Questions about my home-made diffusers

I am in the process of making diffusers for the back wall of my HT. Here’s what I’ve done so far: I’ve taken 4 foot long sonotubes of different diameters – 8â€, 10â€, 12†– split them lengthwise and attached them to plywood backs (4’ long X 8†wide for the 8†tubes, 4’ X 10†for the 10†tubes, etc.). I now have several different sized hemi-cylinders. I know that cylinders aren’t the ideal shape, but I just want to break up the slap echo from my rear wall. I plan on capping one end and filling them with either fiberglass or possibly something denser and hanging them vertically along the rear wall.


Here are my questions:


First, how should I finish them? I would love to just cover them with corduroy cloth (or even felt) because it would look good and be easy to do. But would corduroy be too absorptive at certain frequencies, defeating the effectiveness of the diffusers? I could just paint them which would leave them highly reflective but painted cardboard has a low WAF (the wife is already very tolerant of what I do in the HT – I don’t want to push it). Any ides?


Second, is fiberglass OK as a filler? Loosely or tightly packed? Would something else work better? The way these are coming together, I may end up with both diffusion in the mid and upper frequencies and some bass trapping in the low end. This design is actually very similar to the home-made bass traps used in some studios, except cut in half length-wise. Getting both effects would be great, but the diffusive properties are the higher priority.


Please help.


Thanks


PS to Mr. Bott: I'm going to post this over on the HT Construction forum, too. I hope that's OK.