@jbuhl , yes, you will get some attenuation over 250 Hz or so. I would liken it to pissing into a forest fire. A HiFi room is for sound, appearances are secondary, although it is possible to make a very nice looking sound room. Put 4" acoustic tile at the first reflection points then hang your wool in front of it if you can't stand looking at acoustic foam tiles. The tiles cost about 30 cents each. Amazon sells it, but I prefer these people https://www.thefoamfactory.com/acousticfoam/acousticfoam.html
Wool Blankets as Room treatment
Just noticed Pendelton has some really nice wool blankets that can be hung on the wall. They even sell the fixturing. I would assume the wool blanked would have some beneficial properties for a blank wall?