Should I double up the fiberglass for wall panels?

[KurtR]

I am going to be using 1 1/2" OC 800-FRK (I'm taking off the frk stuff)
Here are the stats http://www.owenscorning.com/comminsu...EnduraGold.pdf
It's not as good as OC700 stuff but I was able to pick this stuff down the street. I wanted to see if it would help if I used 2 2x4 panels per 2x4 panel for the walls. They will mostly be needed for high end freqs. I am thinking of making a 5" deep wood frame with 1 panel on the front then a 1" airgap then another panel then the rest to the wall an airgap. Is it worth it to do this vs. using only a single fiberglass panel per panel? I plan to be using about 10 or so plus bass traps (at least duble up the panels here... maybe triple) for a 12x20 room. I'll take any advice! thanks! -It's a tracking room to record drums ect... One wall is actually brick so I need all the help I can get.

[cramseur]

Maybe Ethan or one of the other smart guys will chime in, if i've got this wrong, but go ahead and layer them.

The thicker you make them, the more absorption you'll get at lower freqs.

Craig

[KurtR]

I was thinking that. Anyody else?

[nathanvacha]

I think a thread just like this came up last week too... And doubling up should help for low end, but i think it shouldn't make much of an impact in higher frequencies.

By making it thicker, the result you end up with is a wider frequency band that you're taming... you'll absorb lower frequencies because of thickness and the wavelengths.

But you don't want the airgap between the two layers! Having an air gap behind the two layers will increase the low end absorption, but you want the gap between the fiberglass and the wall, not between the two layers.

[Glenn Kuras]

>But you don't want the airgap between the two layers! Having an air gap behind the two layers will increase the low end absorption, but you want the gap between the fiberglass and the wall, not between the two layers.<

You are totally correct on this..

I have not worked with the oc800, but it may work for HF absorption.. I would make the panels 2 inechs thick and space off the wall 2 inchs... That should work fine..
Just a side note I really dont think this stuff will work for bass trapping though.. You are going to need OC 703 or OC705 for that..


Glenn

[jajjguy]

The key is the distance between the wall and the room side of the panel. 1 inch is enough for the actual panel thickness. In other words, 5 inches airspace plus 1 inch of panel is about the same as 4 inches of airspace and 2 inches of panel. Better just to increase the airspace and save $$ on panels.

Why? Cuz low-freq waves are very long, and it is important to get the absorption as far into the length of the wave as possible (up to 1/4 wavelength). Why? Cuz porous absorbers (like fiberglass) work by making it harder for the air particles to move back and forth. And the particle movement is greatest at 1/4 wavelength, and is least at the wall. The absorber will have the most effect where there is the most particle motion for it to slow down.

[Glenn Kuras]

Originally Posted by jajjguy

The key is the distance between the wall and the room side of the panel. 1 inch is enough for the actual panel thickness. In other words, 5 inches airspace plus 1 inch of panel is about the same as 4 inches of airspace and 2 inches of panel. Better just to increase the airspace and save $$ on panels.

Why? Cuz low-freq waves are very long, and it is important to get the absorption as far into the length of the wave as possible (up to 1/4 wavelength). Why? Cuz porous absorbers (like fiberglass) work by making it harder for the air particles to move back and forth. And the particle movement is greatest at 1/4 wavelength, and is least at the wall. The absorber will have the most effect where there is the most particle motion for it to slow down.

The wave does not "slow" down but turn into heat.. You are totally right by what you are saying, but don't forget that the length of a 125hz wave is something like 28 feet, so grabbing 1/4 of it would have to be really thick. That is why you want to use 2 inch panels to not only try to grab 1/4 of the wave (with the space) but it is going to help absorb (turn to heat) more..

Glenn

[Ethan Winer]

Guys,

> The absorber will have the most effect where there is the most particle motion for it to slow down ... The wave does not "slow" down but turn into heat <

Just to clarify:

1) The ideal air gap is equal to the panel thickness. So you'll get the most out of a 2 inch thick panel when it's spaced 2 inches off the wall. You can extend the absorption a little lower in frequency by using an even larger gap, but with thin panels (1 or 2 inches thick) that risks creating "holes" in the absorption at higher frequencies.

2) Sound does indeed slow down as it passes through a porous absorber! This is why stuffing fiberglass inside an acoustic suspension speaker cabinet makes the cabinet appear acoustically larger than it really is. This same phenomenon also causes the mode frequencies in a room to shift down when bass traps are added.

--Ethan

[RCM - Ronan]

Ethan, thanks for that info. Do you subscribe to the idea of hanging absorbtion on an angle so that the air gap varies, there by making the treatments effective over a wider range of frequencies?

[Glenn Kuras]

Originally Posted by Ethan Winer

Guys,

> The absorber will have the most effect where there is the most particle motion for it to slow down ... The wave does not "slow" down but turn into heat <

Just to clarify:

1) The ideal air gap is equal to the panel thickness. So you'll get the most out of a 2 inch thick panel when it's spaced 2 inches off the wall. You can extend the absorption a little lower in frequency by using an even larger gap, but with thin panels (1 or 2 inches thick) that risks creating "holes" in the absorption at higher frequencies.

