Front or Back wall diffusers

I would be embarrassed to show a picture as my room is such a cluttered mess (free diffusion, right?). 

Here are some good diagrams. https://www.audioholics.com/room-acoustics/room-acoustics-acoustic-treatments/room-acoustics-acoustic-treatments-page-4

I made a lot of treatment mistakes until Michael Green Audio started saying things in the forum here that got me curious....he was right so I started digging deeper. I discovered the Anthony Gramani video series on the Audioholics YouTube channel during covid times. I followed his advice and it was GOLD for me. So now I just pass on what worked for me and warn people about what didn't work for me (mostly conventional wisdom from pro audio).  

Talk to GIK.  They’ll give you some good advice given your room and offer products that are relatively reasonably priced. 

IME GIK has great products that I purchase....but their advice has been the same as other pro-audio panel makers...and thus bad for hi-fi....which is to load the room with absorption and create a dead room with low reflections....making the room sound smaller and closed in.

With hi-fi, you don't generally want to absorb the first sidewall reflection unless your speaker is very close to the sidewall...this was first discovered by Floyd Toole during the Harmon listening tests that determined preferences. 

It is recommended that the wall behind the speakers be reflective in nature, so that the sound develops properly. 

The wall behind the speakers is a distant reflection for most frequencies with box speakers...especially if you have a long room...so it's generally a lower priority...but diffusion on that wall will create the illusion of more depth and space...which is a cool hi-fi trick. 

Leaving the wall behind the speakers reflective as an optimal strategy? It could be a personal preference but acoustical engineers will tell you to at least break up or scatter large reflective areas...in addition bass traps behind the speakers can help with SBIR.  

@seanheis1 @axo0oxa I’m seeing several people here advocating for diffusion over absorption.  Are there any general rules as to when/where it’s better to use diffusion or absorption?  I’m very interested and not clear on this at all.  My guess is it’s largely room, system, and personal-taste dependent, but just wondering if there are any generally accepted rules on this.  Also surprised someone argued against bass traps that I’d never heard before and had me scratching my head a bit.  Thanks for any thoughts and/or hard-won personal experience. 

General rules? You asked ;-)

1. Leave the first sidewall reflection untreated or diffuse it. 

2. Don't create a row of just absorbers or just diffusers. Leave space between treatments. 

3. Rotate between diffusers and absorbers every other or use hybrid treatments. GIK has scatter plates that go on top of absorbers.

4. If you have a wall right behind your head use a 2 inch absorber there.

5. If you want your room to sound hi-end, diffusers with deep wells is the secret.

6. Scatter plates will preserve precious high frequency energy and help prevent dead room effect, but they aren't a replacement for diffusers with deep wells that diffused midrange frequencies. 

7. The strongest reflection in most rooms is the reflection that pings behind your listening position and then to the front wall...and it will keep doing laps so you need to either diffuse or absorb it. 

8. The best bass trap is free. It's the air gap behind a bass trap which should ideally be the same as the thickness of the bass trap. 

9. The only full range bass trap I know of is an open window or possibly an open door (depending on what's on other side of door). I'm lucky to have a door behind my listening position so I keep it open and my room sounds so much more open and the bass more even compared to when I close the door. 

10. Argument against bass traps? Bass boom can be fun...when the room is excited and ringing it can be thrilling...especially if you're a teenager. ;-)  

Thanks for sharing I think it's sound advice. I have never heard of a bass trap making a space feel larger...for me traps make my room feel smaller and more intimate. 

I have also never heard of putting diffusion directly behind a speaker. My thought is that the frequencies that wrap behind the speaker are too low to be diffused. 

All that matters is that it works for you and you're getting good sound. ;-) 

Also, about 6 years ago, when drawing the original plans for the house of stereo, GIK told me that the front wall should be addressed last if at all. Just saying.

@baylinor GIK told me the same thing as it's the furthest reflection point for anything but bass. And I agree that audiophiles like to look at diffusion on front wall, especially Gotham diffusers.

However, the real disconnect is that GIK is pro audio and we are hi-fi. Diffusion on front wall will add depth and space to the sound stage...a nice hi-fi trick. Pro audio does not care about that. They want flat frequency response and to fight SBIR...so they will build their speakers into the wall or put them right up against the wall in a small mixing room.  

The main difficulty with setting up diffuse panels are you do not want them too close to your listening position. Six feet away is the minimum and at least eight feet away is the preferred. 

@axo0oxa 6-8 feet away for diffusion? To diffuse lower midrange absolutely yes...and you would need a well depth of like 6-10 inches as well. 

Most of us don't have that deep of wells or really deep poly diffusers that can diffuse lower midrange frequencies. Kind of the same challenge as "trapping bass" below 80hz...the panels have to be impractically thick. 

So most of us aren't diffusing lower-mids to begin with, even if we sit far enough way.

Scatter plates don't really scatter below the upper mid-range/lower treble but they still have benefit...they preserve higher frequencies by not allowing them to be absorbed into the foam or insulation that they are attached to. Scatter plates are a very smart way to prevent a dead room and still get low end absorption. 

A lot of us have quadratic diffusers and skyline diffusers and maybe some cylinders that are 4-7 inches deep. Again not going to do much diffusing in the lower midrange but still they are covering quite a bit of midrange...much more than scatter plates and they still diffuse, even if you're 5 feet away from them...though maybe you won't get diffusion at their lower limit if you are sitting too close.