The foil tape is about .03mm thick. What exactly is the membrane going to do that won't be done with just foil tape??

Why would it not work to just treat the corners with the bass traps without any foil for reflection but then not use any mid/high absorbers on the parallel walls.
Would this be that much different than using foil on the bass traps to reflect the highs and some mids but then having to put mid/high absorbers on the parallel walls.
It almost seems to me that what I'd be reflecting from the the foil on the bass traps I'd then have to absorb with the mid/high absorbers on the parallel walls.
Am I over simplifying things? Is it because the 4" bass traps would absorb way to much mids and highs??
Also I'd appreciate if someone could explain why a quadratic diffusor would work any better than my pvs diffusors which actually provide a bigger area of diffusion and it is actually curved to spread the sound into a broader area.

Ethan, that was very cool of you to have made such an FBM review. I just had a friend buy a bunch of that stuff. I am making some simple 4" bass traps for her cheap to compensate a bit.

Again, to the original poster, another diffusion option is the wood slat diffusor. I'm making two 3'x4' units this week using 1"x4" pine and expect they should be pretty nice.

From Steven Klein's site:

"We consider these to be perhaps the best sounding and most versatile acoustic treatment available. Though we have classified them as a diffusion product, they also have an absorption quality due to their spacing and well depth."

http://www.soundcontrolroom.com/products/diffusion/woodSlat.htm

edit: It appears I will not be making these any more. Change of plans ...

I am having trouble finding FSK without spending a lot of money. If I put a sheet of plastic (about he thickness of a trash bag) on the front of each bass trap & then put the foil tape strips on that would that be enough to reflect the mids & highs?
Would the plastic by itself be enough?

Adding plastic yourself will help to reflect mids and highs but it may not give the same improvement at low frequencies you get from FRK fiberglass where the facing is bonded firmly. A thick coating of spray adhesive might work better than tape for that.

--Ethan

Well, I went ahead and bought the FSK from sensiblesoundsolutions.com. I figured I may as well not cut any corners and then regret it later. I can't wait to get these bass traps built and see how my studio sounds. I greatly appreciate all of your help! This site is awesome.