How do bass waves work?

I've just spent the last 3 days isolating my powered sub and main speakers. My entertainment room is an addition with a 4' high crawl space underneath the entire room. The sub was not only boomy but shook the room's contents. So, I placed the main speakers on 3/4" particle board which float on sand in DIY boxes. The sub is actually on a 2'X 2' X 4" concrete garden tile which then rests on the sand box. These sand boxes have spikes to the floor. It worked - hardly any speaker energy is being transfered to the floor. The bass is incredibly tight and the highs are crystal clear. I have EQ'd my LF cross-over with the help from a concert violinist. Yet,when I play music with heavy bass (such as cut #1 from the Titanic soundtrack) my room still vibrates - but the not the floor that the speakers are sitting on. Why might that be? Thanks!