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OC 703 FRK... to foil or not to foil????
Old 3rd September 2010
  #61
SAC
Registered User
 

...provided the 'FRK' is not applied upside down or 'reverse side out' which would tend to invert the phase, or just simply confuse the waves completely. Oh the drama...

And then the months or years of trauma and tears and counseling and...

And we haven't even explored the potential impact of VOCs being released from plastic applications....

...Pardon me, I'm overwhelmed already.hehhehheh


Here's an idea - as these threads seem to spawn on a near perpetual manner like bunnies... someone might simply assemble a sticky list of guidelines for the broadband absorbers and for corner bass traps - a very simple cursory chart of minimal thicknesses and weights for the most common materials and configurations - say Fiberglass, rock wool and perhaps one other like the safe n sound cotton stuff, or grass clippings or whatever stuff is supposed to be safe...(that's what we need! Another does Fiberglass kill you quickly or slowly thread!!!)tuttheh

Ignore framing, as the effect of both edge absorption and edge diffraction contribute only between 1-3% additional loss - so that's essentially a wash and relatively insignificant issue relative to the absorptive planar surface area.

But let's not go too far lest we eliminate all of the sources of endless inane debate and speculation!


hehhehhehheh
Old 5th September 2010
  #62
Gear Head
 

Question

Quote:
Originally Posted by Ethan Winer View Post
Exactly. Anything in the corners, out of the way, should have FRK. Any places where you need HF absorption, such as all reflection points and possibly other places on a low ceiling, should be fully absorbing.
Ethan,

I will quote one of the paragraphs from your "acoustic treatment..." page located here Acoustic Treatment and Design for Recording Studios and Listening Rooms traps.

Under the "Live or Dead..." section, you mention this...

If you are using 705-FRK rigid fiberglass or an equivalent product, you can cover more of the wall and still control the liveness by alternating the direction of the paper backing. That is, one piece of fiberglass will have the paper facing the wall to expose the more absorbent fiberglass, and the next piece will have the paper facing out to reflect the mid and high frequencies. In fact, when the paper is facing into the room the lower frequencies are absorbed even better than when it is faces the wall.



I know this is referring to a room larger than 10 x 10 and it is meant to help with the liveliness and ambience of recording... especially live acoustic instruments. And I understand what the paper does when placed on the front (facing the room). It reflects mids and highs and aids in low end absorption (gap plays a part as well) My question is this...

1. In the quoted section under "live or dead", do you mean with or without a gap?

2. If the paper is facing the wall and the absorber is flush against the wall, with no gap... essentially there is no difference between no paper (fully absorbent) because the paper is essentially part of the wall (the back of the absorber)... correct? However, if a gap is introduced here, say from a frame like mine (see earlier picture attachment)... exactly what happens sonically?????? What happens here differently with the paper on the back as opposed to without the paper on the back. That's the part I'm not understanding.
Old 6th September 2010
  #63
Gear Guru
Just One

Quote:
2. If the paper is facing the wall and the absorber is flush against the wall, with no gap... essentially there is no difference between no paper (fully absorbent) because the paper is essentially part of the wall (the back of the absorber)... correct? However, if a gap is introduced here, say from a frame like mine (see picture attachment)... exactly what happens sonically?????? What happens here differently with the paper on the back as opposed to without the paper on the back. That's the part I'm not understanding.
Correct, obviously, with no gap, no effect from foil at the back. Useful for damp or thermal blocking though.
With a gap and FRK on the back you will get some increased LF absorption.
I tested this, see post 12 here OC 703 FRK... to foil or not to foil????
Not a huge difference, but a clear enough advantage. If your material comes with Foil already on it, I would certainly leave it on.

DD
Old 6th September 2010
  #64
Gear Head
 

Quote:
Originally Posted by DanDan View Post
\
I am trying to compare FRK and no FRK from published Lab results here.
Unfortunately there is no airgap in one test, and a huge gap but no FRK in another. Finally the one test which might matter, FRK, no FRK, up down, same gap, I can't show you.
I'm assuming the FRK waterfall is the one with no gap... correct? If the other waterfall is a "huge gap" with no frk, how do we know from those waterfalls, that frk with a gap has better results if those results cannot be shown???

By the way, Thanks for contributing.
Old 6th September 2010
  #65
Gear Guru
2+2

Thanks for you comment mixed.

