The 2 cents I've learnt on the diffusion vs absorption debate

[awkwardbydesign]

Yes and I think that's true for most. I have consciously got my listening position forward of the back wall for acoustic as well as practical reasons (storage behind) but two of the early reflections points I just referred to are the rear wall ones.

I am frequently confused* by rear wall/front wall. Which is which?
*And many other things.

 

[sjs]

For context the three closest early reflection points in my room are about 1.3 m from my head.

What sort of diffusers do you have in mind and what frequency range are they effective over? Yes absorbers have limited frequency range too but from examples I've seen I believe diffusers are usually effective over a narrower bandwidth?

Sounds like a small room

I have used RPG Diffractal, Modffusor or Fluttfree T, with Bad Arc panels on the rear wall if there is a distance behind the listener and absorption is required, or Diffractal if there isn't much distance, or the extra absorption is not required.

A lot of online info is based around home cinema rooms or mixing studios, where you may well want quite a dead space, rather than control rooms, mastering studios or music rooms where you want more life.

Personally I like to think of home listening room more like a concert hall, try to get good early reflections for a sense of being enveloped, and sensible control of reverberation to allow the music to breath.

All this is IMHO and obviously ymmv.

 

[sjs]

Yes and I think that's true for most. I have consciously got my listening position forward of the back wall for acoustic as well as practical reasons (storage behind) but two of the early reflections points I just referred to are the rear wall ones.

I have about 1.3m behind my listening position to the rear wall, and have 3 Bad Arc panels above the side board to provide diffusion with some absorption.

 

[JANDL100]

Thanks @sjs , very enlightening.

Does it work differently for omni-directional speakers?

 

[Nopiano]

I am frequently confused* by rear wall/front wall. Which is which?
*And many other things.

The front wall is behind the speakers. The rear wall is behind your head.

But it’s often muddled in reviews when the wall to the rear of the speakers is called the ‘rear wall’, but it’s really the front wall!

 

[sjs]

Thanks @sjs , very enlightening.

Does it work differently for omni-directional speakers?

It will mean they interact with the room with mid to high frequency first reflections more than regular box speakers.

Horns are typically more directional and interact with the room less in terms of first reflections.

 

[MartinC]

The front wall is behind the speakers. The rear wall is behind your head.

But it’s often muddled in reviews when the wall to the rear of the speakers is called the ‘rear wall’, but it’s really the front wall!

^This.

It's what's relative to your head. The front wall is in front of you, the back wall behind you.

 

[Stig]

I designed and made my own treated listening room recently. Mainly absorption ranging from 50cm (effective) treatment in the corners to 10cm at the first reflection points (including the ceiling). The balance was perfect apart from the window which was creating a node in the vocal range. Treating that with absorption undid all the good from the other panels and it suddenly became dead sounding. To overcome this I designed and made 3 quadratic residue diffusers based on prime 7, which did the trick. The result is absolutely sparkling. There are no frequencies fighting each other, every one separated and clearly audible and the sound staging is immense. I can have instrument playing right by my ears whilst others are ‘seen’ way beyond the front wall.
By making my own I was able to check that each one made a positive improvement to the room before making more. Yes there is a lot of theory and opinion out there, and I read an awful lot before starting, but you will only tell whether it’s worthwhile is by giving it a go.

 

[rdale]

I designed and made my own treated listening room recently. Mainly absorption ranging from 50cm (effective) treatment in the corners to 10cm at the first reflection points (including the ceiling). The balance was perfect apart from the window which was creating a node in the vocal range. Treating that with absorption undid all the good from the other panels and it suddenly became dead sounding. To overcome this I designed and made 3 quadratic residue diffusers based on prime 7, which did the trick. The result is absolutely sparkling. There are no frequencies fighting each other, every one separated and clearly audible and the sound staging is immense. I can have instrument playing right by my ears whilst others are ‘seen’ way beyond the front wall.
By making my own I was able to check that each one made a positive improvement to the room before making more. Yes there is a lot of theory and opinion out there, and I read an awful lot before starting, but you will only tell whether it’s worthwhile is by giving it a go.

Stunning!

 

[MartinC]

Sounds like a small room

Something like 4.6 m x 3.3 m x 2.3 m from memory (L x W x H), and not helped by an asymmetric layout (which is unavoidable).

