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REW Before and After Room Treatment (Advice on decay)


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Hi all,

 

I have been in the process of treating my room with DIY acoustic panels using XHD panels and some Artnovion Diffusers and wanted to get some advice from those more knowledgeable on the before and after measurements and initial impressions.

 

To treat, i made the following;

  1. 4 bass traps using 2 XHD50mm sheets straddling corners
  2. Rear wall XHD50 panel
  3. Sidewall XHD50 panels x 3 each side
  4. Rear diffusers above absorption panel

 

REW FR, Waterfall and RT60 before and afters (these measurements and L+R+SW, no room correction);

 

1. FR: Red before and blue after

FR.thumb.jpg.859104812d0d33de5f2432e75dabb728.jpg

 

2. Waterfall

output_gxn7DB.thumb.gif.f8f3c01331765a553cc2a2d286e5c713.gif

3. RT60

output_e3ZKVS.thumb.gif.7c5c9e61f1ee64ba34702b198ec0b59b.gif

 

Impressions: Slap Echo completely gone, the room feels much less lively. Focus and imagine is better and dialogue ringing is gone however the room feels much less spacious and closed in (not sure i like it)

 

For Music, i much preferred the room when it had just the 4 bass traps or was untreated. With all treatment the room is extremely dry, the mids and highs are somewhat flat and no amount of volume gets the airiness back. I have yet to try music with all sidewall panels removed. Movies i have not had a load of time in there yet but similar obvious changes are that the sound is less enveloping than before, dialogue is clearer though once again not sure i like the room being this sedate.

 

What is everyone's thoughts on the before and after? the RT60 to me looks uniform above 150hz compared to before though on the low end of the recommended 200-500ms decay times. For me what i hear with the highs is backed up by the FR which shows in blue where levels are pretty much decreased along the whole band especially the high which has some weird phasing effect up top.

 

The sidewall panels seem to be the source of the soundstage compression, not sure i want to keep them or if i put a reflective layer on top to bring back some top end.

 

appreciate any comments/recommendations.

Steve

 

 

 

 

IMG_5884.thumb.jpg.4f04dee7f4586f46936189a15e488cb6.jpgIMG_5883.thumb.jpg.4e7c3c9e9f766608a59011d1b3689c2a.jpgIMG_5882.thumb.jpg.a01e4bc7703fecfde65467a5da7cf7ee.jpgIMG_5825.thumb.jpg.8c74649123dc3c68dfc2e451a7b8f855.jpg

 

Edited by Stevan.B
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You have quite low values now.   That's a fairly larg amount of abosorbtions.  You say it sounds like I'd expect you to  ;)

  Thoughts....

 

 

Don't measure L+R+SW ..... Just do L or R + SW .... the rason is that you can easily introduce HF issues in the results (eg. perhaps some of the notches in the blue chart) .....  although if you're prepared to look past these issues, then L+R+SW is ok.   Just don't wonder why is the treated result more ragged at HF, before you exclude measuring L+R as the culprit.

 

Sit further forward (if that works re: your screen).

 

Put the rear diffuser at ear level ... and potetnially nix the rear absorbtion (can you try it [the abosrber] up front?... I like absrobtion in the front of the room)

 

Maybe you have a strange "hole" in your RT values at 100-200 ish? .... I would have been targting more like 300-400ms.

 

When you try taking out much of the absorbtion... just focus on the speaker reflection points.

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Hey Dave

your ears are telling you that the room absorption and time signatures are all out. You’re now experiencing the unfortunate fact the absorption is not reverberation. Reverb time used to be used as a proxy for attenuation. However the science has got a lot better since the 1950s. 
Any room treatment MUST start with bass treatment. As can be seen in the SPL graphs large low frequency energy waves are sloshing around your listening room completely unattenuated. These high energy waves are also producing the harmonics that you see on your SPL graphs, reaching well into the voice range. 
happy to help out if you wish. 

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  • 2 months later...

nice room - good work ?