My own test FRK or Not, shows real panels in a real room, tested with FRK and without. The small differences in the Waterfalls are all we have.
Enough for me to recommend leaving the Foil on though.

The OC published tests do not compare scenarios directly useful to us.
However, they do show an increase in LF performance with FRK.
They also show an increase with an airgap.

The test police are bound to come kicking in the door, but personally I am prepared to add those two increases and say that it is likely that FRK on the back side, with an airgap has better LF absorption in the frequency zone we require, than bare insulation.

Plus, my own test pretty much proves that.

I would point out that a very well known commercial product is exactly as I describe. A bonded Foil membrane facing the airgap.

DD
Old 7th September 2010
  #66
Gear Guru
 
Glenn Kuras's Avatar
Quote:
Is 6" OC 703 ideal here (of course I know that thicker is better)?
Over 4" it is better, but would only recommend it over 4" if you are not going to have less panels. Meaning if your budget is low then stick with 4".

Quote:
The test police are bound to come kicking in the door, but personally I am prepared to add those two increases and say that it is likely that FRK on the back side, with an airgap has better LF absorption in the frequency zone we require, than bare insulation.
YMMV. heh
Old 7th September 2010
  #67
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by Mixed_Breed View Post
1. In the quoted section under "live or dead", do you mean with or without a gap?
Either way, with a gap improving LF absorption of course.

--Ethan

________________
The Acoustic Treatment Experts
Old 9th September 2010
  #68
Gear Head
 

Question

Quote:
Originally Posted by Ethan Winer View Post
Any places where you need HF absorption, such as all reflection points and possibly other places on a low ceiling, should be fully absorbing. Ethan
Ethan,

Say a corner is a direct reflection point, and I need a fully absorbing bass trap (4" thick)... meaning no frk on the front... Is it okay to put the frk on the back (straddling bass trap/direct reflection point) OR should I have no FRK at all in this situation?

All welcome to respond. Thanks again Ethan, Dan, and Glenn for your support. I am learning alot.
Old 9th September 2010
  #69
Gear Head
 

Question

Quote:
Originally Posted by Ethan Winer View Post
Either way, with a gap improving LF absorption of course.

--Ethan
Ethan, What about question # 2? Do I leave that "membrane" (FRK) on the back in that situation? If so, I'm mad I removed it all on atleast six 2" braodband panels, and three 4" clouds. Lots of messy work. But oh well, it is what it is. Maybe I can use those in a vocal booth for a more dead sound.

Guess I'll leave it on the back of the remaining braodband absorbers I build... to get that slight improvement in the LF absorption. I guess I'm just a bit concered about Glenns "better" results in that messy room with the FRK on the back once it was removed. I wish I knew more of the variables and factors in that situation.
Old 9th September 2010
  #70
Gear Guru
Oh Well

Mixed, I can sympathise, or maybe you can sympathise with me.
I took a notion and removed FRK from perfectly good commercially made traps which had FRK on the back. I had an idea that it was resonating and sucking a bit of warmth e.g. 200Hz or whatever from the room. I measured before and after. You can see the results for yourself. I subsequently replaced a lot of the foil removed with foiled. As we were.
It is not a big difference, and it is not a conclusive test. On the probabilities I would say with 4 inch traps, leave it on the back. I can see no down side and a small benefit. Glenn had the opposite experience, probably from the same curiosity, but his traps were two inch. I would go with the results from both, i.e. thin traps, leave it off, 4 inch leave it on. It is just slightly tested guessing and remember it was not a big difference. Take a look for your self at my test waterfalls and you will see what I mean. Post 12.
DD
Old 9th September 2010
  #71
Gear Guru
 
Glenn Kuras's Avatar
Quote:
Originally Posted by Mixed_Breed View Post

Guess I'll leave it on the back of the remaining braodband absorbers I build... to get that slight improvement in the LF absorption. I guess I'm just a bit concered about Glenns "better" results in that messy room with the FRK on the back once it was removed. I wish I knew more of the variables and factors in that situation.
Dan pretty much cleared it up. One of these days I would like to test this in a lab to really see what is up.
Old 9th September 2010
  #72
Gear Guru
Weird

It gets weird. Some time ago a poster tried FRK and other membranes on the front of his SuperChunks. No matter what he tried no LF improvement. An increase in HF decay time but no LF action. Go figure.
DD
Old 9th September 2010
  #73
Gear Guru
 
