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Room analysis shows large 64hz peak - details + pics - any advice? Studio Monitors
Old 27th December 2010
  #31
Gear Guru
Moving along

Signalsuite is designed, not exactly for this purpose, but it has a very smooth sweeping action. With most generators it is possible to input a number, maybe with a decimal place or two and force the issue. Slow but it works, in conjunction with your Sound Level Meter. I have seen the iPhone used for Live PA analysis. The microphone seems surprisingly good.
You are doing all the right things here.
SuperChunks are easy to construct if you use this design, the little triangle bit stops the lot falling on you and provide great screw points for the front finish.
http://www.hometheatershack.com/foru...-finished.html

Your current information says the wall centre is very active. A thick absorbent trap would do some business there but there can be no doubt that in your case tuned would be the best shot. By the way does the back wall show the same type of behaviour?
A tuned perforated panel trap is in essence very simple. It is a sealed box, with a perforated front, with some damping absorption inside.
They are often constructed on the wall which removes the need for a back.
Download Chris Whealy's Calculator and design your own using available materials. Check out the BBC designs for perspective and actual construction details.
For real world practical details on how to make the thing actually perform, I recommend asking Jens directly. If I were making one, I would. Details would be- how far is the absorption layer from the perf panel, or can it touch it?

Could you let me have accurate room dimensions plse.

DD
Old 27th December 2010
  #32
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The Beatsmith's Avatar
 

Quote:
Originally Posted by DanDan View Post
SuperChunks are easy to construct if you use this design, the little triangle bit stops the lot falling on you and provide great screw points for the front finish. Corner Traps finally finished! - Home Theater Forum and Systems - HomeTheaterShack.com
Great! I've seen that page before, although i have to admit to being quite partial to simply 'filling' the space behind my current 7', 4" corner traps if the difference is performance is not worth teh few hundred quid. I'm not sure what exactly i'd fill it with, though - is loft insulation from Wickes OK. And 'open' or can/should it be sealed in a bin bag/original packaging? Can you suggest something? That would be marvellous :-) Wickes have a buy one get TWO free on their loft insulation, but there are 3 different types (top layer, base layer, etc). I assume i could just wrap it with string to keep it 'tight' (roughly 30cm in diameter) and stack the rolls in the corner.

Quote:
Your current information says the wall centre is very active. A thick absorbent trap would do some business there but there can be no doubt that in your case tuned would be the best shot. By the way does the back wall show the same type of behaviour?
Yes. As you can see from the pictures, the back wall is a bit more difficult to assess because of the stairs (i realise the bass will travel through it), and the alcove (which i've hung a 4" trap into), and not least the lack of walls.

Do you mean wall center as in side wall or front wall? I've tried placing a lot of what i have on the front wall, and the difference was negligible, so it would have to be tuned, i guess.

Quote:
A tuned perforated panel trap is in essence very simple. It is a sealed box, with a perforated front, with some damping absorption inside.
They are often constructed on the wall which removes the need for a back.
Download Chris Whealy's Calculator and design your own using available materials. Check out the BBC designs for perspective and actual construction details. For real world practical details on how to make the thing actually perform, I recommend asking Jens directly. If I were making one, I would. Details would be- how far is the absorption layer from the perf panel, or can it touch it?
I am definitely positive about making it/them, if i can. If it's possible for me to seal the back with wood and have it freestanding, that would be ideal for obvious reasons. I'm not exactly sure where they would live - perhaps behind first reflection points? I will google for Chris Whealy's Calculator now.

Quote:
Could you let me have accurate room dimensions plse
I can't give you any more accurate than i currently have i'm afraid - L: 715cm W: 530cm H: 220cm. In terms of the wall with plasterboard on it, your guess is as good as mine. Half a foot extra? I have no idea.

Many thanks.
Old 27th December 2010
  #33
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This, along with the C. Whealy calculator, seems to be quite helpful: Tutorial: How to build a perforated panel absorber (bass trap))

I am assuming this would be placed behind (ie closer to the wall) some 1st reflection point side panels (currently my 4inch broadband panels with exposed wood)?

