Absorption, Diffusion or a combination of it all?

@jpan , @audphile1 Thanks for your feedback.

Floyd Toole did listening tests to determine if listeners preferred absorption, diffusion, or bare wall at the first sidewall reflection point. 

Diffusion and bare wall were the most preferred....with absorption by far the least preferred for sidewall first reflection. Going off memory only like 14% preferred to absorb sidewall. 

Why do so many people recommend absorbing sidewall first reflections? It has to do with pro-audio rules of thumb and advice given by acoustic product companies such as GIK.

Pro-audio wants as much direct sound as possible, to take the room out of the equation....basically a headphone type experience with speakers so their mixes with translate. 

Hi-fi uses the room to enhance the experience. That's why we don't listen at a desk or shove our speakers up against the wall. 

Having said that, very close sidewall or close behind our head reflections can be very destructive and smear the sound...as long as we have some space though, our genius brains can sort out the direct sound from the indirect sound and we get this really nice ambiance or reverb without the smearing.  

Experimented today with all the panels (GIK 242) except bass traps leaned against side wall at first reflection points. It helped with better focus, imaging was more precise and the soundstage deeper and wider. Front wall was bare. 
I think it depends on the room size. Diffusion may work combined with absorption in my small room. If the room was larger it’s possible the diffusion alone would be fine. Not sure. I’ll need to try. So far I think Mike Major is on point with absorption. 

I see advice all over the map here yet nobody condsiders the size of the room? It's not one size fits all!

OP, diffusion is great but unfortunately not of much use in a small room simply because you need to be seated a minimum distance away for the effect. Situated close to your ear will just not do.

My suggestion is to at least heed the advice to measure the room yourself. That way you can ignore the noise being made about creating a room that is dead.  It has been mentioned to get GIK to 'analyse your room' and then buy their products. Well they are in business to sell stuff and will, as has happened to some I know, oversell if you keep buying. 

To measure: Install REW, it's free

Buy a microphone: for the cost of a dinner.

This will provide the tools to achieve the ideal response in your particular room. Tables online will supply the target time required for the sound to decay, across the spectrum by a certain amount, this amount also found in the tables.

What I can assure you is that with the confidence you gain with understanding the requirements for treatment, and can measure any changes from adding traps or panels, will be the biggest step towards an immersive and realistic sound. Ideally the treatment will essentially largely remove your room's sonic imprint and transport you to the venue.

No electronic component exists that could correct the acoustics of a room regardless of cost. The recommendation to 'just get DSP" to sort out the problems can not sort out the damage that strong early reflections cause. How can any electronic gizmo know how much decay to apply and at which frequencies to apply it?

Should you hire 'professionals' to do an installation you can of course measure the results to ensure they do not reduce the decay time beyond the recommended time, which is generally 300 to 400ms. Overdoing the absorption is what renders the room being too dead. You newfound skills will allow you to prevent this.  It will also help you find the best position for the speakers and a sub or three.    😀

The subject is fascinating, understandable and most importantly, essential for great sound. I repeat:  No $5000 cable nor $10000 amp can do anything to tame the elephant.   But you can  😎

Love this topic as it’s not as common but extremely important.  Working with the folks at GIK (or other acoustic expert) is key.  REW has been a very helpful tool along with my ears, and the USB mic was a worthwhile investment as I’ve used it multiple times over my three year journey in treating my room.  I cannot recommend it enough. And the GIK folks will use those REW measurements to help diagnose your room and suggest treatments.  My listening chair is only 2’ off the back wall so pure diffusion wasn’t recommended.  I’ve read elsewhere that pure diffusion on the back wall isn’t beneficial unless your listening chair is 6’ or more away from it.  GIK  instead suggested their combination diffusion/absorption Alpha series panels, as I had low frequencies that needed to be tamed along with me trying to make my room sound bigger,  My last and final addition was adding 3 x Q7D diffusers to the front wall and a pair of wall hung monster bass traps directly behind the speakers.  My small square room has never sounded better.