is likely to be a problem.
Every suspended floor (even concrete ones) will suffer from this to some extent.
If I had to locate my TT on a floor-mounted rack....I would ensure that it was on an isolating platform like a Vibraplane of Minus K. Not sure about Dover's Jello however :-)
Your 'floating' plinth idea sounds like an attempt at similar isolation.
It should work to some degree depending on the severity of your structure-borne feedback problem?
Please let us know how you go with it?

Regards

Halcro -
Have to concur with the wall hung shelf. This is one of the best bang for the buck upgrades for TT's of all persuasions in my view and well worth the time and effort. Biggest difference I noticed was a cleaner and more transparent bottom end.

Dover,

This is one of the best bang for the buck upgrades for TT's of all persuasions in my view and well worth the time and effort.

Amen.
The audiophiles I really feel sorry for are those who live in modern high-rise apartment buildings like those in Singapore, Hong Kong, China and Australia.
Many of these are built using thin prestressed concrete slabs as the floors.
Being thin and 'stressed'.....these floors are similar to trampolines and are continually in a state of motion. If you put electronic instruments at various locations on these floors.....you can actually hear them 'singing' although most of the 'singing' is sub-sonic.
To make matters even worse........the dividing walls of these apartments are of often lightweight soundproof construction supported not on the wall below......but on the flexing thin prestressed slab.
This means that a wall-mounted shelf will be afflicted with the same structure-borne feedback issues as the floor itself?

Lew,
What you are hearing when you 'tap' on the shelf.....is the effect of the structural stresses within the shelf.
These stresses differ throughout any material depending on methods of support, locations of maximum and minimum bending moments, locations of maximum and minimum shear stresses and locations of all the various deflection points.
These stresses will also differ (in the same location) throughout the DEPTH of the material....normally compressive stresses at the surface, changing to tensile stresses on the bottom (reverse these for a cantilever).

These stresses will normally not affect the material's reaction to air-borne sound transmission.....most waves reflected or passing through.
Tapping a shelf to test for air-borne acoustic performance is similar to the infamous 'tap-test' employed on turntable plinths by some incompetent reviewers.
I liken it to the analogy of tapping on one's head to test for hearing ability? :-)

Regards...and peace

Thanks Halcro,

And I will of course feedback on my findings. I think the grounding issue really is a major one, despite my use of wall shelf mounting and experimentation with a number of platforms and methods of isolation. Walls rarely seem as neutral to vibration as I would wish and even wall mounting carries detectable vibrations - listening through my system within a fairly solid 19th Century English home. Along with decoupling tonearm and TT (arm-tower/pod), the use of pneumatic footers was (as I suggested) the most marked improvement to the quality of analogue reproduction in my experience: quality of system, hearing sensitivity and expectations not withstanding. That this is the case is simply beyond doubt for me and so my only questions are:

1. Does the decoupled arm/TT really offer the ultimate feasible set up? and

2. Will pneumatic decoupling of a coupled (or, 'plinth based') arm/TT from the grounding/platform really offer the ultimate feasible set up?

That's what I'll be looking into in a suitably empirical way and that's really all that I'll be able to report back on. What others choose to make of that or 'believe' will obviously remain beyond my compass.

As always...