Hi Ethan, i have read your work and respect it alot. Really helpful for newbie and i send every neophyte at your site.
I would like to know your acoustician point of view over this diffusor:
http://www.pmerecords.com/Diffusor.cfm and realtraps diffusor. Of course, realtraps diffusor look alot more professionnal.
So my question is : Since diffusor are placed more in the middle of wall, is it really that helpful to have bass absoption there(since it must have a layer on the absoption part to reflect mid(and high) frequency(it's a diffusor after all), witch let only the low frequencys to be trapping).

thx you for your answer

Yes, that looks like a legitimate QRD type diffusor, so it should do a good job at mid and high frequencies.

While corners are the first place to put bass traps, the rear (and front) walls are also very good. Sound from the speaker passes you, then bounces of the wall behind to create peaks and nulls. So the entire rear wall is always a good place for bass traps, and the front wall is good too to reduce the length-mode resonance.

--Ethan

thank you!