Making Your Own 2D Diffusors

I've been wanting to try some diffusor panels behind my Quad 988's (to tame the back wave), but have been put off by the cost of the industry standard 2D diffusor panels. So, I've started researching making my own in a similar style. I think I've found a solution that saves roughly 75%-80% of the cost and requires just a table saw and some time to put it together.

For the purpose of comparison, let's consider the specs of the leading product. They are roughly 24"x24" in area and 6" deep, weigh 4 lbs, and comprise a 12x12 matrix of variable depth 2"x2" columns made from an made from extruded polystyrene and painted white. Based on these dimensions, and assuming an average column depth of 3", yields a polystrene foam density of 3 lbs/cubic foot.

Given my adversity to the cost of these diffusor panels ($150 each), I set about looking for a way to make their equivalents. At first, I thought I could maybe make a mold, buy some liquid pour foam, and fill the mold multiple times. However, the pour foam is extremely sticky and the mold has very complex geometry, and it would be nearly impossible to seperate the two unless you used either visquene coating or motor oil (neither of which are workable in this case).

Instead, I found a source of solid foam sheets that are cut to specified thickness and can be ordered in densities ranging from 4 to 20 pounds per cubic foot. The foam is described as "fine-celled high-density polyurethane modeling foam", and the manufacturer tells me it can be cleanly cut with a table saw, and finished with paint, polyurethane or lacquer. (Note that both the #7100 and #6700 foams are applicable). By buying a 24"x96"x2" sheet of 4 lb/cf foam for $150, one could send it through the table saw 24 times to make 2"x2" columns, and then cut the columns into various lengths (depths). A 2'x2' wooden frame could be constructed with a 1/4" plywood backboard, and the frame could be filled with the variable depth columns, gluing each one to the others with contact cement. A formula/schematic for assembling a random combination of columns (5 different depths) is available online. One could either assemble the diffusors within the frame and then take them out of the frame once the glue has dried or leave them in the frame and stretch acoustically transparent fabric over the frame to make them more WAF pallatable. In the first case, one could make 5 panels for the cost of one commercial panel, in the second case 4 panels.

All this looks good to me, and I may give it a try soon. The foam manufacturer has a minimum order of $250, which makes too many panels for my room, so I may go at the project with a fellow audiophile. Also, if you have no foam manufacturer nearby, they could cut sheets to a shipable dimension (e.g. 2'x4') and send you multple sheets. Interesting, huh?