Under the KLF-30's I have 2 different materials, on the top (the white thing u see in the pic) is a hard marlble slab which gives more depth to the bass and would also be good for spiking the mains (which i am yet to try). Below the slab is an anti-vibration pad, made from thick cork-sheet. Its basicly used for industrial purposes to prevent the vibration on the floor. I'm living in an apartment and had a lot of complaints from the people downstairs.. when i play these babies loud the floor would shake. The cork sheet had solved that problem.