 

I agree with @davewantsmoore

  • check the spec's on the rear diffuser - you don't want to sit closer than about 3 x the wavelength of the lowest frequency diffused, otherwise you may hear "artifacts" from the diffuser doing its job. As Dave says, move the couch forward if you can 
  • I'd re-deploy the lateral sidewall absorbers to straddling corners somewhere to bring back some sidewall reflections
  • given you have 2 subs, if you have DSP control of each (delay and EQ), try using Multi Sub Optimizer (MSO) a free tool that you use in conjunction with REW to dial in a smooth bass response optimised across the listening couch

cheers

Mike

 

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7 minutes ago, almikel said:

nice room - good work ?

 

I agree with @davewantsmoore

  • check the spec's on the rear diffuser - you don't want to sit closer than about 3 x the wavelength of the lowest frequency diffused, otherwise you may hear "artifacts" from the diffuser doing its job. As Dave says, move the couch forward if you can 
  • I'd re-deploy the lateral sidewall absorbers to straddling corners somewhere to bring back some sidewall reflections
  • given you have 2 subs, if you have DSP control of each (delay and EQ), try using Multi Sub Optimizer (MSO) a free tool that you use in conjunction with REW to dial in a smooth bass response optimised across the listening couch

cheers

Mike

 

It’s been a bit since I posted this, I have a dual ultimax setup tuned with a mini DSp now. 
 

I have also removed the middle sidewall absorber. Just have to install diffusers on the ceiling and I’ll leave it there for now. 
 

 

70AC49F3-E12B-4533-BE83-2755FA879FB1.jpeg

F55328F4-F77E-481A-925E-A037B9ACC60E.jpeg

9782CC1A-E81B-4F59-A039-08E8EB847772.jpeg

C0279EBA-E1E3-414F-839D-2A319EAB4448.jpeg

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Looking great. Love the colour scheme

 

I'd suggest only using the absorption panels on the 1st reflection point on the side walls and also behind the front speakers

 

You want to add more diffusion if your still struggling with getting life in the room

 

I'd replace the absorption panel on the the rear wall with diffusers instead in a 2x6 configuration you want to cover 2/3 of the rear wall with diffusion 

 

Also corner bass traps to the rear there's some serious bass going on with  those subs ?

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1 hour ago, mpearce38 said:

Here is a pic of a good rear wall layout

 

https://images.app.goo.gl/nQ42BEzF6EmqP2oS7

 

 

Tbh the rear wall absorber got rid of a terrible slap echo I had between the front and rear walls, made a huge difference especially speech intelligibility but yes it’s killed some liveliness. 
 

I only sit around 1m from the rear wall, the next project is to do some DIY slat diffusers that will overlay the absorbers  to create a combi panel and see how we go. 

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On 05/10/2020 at 9:53 AM, almikel said:

nice room - good work ?

 

I agree with @davewantsmoore

  • check the spec's on the rear diffuser - you don't want to sit closer than about 3 x the wavelength of the lowest frequency diffused, otherwise you may hear "artifacts" from the diffuser doing its job. As Dave says, move the couch forward if you can 
  • I'd re-deploy the lateral sidewall absorbers to straddling corners somewhere to bring back some sidewall reflections
  • given you have 2 subs, if you have DSP control of each (delay and EQ), try using Multi Sub Optimizer (MSO) a free tool that you use in conjunction with REW to dial in a smooth bass response optimised across the listening couch

cheers

Mike

 

Thanks for the tips Mike, the room layout was in consultation with Paul at Red Spade, the next step would be to try some DIY slat diffuser overlays on the panels and see if the sound is preferable. 
 

I have dual XHD50 traps in every corner but this really stops impacting attenuation below 80-100hz so there’s that eventually to attend to. 

The couch is around 1.2m into a 5m room, the bass response is pretty much flat from 15-70hz, I can’t really move it forward without impacting the viewing distance I’ve designed for the screen (plus some

aesthetic reasons with the side door)

 

I have some measurements post Mini DSP sub integration, we created 4 bass profiles and currently using the “insane bass” profile ? 

 

I’ll put something up soon. 

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1 hour ago, hopefullguy said:

maybe a thread on your making of the subs, good/bad, tips and pricing

Don’t give me the credit mate! I had Paul at Red Spade make these up for me after doing some consultation on the room and targets. 
 

