Front or Back wall diffusers

I would start on front. If you are set up along the long dimension, then the rear wall will be less important. My rear wall is pretty far back and I have book shelves there. That has given the biggest gains. Then sidewalls. You can simulate with heavy blankets or carpets.

As a general rule I like absorption right behind the MLP on the back wall and diffusors to the L and R of the absorption. Try front wall first.

It is recommended that the wall behind the speakers be reflective in nature, so that the sound develops properly. On the contrary, the wall located behind the listening position should be absorptive, so that the rear reflection of the sound does not interfere with the perception of the stereophonic image.

It is recommended that the wall behind the speakers be reflective in nature, so that the sound develops properly. On the contrary, the wall located behind the listening position should be absorptive, so that the rear reflection of the sound does not interfere with the perception of the stereophonic image.

Weird how you seem to answer your own question.

This is my point of view and it makes sense, but other people think differently and have diffusers on the rear wall. I would like a greater consensus and be sure to get the best result.

@avl1947 

I use Anthony Grimani's acoutic recipe and have pics posted in my profile, see the diagram below. He uses combo panels on the front wall and you can see how he stagers treatment on the backwall:

Example of a combo panel:

https://www.amazon.com/Absorption-Diffuse-Acoustic-«Pulsar»-rec-studio-laminated/dp/B07LFKTJB6/ref=sr_1_26?crid=2N19LG1S1XJ00&keywords=diffuser+acoustic&qid=1689370084&sprefix=diffuser+acoustic%2Caps%2C242&sr=8-26&ufe=app_do%3Aamzn1.fos.f5122f16-c3e8-4386-bf32-63e904010ad0

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

It is recommended that the wall behind the speakers be reflective in nature, so that the sound develops properly. On the contrary, the wall located behind the listening position should be absorptive, so that the rear reflection of the sound does not interfere with the perception of the stereophonic image.

 

Weird how you seem to answer your own question.

@avl1947  I agree with you. Absorbion behind the listening position. I'll add that the corners of the front and side walls will often need bass traps or absorbion panels. This not only controls bass, but helps create and shape the soundstage

Without more info, you only will receive useless advice. Need to know speaker position, listening position, etc.  

@avl1947 

It's obviously room dependent. In mine diffusers/absorbers on back wall and diffusers only on rear of both sidewalls. Also diffusers at first reflection points on sidewalls and absorbers right next to them on second reflection points. Plus diffusers on ceiling between listening chair and speakers. Hardly any diffusing on front wall specially since speakers are 54" from front wall. I believe many audiophiles put diffusers on front wall because they like to look at it. To each his own. I go strictly for sound. You questioning the matter is smart. You can see most of my acoustic setup on my house of stereo system. Enjoy the journey.

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.

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.

That's interesting. After I fully treated my room I noticed that my music wasn't very lively and imaging wasn't very good. I began to remove panels from the front wall and the more space on the wall, the better it sounded. Now I have no treatments on my front wall and music sounds better than I could have hoped for. Listening to large scale classical I'm experiencing a wide 3D soundstage with concert hall ambience. 

That's a generous sized room. The main thing to remember is you are treating a system that consists of the speakers, where they are in the room, and thus how the acoustically load the room, and the room characteristics themselves, including all walls ceiling and floor. No one wall or surface is more important than any other except for two things: 1) Controlling first reflections on the side walls and ceiling. 2) Bass traps are different, as corner placement is far more effective.

Acoustics isn't opinion, it's applied math and physics,  and it's pretty well documented and computer modeled at this point. A room of your size will require somewhere between 100 and 140 ft2 of 2" acoustical panels between the 4 walls and ceiling, plus 2-4 Bass traps. Figure $12-15 per ft2, installed for 2'X4' panel or around so maybe $2500 all in, depending on your choices of fabric and local labor rates. The panels aren't hard to DIY install, but it's definitely better with 2 people and appropriate ladders. A pro will also use a laser to make sure panels are installed square and level.

Take your time, do the math and enjoy the results. You'll wonder why you waited so long. 

A room of your size will require somewhere between 100 and 140 ft2 of 2" acoustical panels between the 4 walls and ceiling, plus 2-4 Bass traps.

Without knowing more about OP's room -- wall materials, rugs, furniture (especially couches, etc.), windows, etc. I'm not sure where in this estimate his room falls, indeed if it falls within this range at all.

No disagreement that doing the math is important, but the math can only be done if as much as possible about room contents and materials is known, first.

GIK and companies like that need to sell product. Yes they analyze your room but they are going to try to sell you as much as they can too. Most of the people on 

Oops! Most of the people on this forum have the means to consult a professional acoustician and I am surprised most don’t. Jeff at HDacoustics is very good and will analyze your room and tell you what is needed and where to put it. He has vendors he works with as far as panels go but he doesn’t push you to purchase. You can use his design and go from there if you want. Good luck! 

That's really a loaded question. There are endless variations, opinions, rules and suggestions to treating a room. I used all the above when treating my room but ultimately it came down to what sounded good to my ears and not so much following the rules to the letter. Start small and focus on treating your room to improve sound quality, not to look cool. 

