Density of Fiberglass

[JuliánFernández]

Hi, i have some spear fluffy fiberglass that i would like to use on my bass traps...
The wool is about 15 kg/m3, and the question is...
How deep should i make the corner bass trap using wool that light?

I was thinking on making bass traps using rolls of wool standing on corners... what do you say?

[Gorty]

Originally Posted by JuliánFernández

I was thinking on making bass traps using rolls of wool standing on corners... what do you say?

The rolls of wool/fibreglass in rolls standing in the corners would make great bass trapping. Covering them with some burlap or thin material will make them more aesthetically appealing!

[JuliánFernández]

Wow, great... kind of weird i never found that kind of trap in another thread... nevermind.
Gorty (or everyone else) low density is not critical in this design?

[mixsit]

Originally Posted by JuliánFernández

Wow, great... kind of weird i never found that kind of trap in another thread... nevermind.
Gorty (or everyone else) low density is not critical in this design?

Depth is more than density.

[JuliánFernández]

In Argentina, rolls of low density wool are cheaper than 50 kg/m3 rigid panels... If rolls work well then i have a great and cheap solution...
Why not everyone is using this method?!

[knightfly]

Julian, the reason everyone isn't using this method is because it is NOT as good - the only place density of fiberglass or rockwool isn't QUITE as critical is INSIDE a WALL, when used as damping of the wallboard panels.

When used in less than maybe 3 Meter thick traps or more, the stuff you have won't absorb to as low frequencies nor as evenly nor as MUCH as the 48-50 kG/m^3 stuff that's more expensive. (To convert to Pounds per cubic foot, divide the kG number by 16.)

Keep in mind that fiberglass insulation is sold basically by the WEIGHT - so if yours is 4 times as dense, it'll cost about 4 times as MUCH for a given thickness, and it'll absorb more sound because it has tighter woven material and more of it.

Not saying that rolls of the stuff in your picture won't do anything, just nowhere near as much or as well.

The reason people like Rod, Ethan, John and myself recommend what we do is because it WORKS. None of us want you to have to spend more than necessary to get your room sounding good, so we won't recommend things that'll only make you buy TWICE... Steve

[bpape]

I'd have to caveat that a little bit. If you're making an absorber that's 18" thick, less dense material will work just fine. In 4-6" absorbers, no, density is much more important.

In reality, the difference between the 15 and 50 density assuming 18" thickness is going to be exclusively below 45Hz or so. Doesn't mean that the lighter stuff won't do anything down that low, just that it won't do quite as much.

If the cost difference isn't pretty dramatic, then I'd go ahead and buy the denser materials. If it's more than double, you can buy twice as much and compress it to double the density.

So, if you're doing music with a lot of content down that low, then the additional density may well be worth your investment. If not and your budget is limited, I'd rather invest in more treatment for the room overall with the limited budget rather than having have as much that's 10-20% better down in the extreme bottom end.

Bryan

[Gorty]

Originally Posted by JuliánFernández

Hi, i have some spear fluffy fiberglass that i would like to use on my bass traps...
The wool is about 15 kg/m3, and the question is...
How deep should i make the corner bass trap using wool that light?

I was thinking on making bass traps using rolls of wool standing on corners... what do you say?

After reading the other post's here you can see the density of the material you have here will be effective somewhat, just not as effective as the more dense rigid fibreglass.
The general consensis is to straddle the corners for bass trapping, however I am trying to find the arcticle I read that had cylindrical type bass traps featured. If you have a limited budget you could roll the material you have tighter or compress to obtain more density.

[Innovations]

When the material isn't dense enough the air moves too freely through it to break up the sound waves. If it can move too freely through four inches it will move to freely through sixteen.

So since this is leftover material the trick to make some usefull use of it is going to be to find a way to compress it while still having it be exposed to the sound waves.

[JuliánFernández]

The rolls factory-unpacked are quite compressed, not sure how am i supposed to mesuare it anyways...
I´m talking about 18 or 20" of wool...

