HangDawg
bUnGhOlIo
I finally found a place close to me that has this stuff but it has a foil facing on it. Will this work the same or does it have to be the non-faced type?
D
darwin
New member
Use the faced on the most interior (closest to the inside of the room) wall. It acts as a vapor barrier. If you have two layers of insulation (two stud walls), don't used faced on the layer that is closest to the exterior. This will tend to trap water in your wall. This is, at least, my meager understanding.
John Sayers
Solar Power!!
The foil facing allows it to be used in other situations like lining aircon ducts to stop noise transmission down them, plus it keeps the heat in. It can also be used on roofing to minimise heat from the sun getting and heat within getting out.
If you use it with the foil facing you will reduce the high end absorption also.
cheers
john
If you use it with the foil facing you will reduce the high end absorption also.
cheers
john
HangDawg
bUnGhOlIo
Since your here John. I have a low ceiling in the tracking room,
should I cover the entire thing in this stuff? How thick 1" or 2".
Thanks.
should I cover the entire thing in this stuff? How thick 1" or 2".
Thanks.
Ethan Winer
Acoustics Expert
John,
> If you use it with the foil facing you will reduce the high end absorption also. <
Yes, but that will increase the low frequency absorption!
--Ethan
> If you use it with the foil facing you will reduce the high end absorption also. <
Yes, but that will increase the low frequency absorption!
--Ethan
John Sayers
Solar Power!!
yeah - the foil acts like a membrane absorber doesn't it.
cheers
JOhn
RICK FITZPATRICK
New member
Really, how? I thought panel or membranes had to be stiff to a certain degree or trap an airspace
If thats the case John, why can't you hang foil in wall cavitys everywhere, and receive bass absorption that way? Or was HangDawg refering to exposed 703, like in bass traps? Just curious, as sometimes, the discussion/answers arn't clear enough for me, as my absorption coeffecient of the brain is somewhat attenuated
fitz
HangDawg
bUnGhOlIo
I was refering to the foil covered 703 stuff. I think they meant leaving it on the fiberglas decreases high frequency absorbtion and increases the low.
Ethan Winer
Acoustics Expert
Dawg,
> I was refering to the foil covered 703 stuff. <
Yes, I know. The foil acts as a sort of membrane, though the principle is not the same as a sealed membrane bass trap. This is from the Owens-Corning spec sheet showing 705 with and without the paper/foil facing:
2" 705 unfaced: 0.16 0.71 1.02 1.01 0.98 0.98
2" 705 w/facing: 0.60 0.50 0.63 0.82 0.45 0.34
The numbers from left to right are octave bands from 125 Hz. to 4 KHz.
--Ethan
> I was refering to the foil covered 703 stuff. <
Yes, I know. The foil acts as a sort of membrane, though the principle is not the same as a sealed membrane bass trap. This is from the Owens-Corning spec sheet showing 705 with and without the paper/foil facing:
2" 705 unfaced: 0.16 0.71 1.02 1.01 0.98 0.98
2" 705 w/facing: 0.60 0.50 0.63 0.82 0.45 0.34
The numbers from left to right are octave bands from 125 Hz. to 4 KHz.
--Ethan
HangDawg
bUnGhOlIo
So, what about my ceiling? Should I cover the entire thing with this stuff? It's low, approx 7' 10" Would 1" be thick enough?
John Sayers
Solar Power!!
Should I cover the entire thing with this stuff?
yes but I'd put the foil as the backing. 2" would be better.
cheers
john
yes but I'd put the foil as the backing. 2" would be better.
cheers
john
RICK FITZPATRICK
New member
Hello gents, OK, I get it, the numbers are almost reversed, within reason, correct?
Without understanding the principle, would it be similar to limp mass, or something else? Can you adhear something to the backside of the foil to increase the effect? Or does that attenuate it? So the foil would be facing the interior face of a trap, the exposed face of a sheetrock ceilng when applied directly to it, and in the case of wall cavitys, it should face the exterior sheithing, am I correct or missing something? Its nice to know, as you could use it in different configurations with 703 to obtain a broader band of absorption. Is that also correct?
