Need help with acoustic treatment for brightness.

Hear's a real cheap and easy solution. Go over to Home Depot and buy a sheet of Hardboard (like pegboard without the holes). Cut it to the size you need (depot can do this for you). Buy some 3/4" poplar and cut it into 1" strips and staple and glue it so outside edge of the poplar is flush with the outside edge of the hardboard. Get some standard fiberglass ceiling tiles and peel off the white face. Use a little construction adhesive to secure it to the hardboard. Sand the outside edges of the poplar with some 150 grit sand paper and make sure to "break" the edges and corners so that when you stretch fabric over the frame it does not tear. Pickup some fabric at the local sewing shop and stretch it over the frame and staple to the back of the hardboard. I made 48 of these for my hometheater for less the $500.00 including the fabric (100 linear yards at $3.00 a yard)! I consulted with Rives audio so that I did not overdamp the room. I actually made some "dummy" panels by flipping them over and covering the harboard side with fabric.

Good luck,

Rives- you are way cool. To offer free advice when you do this professionally is more than generous. I did use your test cd with the Radio Shack spl meter to record the 5000hz. So I guess I gave ya a little business. I suppose I should lean towards the diffusion as my room is pretty dead already. Unfortunately the diffusion option seems likely more expensive than absorption.
Prpixel- thanks for the construction plan. It's nice to know some of these tasks can be solved with some sweat equity.

Holzhauer--thanks for the compliment. I believe education and thus awareness of the issues does ultimately increase business over time, so we are happy to offer these pointers. It's not the same as designing a room, but hopefully it will help.