Many years ago I purchased a pair of Dunlavy SC-IV demos from Soundex in PA. I was not impressed with the sound but I knew it was the room and not the speakers. I ended up buying acoustic ceiling tiles from a high school classmate who had a ceiling business. I used 48 2' x 2' tiles for a 16' x 20' room. The door to the room has a different 2' x 6' tile. The results were amazing and I still have them there today. I've seen them on Amazon. You can get them in either 2' x 2' or 2' x 8' sizes. They're about 1" thick and consist mostly of a yellow fiberglass material. The cover surface resembles black course sandpaper. They aren't pretty and I wouldn't recommend them for anything other than a dedicated listening room. Years after I installed them I was on a construction project called NFL films. One of the two buildings was all recording studios of different sizes. I was happy to see that they basically did the same thing I did with the damping on the walls.
Hope this helps,
Frank
Hope this helps,
Frank