Diffusion vs absorption? My set up

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Skye

Re: Diffusion vs absorption? My set up
« Reply #20 on: 17 May 2012, 12:32 pm »
I've never tried it, I was just looking for some placement recommendations. Have you tried any of his placement or room treatment methods?

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #21 on: 17 May 2012, 01:54 pm »
Hi Bjorn,

Is the OP setting up a mixing desk / studio or a 2 channel stereo listening room?

If the later I'd generally be suggesting diffusion on the front wall (with traps in corners) and absorption directly behind the listener.  Personally, I've had good results using diffusion at the 1st side wall reflection points as well - but that may be a matter of personal taste.
You can use diffusion on sidewalls if you prefer, but it will not be accurate. Areas like tonality, localization, clarity and intelligilibilty will suffer compared to attenuating reflections with absorption or redirection. Depends if you want your room to color or if you want to hear the recording/mix alone. Diffusion in the rear of the room is vital though. When one has done this properly, without overdampening, and have lateral diffuse energy, I would be surprised if many still want to have diffusors on sidewalls.

werd

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Re: Diffusion vs absorption? My set up
« Reply #22 on: 17 May 2012, 02:45 pm »
You can use diffusion on sidewalls if you prefer, but it will not be accurate. Areas like tonality, localization, clarity and intelligilibilty will suffer compared to attenuating reflections with absorption or redirection. Depends if you want your room to color or if you want to hear the recording/mix alone. Diffusion in the rear of the room is vital though. When one has done this properly, without overdampening, and have lateral diffuse energy, I would be surprised if many still want to have diffusors on sidewalls.

Hi

What about listening volume ? Does the volume you listen to music effect a treatment strategy? I do lots of late nite listening. Diffusing maybe more appropriate here on sidewalls?

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #23 on: 17 May 2012, 05:30 pm »
Hi

What about listening volume ? Does the volume you listen to music effect a treatment strategy? I do lots of late nite listening. Diffusing maybe more appropriate here on sidewalls?
Can't see that makes any difference to what I've already said. If anything, it's probably even more important to treat to enhance clarity and intelligibility when one is listening with low levels.

werd

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Re: Diffusion vs absorption? My set up
« Reply #24 on: 17 May 2012, 05:51 pm »
Can't see that makes any difference to what I've already said. If anything, it's probably even more important to treat to enhance clarity and intelligibility when one is listening with low levels.

Ok thanks !

McTwins

Re: Diffusion vs absorption? My set up
« Reply #25 on: 17 May 2012, 06:22 pm »
You can use diffusion on sidewalls if you prefer, but it will not be accurate. Areas like tonality, localization, clarity and intelligilibilty will suffer compared to attenuating reflections with absorption or redirection. Depends if you want your room to color or if you want to hear the recording/mix alone. Diffusion in the rear of the room is vital though. When one has done this properly, without overdampening, and have lateral diffuse energy, I would be surprised if many still want to have diffusors on sidewalls.

Do you go by the name bwo from gearslutz. :green:

kiwi_1282001

Re: Diffusion vs absorption? My set up
« Reply #26 on: 17 May 2012, 07:53 pm »
You can use diffusion on sidewalls if you prefer, but it will not be accurate. Areas like tonality, localization, clarity and intelligilibilty will suffer compared to attenuating reflections with absorption or redirection. Depends if you want your room to color or if you want to hear the recording/mix alone. Diffusion in the rear of the room is vital though. When one has done this properly, without overdampening, and have lateral diffuse energy, I would be surprised if many still want to have diffusors on sidewalls.

Respectively I have to disagree.   I AB'd absorption vs. diffusion on sidewall (listening and measurements) and much preferred the later.  I found that resolution, localisation and intelligibility all improved with diffusion though there was some cost on imaging. 

Skye

Re: Diffusion vs absorption? My set up
« Reply #27 on: 17 May 2012, 08:03 pm »
Respectively I have to disagree.   I AB'd absorption vs. diffusion on sidewall (listening and measurements) and much preferred the later.  I found that resolution, localisation and intelligibility all improved with diffusion though there was some cost on imaging.

Isn't localization the same as imaging?

