I am helping my parents and their builder with a dedicated home theater room in a house they are building. They want to build a raised stage (like maybe 6") in the front, on which the speakers would sit...just to add some definition to the room. My question is, should the stage be hollow (I don't think so) or what should I fill the stage with? Sand, concrete, insulation??? Since speakers (and possibly a sub) will be on the stage, I do not want it to rattle or reverberate any.