I believe he will make this a standard design going forward as it’s come out quite beautiful. 
 

the boxes are around 550mm cube with height at 600mm, they run off a crown XLS2502 amp and are finished in a matte black paint. The grills have recessed magnets in them to affix to the box.  

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On 08/10/2020 at 5:59 AM, mpearce38 said:

Here is a pic of a good rear wall layout

 

https://images.app.goo.gl/nQ42BEzF6EmqP2oS7

 

 

You need to you sit far enough away from diffusers to give them a chance to develop the diffuse sound field.

Cox and D'Antonio from RPG, who have been leaders in diffuser technology for decades, recommend the minimum listening distance as 3 x the lowest wavelength being diffused.

 

The panels in the linked picture look like QRDs, but when I looked a bit closer at the panels they were 6 wells wide, and appear symmetrical on the vertical axis - so each individual panel is possibly 2 x N3 (ie 3 well) QRDs mirror imaged.

 

The amount of actual "diffusion" of those panels wouldn't be huge, so the minimum listening distance could be relaxed (their Marketing department could spin that as a benefit), but if you're building/buying 1D QRD diffusers, IMHO you want at least N5. 

Maybe with 2D QRDs (ie skylines), N3 is enough...I've never looked closely at the commercially available 2D skylines.

 

Always be suspicious of commercial QRD diffusers that don't have prime numbers - their diffusion is only as good as the prime factor (eg 12 wells wide only provides the diffusion of 4 x N3 panels).

 

If building your own QRD - 1D (like a cutlery drawer) or 2D (skyline), all the design work can be done in an amazing free tool https://www.subwoofer-builder.com/qrdude.htm

I'm very grateful to the amazing people that put together free tools like REW, QRDude, MSO etc ?

 

On 08/10/2020 at 7:43 AM, Stevan.B said:

the next step would be to try some DIY slat diffuser overlays on the panels and see if the sound is preferable. 

The great thing about slats (1D BAD panels), is that they don't generate the amount of diffusion that QRDs generate, so they have reduced minimum listening distance requirements, and are easy to DIY (unlike QRD diffusers).

 

Often if you've added enough absorption to the room to manage the bass, you've killed the treble. You can bring back the treble by progressively covering your absorption with slats in a BAD pattern.

 

For that absorber on the back wall behind the couch, you could try a really simple and inexpensive experiment...

Get a big roll of gaffer tape or duct tape (or both) - stick a small piece of tape to the absorber and see if it comes off cleanly.

If it does then lay vertical strips of tape on the absorber in a BAD sequence...

...plenty of BAD sequences are on the web, or use the "flipping a coin" method...PM me if this doesn't make sense...

 

The tape will reflect more treble back into the room - not as much as wooden slats, but some...

...if you like the sound but want still more treble back in the room, just add more tape horizontally in a BAD pattern...you've made a 2D BAD panel 

 

I haven't tried this, as all my absorption is raw Acoustisorb 3 - and the tape would tear it to shreds if I removed it.

I can't take credit for this idea - it was @Peter the Greekwho suggested it to me...but the science is sound.

 

cheers

Mike

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Guest Peter the Greek

You could pin strips of laminating film instead of tape as a method. Sort of like titrating a result, a strip at a time until you like it. A bit like this. The second being the tape option

 

163266876_15091320Coloum20WIP20adding20plastic_zpshaxs7fyj.thumb.jpg.4b86e67aec1cbf22f956054630ccd5d4.jpg1372008801_1510132020Perf20panel20better_zpsmtzewvbk.jpg.b3733fd760de5dd50e0699fe227f3bbe.jpg

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On 08/10/2020 at 7:43 AM, Stevan.B said:

I have dual XHD50 traps in every corner but this really stops impacting attenuation below 80-100hz so there’s that eventually to attend to. 

Hi Stevan,

I'm assuming dual XHD50 means 100mm thick? and straddling the 4 vertical room corners? How wide are they?

 

Unfortunately absorption has to be big to absorb at lower frequencies - really big to operate below 150Hz, and truly massive to operate < 100Hz...so big you look for other solutions...