Could you describe the cost on imaging?

kiwi_1282001

Re: Diffusion vs absorption? My set up
« Reply #28 on: 18 May 2012, 04:57 pm »
No.  Localisation is placement of instruments in a sound-stage.  Image (used here) is the referencing the central image.  Click on the globe under my name.  It will take you to my virtual system where I explain my observations in some detail.


Bjorn

Re: Diffusion vs absorption? My set up
« Reply #29 on: 18 May 2012, 05:07 pm »
Respectively I have to disagree.   I AB'd absorption vs. diffusion on sidewall (listening and measurements) and much preferred the later.  I found that resolution, localisation and intelligibility all improved with diffusion though there was some cost on imaging.
Well, you are debating against years of research when it comes to accuracy. I'm not going to discuss preferences though. Many variables with the setup come into place with what's preferable.

Can you post an ETC of each speaker with both treatments? It would be interesting to see if placement, reflective material or different size has brought you to this conclusion.

I do see that you use quite thin absorption panels. This will alter the frequncy response since they bascially will absorb highs and mid highs. It will function like an EQ. And I see no diffusion in the rear of your room.

nwboater

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Re: Diffusion vs absorption? My set up
« Reply #30 on: 19 May 2012, 05:16 pm »
No.  Localisation is placement of instruments in a sound-stage.  Image (used here) is the referencing the central image.  Click on the globe under my name.  It will take you to my virtual system where I explain my observations in some detail.

I just read all four pages of your thread in AudioEnz. A fascinating and very informative/helpful read. It was fascinating to study your journey and the huge improvements you gained.

Very few people document and explain their changes any where near as well as you have. I found it way more helpful than reading piles of documents on the theory of room setup.

Thank you very much.

Rod

Big Red Machine

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Re: Diffusion vs absorption? My set up
« Reply #31 on: 19 May 2012, 06:47 pm »
Respectively I have to disagree.   I AB'd absorption vs. diffusion on sidewall (listening and measurements) and much preferred the later.  I found that resolution, localisation and intelligibility all improved with diffusion though there was some cost on imaging.

Same here.  But if my room was wider it may be a different story.  At 13' 8" wide diffusion on the side walls really makes my room feel bigger and I have no difficulty distinguishing musicians in the stage.  I have plenty of bass trapping in the room as well.

youngho

Re: Diffusion vs absorption? My set up
« Reply #32 on: 21 May 2012, 10:59 am »
Hi Bjorn,
If the later I'd generally be suggesting diffusion on the front wall (with traps in corners) and absorption directly behind the listener.  Personally, I've had good results using diffusion at the 1st side wall reflection points as well - but that may be a matter of personal taste.

In "Sound Reproduction," Toole suggests the use of wideband diffusers as a possible alternative to broadband absorption at the first sidewall reflection points, which may be optional in certain situations (wide dispersion speakers, listener preference, etc). In one chapter, he also mentions the use of diffusion OR absorption in the center of the rear wall (he goes into this a little further one pages 22-23 at http://www.wghwoodworking.com/audio/LoudspeakersandRoomsPt2.pdf)

Diffusers only direct a fraction of the original energy in any one particular direction (like directly towards the listener), and they MAY potentially preserve the spectral content of the off-axis response better than absorption, which is not uniform at all frequencies or angles of reflection (especially when covered with so-called acoustically transparent cloth, particularly at increasing angles). However, some distance from the diffuser may be required to avoid phase anomalies at the listening position.

Nuance

Re: Diffusion vs absorption? My set up
« Reply #33 on: 22 May 2012, 01:04 pm »
Yes, but very generally said. More spesific would be to say that one treats early reflections with either absorption or redirection and later arriving reflections from behind with diffusion if the distance permits it. One needs to take note that absorption should only be used at those spots that create early reflections in sweetspot. We don't want to use absorption (and especially not thin panels) unecessarily which can easily leave the room dead and dry. The goal is to create an RFZ (reflection free zone) and that can also be done by redirecting the reflections to the rear of the room where they will eventually be diffused. In most cases for instances, provided the rear of the room is properly treated, there's seldom a need to absorp high frequencied behind the speakers. Most speakers don't backfire high frequencies. Bass absorption is crucial though behind them. To find out exactly what do to, measuring and utilizing ETC is the key.

