Room treatments

Two areas where I had great success are

1. Behind the listening position I installed an 8ft vinyl blind that dropped down only 15 inches

2. On top of a book case (close to the listening position) placed a layer of 1" foam with a thick layer of vinyl on top

Those two stoppers the bulk of reflections issues I had in that room and were pretty affordable and quite invisible (the blind was behind some drapes

Turns out vinyl is one of the better materials for converting sound into heat

@masterplan - another product I have used with great success are the 2' x 4' vinyl faced fiberglass ceiling tiles used in drop ceilings.

I created a 4" thick "brick" (about 6-7 tiles) with the vinyl sides facing out.
I covered the brick with black landscaping felt to prevent  the little glass fibers from falling out.

I placed the brick under the sofa and at the back of chairs (we had hardwood floors) but if you have carpet then they would probably not be required.

You can also use them behind canvas pictures for additional damping effect.

Just use a sharp carpet knife to cut them

Regards...