manning1,

foam carpet pads are not actually very absorbent - mostly closed cell foam. Open cell foam works better. Auralex makes pretty expensive stuff, but there is a knock-off company in Michigan that has similar products for a fraction of the price.

http://www.foambymail.com/soundproofing.html

Another cheap way to go is to find the used office furniture outlet in your area - find out if they are selling any of the old cubicle partitions that normally have quite high absorbent properties. If they are ugly, cover them with some light, decorative breathable fabric.

-Scott