What if the wall behind the listening position is dozens of feet away and isn't a problem as far as reflected sound goes?  For instance, my room is odd in that it is only 12 feet wide, but it's 45 feet long, and then "L's" into another section at the very back (behind the LP) of the room; it's a basement.  Anyway, would it be best to adsorb the lateral first reflections or diffuse them in a room that narrow?  I plan to to widen it at some point, but I have to leave it as is for now.

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #34 on: 22 May 2012, 01:30 pm »
What if the wall behind the listening position is dozens of feet away and isn't a problem as far as reflected sound goes?  For instance, my room is odd in that it is only 12 feet wide, but it's 45 feet long, and then "L's" into another section at the very back (behind the LP) of the room; it's a basement.  Anyway, would it be best to adsorb the lateral first reflections or diffuse them in a room that narrow?  I plan to to widen it at some point, but I have to leave it as is for now.
First of all it depends on your goal. If you want an accurate listening environment as possible, one wouldn't use diffusion to treat early reflections. I'm well aware of Toole's researches, but they are not about accuracy alone and they really raise more questions then answers any. That's another discussion.

When it comes to your rear walls, it can still cause high gain reflections even with a room with your length. 45 feet isn't really that big when it comes to acoustics. But I can't quite picture how you room looks, so difficult to say anything for sure. Measurements would give the answer whether you have late arriving detrimental reflections or not. If you don't have any and they just die out, you avoid certain problems but you may end up with a pretty dead and dry sound. A reflective backwave from diffusors is beneficial and brings a feeling of envelopment and liveliness that you will lack. Something you could consider is setting up angled wall dividers that will redirect the energy to rear sidewalls where you have diffusors but will still pass the bass through.
« Last Edit: 22 May 2012, 02:41 pm by Bjorn »

Skye

Re: Diffusion vs absorption? My set up
« Reply #35 on: 22 May 2012, 02:23 pm »
A lot of this discussion is very helpful. I was about to ask a number of questions, but someone else always sneaks them in first, and I get them answered without ever typing a message!  8)

This thread has given me a good idea how I want to treat my room. And this late discussion of absorption vs diffusion on first reflection points, especially in a narrow room, is very good to know. When I can represent my plan with images and details, I'll be sure to post it in the Acoustics Circle to get some advice.

Nuance

Re: Diffusion vs absorption? My set up
« Reply #36 on: 22 May 2012, 04:31 pm »
First of all it depends on your goal. If you want an accurate listening environment as possible, one wouldn't use diffusion to treat early reflections. I'm well aware of Toole's researches, but they are not about accuracy alone and they really raise more questions then answers any. That's another discussion.

When it comes to your rear walls, it can still cause high gain reflections even with a room with your length. 45 feet isn't really that big when it comes to acoustics. But I can't quite picture how you room looks, so difficult to say anything for sure. Measurements would give the answer whether you have late arriving detrimental reflections or not. If you don't have any and they just die out, you avoid certain problems but you may end up with a pretty dead and dry sound. A reflective backwave from diffusors is beneficial and brings a feeling of envelopment and liveliness that you will lack. Something you could consider is setting up angled wall dividers that will redirect the energy to rear sidewalls where you have diffusors but will still pass the bass through.

I attached a (crappy) picture.  The DVD rack has since been moved, but other than that the layout is the same.  Obviously I am limited in what I can do, but the speakers fire down the long dimension and are about 7.5 feet apart (flanked by dual subs) and just over 2 feet from the side walls; they are 4 feet from the wall behind them.  The listening position is 10.5 feet from the speakers.  As you can see I have a first reflection absorption panel at the lateral walls, and a pair of bass traps in the corners.  The room isn't dedicated and extends well beyond the couch (passed where I was standing when I took the picture), which then becomes the children's play area (lots of toy boxes, toys and various kiddy stuff everywhere).  The room then L's around and open to another 12x15 section (complete opposite end of the TV and speaker system).  Obviously it's not an ideal setup, and my plan is to expand the right wall another 5 feet (the laundry room is way too big), and perhaps use wall dividers like you mentioned behind the listening position.




Anyway, do you have an suggestions?  And yes, I want an accurate listening environment (as much as I can get with this crappy room).  My apologies to the OP - don't mean to hijack the thread.  I didn't want to start another one, though, since I am pondering adding diffusion myself.  Thanks for letting me post in your thread.