Just load up the room with a couple dozen 5’ - 6’ artificial Ficus trees. They are cheap and very effective. Use along the walls, between the speakers and alongside and behind the listening position.

Ficus! Yeah...or go with furniture like I do...I like my "room sound" and no, you can't come over and hear it.

You have a very nice system.  If you diffuse the front wall between the speakers they will image even better which is really saying something.  The idea of diffusion is to scatter the signal so the reflected sound doesn't return to the listener as a single competing signal.  You don't want a second signal competing with the direct signal from the mains.  As a rule of thumb one cannot over diffuse a room so you can be aggressive with the amount of area the diffuser covers on the front wall.  If you diffuse the front wall and use bass traps in the corners the DAWs will really sing.  Good luck and Cheers

This is my back wall, I have absorption panels just below my on wall slim subwoofer. To the right you can see the Auralex Pyramid Sustain diffusors which are back filled with polyfill so they double as bass traps. It doesn’t have to be either or. In this pic you can’t see the treatments to the left of the sub but it alternates, absorbers to the left of the sub, then diffusors, then absorbers, etc.

As others said, every room & system is different. There are no cookie cutter rules. I personally do the following:

Diffusers in the front and back wall. Depending on the distance from the back wall, the impact they have there is bigger. My diffusers are actually combination diffuser absorption and bass trap (GIK Alpha 6” and 4”)

Absorbers and diffusers (a mix of them two) in side walls and ceiling. Lots of experimentation needed. Actual work. Listening and REW measurements. There is no free lunch.

Base traps in both front and back corners.

In my opinion and experience, the coverage area is important. You cannot just slap a few panels here and there and call it a day.

‘Good luck. Lots of work but rewarding at the end

To add my 2c’s.

I have 7 Stillpoint Apertures 2’s, they claim to provide absorption, diffusion and reflection.

2 are in the front between the speakers (see my system page.)

2 each on each side wall (4 total) at first reflection point.

1 behind my listening position.

4 ASC tube traps in the corners.

And a couple of absorbent panels behind the speakers.

ozzy

The need for acoustic treatments is room dependent and I just share my experience for whatever it is worth. Three critical elements are (1) diffusers on front wall, (2) bass traps on both corners and (3) the distance between the speaker tweeter and front wall. (3 ft as a rule of thumb) As a gentleman mentioned earlier, you do not want the reflected signal be perceived as a direct signal and mess up the image of sound. If you need to place speakers closer to wall, some form of absorbers (like curtains I used) behind the speakers is also recommended. As far as the back wall is concerned, if your sitting position is cleared roughly 1/3 of the room from the back wall, the treatment behind is less critical.  Lastly, do not overdamp your room!!

if your sitting position is cleared roughly 1/3 of the room from the back wall, the treatment behind is less critical. 

Do you know how long bass waves are? You must be referring to a castle.

yes, it can still have standing wave, nodes, etc., issues in the bass region. I apologize for the misspoken.

If we are talking front wall I would say floor to ceiling bass traps in the corners are first step. If we are talking back wall I would say absorption behind MLP is first step. Then you can experiment with diffusion. 

I would agree in that trend of treatment. The most benefit I have found in my room is from the bass trap.  I have high ceiling (10 ft) and also the WAF so I did not install the bass trap all the way but the immediate sonic improvement from only the back of speakers is noticeable, less reverbration and cleaner vocals.  

Which walls are the front and back. 14ft or 24ft ?

Do you have windows on any of the walls ? 

Floor to ceiling bass traps as others suggest , then in my opinion buy 2 @ 2X4 2" thick absorbers  and 2 of the 2D or curved diffusers , then place them in the front middle and side walls , then swap them . this is the only way to determine what sounds best to you . Then you can add more as needed or wanted .

One thing that hasn’t been brought up is measurements, if you measure it helps confirm your choices. You don’t have to get "technical" to measure. I got a PW Link preamp from paradigm with ARC room correctionfor$199. I use the digital out from the Link into my dac, and presto, check out the before and after. The before graph is already pretty tight because of my room treatments, ARC just dialed in for that last bit of OTT clarity:

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. The two biggest issues center on the size of bass waves and the distortion of early reflection points. Diffusion of sound using panels is a luxury most people do not have due to the distance requirements. I use two 3D diffuse panel behind my speakers, on the front wall. I sit too close to the rear wall for them to be of any help, so on the rear I use absorption panels so I slow down those reflected sound waves and give the room an illusion of being longer than it truly is. The diffusion panels on the front wall help distribute the sound bouncing off that wall so it becomes even more delayed before it reaches my ears. The idea is to delay and scatter the sound waves around the room.

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. 

@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. 

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.  

Diffusers at first reflections on side walls and ceiling. Also wall behind listening position.   This works for my Sashas 

@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. ;-)  

@seanheis1 

Can you please post pics of your own setup as an example of your general rules? Thanks

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).  

