So, there are a million designs for acoustic panels, but I made one today that (at least I think) turned out pretty cool, so I'd thought I'd share.
This is a pretty big panel - its a 1x6 frame with 4" of 703 in it.
I used some small pieces of wood to provide a backing for the 703, which by default helped guarantee a small (1.5") air gap "built into" the panel when its hanging (should help the low end out a bit).
The sides that are covered aren't red oak (like the top and molding). They are just stock wood (aka cheap!). I used a jigsaw to cut out some rough rectangles in between the back supports. This helped cut down on weight, exposes a few more feet^2 of insulation, etc...
The molding is 1" outside corner molding. It only covers where there is already wood, so it shouldn't have an impact on reflections. I couldn't figure out to miter the "tri-corners", so I just did them as shown. They look OK, but if anyone knows a finish carpenter that is good on angles... My miter saw only rotates L and R (blade doesn't tilt), so it may be near impossible on mine. I used paneling nails instead of finish/brad nails, because I wanted the look of the little dots (which turned out to be a pain, since red oak really doesn't like accepting weak little nails...)
If anyone has any interest, I can provide more specific construction details. (Same thing for my gobo - My DIY Gobo
Its pretty cheap to build, especially since the only good wood is the molding + top/bottom.