...based on your photos I can't see any absorption big enough to be absorbing much below 150Hz or so...

 

...this is not meant as criticism - you have a fantastic room ! 

...but there's so much "fake news" on the interweb on what absorption treatment can do - which has reducing effect < 150Hz or so without getting huge.

 

Don't get me wrong - I love absorption treatment - I have loads and it cleans up my room's bass response >150 Hz or so amazingly, maybe even lower...I have a lightly constructed room and all the low bass leaks out.

In my room a few bands of EQ cut is all that's required below where the absorption is effective to have a great "in room" bass response.

 

On 08/10/2020 at 7:43 AM, Stevan.B said:

I have dual XHD50 traps in every corner

There are 20 corners in a room - 8 tri-corners, 4 vertical wall/wall corners, 4 wall/floor corners, and 4 wall/ceiling corners.

Below the transition point in your room, as long as the absorption is straddling a corner - it doesn't matter which corner - it will help the room's bass response - how low the absorption treatment works depends on size (depth and area).

 

To achieve reasonable absorption down to 150Hz or so, IMHO based on a bunch of rooms I've done, 200mm thick x 600mm wide of Polymax XHD floor to ceiling in the 4 vertical wall/wall corners is a good start.

 

600mm wide absorption straddling corners is IMO the minimum width if seeking to absorb bass down to 150Hz, only because 2400mm x 1200mm sheets cut neatly to 600mm wide - 1200mm wide sheets of absorption straddling corners will be way more effective because of the extra air gap...

 

...none of the modelling tools I've found model absorption straddling corners ? ...

 

...I'd be very confident the bass absorption of a 1200mm wide x 100mm thick floor to ceiling trap will be effective way lower than a 600mm wide x 200mm thick floor to ceiling trap....but obviously takes up significantly more room real estate.

 

My approach to room treatment is to always target the room's bass response first:

  • use as much absorption (large and deep) straddling corners (any corner) as you can get away with/put up with.
  • If your "in room" bass is now under control - big win ?
  1. if not you'll need to look at either EQ or specialist treatment (eg pressure traps) to get the room's bass under control
  • Once the "in room" bass is under control, you may be absorbing too much treble...by straddling corners with absorption you've avoided 1st reflection points, so treble can still bounce around, but the amount of absorption to achieve a good "in room" bass response may still have absorbed too much treble...
  1. add slats in a 1D BAD pattern in front of the absorption progressively until you have enough treble back in the room...or add a plastic membrane in front of the absorption...or both

IME getting a room's bass response right is 80% of the solution - and I like 80% solutions...you can chase your tail for the additional 20%...keep in mind "best" is the enemy of "good"...a quote usually attributed to Voltaire...

 

cheers

Mike

 

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On 08/10/2020 at 5:56 AM, mpearce38 said:

 

I'd suggest...using the absorption panels... behind the front speakers

 

I agree with this...but also any other corner you want to place absorption to improve the room's bass absorption...

 

On 08/10/2020 at 5:56 AM, mpearce38 said:

You want to add more diffusion if your still struggling with getting life in the room

I also agree with this

 

On 08/10/2020 at 5:56 AM, mpearce38 said:

I'd suggest only using the absorption panels on the 1st reflection point on the side walls

I question this - good science says provided your speakers have a consistent "off axis" response - lateral 1st reflections should maintain their spectral content - treatment at lateral 1st reflection points will absorb more treble than bass, making the spectral balance of the lateral 1st reflections different to the direct sound from the speakers.

 

I can't comment on the "off axis" response of the OP's speakers, but I generally try to avoid treatment at lateral 1st reflection points...it doesn't help the room's bass response...which IMHO should be the primary target for room treatment.

 

cheers,

Mike

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On 08/10/2020 at 7:43 AM, Stevan.B said:

I have some measurements post Mini DSP sub integration, we created 4 bass profiles and currently using the “insane bass” profile ? 

I typically run the same EQ across multiple profiles on my DEQX, just increasing the gain overall from loud to "night club" levels..."night club" levels require careful monitoring for clipping depending on the recording...