I'm tinkering with the calculator now (for perforated panels), trying different sizes etc to get good absorption peaking at around 65hz. doesn't look to hard to build (famous last words) as long as you have measurements etc perfectly correct... in terms of materials etc, i still need to look into that. I also need to figure out if it's OK to have it backed with wood, and if so, how thick, etc. I am pretty sure it all assumes the 'back' is a wall.

Still reading,

Thanks
Attached Thumbnails
Room analysis shows large 64hz peak - details + pics - any advice?-perf-panel-properties.png  
Old 28th December 2010
  #34
Gear Guru
Helm

Hi Beat, yes, as close as possible to the boundary, yes. Many designs use the boundary i.e. the wall as the back of the box. I note in various BBC docs that the back and sides of boxes showed resonances separate from the intended.
A perfect helmholtz would have massive inert boundaries. Again the wall itself would be the ideal back, but failing that, I reckon MDF.
At early reflection killing points you will need to include a HF absorbing face. The BBC used carpet on the front of their membrane boxes. I believe placing absorption close to the front, as in your case, will strongly affect the performance of the perfs. In Whealy the position and thickness of absorption within the box has radical effects in frequency and Q. I have no doubt that absorption outside the box but extremely close will have similar effects. How to calculate your resonant frequency then? Is there need for any absorption/damping within the box? Too much damping and these things will do little or nothing.
The devil is clearly in the detail.
Jens may reappear to help with details, but I suggest you PM G.E. also.
As G.E. pointed out to me, at the end of much experiment the BBC chose to use a Panel Design, rather than Perf or Limp Membrane. Worth noting. http://downloads.bbc.co.uk/rd/pubs/reports/1992-10.pdf
DD
Old 28th December 2010
  #35
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The Beatsmith's Avatar
 

Thanks for persisting with your help, Dan. I will PM Jens (GE = JE in your post?) if he is the man in the know about constructing these panels, i hope he has some time to help. It seems difficult to find a much information on thesewhen compared with how many broadband absorption panel tutorial/guides/videos there are! I haven't even seen a decent picture of a membrane trap, let alone a step by step idiots guide heh

I will note that in the case of the BBC paper you linked, they were looking for a more 'general' bass absorption solution vs. a specific frequency spike/null, as is the case here.

When making something so specific to the room, it would be great if it were cheaper/easier to make, as if i have to move in a few months, it won't be too much time/money wasted.

In the meantime i'm going to make three 2" panels tomorrow - 2 for the cloud above mix spot and one to hang on the underside of the slanted stairs. I'll also go to pick up some fluffy insulation to place in round 'bales' behind my straddle corner traps - if you have any suggestions on which fluffy stuff to get out of these three, i'd appreciate that:

http://www.wickes.co.uk/200mm-Loft-R...on/invt/161279
http://www.wickes.co.uk/Loft-Roll-In...on/invt/161210
http://www.wickes.co.uk/Loft-Roll-In...on/invt/161209

Thanks,

Eddie
Old 29th December 2010
  #36
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Quote:
Originally Posted by The Beatsmith View Post
This, along with the C. Whealy calculator, seems to be quite helpful: Tutorial: How to build a perforated panel absorber (bass trap))
The author of that tutorial says that these tuned absorbers are 80% effective one octave above and below the tuning frequency... I have not seen much evidence of this being true, from my efforts to find such a broadband trap for the lowest frequencies.

If you look at the results of your Whealy/Excel trap, unlike what the author of the above tutorial suggests, it is NOT 80% effective one octave below the tuning frequency. And it is totally ineffective one octave above.
This seems to be the real problem that people have experienced with tuned absorbers... in-situ results often don't equal the theoretical predictions.

Keenly watching this space to learn from your experience. Hope you build them tuned absorbers, and hey! if they work out well for you, I might give them a shot myself. I too have problems in that area.