I agree that info./advice focused on stereo listening rooms is pretty limited.

Re. diffusion I am genuinely interested in the frequency range issue. The products you mentioned are in line with others I've seen which do operate over a significantly narrower bandwidth than even a thin acoustic absorber like a GIK 242 panel (which covers ballpark 400 Hz to 20 kHz). To me this then raises the question of which frequency range to target and why? And why the frequencies not addressed are not worth addressing? I appreciate the answer may be a question of what trade-off is subjectively preferable.

For myself I'm definitely going to go with the plan I described above to try as I already have the resources to build the required panels. With the exception of a couple of ceiling panels I have actually ordered from Blue Frog Audio, as they'd be the only two I wanted to be white and I also didn't want to worry about how best to stop the absorber potentially sagging over time. I do very much still view this as an ongoing experiment to see what may ultimately work best and and am very open to other ideas.

 

[JANDL100]

Wow, spaced mains cables!

 

[Stig]

Wow, spaced mains cables!

I went full nerd with the room, starting with installing an independent mains feed from the consumer unit, separate equipment stands for brain and brawn separates and keeping the ‘sacred ground’ in between the speaker clear.

 

[awkwardbydesign]

I went full nerd with the room,

Pff. No cable lifters!

 

[StingRay]

I am frequently confused* by rear wall/front wall. Which is which?
*And many other things.

Front wall, is the one in front of you, or behind the speakers.

 

[MartinC]

For myself I'm definitely going to go with the plan I described above to try as I already have the resources to build the required panels. With the exception of a couple of ceiling panels I have actually ordered from Blue Frog Audio, as they'd be the only two I wanted to be white and I also didn't want to worry about how best to stop the absorber potentially sagging over time.

^As I mentioned this above I just thought I'd share that these panels arrived today. They seem well made and I'm very happy with how they look. I've not bought from them before but would be happy to again. The only tip I'd give is that I found communication best via WhatsApp rather than e-mail.

http://www.bluefrogaudio.co.uk/

 

[newlash09]

I know that diffusers are mathematically designed. But would something stylish like the below white wall tile at first reflection points do anything.

 

[MartinC]

Hopefully @sjs will check back in to this thread at some point to share his thoughts on the questions above.

@newlash09 Do the manufacturers of those panels give any performance information? My gut reaction from the photo is that they will absolutely do something but over a fairly narrow and high-frequency range. I'm saying that as the difference between the highest and lowest parts of the surface doesn't look very great.

Aesthetically there are definitely lots of great looking diffusion products out there!

 

[newlash09]

Unfortunately there is no info about the technical specs of these panels sir.
I've checked these out in person in the shop before. They are made with some kind of plastic polymer and are very light. So that rules out any possibilities of absorption. And as rightly mentioned the groove depth is too shallow to have any meaningful dispersion, they probably work very high up in the treble region. So might just a aesthetic fix, and probably slightly better than a bare wall

 

[newlash09]

Unfortunately there is no info about the technical specs of these panels sir.
I've checked these out in person in the shop before. They are made with some kind of plastic polymer and are very light. So that rules out any possibilities of absorption. And as rightly mentioned the groove depth is too shallow to have any meaningful dispersion, they probably work very high up in the treble region. So might just be a aesthetic fix, and probably slightly better than a bare wall

 

[Stig]

I found YouTube blogs by Jesco @AcousticInsider very useful. He talks about acoustic treatment in mixing rooms but actually most of what he talks about can translate to listening rooms. If you sign up to his blogs he will send you some very useful essays on which treatment is best and why. He talks a lot of sense in a no nonsense way.

There is a truly superb website looking into diffuser theory, why they work and even includes a QRD calculator, for self builders, all for free at :

https://www.subwoofer-builder.com/qrd.htm

(For those that want to delve even deeper there is a very detail analysis on diffuser theory to be found in the book:

Acoustic absorbers and diffusers: theory, design, and application By Trevor J. Cox, Peter D'Antonio.)

I found that (for small rooms) absorption works very well but you need lots of it in terms of thickness and wall coverage.

I made mine out of Knauf Earthwool RS45 which has good acoustic absorption properties and semi rigid so won’t sag in the frame. They are covered with acoustically transparent Camira Lucia fabric. Both insulation and material are used by a well know acoustic panel manufacturer.