[Organizers] How can we improve acoustics in a gym?

Sorry, I sent this post to the callers list and it should have gone to the organizers list. Thanks for your help! Our dance group in Charlotte NC is considering a long-term lease on an unused gym. Terms are great, we have a strong lead on a temporary portable floor while we raise money for a better floor. Acoustics, however, are horrendous. It's a big concrete box. What are some relatively quick and cheap ways we can get the acoustics to an OK level while we do the fundraising to do the job right? We need to move in fast as we presently have no better alternatives for our weekly dance. We're thinking about hanging quilts and heavy curtains from ropes along the walls and maybe up in the high ceiling. Any ideas? Suggestions? Thanks. Gretchen Caldwell gretchendance(a)yahoo.com Charlotte NC