Window Treatments to Remove reflected sound

Wood slated blinds work better than metal but are very expensive. Fabric blinds/carpets/curtains - heavier the better.

If you get curtains, err on the "too much fabric" side. The more folds the better.

I have a related question. Anyone know how to treat "ringing" of large pane windows. I've got a 48"x56" double pane that rings, becomes excited at various voice frequencies. Man, they don't make windows like they used to (thin glass for double panes).

I have what you are referring to as "celluar" blinds behind my listening position. (It covers a large bay window, and two smaller windows, at the side angle points, behind the couch.) BTW, I refer to them as "black-out" blinds, since that is why they have the "air pocket" that you mentioned. It keeps the light from coming in and messing up the picture on the RPTV on the wall opposite of the bay window.

They seem to work very well, IMHO, as it disperses the sound pretty well, and I don't get much in the way of sound reflections from the rear.
(Whether this is the perfect solution, from an accoustical standpoint, I am not sure. But since it does not add rear sound reflections to mess up the imaging and soundstaging from the direct sound coming from the speakers, I am okay with it.)

Perfect? Probably not, but since I am constrained by the old WAF, I don't really have a choice.

My two cents worth anyway.

Good Luck!