DIY speaker isolation base for a wood floor

My speakers are 75 lbs plus 2 16x16 granite slabs. Thanks!!!

geoffkait"I agree cork is a wonderful audiophile material"

I think that the reason many people reject, undervalue, or discount cork is that it is not a engineered man made material so for those who like to read, analyze, and assess product information sheets it does not offer the same satisfaction. However for those who actually have "real world" experience which means doing, testing, and listening and not just reading and "calculating" it can be very useful, effective, and advantageous.  

Anyone looking for rubbery damping materials has a couple more to choose from: EAR Isodamp (used in industry) and Navcom (used in the gun business). One form of Isodamp is made expressly for constrained-layer damping, another for damping of metal parts such as electronic enclosures. Michael Percy Audio sells both. 

I mean no disrespect but I put that horrid blue EAR stuff almost as low on the totem pole as Sorbothane. EAR rubber grommets, sheets and feet look so darn cool, too. Oh,well, onwards and upwards, guys. Anybody actually listen to this stuff or is the March of the Lemmings to the sea? Marigo VTS Dots constrained layer dampers are a no brained. Marigo has various sizes for a multitude of applications, including but not limited to, bottom of glass of vacuum tubes, speaker diaphragm cage, tonearm base, turntable platter, speaker drivers themselves, power plugs, glass windows and sliding doors, walls, printed circuit boards, speaker cabinets.

blueranger,

I am assuming each granite slab is about 25lbs, and the sorbathane is between them, so assume a 100lb total load.

georgehifi posted a link above to an Ebay seller. They sell 2.5" diameter disks of 70, 50 and 30 hardness. My rough calcs say that if you cut those in half (so half circle), and use 4 of them, they should depress about 25%.  That is not going to isolate the lowest bass frequencies, but will be a good improvement over what you have now. One area I agree with geoffkait on is that springs are best for low low frequency isolation.

I expect you have lots of cork around, so you can start experimenting. As opposed to single large sheets of cork, cut them into say 2" squares and stack them say 1/2" high, and use 4 stacks for stability. You want the cork supports small enough (and not too small) that the cork is compressing say 10-20%.