"do it yourself" acoustics

acoustic fabric wallpaper.......the wallpaper shop will have a sample book.......it's spouse friendly because it comes in many colors,solids and patterns.

I can't spell diktionary

Wall-to-wall carpeting and sofa-cusion foam to dampen first reflections off of the wall. This is about all I need but I've been meaning to hang a quilt on back wall.
Also, if you're using a leather easy chair, put a towel on the head rest to soak up reflections.
BTW, the sofa foam is about six feet in length and runs about $80 (purchased at fabrics store).

13 by 13 is tough since the same frequencies are reinforced and cancelled by two of your three dimensions. If you can move the system to a different room, you'll definately be better off. If you have 8 foot ceilings, you will get artificially strong bass at 44, 87, 130, 174, 217, and 261 Hz with big gaps inbetween. Bass below 44 Hz will be hard to come by. That's tough to correct. You may need to either get a very narrow bandwidth equalizer or go to the Rives website and look into that equipment.

Full bookshelves on side walls - both, to get rid of the squareness or your room?