Absorption, Diffusion or a combination of it all?

As with everything else in this hobby, it takes a lot of experimentation to get the best results. You can get a head start by hiring an experienced acoustician to come an evaluate your room and provide recommendations, but your personal tastes need to dictate the final solution. 

It's relatively easy and inexpensive to experiment with absorption since low cost fiberglass or rock wool panels can be purchased from your local home-improvement store (Lowes, Home Depot, etc.), or you can just use spare blankets, pillows, quilts, etc. 

Diffusion is a bit more challenging since good diffusors are somewhat costly. I haven't found the cheap diffusor panels to be that effective.

But once you get it reasonably dialed in, acoustic treatments provide a LOT of bang for the buck. 

I got an email chain going with Mike Major of GIK. His recommendation based on information and pictures I provided is to fill the side walls up with at least 5” thick absorption panels all the way to the level of listening chair and go as thick as possible with bass traps on the front wall. 
 

I’m evaluating all suggestions at this point as I continue the researching. 

@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.