QRD diffuser question

[Milkduds]

I am doing some sound treatment upgrades to my listening room and plan to build some QRD diffusers. Is there a sweet spot for which prime number to use? I know the diffusers get more involved as the number increases. I kind of like the QRD with 11 wells but I'd like to know more about the major differences and if it's worth higher numbers. My room is about 16 x 30 so it's pretty large compared to many home listening rooms. I'm already doing plenty absorption panels on the walls and ceiling, 8" on the walls and 4" on the ceilings. I can go up to 8" deep for the QRD diffusers which seems to give a pretty wide diffusion range with 11 wells.

Also, is it best to install the QRD diffusers on the wall at first/secondary reflection points?

Thanks,
Milkduds

 

[Horneydude]

Also, is it best to install the QRD diffusers on the wall at first/secondary reflection points?

Without knowing more about the room (in respect to windows, doors, speaker placement etc.) it is not easy to give specific advise. My experience is that diffusers on reflection points can work, as long as they cover the important midband, say 1000-5000 Hz. You will need multiple panels side by side, just one 11 wells diffuser won't do enough. Also on the back wall, or in front between the speakers. You may find some pictures on the internet. I found it beneficiary to also have diffusers left and right of the listening spot. You may combine diffusing with absorption mixed together at the same spots. Keep the left-right symmetry if possible. Diffusing at the ceiling reflection points combined with absorption above the listening spot may also be a good idea. Ultimately, you will have to experiment with different placements of diffusers and absorbers, shuffling them around and taking notes.

 

[EmSuppSW]

I found it beneficiary to also have diffusers left and right of the listening spot.

I've done tests with polycylindrical / curved surfaces placed on cross reflection points to maximize the effect in time domain, ie. diffusing/scattering the first reflections that takes the longest path in my small room. Although polycylinders are not actual diffusers the principle can still work with QRDs and BAD/GUD panels etc..

 

[Milkduds]

Thanks for the help. I looked at a brand of poly cylindrcal diffusers but I think's more cost effective for me to build 4 QRD 13 diffusers. I have the math down for this. Approximately 25"W x 60"H x 8"D Range is about 400 hz to 3900 hz. I can move around to various walls.