I find Stillpoint feet with Risers very effective, but obviously it depends on the deck and rack. They are much cheaper
Grand Prix Formula vs BDR shelf for source
under a turntable specifically...how do they differ sonically? I want a good shelf atop my rack for my TNT to call home. both are available in sizes large enough, and both are obscenely expensive, although the gp is $600 less retail. any others I should consider besides symposium?