I just finished converting a built-in box or cove that held a big old TV. It put an open box in the room and is a nightmare for audio perfection. After lining the sides and top with carpeting I have add 12' x 12" accoustic tiles to back and corners. The base is a 3/4" plywood sheet that sits on braces on each side. I built a laminate of my own. First layer is 1/4" cork, then a layer of rubbery shelf sheeting, then carpet, then a 3/4" finished poplar board (well varnished), then the 2' x 1' ceramic tile that I glued a layer of felt to the back so it would not scrape the wood.
My TD-160 now sits on Vibrapod risers that sit on this sandwich that has NO significant vibrations at all. If you don't have a slab of marble the 2' x 1' pieces are about $3.00 each and easy to stack a few up if you want the real heavy weight. A slab of marble would not be any better performer than a well thought out layering and lamintion.
Add on: instead of spikes on my 4 foot homemade towers I have baking pans that fit the 12" x 18" footprint of the 100+pound speakers and filled them with sand. On a carpeted, poured concrete basement floor the vibration issue is 'dead' in the sand.
My TD-160 now sits on Vibrapod risers that sit on this sandwich that has NO significant vibrations at all. If you don't have a slab of marble the 2' x 1' pieces are about $3.00 each and easy to stack a few up if you want the real heavy weight. A slab of marble would not be any better performer than a well thought out layering and lamintion.
Add on: instead of spikes on my 4 foot homemade towers I have baking pans that fit the 12" x 18" footprint of the 100+pound speakers and filled them with sand. On a carpeted, poured concrete basement floor the vibration issue is 'dead' in the sand.