What I don't understand fully, is the wall cavity use. You said it acts as a vapor barrier, so that implys a wall cavity, so with out being exposed to sound waves directly, how does it absorb a lower frequency? Through the interior face material? And since the cavity would have its own resonant frequency, would that have anything to do with it, or am I barking at the wrong tree?
Thanks for the help.
fitz
Without understanding the principle, would it be similar to limp mass, or something else? Can you adhear something to the backside of the foil to increase the effect? Or does that attenuate it? So the foil would be facing the interior face of a trap, the exposed face of a sheetrock ceilng when applied directly to it, and in the case of wall cavitys, it should face the exterior sheithing, am I correct or missing something? Its nice to know, as you could use it in different configurations with 703 to obtain a broader band of absorption. Is that also correct?
What I don't understand fully, is the wall cavity use. You said it acts as a vapor barrier, so that implys a wall cavity, so with out being exposed to sound waves directly, how does it absorb a lower frequency? Through the interior face material? And since the cavity would have its own resonant frequency, would that have anything to do with it, or am I barking at the wrong tree?
Thanks for the help.
fitz
RICK FITZPATRICK
New member
Hmmm, would that also imply, in a wall cavity, this foil would also improve the STC of the wall, or am I still barking blind?
fitz
fitz
Ethan Winer
Acoustics Expert
Fitz,
> Can you adhear something to the backside of the foil to increase the effect? <
I don't know for sure, but I'll guess you should leave the foil as it is since that's how it was designed and measured.
> in the case of wall cavitys, it should face the exterior sheithing <
The best low frequency absorption is when the foil is facing into the room. If it's against the wall the foil won't be free to vibrate. But that means it will reflect mids and highs because you have a foil surface rather than the more absorbent fiberglass. For fiberglass in a corner I'd put the foil facing the room to work best at low frequencies. You can then alternate the pieces on the walls so every other one has foil facing into the room to avoid making the room too dead. For the panels with the foil facing the wall, mount them on thin (1/4-inch) strips of wood to leave a small gap so the foil can vibrate.
> would that also imply, in a wall cavity, this foil would also improve the STC of the wall, or am I still barking blind <
Fiberglass attached to a wall is unlikely to reduce low frequency sound transmission through the wall by more than a dB. or two.
--Ethan
> Can you adhear something to the backside of the foil to increase the effect? <
I don't know for sure, but I'll guess you should leave the foil as it is since that's how it was designed and measured.
> in the case of wall cavitys, it should face the exterior sheithing <
The best low frequency absorption is when the foil is facing into the room. If it's against the wall the foil won't be free to vibrate. But that means it will reflect mids and highs because you have a foil surface rather than the more absorbent fiberglass. For fiberglass in a corner I'd put the foil facing the room to work best at low frequencies. You can then alternate the pieces on the walls so every other one has foil facing into the room to avoid making the room too dead. For the panels with the foil facing the wall, mount them on thin (1/4-inch) strips of wood to leave a small gap so the foil can vibrate.
> would that also imply, in a wall cavity, this foil would also improve the STC of the wall, or am I still barking blind <
Fiberglass attached to a wall is unlikely to reduce low frequency sound transmission through the wall by more than a dB. or two.
--Ethan
RICK FITZPATRICK
New member
Hello Ethan, ok, when it is facing into a room, in that context is it acting as a limp mass, no matter it weighs very little? I'm trying to understand by what principle it absorbs low frequency. And does the size dictate the frequency range it absorbs? Ethan, when people tell me to use something to gain something and not explain why, it makes me wonder. If I know whys and hows then sometimes I can see other ways or uses. But some people say, "you don't need to know, you wouldn't understand it if I told you."
