This depends on the size of your room as well as your ceiling. A small room with an undamped ceiling will require maximum shaginess, whereas a larger room (>300sqft) with a somewhat damped ceiling will require only wall to wall thin carpeting. Naked concrete is not advisable)
What about the floor?
I have a dedicated room for audio. It was not built from scratch but a room I choose to be my listening room in my home. It sounds average to good without any treatments but the house has a shag room to room carpet that I will be trashing. I will be staining a concrete floor and adding a large throw rug.
What kind of floor covering do you guys/gals have in your listening area and how does it affect your audio system's sound?