Bob Abrams
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bonded acoustical cotton
In searching around for a cheap method for bass trapping - I'm an intermediate level double bass player working in a small , furniture-filled room - I came across this website <acousticalsurfaces.com> that offers a bonded acoustical cotton product that produces a a noine reduction coefficient of .97 at 125 Hz. I can't seem to find any discussion of this material in a limited search. Who can tell me about pros/cons? Thanks.
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tor
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RE: bonded acoustical cotton
2006/07/21 17:20:12
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You could try visiting www.realtraps.com and talk to Ethan Viner, who happens to be a member of this forum. He often has real good info on questions like yours. I'm sure he'll answer any e-mail, and also try to contact him here. Good luck
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Bob Abrams
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RE: bonded acoustical cotton
2006/07/21 19:25:41
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Thanks, Tor. I have read most everything from Ethan and looked at his videos, but hadn't seen anything about compressed cotton as a bass trap. Thus, my query to the Forum guys. I will now telephone Ethan. He'll have just the right answer, I'm sure. Bob
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Ethan Winer
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RE: bonded acoustical cotton
2006/07/24 13:45:52
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Hey Bob,
> a bonded acoustical cotton product that produces a a noine reduction coefficient of .97 at 125 Hz. I can't seem to find any discussion of this material in a limited search. Who can tell me about pros/cons? <
Acoustic cotton works fine, but it's much more expensive than equivalent rigid fiberglass. Cotton seems to appeal to people who (incorrectly) fear that fiberglass is a carcinogen or is otherwise dangerous. Fiberglass is a skin irritant, so you should wear gloves when working with it, and cover the fiberglass with fabric to keep the fibers in place.
--Ethan
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yep
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RE: bonded acoustical cotton
2006/07/24 14:15:22
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What Ethan said.
You could, of course, buy some prefab bass traps such as those sold by Ethan's outstanding company, and have an easy, elegant, and reasonably-priced solution delivered to your door, or you can DIY and make some excellent bass traps yourself from rockwool/rigid fiberglass, or even home furnishings. There are a lot of threads on this in the gear and techniques forums. A search on "bass traps" over the last year or two will turn up some useful info.
Cheers.
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tarsier
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RE: bonded acoustical cotton
2006/07/24 15:49:22
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ORIGINAL: Ethan Winer
Acoustic cotton works fine, but it's much more expensive than equivalent rigid fiberglass.
Saying that it "works fine" is a bit ambiguous--so when you say "equivalent rigid fiberglass" do you mean that acoustic cotton is pretty much the same as rigid fiberglass acoustically, it just costs more?
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pedalboy
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RE: bonded acoustical cotton
2006/07/24 16:30:29
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Without getting complicated, the performance is a product of the fibre thickness and the spacing between fibres - this in turn determines the resistance to air flow or resistivity. Very generally speaking the higher the resistivity the better the absorption (up to a limit obviously). You need resistivity data or absorption data to compare products. High density fibreglass (35- 50 kg/m3) almost always works out to be the most cost effective means of providing porous absorption. For decent low frequency performance you will need to either make sure the fibreglass is thick (100 mm +) this will provide broad band absorption or alternatiuvely put a membrane (steel or timber) on a cavity (filled with fibreglass) for just low frequency absorption. Can't remember the formula off the top of my head for weight of panel for frequency etc - should be on the net.
Smith St Studios - NZ Delta 1010LT AMD 2800 Athlon64 Sonar 4 SE
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Ethan Winer
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RE: bonded acoustical cotton
2006/07/25 12:54:33
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> Saying that it "works fine" is a bit ambiguous--so when you say "equivalent rigid fiberglass" do you mean that acoustic cotton is pretty much the same as rigid fiberglass acoustically, it just costs more? < More or less.  The problem is it's almost impossible to tell if one product is exactly the same as another because of the variation in acoustic testing labs. If you test the exact same material in ten labs you'll get ten different results. heck, if you test the same material in the same lab ten times in a row you'll also get ten different results. The biggest variations are at low frequencies, and that's what matters most. Labs can vary as much as 50 percent at 125 Hz, and a lot more below that. Also, labs don't report below 100 Hz anyway, so the best you can do is look for trends among various products. But all that said, the bottom line is acoustic cotton works fine, it just costs more than rigid fiberglass. And unlike fiberglass, cotton is not fire proof. --Ethan
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