I tweak the bass level on the remote...the baseline level of bass is pretty high - it gets turned down on the remote occasionally (very occasionally ?)  

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1 hour ago, almikel said:

 

...I'd be very confident the bass absorption of a 1200mm wide x 100mm thick floor to ceiling trap will be effective way lower than a 600mm wide x 200mm thick floor to ceiling trap....but obviously takes up significantly more room real estate.

 

 

That’s what I do. The 1200x2400 panels fit perfectly for this purpose, and you avoid the chore of cutting them. A 1200mm wide corner-straddling panel only extends 60cm from the corner (plus panel thickness), so it doesn’t look monstrous or take up too much space. What were you going to put in the corners behind the speakers anyway? :)

48 minutes ago, almikel said:

 

I question this - good science says provided your speakers have a consistent "off axis" response - lateral 1st reflections should maintain their spectral content - treatment at lateral 1st reflection points will absorb more treble than bass, making the spectral balance of the lateral 1st reflections different to the direct sound from the speakers.

 

Agreed. I prefer diffusion as 1st refection point treatment on the side walls. One just has to watch the minimum distance (~1.5-2x the longest diffused wavelength) to the listening position to avoid comb filtering artifacts.

 

 

 

Edited by Steffen
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On 09/10/2020 at 9:58 PM, Steffen said:

One just has to watch the minimum distance (~1.5-2x the longest diffused wavelength) to the listening position to avoid comb filtering artifacts.

Cox and D'Antonio (the gurus of diffusion) recommend 3x the longest wavelength diffused...but @Steffen's point stands - you need distance from a diifuser.

 

Mike

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On 09/10/2020 at 9:49 PM, almikel said:

Hi Stevan,

I'm assuming dual XHD50 means 100mm thick? and straddling the 4 vertical room corners? How wide are they?

 

Unfortunately absorption has to be big to absorb at lower frequencies - really big to operate below 150Hz, and truly massive to operate < 100Hz...so big you look for other solutions...

...based on your photos I can't see any absorption big enough to be absorbing much below 150Hz or so...

 

...this is not meant as criticism - you have a fantastic room ! 

...but there's so much "fake news" on the interweb on what absorption treatment can do - which has reducing effect < 150Hz or so without getting huge.

 

Don't get me wrong - I love absorption treatment - I have loads and it cleans up my room's bass response >150 Hz or so amazingly, maybe even lower...I have a lightly constructed room and all the low bass leaks out.

In my room a few bands of EQ cut is all that's required below where the absorption is effective to have a great "in room" bass response.

 

There are 20 corners in a room - 8 tri-corners, 4 vertical wall/wall corners, 4 wall/floor corners, and 4 wall/ceiling corners.

Below the transition point in your room, as long as the absorption is straddling a corner - it doesn't matter which corner - it will help the room's bass response - how low the absorption treatment works depends on size (depth and area).

 

To achieve reasonable absorption down to 150Hz or so, IMHO based on a bunch of rooms I've done, 200mm thick x 600mm wide of Polymax XHD floor to ceiling in the 4 vertical wall/wall corners is a good start.

 

600mm wide absorption straddling corners is IMO the minimum width if seeking to absorb bass down to 150Hz, only because 2400mm x 1200mm sheets cut neatly to 600mm wide - 1200mm wide sheets of absorption straddling corners will be way more effective because of the extra air gap...

 

...none of the modelling tools I've found model absorption straddling corners ? ...

 

...I'd be very confident the bass absorption of a 1200mm wide x 100mm thick floor to ceiling trap will be effective way lower than a 600mm wide x 200mm thick floor to ceiling trap....but obviously takes up significantly more room real estate.

 

My approach to room treatment is to always target the room's bass response first:

  • use as much absorption (large and deep) straddling corners (any corner) as you can get away with/put up with.
  • If your "in room" bass is now under control - big win ?
  1. if not you'll need to look at either EQ or specialist treatment (eg pressure traps) to get the room's bass under control
  • Once the "in room" bass is under control, you may be absorbing too much treble...by straddling corners with absorption you've avoided 1st reflection points, so treble can still bounce around, but the amount of absorption to achieve a good "in room" bass response may still have absorbed too much treble...
  1. add slats in a 1D BAD pattern in front of the absorption progressively until you have enough treble back in the room...or add a plastic membrane in front of the absorption...or both

IME getting a room's bass response right is 80% of the solution - and I like 80% solutions...you can chase your tail for the additional 20%...keep in mind "best" is the enemy of "good"...a quote usually attributed to Voltaire...

