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Diffusion vs. Sound Absorption views

I have Spatial Audio M4 Triode Master open baffle speaker in my listening room.  I have sound treatment behind the top of the speakers with sound absorption panels hung on the wall and an Aurelex foam panel down to the floor. 

It was recently brought to my attention that sound diffusion panels behind the speakers might yield an improvement in SQ over the sound absorption panels.  The advice I got is that OB speakers benefit more from rear wall sound treatment with diffusion rather than absorption.  I put the issue to you learned folks for advice.  Thanks. 
whitestix
three_easy_payments's avatar
three_easy_payments
2,097 posts
 
Lately I've been incrementally adding more acoustic treatments to my room and have been discussing my objectives with GIK.  I'd suggest giving them a call (or probably other similar outfits) who really are the professionals and are very helpful in real time.  For me, some of their most effective single products treat through both absorption as well as diffusion.
auxinput
2,920 posts
 
Agreed, in my experience both absorption AND diffusion was needed.  However, I would look at people who have specific experience with open baffle speakers.  You can try use diffussion panels behind the speaker, but make sure they are generic diffusion, such as an array of pyramids or a convex diffuser such as the GIK Evolution PolyFusor.  I would highly recommend NOT using a quadratic/QRD diffusor right behind the speaker.  The QRD diffusors can do weird things to the phasing of sound waves if they are so close to the speaker or the listener.  A QRD diffusor could work well on the front wall in between the speakers (as long as there is good distance away from the speakers) or on the back wall.  However, I have found that each room is different and I had to experiment a LOT with placing QRD diffusors.  Many locations of the QRD diffusor made the sound worse. 
bdp24's avatar
bdp24
9,747 posts
 

Diffusors behind dipole/planar loudspeakers are preferred to absorbers by many, though not all, owners of such speakers, for a couple of reasons. Too much absorption can result in a room overly "dead", but that’s true no matter what the speaker design. But since dipoles put out as much sound from the rear as from the front, diffusors behind them creates more depth (detractors claim it is false depth added to recordings containing no such depth), and a "bigger" sound, which is one thing planar lovers like about them.

@auxinput makes a good point about the distance required for diffusors. Not only between the absorber and the speaker, but between it and the listener. A couple feet to the speaker and 6’ to the listener, minimum, is a good rule-of-thumb. Do call GIK, they will provide you with excellent advice. I’ll soon be installing a set of their Gridfusers on the wall behind my planars.

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