@seanheis1 I think I may speak for many here that we care a lot more about sound than clutter, and since a picture is worth 1000 words I think many here (including me) may benefit from seeing what you’re talking about.  But, if it really makes you uncomfortable please just disregard. 

In some recording studios they go with a dead end / live end design approach. This is absorption behind the speakers and then extending it along the side walls approximately halfway down the rooms length. The last half is treated as reflective as it the rear wall. I've experimented with this design and found it killed the sound. The room became too dead and the music lost too much of it's liveliness for my taste. You however could hear all the fine detail within the music very easily which is what you would want when mixing music.

Someone up post mentioned keeping the side walls live as opposed to dampening them. If your speakers are not too close to the side walls this is a better approach than just dampening them like everyone else does. Those first early reflection points are typically treated for absorption because in most cases people have smaller listening rooms and cannot hold there speakers far enough off the side walls. If you do diffuse the side wall make sure the distance to your listening position is greater than 6 feet. The key is to stop the really early reflected sound waves. Those really early reflected sound waves are the ones that create distortion. There is a lag number that you can look up but designing for it requires special measuring equipment and programs so most everyone just use general rules of thumb picked up on forums, like this one or what can be read in the many articles on the subject or from a sales person you are thinking of buying panels from.

The basic rule I follow is to install absorption panels on the side wall right in front of the speakers, at that first reflection point, if your speakers are 36" or closer to the side wall. The front wall can be left fairly reflective if you can pull your speakers out into the room. My speakers are 53 inches out into the room so I felt absorption panels on the front wall was not necessary. The room's size of 12'Wx15'D with a 9' ceiling height. Due to this smaller size I added bass traps to the front two corners. Bass waves are huge and almost no one has a room large enough to allow them to fully develop, so in most cases the installation of bass traps is a good investment and will help. When using a small pair of two way bookshelf speakers then bass traps may not be as important as if you had a pair of full range speakers or if you use subwoofers. Bass traps alone are not the solution to great bass but are very helpful. Directly behind my speakers I placed my diffusion panels. In my opinion these panels are far enough from my listening position to not create an issue and they help make the sound more lively and create the illusion that the room is larger than it really is. The bass traps also help create the illusion of a larger space. Dead center between the speakers on the front wall there is no treatment. The speakers are far enough out into the room that treatment is not required and it helps keep the room sound lively. My listening position is pretty close to the rear wall. For that reason I was concerned about early reflection distortion so I installed three 6" thick absorption panels. Due to their thickness they absorb a wide frequency range. Thin absorption panels absorb mainly the high frequencies so be careful if you choose to use them. To the side walls in line with where I sit are CD racks. The CDs are placed at random spacing and some stick out further than others so I believe this helps with diffusion. I use a large wool area rug with thick padding between the listening spot and the speakers, again this aids in absorption.

When you walk into the room your ears feel a difference in pressure from the room you just left. If you clap your hands there is no slab echo. Some people may feel that would be a sign of an over damped room, but for me the room is lively enough and I have very clean and detailed bass

I hope my reasoning for how I treated my room gives you an idea on how you might think through how you might treat your room with both absorption and diffusion panels along with furniture and room features you have no ability to eliminate.

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. ;-) 

Definitely the front wall, in my opinion.

I've posted a photo of the front of my room in the Virtual System area. I've had three pairs of GIK Gotham Quadratic Diffusers deployed in the middle of the room boundary behind the speakers for over a year (I had a single pair before that) and have found they make a substantial difference—the perceived size of the room is larger and the sound is smoother. Because I'm a reviewer,  lots of speakers come and go, and I've  found the GIKs to be effective with various loudspeaker types—dynamic and electrostatic designs, ported and sealed box, floor standers and stand mounts. As room treatments go, they aren't expensive ($359 per pair) and even my wife doesn't find them unattractive.

In the photo, they are mounted in heavy wooden frames I had built. The speakers in the photo are JansZen Valentina P8s, which I own especially for use with the BACCH-SP crosstalk cancellation processor but the GIKs also are of considerable benefit when I'm listening to my Magicos.

Andy Quint

Thanks for the helpful feedback. I never thought my untreated (other than a large area rug and bookshelves on one side) basement listening room sounded too bad — no frequencies seem emphasized or attenuated — and now thinking that might be largely because my speakers are 6’ out into the room and over 3’ from the sidewalls (ah the joys of a dedicated listening room with no WAF interference). That said, I know there are improvements to be had. I’d always thought I’d judiciously add some absorptive panels, but after hearing the feedback here and as I enjoy the spaciousness and reverb trails my system preserves/produces I’m thinking of skewing more to diffusion maybe mixed with some absorptive panels and bass traps as or if needed. One thing that seems assured is that to get it “right” for my room, system, and personal tastes there’s gonna be trial and error involved and that there’s no magic formula to achieve that, but I actually like that because that’s how I’ve learned many important audio-related lessons along the way. Anyway, great stuff and thanks again.

Andy @aquint : gorgeous room! Thanks for sharing and chiming in

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.