Is your hardwood floor on a concrete slab? Or is there a crawlspace underneath? If there is a crawlspace underneath, it may resonate at midbass frequencies and the increase in bass might sort of match the increase of mids and treble from having a live room. Hard to say without being there.

When you clap your hands is it sharp? I mean, do you hear wall reflections almost as loud as the direct sound from your hands? If you stomp on the floor does it boom? Does it sound solid like rock or hollow like an empty barrel?