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To FRK or not to FRK - That's my question.
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Jamman
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#1
19th June 2012
Old 19th June 2012
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To FRK or not to FRK - That's my question.

Hi all,

I am in the process of building some bass traps to go across corners in my room.

I am building them from sheets of the KNAUF equivalent of OC 703. The sheets are 2" thick and have FRK on them. I plan to stack two together for a total of 4" of 703.

I know people often have one side faced with FRK to avoid killing all the highs. My question is whether there is any merit or any problem to have FSK on BOTH the front and the back of the trap? IE - should I remove the FRK from one of the panels or leave it be? If leave it be, should it face the outside, or should it be between the two 2" sheets?

And finally, if I do remove the FRK, does anyone know whether the process of peeling it off throws a lot of fibers in the air or would they stay pretty intact on the sheet?

Thanks for any info!
#2
19th June 2012
Old 19th June 2012
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Whether you want the "reflective" side to face out at all depends if that reflection is going to get to your ears in those first 20ms or so.

At a side wall first reflection point, absolutely not. Tear the FRK off.

If the above is satisfied, then whether it can be on the back as well depends on its placement. Flat against the wall, I cant see it doing any harm since a rigid reflective surface will be behind it anyway. Across a corner, I am not sure.

I have torn off the FRK from 703 before. You lose a little bit of your sheet doing this. Maybe 1/8-1/4". I didnt experience airborn problems with it if your worried about inhaling it.
#3
20th June 2012
Old 20th June 2012
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Quote:
Originally Posted by Jamman View Post
My question is whether there is any merit or any problem to have FSK on BOTH the front and the back of the trap?
For bass traps away from reflection points you want one FRK surface only, facing the room. For panels at reflection points and possibly behind you on the rear wall of a control room, turn the FRK around so it faces the wall. In both cases you do not want an additional layer of FRK in between the sandwich of two panels placed adjacent to be thicker, nor do you want FRK on both the front and the rear.

--Ethan

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Jamman
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#4
20th June 2012
Old 20th June 2012
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Thank you to both of you!

I guess this means I need to peel some FRK.

Thanks.
#5
28th June 2012
Old 28th June 2012
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ygayle is offline
Quote:
Originally Posted by Ethan Winer View Post
For bass traps away from reflection points you want one FRK surface only, facing the room. For panels at reflection points and possibly behind you on the rear wall of a control room, turn the FRK around so it faces the wall. In both cases you do not want an additional layer of FRK in between the sandwich of two panels placed adjacent to be thicker, nor do you want FRK on both the front and the rear.

--Ethan

The Acoustic Treatment Experts
Hi Ethan, I'm newbie who's looking at doing something similar but I'm a bit unclear with your response. With the traps at the rear wall or reflection points, you said to have the FRK facing the wall. I'm assuming that would still absorb some low end but reflect the high end (I hope that's correct). If so, how does that affect stereo imaging?
#6
29th June 2012
Old 29th June 2012
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If the panel is mounted with no gap and the FRK is touching the wall, then the FRK does nothing. But at least you don't have to bother removing it. If you do mount the panel with an air gap, then the FRK actually helps a bit to increase absorption at lower frequencies. Either way, not having FRK facing toward the room is what improves imaging and clarity. Then the insulation absorbs mid and high frequencies well.

--Ethan
#7
30th June 2012
Old 30th June 2012
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I am planning on making some bass traps out of ultratouch cotton. Do you think putting a paper poster on the outward facing side would act similarly to the FRK layer?
#8
30th June 2012
Old 30th June 2012
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Quote:
Originally Posted by alexlastname View Post
I am planning on making some bass traps out of ultratouch cotton. Do you think putting a paper poster on the outward facing side would act similarly to the FRK layer?
Yes that should actually work pretty well. Make sure you make them no less then 4" thick.
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#9
26th September 2012
Old 26th September 2012
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I'm gonna borrow this thread a bit

I have been wondering these same things with my panels. Mine don't have "metallic" FRK, but some kind of felt or something. Mine are similar to Ecophon Sombra, but i can't find any details from the specifications how the "felt" works acousticaly.

In my previous space i had a big cloud made with that system + bunch of 4" traps where i had glued two sheets together so that the felt was on both sides. Reason i originally got those as i wanted black non-reflective ceiling and those are made exactly for that in movie theaters. That also saved work on having to put any fabric over them. Only problem with the cloud was that it was so low that many times that took guitar off my neck i poked hole to the felt. Normal fabric would not break as easily.

I'm currently treating my new space that is oddly shaped and i need to put big Ikea Expedit bookshelf to the front wall as it's the only wall that has enough space. It will leave 400mm space on both sides that i'm gonna fill with insulation. That would give me 400x400mm softit traps to both front corners.

I was gonna cover the softits with fabric, but i got idea of covering them with wallpaper/tapestry. Wallpapers come in good designs that would make the softits look good. I'm just wondering how the thick paper work with sound. Bass goes trough anything, but what would that do the mids? As those are in front corners the highs don't matter. How low 400mm (16") softits go?

As my softis are only 16" i'm gonna fill them with rigid rockwool that i have. In deeper traps the softer "pink stuff" might be better. Correct?

Thank you!
#10
27th September 2012
Old 27th September 2012
  #10
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Quote:
Originally Posted by El-Burrito View Post
I'm gonna borrow this thread a bit

I have been wondering these same things with my panels. Mine don't have "metallic" FRK, but some kind of felt or something. Mine are similar to Ecophon Sombra, but i can't find any details from the specifications how the "felt" works acousticaly.