I´m not quite sure what to do... should i buy 4" of rigid fiberglass as corner traps or should i stack my 18" rolls for best results..?

[Innovations]

The target should be three to five pounds per cubic foot. Usually home thermal insulation is shipped packed tightly but also wrapped in shrink plastic to keep it clean and compressed. The plastic will cause the sound to bounce off. That's the balance with absorbers, you want the materials to be just tight enough that the sound cannot get through without being disrupted by all the tiny passages but still open enough that the sound moves into the material and doesn't just bounce off the surface.

[JuliánFernández]

Innovations... i didn´t follow you... are you saying that the wool with plastic will reflect some HF waves but still absorb LF waves?
That´s kind of good, right?

[Innovations]

The plastic will reflect both high and low frequency waves. There is a chance that the surface might function as a membrane absorber for the bass frequencies, but it is pure guesswork as to what frequency range it will work with.

[Innovations]

Here is an example of what one guy did to make properly dense absorbers out of wall-type insulation. As you can see it took quite a bit of work.

http://webpages.charter.net/jdgeisen.../BassTrap1.htm

[JuliánFernández]

Originally Posted by bpape

In reality, the difference between the 15 and 50 density assuming 18" thickness is going to be exclusively below 45Hz or so. Doesn't mean that the lighter stuff won't do anything down that low, just that it won't do quite as much.

Innovations, thanks for the link... but what about what Bryan said?
It seems that not everyone agrees with that one...

[Innovations]

because honestly without test results you don't actually know anything.

[bpape]

From Bob Golds site - actual tests from OC directly:

4" OC705 A Mount flat on the wall
0.75 1.19 1.17 1.05 0.97 0.98 1.10

6" OC703 A Mount flat on the wall
1.19 1.21 1.13 1.05 1.04 1.04

6" standard fluffy fiberglass A Mount flat on the wall
0.64 1.14 1.09 0.99 1.00 1.21

12" standard fluffy fiberglass A Mount flat on the wall
1.14 1.09 1.09 0.99 1.00 1.21

Down lower (below where standard testing is allowed due to room differences), the thicker material will still perform better. Now, doing 12" of 703 - better yet - but twice the money.

Also understand that different materials are different - not just by density - but by gas flow resistivity. Fiberglass, mineral wool, and acoustical cotton of the same thickness and density have different properties:

2" OC703
0.17 0.86 1.14 1.07 1.02 0.98

2" 3.5lb Mineral Wool
0.26 0.68 1.14 1.13 1.06 1.07

2" 3lb Acoustical Cotton
0.35 0.94 1.32 1.22 1.06 1.03

Bryan

[Innovations]

Thanks Bryan, do you have a link for that? All the product sheets I could find on OC's site had only thermal properties for the fluffy stuff.

[JuliánFernández]

Originally Posted by bpape

12" standard fluffy fiberglass A Mount flat on the wall
1.14 1.09 1.09 0.99 1.00 1.21

Thanks Bryan...

btw, here´s the link...

http://www.bobgolds.com/AbsorptionCoefficients.htm

[bpape]

Just understand that having a better number at 125Hz doesn't guarantee a better number at 50Hz - but it usually doesn't hurt. As I said, 12" of 703 will outdo 12" of fluffy. Some people will mix and put 4" of 703 in front and 9-12" of fluffy behind.

Bryan

[JuliánFernández]

I understand that, Bryan, thanks for the tips...
I like the idea of mixing fluffy and rigid stuff... That way i can use the spear wool i already have, and later buy some rigid fiberglass to improve my bass
traps!

Thanks everyone for turning this into a great thread!

[knightfly]

Sounds like a good plan to me too; that would put the heavier stuff away from the wall where it'd do the most good, and it wouldn't require you to tear anything out if the fluffy stuff doesn't quite finish the job at the very low end... Steve