Glenn Kuras's Avatar
Quote:
Originally Posted by DanDan View Post
It gets weird. Some time ago a poster tried FRK and other membranes on the front of his SuperChunks. No matter what he tried no LF improvement. An increase in HF decay time but no LF action. Go figure.
DD
My theory would be that the spring action has some kind effect with the panel. Just a theory though. heh
Old 9th September 2010
  #74
Gear Guru
Drum

Yes, if you thump a FRK panel particularly in a corner. I love to get them in a corner and beat them.....
It has an audible boom, like a drum head.
The SuperChunk with FRK on front doesn't seem to have that resonance.

Someday, tests....

DD
Old 9th September 2010
  #75
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by Mixed_Breed View Post
Say a corner is a direct reflection point
How is that possible with a normal speaker setup?

Quote:
Is it okay to put the frk on the back (straddling bass trap/direct reflection point) OR should I have no FRK at all in this situation?
FRK on the back can only help when there's an air gap, but if the panel is flat against a wall it doesn't matter.

--Ethan

________________
The Acoustic Treatment Experts
Old 10th December 2010
  #76
Lives for gear
 
JLiRD808's Avatar
Quote:
Originally Posted by Mixed_Breed View Post
Ethan, I thought the ceiling cloud should have the foil facing the ceiling (the gap)????
I am also wondering this....foil facing up?

thanks
Old 10th December 2010
  #77
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Foil facing the room is not good for reflection panels, but it helps increase LF absorption a little when facing the other way.

--Ethan

________________
The Acoustic Treatment Experts
Old 10th December 2010
  #78
JWL
Lives for gear
 
JWL's Avatar
 

Quote:
Originally Posted by DanDan View Post
It gets weird. Some time ago a poster tried FRK and other membranes on the front of his SuperChunks. No matter what he tried no LF improvement. An increase in HF decay time but no LF action. Go figure.
DD
Sorry for jumping in late. If I had to guess, I'd say it's because the membrane wasn't properly adhered to the absorbent material underneath. This is quite a common mistake.
Old 10th December 2010
  #79
Gear Guru
Confidence

Quote:
If I had to guess, I'd say it's because the membrane wasn't properly adhered to the absorbent material underneath.
That seems very likely. People are unwilling to spray glue a membrane on well due to the mess taking it back off if it doesn't work out.
There are uncertainties regarding material, thickness, etc.
It seems funny that in a membrane/panel trap, the sheet is spaced away from the absorbent in order to vibrate sort of freely but damped by the proximity of the absorbent. In the other case a thin light sheet needs to be fully bonded to the absorbent. We know this works with panels of 705 etc. but I have seen nothing to show it working on SuperChunks yet.

DD
Old 10th December 2010
  #80
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by DanDan View Post
In the other case a thin light sheet needs to be fully bonded to the absorbent. We know this works with panels of 705 etc. but I have seen nothing to show it working on SuperChunks yet.
Yes, a bonded membrane works the same way with corner fill, for the same reason.

--Ethan

________________
The Acoustic Treatment Experts
Old 10th December 2010
  #81
Lives for gear
Sorry to jump in here late...
I have heard that adhering paper to one side of unfaced 703 achieves the FRK effect. would it be wise to also used aluminum foil on the paper if unfaced 703 is all I have available?
Old 10th December 2010
  #82
Gear Guru
Contact

The self adhesive decorative product 'contact' seems like a great idea.
DD
Old 7th March 2011
  #83
Here for the gear
 

So guys, what about foil backing BETWEEN two layers of RFG? As in two layers of 3" thick 703, one of which is backed with foil against the other one, with the normal air gap between the back one and the wall. Based on what little theory we have to go on, should this be better or worse than either configuration of 6" of uninterrupted 703? It seems to me that it would provide bass absorption halfway between (or peaking at a frequency halfway between) having it face the air gap and having it face the room, due to the distance from the wall, but without the resonance Dan has found with it facing the wall, and without reflecting mid-high frequencies like it does facing the room. Am I missing something?
Old 7th March 2011
  #84
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avare's Avatar
 

Quote:
Originally Posted by Frasier View Post
Am I missing something?
Yes. In your scenario, what is not good about 6" of 703 by itself?

The membrane will do something. What it will do is unknown without testing.

