Two layers of Baltic Birch plywood (13 ply, 3/4" thick), with a layer of viscoelastic material (Green Glue, or Acoustic Sciences Corp. WallDamp) between them. Finish with lacquer or polyurethane. Place on a set of Townshend Audio Seismic Pods, or for a low price option a set of the aluminum "spring spikes" available on ebay.
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