spikes under a subwoofer ?

In the case of the sub dude,if you want to take it to a higher level...a must have is the sub-trap made by ASC. I've been using one for years and it comes highly recommended...

http://www.asc-hifi.com/sub-trap.htm

One of the oldest threads I have seen come alive! However, I have two JL Audio F113's and my floor is carpet on wood with underfloor. The Auralex works great and greatly reduces the unwanted frequencies that were caused by the sub coupled to the floor which transferred into walls furniture etc... I highly recommend raising and decoupling a sub off this type of floor.

I cut 2 yoga foam blocks to make 4 smaller blocks and put them under the sub. It was too boomy sitting directly on the floor.
Sorry I can't be more technical than that.