I just got a new turntable which did not fit into my old cabinet so I set about building a new one and again the perennial question of what to make the support shelf out of? I thought about granite but it has its own frequency response so I wanted to find something more neutral. I asked around and was told ebony was as acoustically neutral as anything and plexiglass was equally as neutral.
This got me thinking as after we had had an outside deck built the contractor had left behind a supply of ipe or Brazillian cherry.This is a very dense wood not as dense as ebony but almost. (You can't get ebony anyway) So I made a frame out of 4 1/2" x 4 1/2" legs and 1 1/2"cross pieces. I laminated about 9 pieces of 3"x 2"to make the platform then made another platform of 3/4" thick ipe and betwen two levels each of rubber and cork alternately to make a platform 3 1/2" thick. I suspended this platform on four cushions of 1 1/2" x 1 1/2" cork 1/4" rubber and cork sandwiches. I also suspended the whole cabinet on larger versions of my cork/rubber sandwiches
This was great for a while and sounded phenomenal until the platforms started to warp. Everything went awry. What to do?
I decided now on plexiglass. Plexiglass has to be supported all around otherwise it will sag. So I purchased a couple of 1" sheets of plexiglass put 1/4" cork between them, but only around the periphery 1 1/2" wide and another layer of 1/4"cork 1 1/2" wide under the lower sheet of plexiglass. Set up my turntable again and I have to admit that it sounds even better. Every thing seems to float.
I don't know if that helps but I think the secret is in isolating each level as much as possible and I think my borders of cork helped do the trick. So if you have granite and then wood try and set up a neutral barrier.
I live in a very old wooden house (1730} so you can imagine the floors are rather bouncy and vibrations from footsteps and everything else can have an effect. But with this set up nothing moves. It seems to work.
Best regards