Using foam for low frequencies absorption

Hi there! I've been looking into this forum, reading about acoustics and searching for an answer for my question. I know that usually foam isn't ideal for low freq absorption, but what I did is slightly different from what i read in other people's posts about foam. I've built wooden frames at the size of 113cm X 70cm(hXw), and filled them with 5 layers of foam, when each layer's thick is 1"-1.5". there's an air gap of 0.5"-1" between every layer. so the whole frame with the foam is something like 10" thick, maybe even more. Each frame, with the foam and wood, weighs about 10-12 kg. These frames are ment to be bass traps, which I'll place 14" from each corner in the room. How efficient these traps are going to be? will they improve the romm's bass response the the same way a fiberglass bass trap would? I know that these are general questions, but are they a waste of time or something that's going to work and soundproof the room?

You're not going to soundproof anything with those.

How efficient these traps are going to be? will they improve the romm's bass response the the same way a fiberglass bass trap would? I know that these are general questions, but are they a waste of time or something that's going to work and soundproof the room?

As efficient as any design with that thickness. Yiou will do better to put all the foam together at the front of the trap. that is where the air velocity is greatest, and the foam will absorb. With a total thickness of 300 mm you will get flat free field absorption down to around 60 Hz. Very good. It will do nothing for soundproofing.

I've done derivatives of that with foam, and it seems to work, though I have no tests to prove it. I made triangular shapes out of foam and stacked them on corners. I have also made the foam sheet with 10cm airgap behind. I think they are working, well atleast I can notice the high frequency absorption. As for low frequencies, I don't know. But hey, it's gotta be doin something.

Sorry for confusing with soundproof. I ment Absorption, and I got my answer. Thank you!

You may want to think about maybe using a 4" piece of mineral wool or 703 instead of foam and space the panel off the wall about 4". You can also take 2 of the 2" board and put them together to make a 4" piece. If you have the time take look at this link http://www.ethanwiner.com/acoustics.html Ethan seems to explain all this stuff pretty well. Glenn GIK Panels

Hi, I read Ethan Winer's article twice, and it really tought me alot about acoustics! The thing is that fiberglass is causing cancer, and probably the only thing which will divide between me and the fiberglass would be felt. and that's too risky for me. That's why I used such a huge amount of foam, so it will compensate the lack of fiberglass. Should I add a plywood plate at the front of my current traps so it will absorb really low freqs(and reflect the highs)? and on that plate I can add a thin layer of foam, so it will absorb low frequencies too? would that work? or maybe I should leave my traps the way they are or just covering their front with felt. Thanks again!

The thing is that fiberglass is causing cancer

Read this: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=1742 It will help you a lot. Don't forget the mineral wool option! Andre

What brand of foam are you using? If it's not fire retardant, even assuming that fiberglass causes cancer (it doesn't), FIRE will kill you QUICKER... :? Steve

I went straight to the company who makes them. they gave me a nice price for the foam. These are fire retardant(I checked it myself). As for the fiberglass, I don't have a nylon suit to wear while working with this material, and I do think it's causing cancer(I read the thread you addressed me to before), cause no marketing genius would write on his product that it causing cancer. So probably I won't build frames with fiberglass my self, maybe I'll go to some professional and he'll build this. Back to the topic, would my traps with their current configuration, absorb low frequencies? Thanks,

Back to the topic, would my traps with their current configuration, absorb low frequencies?

What did you not understand about my first post in this thread? Read about absorbers of that thickness and that will be simialr to your results. Aassuming you get open cell foam... Andre

ok, thank you and sorry.

I've read similar articles to the one Rod posted regarding cancer and fibreglass. In fact the fire retardents, known as polybrominated diphenyl ethers (PBDE’s), coming off the plastic case of your puter monitor is more carcenogenic :) cheers john

John, AFAIK, there hasn't been any conclusive research showing that PDBEs are carcinogenic. They have been measured in unusually high concentrations in breast milk and they are a known "thyroid disruptor." Check this link. Regardless of the studies, it's probably worth noting that Auralex does not use PBDEs in our acoustical foams. We are using a newer, "greener," flame retardant. :D

Jeff, does that mean your foam now burns with a green flame? :mrgreen: :mrgreen: :mrgreen: JUST KIDDING, guys; anyone out there with an extremely LITERAL mind, please IGNORE me, just flickin' Jeff 'cause he's such a gentleman and I'm such a SMARTASS... Steve

Regardless of whether something is more carcegentic than the other, carcegenic is carcegenic. With the fibreglass and the plastic computer thing you mentioned. You're increasing the amount of carcegins in the room. If I had known that fibreglass was carcegenic, I would have worn a mask and well clothed myself in the enclosed room I was in. Instead of rolling around on them thinking they were harmless.

From the REFERENCE section, Construction forum, 9th from the top - http://www.johnlsayers.com/phpBB2/viewtopic.php?t=1742 This section has been REPEATEDLY linked, including in this top-of-page post - http://www.johnlsayers.com/phpBB2/viewtopic.php?t=3231 A quote from the link, in case you STILL won't follow the links we give - "If you wear protective clothing and masks while working on this stuff, then shower after, the rest is mostly "chicken little" from the more recent reports" and, "Basically, don't breathe the fibers when you're working with it, clean up after" - Your statement, "If I had known that fibreglass was carcegenic, I would have worn a mask and well clothed myself in the enclosed room I was in. Instead of rolling around on them thinking they were harmless." - Tells me you would rather blame others than follow directions in the first place. The information is here, members are asked to read it BEFORE EVEN POSTING, yet I get responses like yours; WTF else am I supposed to do, besides just letting Darwin's theory prove itself?? Steve

When I made my panels I sprayed them with adhesive to make the speaker grill material stick on the front and I sprayed the backs as well to kind of seal the glass from fraying. It works really good.

One possible downside of spraying the fronts of panels with ANYTHING may be a reduction in high frequency absorption; although the cloth covering should reverse that somewhat. As always though, your ears are the final test - if it sounds good, it IS good... :) Steve