phattoo- I cannot fine any scientific data, but I know that back in the late 1980's early 1990's I was selling quite a few of the Velodyne ULD series of subwoofers (12'', 15'' & 18'') and owned one of each at different times, and a lot of the installs would include a LARGE potted plant which tighten up the sound and couple to the floor/room better and that allowed me to turn it down but keep the tone and room pressure. I have some lead sheets around and will play with putting them on top of my Omega sub, just for kicks. Post any data you find to support or refute. Happy listening, Chris.