Reading @elliottbnewcombjr's post and looking at his photos reminded me of this rather old site, Mother of Tonehttp://www.mother-of-tone.com/index.htm. It deals with vibrations and materials that carry them.
They sell, as well as instruct on construction of, birch wooden panels treated with organic lacquers that have favorable vibrational qualities pleasing to the ear. There's also a section of room acoustics that might be worth a read that goes contrary to some of what's been posted here.
Here's a shot of the owner of Audiovector's room and the treatment of the front wall:
Posting this had my muse whisper in my ear that something as simple as textured wallpaper can do wonders for reducing echo and reflection, which may be all one needs for their room. Just more food for thought.