It has been a while since I provided an update to this thread. Since my last post, I have researched several companies who provide room treatment products, looking at absorption data, form factor, etc. As I have reported earlier, even though I have received strong encouragement from several contributors to consider DIY treatments, I opted to purchase a manufactured product.
The treatments I have selected (and now installed) are typical 2’x4’ velocity panels, with 4 inches of actual absorption material and a 2 inch air space between the material and the wall. The manufacturer calls these panels “bass traps”, although they don’t do much below 80 Hz.
I installed two panels on the back wall behind the MLP (the wall is only 48 inches wide) in an attempt to tame the most troublesome reflections. I installed two more panels in the rear corner to assist in bass response. I now have a total of eight 2’x4’ “bass traps”, the four new panels, plus four RealTraps MiniTraps in the front two corners. There is not much more room for bass traps in my listening room.
Here is the impulse response before the four new panels. My objective was to get the reflections at 4.5m (-11dB), 6.3m (-10.5db), and 11.3m (-15dB) to where all were under 20dB.
Here is the impulse response after the new panels were installed. The primary reflection from the back wall at 6.3m is now -30dB, which is better. The remaining reflections are pretty close to -20dB, so overall the results are not too bad.
Here is the resulting bass response (no smoothing):
Bass response improvement is marginal, but to my ears the bass sounds pretty good.
So, I plan on taking a break from room treatments for a while and allowing my ears to become accustomed to these changes. I have gained a fair bit of knowledge with respect to generating and analyzing impulse response graphs and waterfalls, and learned to appreciate how well R-30 works! My thanks to all the contributors who have helped me in this interesting project.