Hi sel53
I have a dedicated 2 channel only listening room tha measures 17’ front to rear wall by 12’ wide with an 8’ ceiling with wall to wall carpeting. I’ve been trying various acoustic treatment options for about 5 years. All of my comments apply only to what I hear in my room.
To answer your original question, when I installed QRD bamboo diffusers on the wall behind the speakers, it cleaned up the midrange and the high frequencies. Instruments were no longer jumbled together. Much less confusion. Voices were more articulate and I now found it easier to understand the words. The midrange & high frequencies were more open and I noticed the highs seemed to be better extended.
In my experience, there seems to be areas that are more important than others and this is where I would start.
1. Bass traps in the corners behind the speakers.
Before I added those, my room had no bass. I would spend stupid amounts money on speakers and couldn’t figure out why I had no bass. It took a couple of years to realize that the room had really bad nodes that would just eat up the bass. The bass traps helped a lot. I have them from floor to ceiling, bass problem solved!
2. The diffusers on the wall behind the speakers, in the middle.
These made a significant difference. Everything was cleaner, with noticeably better clarity. Soundstage was wider and deeper. Smaller background details that I didn’t even know were in the recoding were now revealed. Complex orchestral passages were much less confused.
3. Absorbent panels 1’ - 2’ on the side walls (if there are walls to the side of the speakers) in front of the speakers.
The purpose of these panels is to kill that first reflection bouncing off the walls in front of each speaker. This improves image specificity. Instruments within the soundstage are more stable. Again, everything is less confused.
I would also recommend playing with the placement of your listening chair by moving it closer to or farther away from the speakers. This can make a surprising difference.
The most important advise I could give you is don’t overdamp the room. This is easy to do. This will render the room dead, dull & lifeless. The only way to avoid that is to add small amounts of each option and then listen. Take your time and listen before adding more. If you’re convinced you’re going in the right direction, then add a little bit more. Again, listen carefully. If it starts to sound worse, you know you’ve added too much. Go back and take out that last bit. A properly treated room will have great energy and the music will come to life. Trust your ears, when it’s right, you’ll know it.
IMHO, the two most important things for great sound is the room and the setup. You can spend a lot of money on great components and put them in a bad room and if they are not setup properly, they will never sound good. You can buy more modestly priced gear and put it in a properly treated room and set up the gear correctly and it will sound great.
I hope these suggestions help you. Take care.
Best regards
Scot