@skyscraper,
I was in a similar position not long ago when I bought my heavy new Transrotor turntable and had to modify my existing flimsy rack to accommodate it and create an isolation base.
Reading the many threads and forums, and soliciting info from other audiophiles was enough to make me start tearing my hair out because you encounter so many different views and advice.
I took some of the info, and then the rest in to my own hands, bought tons of isolation materials and footers, and tried them out, especially measuring with seismometer apps on my ipad/iphone.
FWIW, here’s what I ended up with:
I re-enforced the top (thin) mdf shelf of my Lovan rack with 1/8" steel. It’s quite remarkable how much solidity that steel creates when bonded to the mdf (I used a product called "wall damp" used to damp vibrations in walls, as the bond).
Isolation base:
2 1/2" Maple block
1/8" steel sheet
MDF layer of 3/4" and 1/2" sheet, bonded by wall damping
sitting on Townshend Isolation Pods (spring based pods)
(Actually, I also threw in some thin sound-damped steel discs that I had ordered to test, between the pods and the MDF, mostly because I had them to use).
As far as reducing external vibrations reaching the isolation base/turntable, nothing - sorbothane sheets, footers etc - came close to the performance of the spring-based Townshend pods. You can see in seismometer measurements, and feel, huge reductions in vibration getting through to whatever they are holding up. If I put the seismometer/ipad on top of one of my other av rack shelves and stomp the wood floor around the base, it registers huge ringing spikes on the read-out. Place it on the isolation base held up by the pods, and almost nothing at all registers stomping hard around the base, and almost nothing at all is felt with a hand on the base.
All the rest of the material below the Maple block is just there to add thickness, weight, more reduction of isolation through combining various materials, and to provide the right weight for the springs to work optimally. I have to emphasize again btw how much bang for the buck stiffness you get just throwing in even a 1/8" sheet of steel in the mix. It even made the whole base layer obviously more solid, no matter where I through it in within the layering.
Don’t ask me if all this had benefits on the sound as I don’t know. There was no practical way to do a before and after. But in terms of a peace-of-mind project, and knowing how much vibrations were reduced, I’m quite happy with the results.
Cheers.