BTW, i think you missed my earlier post linking to commercially available products. The modex corner in particular has easily available components... it'd be much easier and cheaper to build, than the tuned panels we are talking about.
Old 29th December 2010
  #37
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The Beatsmith's Avatar
 

Quote:
Originally Posted by audiothings View Post
The author of that tutorial says that these tuned absorbers are 80% effective one octave above and below the tuning frequency... I have not seen much evidence of this being true, from my efforts to find such a broadband trap for the lowest frequencies.

If you look at the results of your Whealy/Excel trap, unlike what the author of the above tutorial suggests, it is NOT 80% effective one octave below the tuning frequency. And it is totally ineffective one octave above.
This seems to be the real problem that people have experienced with tuned absorbers... in-situ results often don't equal the theoretical predictions.
Hey man! I've read your threads on similar subjects. I agree about the claims - but at least i saw a picture of a DIY panel! It's tough enough just to see a picture of one.

Quote:
Keenly watching this space to learn from your experience. Hope you build them tuned absorbers, and hey! if they work out well for you, I might give them a shot myself. I too have problems in that area.
I've been trying to mix and i just can't do it. It's better to resort to headphones. I really need to get a workable solution pretty quickly as every day that goes by is a waste.

Quote:
BTW, i think you missed my earlier post linking to commercially available products. The modex corner in particular has easily available components... it'd be much easier and cheaper to build, than the tuned panels we are talking about.
I saw the link to the modex stuff... but unless i'm being dumb - they cost a LOT of money, and also cost a lot to transport to the UK? No? Plus i assume i'd need two, either side, right?

I also read that these panels need to be mounted directly to the wall, which i would not be able to do.

I'd LOVE to find a cheap solution that could solve my problems heh

The panels seem relatively 'easy' to build, as long as you have the plans PERFECT, and try to be as accurate as possible when building. However, i realise that tweaking will be required, etc etc.

I don't really see any other option at this point... i would appreciate some extra options, advice, opinions etc!

Thanks

Eddie
Old 29th December 2010
  #38
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avare's Avatar
 

Quote:
Originally Posted by audiothings View Post
The author of that tutorial says that these tuned absorbers are 80% effective one octave above and below the tuning frequency... I have not seen much evidence of this being true, from my efforts to find such a broadband trap for the lowest frequencies.
The effectiveness of a spring based absorber at any frequency as a function of its peak absorption and frequency is equal to the peak absoption times the square root of the greater of the peak frequency and desired frequscny over lesser of the two.

In other words the same as calculating the transmission loss of a MAM system
like a floating floor. Pretty obvious when you think about it for a moment....

Andre
Old 29th December 2010
  #39
Gear Guru
Answers

Use whichever attic roll is easiest to handle. They seem to work fine with the plastic wrapping intact, but I prefer your string idea if they are going in there permanently.
When they say close to a boundary, that would be as close as possible. Bass Waves are big, a few cm is not going to change anything.
I wonder why you are finding your listening experience so dodgy.
Those ADAM's are pretty serious. They will work much better vertically. Stand them up and rotate the tweeters 90 degrees. Try one vertically, then upside down. You may get a better LF one way over the other, one of those woofers outputs 150 down so inverting the speaker places the LF source at quite a different height. Try varying your width also. Seems to me you could place that LF woofer in the 'third' null.

DD
Old 29th December 2010
  #40
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The Beatsmith's Avatar
 

Room analysis shows large 64hz peak - details + pics - any advice?

Thanks Dan. I am going to hold off on the on the fluffy stuff as I could probably buy more RS100/RW5 and make 2ft wide superchunks behind my 4" straddled panels. Wickes is always open and easily accessible. I can get RS100/RW5 etc but requires delivery, taking a little while.

Before you had a chance to answer, I created a new thread about it in the bass trap forum, asking which would be more effective, 2ft superchunks + 4" straddled panels floor to ceiling, or just fluffy rolls + the straddled panels? Which fluffy wool is good behind straddled corner traps?