Perhaps. Perhaps not. I still like to know. Thats what allows me to bolt the rectifier side of a dodge alternater to the firewall of my toyota, when its own alterrnater burned out, and I couldn't afford one. I simply ran wires to from the dodge 1/2 to the toyota alternater. Or use a belt for a crankshaft bearing. Worked great More than one way to get out of the desert alive.
fitz
Perhaps. Perhaps not. I still like to know. Thats what allows me to bolt the rectifier side of a dodge alternater to the firewall of my toyota, when its own alterrnater burned out, and I couldn't afford one. I simply ran wires to from the dodge 1/2 to the toyota alternater. Or use a belt for a crankshaft bearing. Worked great More than one way to get out of the desert alive.
fitz
Ethan Winer
Acoustics Expert
Fitz,
> is it acting as a limp mass, no matter it weighs very little? I'm trying to understand by what principle it absorbs low frequency. <
I'm trying to understand too - the problem is I don't know how it works. I do know it's not the same principle as the diaphragm in a sealed panel trap. In that case it's important for nothing to touch the panel because that would restrict its movement. The panel needs to be able to move freely in order to work efficiently.
> does the size dictate the frequency range it absorbs? <
Again, I have no idea. I would love to test various combinations of 705 with the paper membrane as is, painted to make it heavier, and other such variations. The problem is it's very difficult (read: expensive) to do such tests. I just paid $1500 for a day of testing our RealTraps at IBM's acoustics lab, so this is not something I plan to do regularly!
One thing I am sure of: the specs for 705 with and without the facing show that the facing makes a huge difference at low frequencies. I can also tell you that we tested 705 with the paper membrane facing the room and also facing the wall, and facing the room absorbed a lot better at the low end. At the high end of course it was much worse, because the foil/paper is reflective.
--Ethan
> is it acting as a limp mass, no matter it weighs very little? I'm trying to understand by what principle it absorbs low frequency. <
I'm trying to understand too - the problem is I don't know how it works. I do know it's not the same principle as the diaphragm in a sealed panel trap. In that case it's important for nothing to touch the panel because that would restrict its movement. The panel needs to be able to move freely in order to work efficiently.
> does the size dictate the frequency range it absorbs? <
Again, I have no idea. I would love to test various combinations of 705 with the paper membrane as is, painted to make it heavier, and other such variations. The problem is it's very difficult (read: expensive) to do such tests. I just paid $1500 for a day of testing our RealTraps at IBM's acoustics lab, so this is not something I plan to do regularly!
One thing I am sure of: the specs for 705 with and without the facing show that the facing makes a huge difference at low frequencies. I can also tell you that we tested 705 with the paper membrane facing the room and also facing the wall, and facing the room absorbed a lot better at the low end. At the high end of course it was much worse, because the foil/paper is reflective.
--Ethan
HangDawg
bUnGhOlIo
So what I gather Ethan, when I build your Low Bass traps, I should leave the foil on and have it mounted with the foil facing out towards the room. The mid/high absorber should have foil removed.
Ethan Winer
Acoustics Expert
Dawg,
> So what I gather Ethan, when I build your Low Bass traps, I should leave the foil on and have it mounted with the foil facing out towards the room. <
I've never used faced fiberglass in a panel trap. I think in that case you'll be better off without the facing. Or at least place the facing away from the panel. But I don't really know for sure.
> The mid/high absorber should have foil removed. <
No, leave it on but facing away from the room.
--Ethan
> So what I gather Ethan, when I build your Low Bass traps, I should leave the foil on and have it mounted with the foil facing out towards the room. <
I've never used faced fiberglass in a panel trap. I think in that case you'll be better off without the facing. Or at least place the facing away from the panel. But I don't really know for sure.
> The mid/high absorber should have foil removed. <
No, leave it on but facing away from the room.
--Ethan
HangDawg
bUnGhOlIo
Damn, completely wrong again.