Andre
Old 24th March 2011
  #85
Here for the gear
 

Quote:
Originally Posted by avare View Post
Yes. In your scenario, what is not good about 6" of 703 by itself?

The membrane will do something. What it will do is unknown without testing.

Andre
Well, the stuff I have is foil backed so I figured I may as well leave it on where it'll help. I might just have to do some testing. heh
Old 24th March 2011
  #86
Gear Guru
Foiled

Ethan's test show a small benefit from a surface layer of foil, facing the room.
That is pretty convincing. My tests show a smaller benefit, from a much smaller sample, with foil facing the airgap. No-one has tests on foil sandwiched between layers of 703. It is easy to peel off the unwanted FRK
DD
Old 25th March 2011
  #87
Here for the gear
 

Quote:
Originally Posted by DanDan View Post
Ethan's test show a small benefit from a surface layer of foil, facing the room.
That is pretty convincing. My tests show a smaller benefit, from a much smaller sample, with foil facing the airgap. No-one has tests on foil sandwiched between layers of 703. It is easy to peel off the unwanted FRK
DD
I know, I peeled off a bunch of them to make my corner chunks. But since there seems to be a lack of (public) data in this area and since I'm curious and I'll be measuring my room at some point anyways, I think I'll do some testing with my two back-wall panels before I put the fabric on them. I'll post the results as soon as I have them--in the mean time, any tips on the testing process are welcome.
Old 25th March 2011
  #88
SAC
Registered User
 

Testing with a solid layer inserted between two constrained porous layers is not really necessary.

We know that the high frequency absorption will be limited by the depth of the front layer, and as the membrane is effectively constrained near equally from both sides with near equal pressure and velocity as the unit is not sealed in a resonant enclosure, one can reasonably not expect much of any benefit at the low frequencies.

Again we seem to want to devise a new method of implementation rather than to simply implement proven techniques.

So I guess it all depends upon your goal. If you simply want to try variations, you are of course welcome to do so! But if your goal is to construct a functional unit in a reasonable time frame, it might be prudent to follow the most optimal design given the materials, cost, and time available to implement them. And that, at least with respect solely to the LF absorption by porous absorbers: a low density Superchunk, a rear membrane straddled panel (or possibly a front membrane panel), or a non-surfaced straddled porous panel.
Old 25th March 2011
  #89
Gear Guru
Tests

Frasier, I encourage testing. However it is unlikely to display a conclusive result unless the testing is tweaked for success.

Position the driving speaker and mic at high pressure areas of the most significant mode. For instance place the speaker at the middle of the front wall, half height. This is in the nullls of H and W but a peak of Length.
Place the mic opposite, mid back wall. Focus on the second axial mode, higher frequency, traps more effective.
The sample needs to be large. All four corners. One will show nothing.

DD
Old 25th March 2011
  #90
Here for the gear
 

Quote:
Originally Posted by SAC View Post
We know that the high frequency absorption will be limited by the depth of the front layer, and as the membrane is effectively constrained near equally from both sides with near equal pressure and velocity as the unit is not sealed in a resonant enclosure, one can reasonable not expect much of any benefit at the low frequencies.

So I guess it all depends upon your goal. If you simply want to try variations, you are of course welcome to do so! But if your goal is to construct a functional unit in a reasonable time frame, it might be prudent to follow the most optimal design given the materials, cost, and time available to implement them.
Now that's the kind of reply I was looking for! But all I'd need to do is hang the frames without fabric and slide in the RFG panels in different configurations, so it's not much extra work and no extra cost to satisfy my curiosity and maybe help out the community.

Quote:
Originally Posted by DanDan View Post
Position the driving speaker and mic at high pressure areas of the most significant mode. For instance place the speaker at the middle of the front wall, half height. This is in the nullls of H and W but a peak of Length.
Place the mic opposite, mid back wall. Focus on the second axial mode, higher frequency, traps more effective.
The sample needs to be large. All four corners. One will show nothing.
And those are the kinds of tips I was looking for! Do you mean putting the test traps in all four corners? I already have superchunks almost done for the front two corners; the panels up for testing are those for the back wall and ceiling reflection points (I can position them anywhere other than the ceiling for testing). If I won't get significant results with 4 test panels, then I'll either just test the two in place from the mix position to see what works best for me or forget the testing and just make them without foil.
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