In most rooms a combination of absorption and diffusion will result in the most pleasing acoustics. Too much absorption can result in a dead sounding room which is not pleasant to be in, let alone listen to music in. GIK website has lots of info. Their SlatFusors combine absorption and diffusion.
Alternative absorbent acoustic material?
I finally read the owner’s manual that came with a pair of speakers I bought last spring (Revel M126Be) and there is a a couple of paragraphs that talk about treatment materials. Revel states that: "There are numerous options for absorbent material. None are superior to low-cost fiberglass." And it goes on to say that "It is important to use absorbers that are at least 4 inches thick, to avoid altering the spectral response of the loudspeakers." It also says that "Sculpted foam is less efficient" and needs to be "at least 8 inches thick."
I assume that the low cost fiberglass that Revel is referring to is the insulation that comes on a roll that is available from, for example, Lowes? Has anyone tried this, and if so how did it work out?