This is a progress photo of my new TT isolation base. The idea is pretty basic- inertial mass sitting on damped foam spring pads. The stone is "green" marble- I bought an old table and had it waterjet cut.
One wrinkle is that I'm adding a ¼" aluminum plate to the underside of the stone slab adhered with a layer of viscoelastic polymer sheet ("Hushmat"- around 3/32" thick) to provide "constrained layer damping" to the stone. CLD primarily is designed to dampen flexure, which implies less "drumhead" vibration response in the slab. This should reduce surface acoustic waves on the slab also. Stone is pretty well damped internally but this will make it totally "dead." The ratio of stiffness (varying as the the modulus of elasticity x the cube of the thickness ) factors in- it seems to me you want the E x I ratio to be in the range 1:20 - 1:10 for the damping plate : stone, although there's no definitive guideline (sez the Naval Undersea Warfare Research Station paper I read).
The base will go under my sweet little Sony PS-X55S table. It's a good, solid DD and on these types of tables the only way they control transmission of vibration from the surface they sit upon is via their elastomeric feet. This should assist the feet. My current shelf is undamped steel plate and is quite "lively."
The isolation I chose feet are industrial units made by Wagner. I researched them pretty well and they seem good for this purpose. They are rated at a maximum load of 50psi and thus the whole assembly wall only load them lightly. We'll see how it goes in that regard. I believe the performance would be better nearer the design load. These blocks appear very similar in overall construction to Mapleshade Isolation Blocks, although I can't attest to the material characteristics. They are around a buck each, so it's not an expensive experiment.
The small valence in the front isn't connected to the plinth and will be foam-taped to the shelf, just for appearance. All edges are as-waterjet-cut and appear smooth, a small amount of ripple. Finishing them with clear lacquer today. They look very nice that way.
I'll report back how it sounds. Since I worked pretty hard to get here, it will be a glowing report about "midrange bloom" and superb "PRAT," undoubtedly.
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