I also will take into account your S3A comments as I thought you might recommend, I'll get round to it as soon as I've sorted the corners, cloud, and perf panels! Just so many variables right now.

My listening experience isn't great simply because of how all over the place the bass is. One bass note can be 20db louder than the next! And all kicks are way too tubby. I can't mix like this...

Thanks,

Eddie


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Old 29th December 2010
  #41
Gear Guru
Location Location Location

I hear you. For fine LF work, e.g. Kick and Bass courtship, I use headphones.
I recommend that you try to get those LF woofs into the third nulls as a priority. It just might fix that 64Hz thing. Note, my inverting comments are slightly wrong. Both Woofers act below 150Hz. Over 150 one of them takes a break. So impossible to place them both in exactly the third null when horizontal. Between the third thing and the imaging improvement, you may be quite shocked at the vertical improvement.

DD
Old 29th December 2010
  #42
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The Beatsmith's Avatar
 

Thanks. Regardless of vertical or horizontal orientation (there would only be a couple of cm difference in woofer placement), if i move the stands/woofers to the nulls, wouldn't that mean that they're really far apart and as such, means my mix position would have to be much further back to maintain an equilateral triangle?

I'll experiment more tomorrow. Tonight i'm building the 2" ceiling could traps!

Eddie
Old 29th December 2010
  #43
Gear Guru
Clear

Vertical would placing a 16cm wide source in the null. Horizontal it would be 40cm straddling the null. The width would be 1.76M. Not particularly wide I would have thought. The equilateral thing, as with many other rules is only a suggestion. I won't bore you with the vertical thing any further. I can't really same any more than that I am 100% sure that upright is very much better.

DD
Old 31st December 2010
  #44
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The Beatsmith's Avatar
 

Thanks Dan. I'm up for more experimenting.

I've built the cloud and an extra panel for under the stairs, and am off to wickes to get some of the fluffy stuff to pack behind my corner traps. I'll just get 2 bags and see how messy it is, and if i need to wrap the stuff in fabric?

Or can i place the 'bales' in bin bags for example, as they are only for bass. This would mean they aren't as messy/exposed.

I can't leave them in their 'retail' packaging as i think their diameter is too thick, but i'll give it a shot, i haven't done the maths yet.

Cheers
Attached Thumbnails
Room analysis shows large 64hz peak - details + pics - any advice?-photo.jpg  
Old 1st January 2011
  #45
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DrFrankencopter's Avatar
Have you tried moving your listening position? If you're sitting on a longitudinal mode peak, perhaps moving forwards or backwards by a couple of feet will smooth it out somewhat...

Cheers

Kris
Old 2nd January 2011
  #46
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The Beatsmith's Avatar
 

As i've mentioned, i've tried listening and taking measurements all around the room. In order to get rid of the 65hz hump, i'd have to be 2/3 of the way back into the room, where the walls end....

Cheers
Old 2nd January 2011
  #47
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I'm also considering picking up an Ikea room divider and hanging heavy blankets over it in order to kill off the frankly hilarious flutter echo coming from the kitchen area. There's also a lot of flutter coming from the high ceiling near the stairs, but there is less i can do about that. When i clap i hear it coming from the rear right/kitchen

It's making everything so busy and unclear, it's ridiculous. I clearly need a hell of a lot of absorption around the room, bass problems aside.

I can't wait to get this cloud up too.

Cheers
Old 2nd January 2011
  #48
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unit7's Avatar
Quote:
Originally Posted by The Beatsmith View Post
I clearly need a hell of a lot of absorption
My thought too. I'm not an expert but I had one in my studio two years ago giving me instructions on how to solve things. 40-45Hz was one of the issues in my room. Took a lot more than 4" to get rid of that. I've got 20" of absorption on my back wall and 16" on the front wall and still got a tiny bit of the problem left... Just wanted to mention that I made a cloud for my roof too, and that was a lot more work (at least per square meter covered) than just building a second wall on front- and back walls, fill it with rockwool and cover with some cloth. When I did my room I made a thread. Guess there's a lot of them, but if you're curious it's here: My bass trap

Keep working on it. When you've got it sorted out you'll be a happy man!
Old 2nd January 2011
  #49
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The Beatsmith's Avatar
 

Hey!

