Hi Althea,

You want surfaces that move somewhat, that are able to flex a bit, like a wood sub-floor, with wallboard on the walls. Concrete is the worst kind of surface for getting good sound, because it doesn't absorb any of the energy modes from standing waves in the bass (concrete is immoveable), so they build up and resonate in the room.

Alan Lofft,
Axiom Resident Expert (Retired)