Sound diffusion panels--do they reduce brightness?

Adding absorptions and diffusion at the first reflection points will help reduce image smearing, better anchor images, increase sound stage, and detail ... but do little to reduce the brightness

The cause of the brightness is ... Long RT60 (decay/reverb) times ... when a note is sustained too long ... it's extended ringing will be irritating and fatiguing and be precieved as brightness

In addition to Long Decay times (RT60s) ... Echo Slap and Comb filtering can also add additonal high frequency ringing to the problem

The easist thing to do is visit Ethan Winer's "Real Trap" site and spend the weekend reading and watching some of the videos on the subject ... this will give you the complete picture

Ethan has made it very simple in plain language any one can understand

Here is something you can try to determined if you have an equipment issue or the brightness is being generated by the room

Warm your system up and give a quick listen to one of your reference CDs that you are very familiar with at your regular listening position (sweat spot)

Now replay the same tracks but go into the room in back of your listening room/chairs and give another listen

If my guess is right when you go into the room in back of your listen room ... the brightness will be greatly diminished because you are not sitting in the direct reverberant field that is aggravating the problem in the main listening position

By going into the other room and listening you remove yourself from the extended/sustained ringing in your main listening room that is being caused by the long RT60 times, Echo Slap, and Comb filtering

If your system still sounds overly bright when listening from the back room ... then you have an equipment issue because you are no longer being effected by the room's anomalies when you are listening from the back room ... it is the equipment that is generating the brightness ... metal dome tweeters ... tube in the pre amp fading or poor match ... etc etc etc

If when you listen from the back room the brightness is greatly reduced then

1 I know What the problem is
2 I know What's causing the problem
3 I know Where the problem is occurring
4 I know how to fix it and your significant other will never realize the you've applied some new room acoustics

Please let us know the results of your listening tests