Yeah, i'm only making two 2" x 2' x 4' panels above mix position, not going as far you did. I checked out your thread, really interesting, nice one.

I think blocking off that kitchen area would make a big improvement, bass aside.

No idea how to sort the stairs area, though? Maybe that's for another thread...

Cheers
Old 2nd January 2011
  #50
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unit7's Avatar
Quote:
Originally Posted by The Beatsmith View Post
Hey!

Yeah, i'm only making two 2" x 2' x 4' panels above mix position, not going as far you did. I checked out your thread, really interesting, nice one.

I think blocking off that kitchen area would make a big improvement, bass aside.

No idea how to sort the stairs area, though? Maybe that's for another thread...

Cheers
Cool. Good luck with the treatment! And congrats on one of the coolest avatars aroundheh
Old 6th January 2011
  #51
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Just as an update, i'm working on finalising the plans for the tuned perforated panel traps, to be placed either side of mix position. They're going to be pretty big.

I have also bought a load of fluffy insulation that i'm going to try to leave in the bag, and put behind the corner traps. See pics. It's ugly but i have so much to do, i'm going to leave it. If i unpack it i will (apparently?) lose performance, and i need to make the corner rolls thinner to fit properly behind the 4" panels without them 'sticking out', which again will not be as effective. I'm not so sure how long i'm going to be able to stay here (not out of choice), so i'm starting to care a little less about the aesthetics... if i want it to look better i can just cover the plastic coverings with light frabric so that it's not so noticeable and 'industrial'...

But i'll have to do some tests and see if they've made much difference at all. I'm sure you're all on the edge of your seats in anticipation of my results.

I also had a pretty cool idea to tame the reflections i'm getting from the kitchen area - i will make or purchase a curtain rail which covers the entire area at the back right of the room, and cover with thick curtains and drapes. This will allow the bass through, but stop the high end travelling though, and hopefully massively reduce the echo i get from that area.

I'm not sure what i can do about the echo from the high stairs section, but one thing at a time...

Cheers
Attached Thumbnails
Room analysis shows large 64hz peak - details + pics - any advice?-corners1.jpg   Room analysis shows large 64hz peak - details + pics - any advice?-corners2.jpg  
Old 6th January 2011
  #52
Gear Guru
Inside out

Quote:
to be placed either side of mix position. They're going to be pretty big.
How will you deal with HF reflections from these?

DD
Old 6th January 2011
  #53
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Glenn/gullfo mentioned (on John Sayers) that it would be OK to have free standing 2" or 4" in front of the perf. panels, as long as they aren't touching. I can't remember what distance he recommended because JS won't load for me at the moment, but i will essentially just move my 1st reflection panels so that they're in front of the perf boxes. As long as they aren't blocking the holes, it should be fine?

I'll tell you what, things sound VERY different with the fluffy insulation stacked in the corners. I'll do some tests today to see the real difference.

Cheers!

Eddie
Old 6th January 2011
  #54
Gear Guru
Interesting

Please keep us informed on that Eddie. The prospect of an 'inside out' design within the RFZ is bubbling at the moment.
I don't want to scare you off perf in any way but I do believe the presence of the outer panel will affect the perf performance. I have no idea in what way, frequency, Q but I have reasons for saying this.

I have seen it written that fabric across the holes, i.e. very little but very close to the real action can be sufficient damping.
The EMT140 reverb plate uses a panel of 705ish. The 705 swings in and out from the large steel plate, say 1-30cm. This changes the decay time from, guessing, 0.5 to 5S. So I believe absorption sucks if you get my drift...heh

I hope you find answers to that one, and hope you can share them with us.

