Very interesting. I hadn't thought of the stand height affecting resonance ... if I put my hand on the stands, I can actually feel them vibrating at a specific frequency (which I suspect is also radiated into my room). They are perhaps 25" tall at present and are adjustable in height.

My original intuition was to find damping materials ... but adjusting speaker placement should be much easier. I do have an area rug (without padding) that probably helps a bit.

Thanks Alan for your advice, I will keep playing...

--Jon