The HSU subs that I have now perform worse when I've experimented with isolating them and raising them up.They seem to be engineered to perform at their best close to the floor and on the feet that come with them.
Rel Does Not Recomment Isolation Stands
This came as a surprise. I had just assumed that it should be isolated. Then I discover I was wrong. after doing some research for isolation for mine. Even though I am NOT electronics engineer I think this is an interesting subjet idea. Pardon my utter ignorance. I should have known there was an opposing view. Always is. Just didn't think of it