As with most people, money is tight, so real treatments are out for a while. Let me start by saying that I know nothing is going to match real acoustic treatments. My room is a dedicated room, about 1500 cubic feet, enclosed space. Right now all of the walls are bare. It is wall to wall carpet, with a sofa and a coffee table. It is difficult to put anything on the screen wall behind the main speakers, because my projection screen takes up most of the wall.

Would putting up pictures, bookshelves and such help? I have about 5' of space between the couch and the wall behind me that is unused. I was thinking about putting bookshelves there if it would make a difference.

Any thoughts?

The front wall behind your speakers rarely matters, but you'll benefit from corner bass traps and absorbers at the side-wall and ceiling reflection points. Thick absorbent things like folded over bath towels can absorb reflections, and batts of fiberglass left in their plastic bags can serve as corner bass traps. It might look like hell, but you did ask for cheap. :D

--Ethan

Cheap, my favorite subject. Adding to what Ethan said ( he IS the expert)
A trick I have used is slipping a fiberglass ceiling tile behind some needlepoint my wife did and hang it on the first reflection point on the side walls. Look at the NRC on the packages and see if a store will give you a break on slightly damaged tiles. I have also hidden blankets behind the drapes on the front wall. Bookshelves on the rear wall are great. My favorite is antique Chinese rung I hang on the wall, but that fails the cheap part.

Everything in your room is affecting the sound. A bookcase will act as a trap and also reflect sound. A rug or drapes will absorb sound.

What you need to add (or move) depends on how the room sounds now. Walk around and clap. If there is a bright area, you'll hear it.

BTW you want both reflecting surfaces AND acoustic absorption to balance the sound.

just build some traps. 1"x4" pine is cheap. as is mineral wool (also called ROCKWOOL = brand name) = menards has 2'x4'x4", 4 pieces for $30. some old blankets/sheets will cover it. so, you would get 4 GOOD panels for about $50-60.

in my room, i have found that the first reflection ceiling/wall corner is the MAJOR problem.
it is acting like a megaphone = not good.