A surprise for me...I have Vandersteen 5A's which have spikes designed for them...my speakers were on the spikes with brass floor protectors under the spikes. I moved into a new house with Travertine tile over congrete. Much to my surprise, on some frequencies, the whole speaker which is VERY heavy resonated uncontrolably...I could feel the speaker jumping up and down at these resonating frequencies. I fixed the problem after lots of experimentation by simply putting a bit of Gorilla tape under the floor protectors of the spikes and the speakers are sitting pretty. You never know what you bump into with this hobby.
