Vibration dampening

If you have watched many REL viideos you will know they strongly suggest to NOT use any isolation materials for their subs. I assume this should apply to any sub. The goal of setting up a sub or subs is to not know it is on until you turn it off. Think about that. My 212SX subs sit on a concrete floor with Blue Tac under them so on low organ recordings they do not slide. I do not have the issue you are describing. 

I use springs under mine ( a hint from millercarbon)  I also pull them out from the wall about a foot.  I feel the bass is tighter and less boomy.  A set of isolation springs was less than $30

I too use the springs under my sub and works well, about a foot out yes.

Primacoustic Recoil Platforms are under both my speakers and subs.Their purpose is is to address floor vibrations.

All subs vibrate

thats what low frequencies do

save your money