How high in frequency is diffusion necessary for normal rooms?

[thadman]

I'm constructing some Quadratic Residue Diffusors (for diffusion of course) and was wondering how high in frequency the critical bandwidth of diffusion extends, wherein the most improvements are to be yielded.

The wells are recommended to <1/2WL of the highest reproduced frequency,
for <5khz that'd be 1.34" wide, for <20khz .335". The higher up in frequency, the more labor intensive (significantly more so when you're working with 3D diffusors, wherein you'll square the number of wells).

How high? 5khz? 10khz? 20khz?

[Ron E]

I wouldn't go any smaller than 1" or 3/4", for practical reasons. I am guessing that a slight angle or faceting on your "faces" would take care of higher frequencies if you are really concerned.

Are you making a 2D or a 1D absorber? Obviously the object is 3D, I am asking if you are determining quadratic residue on one or two dimensions along the plane of the wall.

When I get a house, I really want to make a 2D QR wall as an art piece....

[cuibono]

If you haven't already, look up jon risch's posts on audio asylum. He has a lot of good info on absorbers/diffusers, and a website with lots of info/recipes. Last I looked, people on the AA board were saying strategic absorption is more useful than diffusion.

My take on room corrections is that you want them to be very even in absorbtion/diffusion across the frequency range. I don't know how this would relate to a QRD though. Try looking around AA..