Start by investigating the Cardas and Echo Busters websites. The Rives Audio website has some suggestions and tools to use as well.
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I did what you are thinking. Do not waste your $ on fancy sound panels. I used old rugs (on the floor, walls and ceiling. You can also find on the net sources for foam sound panels for little money. I think I paid $80 plus shipping for (4) 4ftx4ft panels. BTW they work well. It may not look great but the sound was very nice. Experiement with overstuffed furniture also.
Bozo's suggestions might make a room overdamped, especially if you have low ceilings.
Also, you might not need much help eliminating bounce on the walls if the finish is rough enough.
I have Maggie 3.6's in my basement. I bought acoustical foam for about 1/3 of the ceiling, and I covered the rest with sheets of fake tongue-and-groove. The floor is covered with a thin hard rug, and there is a second oriental carpet in between the speakers and my listening area.
Walk around the room and clap your hands together sharply. You should hear some resonance. If it's totally dead (no reverb at all) you've overdamped. If it "pings" you need some damping.
Too much bass is an easy problem to fix. Take a sheet or two of the acoustical foam and roll it up into a column and place it in the corners.
Your mids will be a function of speaker placement.
The biggest problem you may face is figuring out ceiling reflection if you are using dynamic drivers. They radiate in a circular shape and a low ceiling sends a lot of energy to the ceiling, down to the floor and back. Dampen with foam just behind the halfway point between the speakers and your listening area. If that's still too bright, move the foam to the midpoint. If it's too dead, move the foam closer to the speaker.
All in all, I spent a few hundred bucks on materials and have a very nice room in my 7' basement.
Rives Audio, F. Alton Everest and Jon Risch's DIY acoustic treatments ought to get you started with good info.
Be careful when trying to build / treat a room. It is possible to use materials that are non-linear across the frequency range. As such, it is possible to create more problems than what you started off with. This could be due to introducing materials that absorb / damp some specific frequencies while increasing reflections in other frequency ranges, etc... While "non-linear absorption" CAN be a "good thing" if properly applied, even some "audiophile approved" products do this without making you aware of it. Spend the money on at least one of Everest's books and read / learn what you can on the web and you'll end up dollars and hours ahead in the long run. Sean
Sean's advice is the best, although I have not visited the Rives Audio site. Hopefully it does not give out simple math answers, like the Cardas room ratios, as those are not sufficient to create a good room.
F. Alton Everest's book "The Master Handbook of Acoustics" is available from Old Colony Sound Labs and from PartsExpress.com. Also, Don Davis is a fine author. Both are in the reference section of any public library. Everest is the most comprehensive.
He shows you how to evaluate the room and how to build the right acoustic control devices, and select how the drywall is mounted, isolate the outside world, and vice versa.
Acoustics is easy to understand- just a fair amount to read/learn. Most professed acoustics designers have never tried to understand all of what is in the Everest book: like guys who got through school never really doing the homework for themselves, but just talk the talk. Read- you'll see. If they knew, then that book-knowledge would be readily apparent in their literature, showing you a much more profound way, like Sean indicates, to understand and control room acoustics.
Green Mountain Audio
I'm sure you need to do some accoustic treatment of the concrete space, but, before you do so, set up the audio gear and play some dixieland jazz. If you have an old horn midrange/tweeter speaker so much the better. I did this once upon a time, and was absolutely astonished. At the time I lived in NY city, and hung out in jazz dives, so I knew how it was supposed to sound.