 

cheers

Mike

 

hi Mike, no bad feelings whatsoever really appreciate your advice on this. 

 

The REW measurements supports your assertions such that effective base absorption with 100mm of XHD with air gaps doesn't do anything below 100hz (100hz is much less effective than say 150hz). It has made the room reverb between 150hz and 20khz flat, this took a lot of getting used to as I was used to the room coloration before. 

 

I have 100mm thick XHD in the 4 vertical corners, due to room aesthetics/speaker placement they are 680mm in the front and 550mm wide in the rear. 

 

My LR speakers are Wharfedale diamond 157's they are about 600mm from the sidewalls, I assume they are not consistent response wise off axis so I absorbed the first reflection points. Also as the speakers are close to the wall and the first reflection will be strong and soon after the initial impulse we decided to do this to start. 

 

As you say, the room is certainly very acoustically dead, I will put something in front of the absorbers to bring back some reverb, I do admit though that its easy to see that the bass still needs a lot of attention, from listening tests though it does sound awesome to me. 

 

 

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2 minutes ago, Stevan.B said:

though it does sound awesome to me. 

?

that's the primary goal!

 

I don't find my room "too" dead - even with loads more absorption than you have - but maybe some would...

...speaker selection makes a difference - my PSE horn top end maintains a reasonably narrow pattern, so not much hits the sidewalls with their toe in (not 1st lateral reflections anyways).

 

I would continue to focus on getting the bass right in your room...and don't forget EQ can work wonders where the room response is minimum phase.

When the room response is minimum phase - appropriate EQ will assist both the frequency domain and the time domain responses...not intuitive but true.

Tools such as Multi Sub Optimizer can help a lot here.

 

Rigid rooms are an entirely different challenge, but in my lightly constructed room, a few bands of EQ cut below where the absorption is effective manages the "in room" bass nicely.

 

Mike

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3 hours ago, almikel said:

?

that's the primary goal!

When I say “awesome” I’m referring to the bass ? the mains have lots of work both with the room and potentially changing the mains/amps later. I have a ghetto 13 band EQ I can play with in the AVR as well. 

 

Paul did the sub integration remote session a couple weeks ago to set up the ultimax’s so they are already optimized for the room (I’ve attached what I have from REW in the rooms latest form). I was getting flat from 10hz-60hz with no HPF, we settled on a 15hz HPF and 8db of boost on the config I’m using through the miniDSP.

 

in terms of bass, I have the frequency response I want, as above through want to get the room and mains singing nicely together :) FYI my room is not lightly constructed I think? It’s timber frame with sound check  gypcock and sound screen insulation. 
 

The REW snapshots show;

1. Sub integration (black is raw and the red is the final response with house curve)

2. Room RT60

3. Subs plus right frequency response 

4. waterfall 

 

In  terms of BAD panels, is there any advantage of using differing width slats to single width with random sequencing? 

3AB638B7-92DA-4BBA-94F7-F0492B98F8BB.jpeg

6D540FAD-3F5B-4273-8561-B8B26E7724BF.jpeg

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0EFABFEA-41C7-43EA-AC4D-C203893C066B.jpeg

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4 hours ago, almikel said:

Cox and D'Antonio (the gurus of diffusion) recommend 3x the longest wavelength diffused...but @Steffen's point stands - you need distance from a diifuser.

Yep, 3x gives a proper smooth diffuse response. That said, assuming the diffuser performs well down to 300Hz, one can “get away” with 2x or even 1.5x since artifacts are not too obvious at those frequencies. Any closer and you will get discernible minima and maxima as you move your head around.

 

I guess the important point to remember is that you can’t put the listening chair near the back wall for lack of room layout options and expect a diffuser panel right behind you to fix that problem.

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