Greetings Tim -
There are three things one can try to do with room treatment. They are:
1. Improve the natural tonal balance of the room;
2. Improve the imaging; and
3. Smooth out the bass response.
As a general principle, the ears like a powerful but diffuse reverberant field whose tonal balance is similar to the tonal balance of the first-arrival sound. The ears do not like strong, distinct early reflections - such are detrimental to imaging. So we will be doing things to absorb or diffuse those early reflections, but we still want plenty of diffuse reverberant energy bouncing around as this gives a rich, pleasing timbre.
Let's look at the first item on our list, the room's tonal balance. Take a walk through your house, talking out loud as you move from room to room. Listen closely to the tonal character of your voice - it will change from room to room. Hopefully, it sounds good in your listening room. If not, then you have some work to do. Also, try snapping your fingers or clapping, and listen to how the snap decays. If there is rinnnnging, then you have high frequency sound bouncing back and forth between two undamped parallel surfaces. You'll need absorption on one.
The more stuff in your room along the walls to break up and diffuse the sound, the better. One of the best-sounding rooms I've encountered is at my mom's house - she has a room essentially lined with old wooden furniture. The reverberant field there is powerful and diffuse, and the timbre rich and warm.
With the information you gained in listening to the voicing of your room, you're now ready to move on to the second thing, imaging.
To improve the imaging, you want to treat the first reflection points in the room. The way to find the first sidewall reflection point is to have a friend hold a mirror flat against the sidewall while you sit in the sweet spot. When you can turn your eyes and see the tweeter's reflection, the mirror is at the first sidewall reflection point. You can go on to find the opposite sidewall reflection point, and then first floor and ceiling reflection points as well. The imaging will be improved if you either absorb or diffuse the sound energy at each of these six early reflections points.
If the tonal balance in your room was hard and rinnngy, then use absorption at these early reflections points. If the tonal balance was just right or a bit on the overdamped side, then use diffusion if possible.
If the imaging is still screwy, treat the first reflection off the wall behind the speakers (use the mirror to see the inner edge of the enclosure at tweeter height). Also, if you have any sharp corners near or between or behind the speakers, they can diffract the sound and act as secondary sound sources. You might try draping towels over them one by one to see which (if any) are affecting the imaging.
Now if the tonal balance of the room still isn't right after you've treated the first reflection points, consider absorption in the corners. This is an especially effective place for absorption. But remember too much absorption will suck the life out of the sound.
A treated room need not look like a treated room. You can use draperies, rugs and stuffed furniture for absorption, just about anything for diffusion, and plants (ficus trees, real or fake, work well) at those first sidewall reflection points if absorption would be overdoing it.
I have mixed feelings about bass traps - they also absorb a heck of a lot of midrange energy, and can make a room sound lifeless. Use as a last resort. No doubt you've already tweaked you speaker locations to get good bass - if you haven't tweaked your listening position (which has just as much effect) then I'd suggest that before resorting to bass traps. A cheap bass trap is a generous pile of newspapers or clothing or pillows in a corner - this might at least let you know if you want to go the bass trap route. Personally, I haven't tried it in my room.
I don't sell any room treatment products because I think it can be done well in other ways, but maybe I'm just a cheapskate.
Best of luck to you!
Duke
