Using foam for low frequencies absorption

[eliya]

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?

[Sword9]

You're not going to soundproof anything with those.

[AVare]

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.

[yoga]

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.

[eliya]

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

[myfipie]

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

[eliya]

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!

[AVare]

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

[knightfly]

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

[eliya]

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,

[AVare]

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

[eliya]

ok, thank you and sorry.

[John Sayers]

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

[lovecow]

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.

[knightfly]

Jeff, does that mean your foam now burns with a green flame?

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