I think i've got just what you're looking for. You can thank Russ for turning me on to this. Look up Audimute accoustic wall treatments. They're like moving blankets, but theyre designed to be hung from the wall to deaden the room.
They come in a variety of sizes, and are very reasonably priced. I've heard the clips arent really worth bothering with. I just nailed mine to the wall... They're designed for exactly what you want, and they work brilliantly.
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