2) Sound does indeed slow down as it passes through a porous absorber! This is why stuffing fiberglass inside an acoustic suspension speaker cabinet makes the cabinet appear acoustically larger than it really is. This same phenomenon also causes the mode frequencies in a room to shift down when bass traps are added.

--Ethan

Thank you for clearing that up, but sound still travels at the same speed... It does absorb though..

Glenn

[jajjguy]

Originally Posted by Ethan Winer

The ideal air gap is equal to the panel thickness. So you'll get the most out of a 2 inch thick panel when it's spaced 2 inches off the wall. You can extend the absorption a little lower in frequency by using an even larger gap, but with thin panels (1 or 2 inches thick) that risks creating "holes" in the absorption at higher frequencies.

This is true, sort of. But if you can only afford 1-inch panels but you can space them 6 inches off the wall, you are doing a lot better than spacing them 1 inch off the wall.

[jajjguy]

Originally Posted by myfipie

The wave does not "slow" down but turn into heat..

No, the wave doesn't slow down. I said the air particles slow down. They oscillate at the same rate, but move less far each time. You are right that this motion is lost as heat.

[tINY]

Note to would-be-acousticians:

Sound is a longitudinal mechanical wave. The probagation speed of this wave is different in various mediums. Adding glass fiber to air changes the elaticity and density of the air and is likely to change the speed of sound.



-tINY

[Anderson]

Originally Posted by tINY

Note to would-be-acousticians:

Sound is a longitudinal mechanical wave. The probagation speed of this wave is different in various mediums. Adding glass fiber to air changes the elaticity and density of the air and is likely to change the speed of sound.



-tINY

Yep, exactly! This can be an PITA when designing panels and rooms....
This is an easier way to look at what happens (a little physics won't hurt anybody I guess):

[Cojo]

Originally Posted by tINY

Note to would-be-acousticians:

Sound is a longitudinal mechanical wave. The probagation speed of this wave is different in various mediums. Adding glass fiber to air changes the elaticity and density of the air and is likely to change the speed of sound.



-tINY

Yes, different medium = different sound speed.

/Cojo

[Glenn Kuras]

Originally Posted by Cojo

Yes, different medium = different sound speed.

/Cojo

Agreed.

[Mitch Lowen]

Originally Posted by myfipie

Thank you for clearing that up, but sound still travels at the same speed... It does absorb though..

Glenn

Uhm.. this guy commented on Ethan Winer. I repeat... this guy commented on Ethan Winer.

This is gonna be the Jay-Z vs. Nas of GS!!!!

[Glenn Kuras]

Originally Posted by jajjguy

No, the wave doesn't slow down. I said the air particles slow down. They oscillate at the same rate, but move less far each time. You are right that this motion is lost as heat.

Oh ok I must have read that wrong.. Sorry about that...

Glenn

[Ethan Winer]

Glenn,

> sound still travels at the same speed <

As tINY explained, sound travels at different speeds through different mediums. This is exactly why decoupling a loudpseaker from what it rests on can give an improvement. Without decoupling, some of the sound travels to your ears through the air at one speed, and some also travels through the floor or wall or whevever at a faster speed. The difference in arrival times causes comb filtering peaks and nulls.

--Ethan

[Ethan Winer]

Jaj,

> if you can only afford 1-inch panels <

Well, in that case...

Actually, if someone can afford only one inch of 703, what are they doing here at Gearslutz? Drooling and dreaming about gear they wish they could afford?

--Ethan

[Glenn Kuras]

Originally Posted by jajjguy

No, the wave doesn't slow down. I said the air particles slow down. They oscillate at the same rate, but move less far each time. You are right that this motion is lost as heat.

Ethan thanks for the comment but the above post cleared it up..

[Scott R. Foster]

Originally Posted by KurtR

I am going to be using 1 1/2" OC 800-FRK (I'm taking off the frk stuff)
SNIP
It's not as good as OC700 stuff but I was able to pick this stuff down the street.

Heya Kurt... I'm up in Jacksonville!

Can you take it back? You should be able to get 703 for an excellent price at:

Seacoast Supply
1751 N. Nova Road
Holly Hill, FL 32117
386/257-1318 (Phone)
386/257-4786 (Fax)

or similar commercial construction supply house.

http://tinyurl.com/g3rjf

Get 2" panels and double em up to make 4" - then mount em with a gap behind of at least 3"... and Bob's your ankle. Don't worry about a larger gap if that is most convenient... a larger gap will work perfectly well.

[Ethan Winer]

Ronan,

> Do you subscribe to the idea of hanging absorbtion on an angle so that the air gap varies <

Sorry, I missed that the first time around. I think it makes more sense to use a single gap equal to the thickness of the panel.

--Ethan