Diffusion vs. Sound Absorption views

Diffusion actually reduces the strength of reflections off of the front wall, behind the speakers. QDR diffusers placed vertically will reflect out horizontally into the room and most QDR's need at least 6ft between them and the listener to fully form a diffused sound field. If a QDR is enhancing reflections vs a bare sheetrock wall, you probably don't have them set up correctly.  All diffusers absorb some of the reflected energy, as well.   

No problem,

Mike

Sir,
Great advice, which I think is pretty much where I am now -- all absorption.  Maybe I could send you a PM and somehow get you a photo of my living room for your opinion.  Thanks, Mark

whitestix, what you have are dipoles. Dipoles radiate in a figure 8 pattern. Very little energy goes to the sides. This actually makes them easier to deal with acoustically because there is only one primary reflection and that is off the front wall. For every foot your speakers are away from the front wall you can add 0.2 millisec to the delay. If your speakers are 3 feet from the wall that would be a delay of 0.6 millisec. This is to fast to be perceived as an echo. All frequencies are not reflected equally. This and the slight delay ruin your image. Diffusing the sound just makes things worse creating more reflections. You want to diminish the volume of the first reflection by absorbing as much as you can in the mid range and treble. Using double sided carpet tape attach two rows of these tiles from floor to ceiling directly behind the speaker. You can alternate the tiles making a nice pattern.
https://www.parts-express.com/sonic-barrier-fwp122-studio-acoustic-foam-wedge-panel-12-x-12-x-2-black-12-pack--260-547
It is an inexpensive thing to do and you will notice that your image sharpens right up. In most cases that is all you need to do. You might notice a slight change in frequency respond with less treble. In most cases this sounds more natural but the big improvement will be in the imaging.

Thanks for the comments and suggestions, a particular solid from from GK.  

@whitestix. 
The drywall you used does not “damp” the room.   In fact by reducing spurious noise from thinner, flexing drywall it provides much enhanced clarity. IMHO virtually every listening room would benefit significantly from your approach. It also significantly enhances accurate bass response :)

I will repeat my warning and caution about using QRD quadratic diffusors.  snapsc had a point about diffusors " out of phase wave interfering with the sound".  The QRD diffusors can definitely cause problems here if they are placed in certain spots.  I have had situations where some of the midrange frequencies were boosted and others were cut, making the sound completely terrible.  The QRD diffusors can also boost high frequencies to the point where it's too bright/harsh sounding.  These side affects are entirely dependant on where you put the QRD diffusor and the specific room you're operating in, so it becomes much of a test and listen exercise.

What’s really needed is a test tone such as found on test CDs, say 315 Hz, which works fine, and an SPL meter. Then, determine locations in the room where sound pressure peaks 6 dB or higher than the average sound pressure in the room at moderately high loudness. Those locations are generally where acoustic devices - panels, resonators, etc. - should be placed. Without a method for placing acoustic treatments it’s like shooting blanks in the dark. As the system evolves you should find that the locations of acoustic devices can change along with the system changes. Ditto speaker locations. It’s a fluid situation.

Conventionally, diffusion improves perceived ambiance while absorption improves imaging.


I suspect that the answer is somewhat dependent on the distance from the rear of the OB loudspeaker to the rear wall.  Why, if the speaker is too close, then there is much more of a chance of the out of phase wave interfering with the sound coming off the front...so absorption should help.Here is a brief but interesting article:

http://www.gikacoustics.com/speaker-boundary-interference-response-sbir/


I think that you can "simulate" the effect of diffusion by moving the panels out from the wall another 2-3' (not that you are going to leave them that way) which will then give you a different combination of direct sound, reflected sound and absorbed sound.

How do you know when panels are needed? I'm interested in the topic, but don't notice a problem with Golden Ear Triton 3+ about a foot from front wall and 6" from side walls. If it already sounds good don't mess with it? Tinker for better sound? Or is there some measuring equipment for this? 

Essentially 
Diffusion everywhere, particularly front and back walls and ceiling in your case. 
Absorption only where benefits are obvious through experimentation 

Since you have Spatials, why not contact Clayton Shaw, owner,
and ask the source. He is a person very willing to share. Overall
I understand absorption be best used to stop early reflections,
ie in front of speakers on side walls and ceiling. Diffusion best on front and back walls.

I am keen to check out this diffusion aspect of sound treatments, as I have a remarkably dampened room (two layers of 5/8" sheetrock with Green Glue in between and several sound panels behind the speakers, and thick carpet in the room.)   I have a long narrow room (13x26x9) with the speakers on the long wall, about 3' from the wall, and I sit about 10' away on a sofa against the rear wall.  Not an ideal setup for sure, but I am working around the edges with what I have.  
If diffusion enhances the spatiality of the sound, then I am interested to explore this aspect of my system.

I listen to about 98% jazz, of the straight-ahead variety.  Miles, Coltrane, MJQ, Brubeck, Desmond and most significantly Stan Getz. 

On a basic level - high frequencies add sparkle and life to music even to those listeners with diminished high frequency hearing. With that in mind I suggest diffusion should be your first priority and when you feel you’ve done a decent job of it then limited absorption behind the speakers as you find provide enhanced detail and depth to your sound. What types of music do you listen to most?

I have found GIK as recommended above, to be a good reasonably priced source for acoustic panels.  I installed them in our previous house and plan on using them in our new one.

If the application allows, I prefer the aspect of free-standing/movable panels not only for initial trial placement purposes, but also for present and future flexibility.  In fact, GIK just sent a flyer out last week mentioning their new "Panel Foot Kit" that will turn almost any of their products into floor standing/movable ones: http://https//www.gikacoustics.com/product/panel-foot-kit/

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. 

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.