DD
Old 6th January 2011
  #55
Gear Addict
 

Quote:
Originally Posted by The Beatsmith View Post
Glenn/gullfo mentioned (on John Sayers) that it would be OK to have free standing 2" or 4" in front of the perf. panels, as long as they aren't touching. I can't remember what distance he recommended because JS won't load for me at the moment, but i will essentially just move my 1st reflection panels so that they're in front of the perf boxes. As long as they aren't blocking the holes, it should be fine?

I'll tell you what, things sound VERY different with the fluffy insulation stacked in the corners. I'll do some tests today to see the real difference.

Cheers!

Eddie
Anticipating the measurements with stuffed fluffy. Please keep us posted on the perf panels too.
Old 7th January 2011
  #56
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Quote:
Originally Posted by tonio View Post
Anticipating the measurements with stuffed fluffy. Please keep us posted on the perf panels too.
Will have to push it back a bit because i have a few projects i had to work on today. I also had a power cut where the main trip switch was triggered, this is the second time this has happened and it doesn't seem to be to do with me turning anything on specifically.

I will say that it's (the bass) now 'workable'! I still look forward to further improvements.

I will get some tests done asap, though.
Old 7th January 2011
  #57
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Quote:
Originally Posted by DanDan View Post
Please keep us informed on that Eddie. The prospect of an 'inside out' design within the RFZ is bubbling at the moment.
I don't want to scare you off perf in any way but I do believe the presence of the outer panel will affect the perf performance. I have no idea in what way, frequency, Q but I have reasons for saying this.

I have seen it written that fabric across the holes, i.e. very little but very close to the real action can be sufficient damping.
The EMT140 reverb plate uses a panel of 705ish. The 705 swings in and out from the large steel plate, say 1-30cm. This changes the decay time from, guessing, 0.5 to 5S. So I believe absorption sucks if you get my drift...heh

I hope you find answers to that one, and hope you can share them with us.

DD
Hey Dan, here's a diagram Glenn made for me: http://www.johnlsayers.com/phpBB2/do...p?id=36822&t=1

He said: "your absorbers can sit in front of them - just not touching. the proximity will have some damping effect but there is also exposure wall around (150mm or so) on a 600x1200 absorber so it should function well."

I'm not sure either way, i too have read conflicting things from trusted sources, so am looking for more clarification myself.

I'm not sure what you mean by an 'inside out' design?

What do you consider is a reasonable distance from the perf. panel? If i have a 4inch porous trap, intuitively i would have had it at least a 4inch gap from the front of the perf. panel.

Cheers!
Old 7th January 2011
  #59
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You are ultimately doing 2 things 1) you're building a tuned trap, 2) you're planning an using a porous absorber for your first reflections. You might be stacking them or not depending on where that trap and first reflection point are located relative to each other. You will also be adjust that relationship to make it work... So I'd suggest solving the trapping requirement first and the sort the first reflection after and sort any interactions then. If they stack, cool...
Old 7th January 2011
  #60
Gear Guru
Progress

By 'inside out' I mean a perf trap with the absorption on the outside.
I believe that the helmholtz action is concentrated at in or near those perfs.
I gleaned this impression from noting that fabric alone on the front of a perf can do some damping. (BBC I think) Plus my own Helmholtz experiment over at studiotips. My tub did resonate and it did get damped, Q broadened, by fluff in the tub.
At some stage someone suggested that the damping should have been in the port tube. I didn't know that or try it at the time, perhaps that is why I could not replicate the spectacular (still hardly credible example in MHOA P228) Hearsay, impressions, and intuition on my part.
Most interestingly to me, Jens post above seems to directly agree.
The devil is in the details. I believe, from Jens post and again intution, that some damping is needed in the chamber. In an 'inside out' design, perhaps we should regard this as damping unwanted resonances of the chamber itself rather than the being a major part of the helm action. I imagine a light material would be good.
I believe a medium density material of 5-10cm outside the perf would be good. I also now believe it should be close to the perf holes, maybe very close. I will furthermore guess that moving it closer or farther will affect the resonant frequency and probably the Q.
I would really appreciate if Jens could bring these opinions into a more certain realm.

DD
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