You can see by the photos I linked to, that I chose a dual approach.
I used spikes to couple the dampening platform to the floor. I also used isolation feet to decouple the subwoofer, and my main speakers from the platforms they each sit on.
In my experience,
the subwoofer with standard feet on the platform (no spikes) resting on the carpet;
the isolation feet on the subs directly on the carpet;
the combination of isolation feet on a spikeless platform on the carpet: all performed less than ideal...
in my experience, in my room. Yes, I repeated myself.
Keep in mind, that most people will consider flat subwoofer feet on carpet to be isolation enough... or a pad... I know I even recommended previously that you experiment with folding some towels or a blanket up and using it as a faux-isolation pad (free experiment).
I can't tell you why the combination approach works better
in my room. To say I understand the physics behind it would be complete BS. However, I know I am not alone in this.
The feet I put on my sub are the SVS Soundpath Isolation Feet. Compared to other products on the market, they aren't that expensive; at $50 bucks or so for a 4-pack they aren't cheap, either. But they really do work!
How you solve for this is ultimately up to you.
My recommendation would be to spring for some Maple Cutting Boards which you can then finish as you wish. You can buy outriggers if you like, or install some spikes underneath. Whichever you choose, you need to make certain it is securely through the carpet and locked into the floorboard and that the top is level.
Ideally, I would also say you want the platform dimensions to be 2" more in width and depth than what you put on it (1" all around).
If you are sold on the idea of increasing mass to more closely match the Subwoofer then you could laminate two boards together. If you want to go full extreme, do Constrained Layer Damping and laminate the two boards with a layer of neoprene or sorbothane in between. (Mind, for that to work, you cannot otherwise fix the two boards together... no nails or screws... adhesive only. In theory, each board will be able to flex and vibrate independently of the other.) (Also, Sorbothane tends to be stupid-expensive.) Here is a link for a place you can order Neoprene sheets (after the lockdown):
Check out the deal on Neoprene High Quality Foam Sheets at Foam Factory, Inc.
www.foambymail.com
The last note: This will only work on the physical transference of energy between subwoofer and floor. You will not be able to stop the acoustical energy from causing their own vibrations.