Skye

Re: Diffusion vs absorption? My set up
« Reply #37 on: 22 May 2012, 04:45 pm »


What's that by the ceiling above the TV?

Did you make the traps or buy them?

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #38 on: 22 May 2012, 05:31 pm »
I attached a (crappy) picture.  The DVD rack has since been moved, but other than that the layout is the same.  Obviously I am limited in what I can do, but the speakers fire down the long dimension and are about 7.5 feet apart (flanked by dual subs) and just over 2 feet from the side walls; they are 4 feet from the wall behind them.  The listening position is 10.5 feet from the speakers.  As you can see I have a first reflection absorption panel at the lateral walls, and a pair of bass traps in the corners.  The room isn't dedicated and extends well beyond the couch (passed where I was standing when I took the picture), which then becomes the children's play area (lots of toy boxes, toys and various kiddy stuff everywhere).  The room then L's around and open to another 12x15 section (complete opposite end of the TV and speaker system).  Obviously it's not an ideal setup, and my plan is to expand the right wall another 5 feet (the laundry room is way too big), and perhaps use wall dividers like you mentioned behind the listening position.

Anyway, do you have an suggestions?  And yes, I want an accurate listening environment (as much as I can get with this crappy room).  My apologies to the OP - don't mean to hijack the thread.  I didn't want to start another one, though, since I am pondering adding diffusion myself.  Thanks for letting me post in your thread.
Looks like a cosy place to enjoy music and movies.
L-shaped room can be tricky. Very often the bass response is different with the speakers. Many struggle with a lack of bass too, but that can vary with placement and what type of wall that divides the room.

Something I would consider in a room that's somewhat narrow is getting speaker with controlled dispersion. For example a good waveguide speaker. These will give less reflections from sidewalls and you don't need to dampen them as much and one can therefore avoid the headphone feeling which easily comes with much absorption on sidewalls. Here's some examples of that type of speaker:
http://gedlee.com/Loudspeakers.htm
http://www.jblpro.com/products/recording&broadcast/lsr6300/JBL.LSR6332.pdf

If this is the setup you will work on, you should dampen part of the ceiling between you and the speakers, dampen the opposite mirror image to each speaker on sidewalls, and use more and bigger basstrapping behind the speakers and in the corner. Unless your speakers are backfiring much of mids and highs, the traps on the frontwall should be made reflective. This can be done by using some layers of plastic between the porous material and acoustic fabric.

The panels on ceiling and sidewalls should not be smaller then a minimum of 4" thickness. Adding an airgap behind would be good. In a narrow room however, you may not want them too thick to remain some spaciousness. Something you can try out. 4" isn't too much of compromise and using panels with that thickness or thicker makes one avoid changing the spectral content. One can build these oneself easily, but if one rather wants to buy I would recommend buying from Acousticmac since they don't use a reflectice membrane on their panels/basstraps. Yes, what they call basstraps are what we should use for early reflections. Basstraps made of porous material really need to be bigger to have a decent effect.

Hopefully you don't have the whole room carpented. Carpet is ok on the floor between the speakers and listening position, but I wouldn't use it other places since it basically just sucks up the highs and too much of that can leave the sound muddy.


Nuance

Re: Diffusion vs absorption? My set up
« Reply #39 on: 22 May 2012, 06:10 pm »
That's a window near the ceiling and a little curtain covering it. :)  The bass traps were purchased; my wife surprised me again for my birthday.  She's a smart lady and obviously listens when I talk audio with her, though I wish she bought them from Gik (they are from ATS).

Well, the speakers aren't going anywhere, but they have very good off-axis/polar response.  The bass response is good, and I have attached an in-room averaging across the three couch locations.

The L in the room is on the opposite end and doesn't' seem to pose a problem regarding bass.  I think adding the second sub helped a lot with that (it's hard to see, but that is what the lamp is sitting on.  They are DIY 15" sealed TC Sounds TC2000's).  I already have a 4" thick first reflection panel at each lateral reflection (used the mirror trick).  The speakers do not backfire, but I can certainly add bass traps behind them.  Thanks for the info guys; you kind of confirmed what I was thinking, but I wasn't sure if I should add diffusion or not, hence my question.