In my previous space i had a big cloud made with that system + bunch of 4" traps where i had glued two sheets together so that the felt was on both sides. Reason i originally got those as i wanted black non-reflective ceiling and those are made exactly for that in movie theaters. That also saved work on having to put any fabric over them. Only problem with the cloud was that it was so low that many times that took guitar off my neck i poked hole to the felt. Normal fabric would not break as easily.

I'm currently treating my new space that is oddly shaped and i need to put big Ikea Expedit bookshelf to the front wall as it's the only wall that has enough space. It will leave 400mm space on both sides that i'm gonna fill with insulation. That would give me 400x400mm softit traps to both front corners.

I was gonna cover the softits with fabric, but i got idea of covering them with wallpaper/tapestry. Wallpapers come in good designs that would make the softits look good. I'm just wondering how the thick paper work with sound. Bass goes trough anything, but what would that do the mids? As those are in front corners the highs don't matter. How low 400mm (16") softits go?

As my softis are only 16" i'm gonna fill them with rigid rockwool that i have. In deeper traps the softer "pink stuff" might be better. Correct?

Thank you!
Lemme guess, You´re an ESP-player. Reverse headstock? M-II perhaps?
Best leave the rigid for thinner panels. Do we even have "pink stuff" in Finland? For fluffier stuff I would recommend Paroc eXtra: 8333 Pa*s/m^2
It´s cheap and commonly available. And Paroc is apparently the only company in the finnish market to release/measure air permeability numbers.
At 400mm even a bit softer (glass wool or smth) might work better, but the difference is small.

Some calculemus:
Porous Absorber Calculator

I like the wallpaper idea. Must look into it for my front wall project. Many of them have plastic in them, so one would expect them to reflect some highs. Maybe there could be some membrane action as well? I´m guessing no tests have been carried out on this.
Also I wonder, how durable they are especially if stretched.
What if You have a cheap fabric underneath for strength, and put the wallpaper on that?
#11
28th September 2012
Old 28th September 2012
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Quote:
Originally Posted by Strand-old-man View Post
Best leave the rigid for thinner panels. Do we even have "pink stuff" in Finland? For fluffier stuff I would recommend Paroc eXtra: 8333 Pa*s/m^2
It´s cheap and commonly available. And Paroc is apparently the only company in the finnish market to release/measure air permeability numbers.
At 400mm even a bit softer (glass wool or smth) might work better, but the difference is small.
I happen to have loads of old rigid rockwool that i was planning to use as it's free. It would be enough for three corners or then split it four corners and fill the rest with fluffy stuff. I referred to pink stuff as it seems the common name in US for fluffy stuff :D Thank for the Paroc tip!

Quote:
Originally Posted by Strand-old-man View Post
I like the wallpaper idea. Must look into it for my front wall project. Many of them have plastic in them, so one would expect them to reflect some highs. Maybe there could be some membrane action as well? I´m guessing no tests have been carried out on this.
Also I wonder, how durable they are especially if stretched.
What if You have a cheap fabric underneath for strength, and put the wallpaper on that?
No need for stretching as i only need to cover the front side of the softits. For 40cm wide side it's easy to cut the wallpaper to fit and the patterns would look good.

Guess i'm just gonna try and measure. In previous measurements that i have done for plastic side on off i have not seen any notable differences in the frequency response, so i don't think my measurement system is accurate enough for that.
#12
16th December 2012
Old 16th December 2012
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Hey, just rescueing this 3 months old thread to ask for advice.

I just learnt that using frk (which I didnt use in the first place because the insulation fiberglass didnt came with) or a very slim plastic membrane (like a poster) will help trapping more low end.

So Im planning to add this to all the existings traps on my room. My question:

1) I didnt build the traps with an airgap (I just place them off the wall to create that space) so is there any problem if I just put the membrane at the back of the panels without going to the painfull task of removing the fabric from the back.

2) However the ceiling cloud was done with an air gap. Same question. Do I need to remove the fabric or I can just put a slim plastic membrane or cardboard sheet on top of it?

Side question about my Corner bass traps: Built them superchunk style front to ceiling. I read from EW, that is ok to cover one third of the trap with frk facing the room so you can get a not so dead room. Again I would like to skip the hassle of unwraping the fabric, etc. Is it ok if I just put the slim membrane in front of the trap? Like attaching some posters?

Thanks
#13
16th December 2012
Old 16th December 2012
  #13
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Yes, posters would be good. But spray-glue them to the material for best results.

--Ethan
#14
16th December 2012
Old 16th December 2012
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Quote:
Originally Posted by Ethan Winer View Post
Yes, posters would be good. But spray-glue them to the material for best results.

--Ethan
Is it ok to use white glue with fiberglass material? Excuse my ignorance

#15
17th December 2012
Old 17th December 2012
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Is it ok to use white glue with fiberglass material?
Maybe if you use a very thin coat. Spray glue is inexpensive and readily available, and I know that works if you use a minimal amount.

--Ethan
#16
17th December 2012
Old 17th December 2012
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Ok thanks, I'll buy it
#17
17th December 2012
Old 17th December 2012
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hey someone can post a link that show what is "posters"?
Sorry english is not my native, and i cannot search for this kind of stuff in google.
#18
17th December 2012
Old 17th December 2012
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Quote:
Originally Posted by Nickkk View Post
hey someone can post a link that show what is "posters"?
Sorry english is not my native, and i cannot search for this kind of stuff in google.
I dont know if you are trolling but anyway

#19
17th December 2012
Old 17th December 2012
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im really not troll. When i try to search posters in google this shows everything like that . Sorry for this, but my english sux
#20
17th December 2012
Old 17th December 2012
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Quote:
Originally Posted by Nickkk View Post
im really not troll. When i try to search posters in google this shows everything like that . Sorry for this, but my english sux
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