Isolation for Granite Surface Plate

@oldskoolmark - I believe you can get MDF in different densities, but it is a special order from specialist outlets.

I buy mine from Home depot - it works well

I wouldn't worry about it because using materials having different densities with some type of absorbing material between them is the important part.

For the sorbothane I would recommend a DURO rating of 40-50 because  softer products will not dampen effectively.

Regards - Steve

"half inflated" kids scooter innertube

I used something like that in the '70s when making holograms, with equipment mounted to granite plate. Worked great for isolation, I'm sure it would work for audio use.

Simple and cheap!

You could try a sheet of thin vinyl based damping material, available at 
 www.partsexpress.com 
Self adhesive.

I bought a 3" thick granite surface plate years ago soley to set up my tt project.
This thing weighs 100lbs, had to be freight shipped.

You use HDF in leu of MDF. Night and day. High density Fiber and the quality of the fiber counts... There are all kinds of MDF, You’re actually better off using thinner pieces because of the hard face on the panels.

1.5 inches of 1/2" sheeting has 6 hard faces were 3/4 has only 4.
When you sandwich 3 vs 2.. :-) HDF.. Harder than OAK some of it.. and no sonic anomalies because of natural wood..

Spring and dampening are the way TT manufactures do it. It’s best to follow suit.. No need to reinvent the wheel, with spikes and all that BS.. They just don’t work..

Remember you’re not getting rid of vibrations from the table, your isolating the table from them. Why on earth would you use spikes.. LOL or anything BUT isolation.. Just the opposite effect when you think about it.. Spikes vs suspension. Kind of a no brainer if you think about it..

BTW, George has got an old proven way to add suspension to ANYTHING, not just a TT.. The ol tire innertube.. Does work great for subs too, I used them for years on 500 lb, bass bins.. ZERO rattle in my shop.. BUT for two block.. BIG BOOM BOOM.. 130 db plus.. Helped with the waves in the neighbors pool too..

Regards