[dsrviola]

I have read that diffuser needs space for them to diffuse the sound. So diffuser are not good for rear wall that is right against the listening sofa. I have a small room (12x20) with sofa right against the rear wall and im thinking, what if i install the diffuser above my head on the rear wall so that the diffused sound gets in the center of the room?
I am looking for difusser because i have read it can make the room sound larger.

ASC makes a panel for this. http://www.acousticsciences.com/matrixpanel I've never used it, but have had good results with a number of their other products. YMMV

[bulldogger]

In small spaces, the only ones that I have found to work are the RPG Skyline type, Two Dimensional Primitive Root Diffusor. In my 24ft by 17ft space, QRD was a waste of time. QRD diffusers made me questions whether diffusion was worth the effort. Absorption seem to be more effective than QRD. However, when I added RPG Skylines, the difference was much greater. I believe you need a large space for QRD type diffusers to work well.

[DTB300]

I have tried EPS type diffusers in my small partial basement - first reflections, front wall, back wall, side walls, etc. and never was totally satisfied with the sound.  It was just a change in sound, not a great improvement in sound quality.  I attributed this to being too close to these items - either me or speakers.

So I tried out some RPG BAD Flat and RPG BAD Curved and these produced much better results - in MY ROOM.  Yes the sound changed, but for me and my tastes the room changed for the better and not just a change.

I never got the chance to try some LP (low profile) Skylines.

[bpape]

Pure QRD type diffusers do have a limit of how close one should sit based on the low limit of the diffuser in terms of frequency.  BAD panels are a different type, not QRD.  We have something similar with our Scatter plate option and it does not have the distance limit.

The one thing I have found with diffusion at the side reflections is that it is more a function of how good the off axis power response is on the speaker one is using. If not good (and many expensive speakers are not terribly good) then absorption is a better answer IMO.

I don't find room size a determining factor as much as the above and how far you're sitting from the diffuser if a QRD.  You can get plenty far from a QRD for instance behidn a Magnepan, side wall reflections, high on the walls to help with slap and flutter, etc.  Just not likely directly behind you.

Bryan

[Speedskater]

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The one thing I have found with diffusion at the side reflections is that it is more a function of how good the off axis power response is on the speaker one is using. If not good ***********  then absorption is a better answer IMO.

**************
Bryan

By 'not good', do you mean in a uniform frequency response sense?  Or do you mean very directional as opposed to omni-directional?

[bpape]

more in terms of frequency response

[DTB300]

Pure QRD type diffusers do have a limit of how close one should sit based on the low limit of the diffuser in terms of frequency.  BAD panels are a different type, not QRD.  We have something similar with our Scatter plate option and it does not have the distance limit.

The distance from either me or the speakers is my issue - small room, gobs of room gain, tons of reflections, long decay times.   

As I tamed down the reflections and decay times, it also effected the high end - too much absorption.  But having less absorption, my decay times went back up.   So something like the Scatter Plate or the RPG BAD in front of an absorber (244's in my case) kept the decay times down, but helped bring back the highs.

I tried to buy just the scatter plate from you/GIK but they are not available unless I buy a panel to go with it.  Since I already own a bunch of 244's I did not need any more panels.   

The one thing I have found with diffusion at the side reflections is that it is more a function of how good the off axis power response is on the speaker one is using. If not good (and many expensive speakers are not terribly good) then absorption is a better answer IMO.

I have tried both absorption/diffusion at first reflections, and in my room and my setup, I prefer absorption.  I have even tried the BAD panels (both types) at first reflection and still preferred absorption.

I don't find room size a determining factor as much as the above and how far you're sitting from the diffuser if a QRD.  You can get plenty far from a QRD for instance behidn a Magnepan, side wall reflections, high on the walls to help with slap and flutter, etc.  Just not likely directly behind you.

I agree, it is distance from the QRD and not the size of the room.