Acoustic Foam types and their densities?

jjitter

New member
Hello All,

I landed on this great forum sometime ago when I finally decided to treat my room with better acoustics and this place has been extremely resourceful.

So I went ahead and made the walls soundproof as much as my budget could allow and want to treat the walls now the best I can.

I have some wooden planks with which I can make 3 broadband absorbers (6ftx3ft, 4in thick). How can these broadbands be placed to become efficient Bass Traps? Corners or against the walls?

Also, I was a bit confused about the kind of foam and density need for absorption of mid/highs. Internet research tells me that a 2"- 4" open cell PU foam with a density of around 24 - 30kg/m3 is a good absorber (the choice again depends on the room and the walls).

But the egg crate foam absorption sheets look quiet different (a little more porous)egg crate foam.jpg as compared to how the foam Pyramid, wedged or grid foam panels look like(much more rigid, less porous).grid panel foam.jpg
My confusion was - Are they both open cell PU foams of different densities? Or are they different types of foams with different densities? Or are they same? I was comparing what I understand by the 2 images attached.

Can someone help me with my question? Dont want to go blank to a foam store.

Thank you!
 
Any acoustic panel supplier should have an absorption coefficient table for their products so you can compare them directly, i.e., to see whether they have similar properties at different frequencies or not. Here's a (slightly biased, but not unreasonable) article I found. The coefficient vs frequency tables in the article are what you want to find for the materials you are looking at.

I don't think the shape of the foam really matters, as it's not acting as a diffuser as much as an absorber.

Science of Absorption | Primacoustic

From what I've read, the bass traps go in the corners first (where 3 surfaces join). After that you can start putting them in places where 2 surfaces join - most commonly the wall-ceiling.
 
Please don't use foam as your main acoustic treatment. Some details about your space would be good, but inevitably rockwool full frequency traps (at least 4" thick) are needed. Thicker rockwool (superchunks) if you have the room. 2" rockwool for ceiling cloud (above mixing position) and at point of first reflection on side walls.
 
Re 'sculpted vs solid batts, I would offer- regardless of the materiel, where the depth of absorbent materials establishes it's effective bandwidth, other than for 'style, every bit of 'half inch shallow area in what ever depth 'rated' the product, is half inch foam.
 
Hey thanks a lot for the replies!

[MENTION=2337]Keith[/MENTION]rogers I now feel sceptical about using foam as an absorber after reading how much less a foam sheet does for absorption than advertised. Is rockwool a better choice. Get a feeling that foam sheets can only be used for very slight alterations after using rockwool as the core material for absorption wherever need.

[MENTION=39487]mjbphotos[/MENTION] ok you pushed me to finally make a diagram. I have attached it below. The kits seem a little out of proportion in the diagram, sorry for that. The one on the left is an acoustic kit and on the right is a basic V-drums set, which is pretty compact. I keep it there so as to connect it to the mixer with a not too long midi cable. The floor is two carpets put together and the window and the balcony door have thick curtains for now. I was definitely planning to treat the ceiling cloud, but do you think I should ditch foam completely, and only look at rockwool as an absorber whenever needed?

The 4" absorbers in the diagram is me thinking of putting grid type 4" foam which has more volume than the wedge or eggcrate types. Should I just go for rockwool in those places instead?

Any suggestions about placing those bass traps or the broadband absorber better?

[MENTION=7442]mixsit[/MENTION] i did calculate some important data as to what the room modes will be in this room and was planning to use that broadband and the wooden box trap for the most troublesome frequencies by adjusting its distance from the wall. Would love to hear your advice on the plan. :)

Thanks a ton again!
 

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Yes, 4" thick rockwool (OX703, 705 or Roxul AFB is you need to conserve money) for all those panels. You'll find they come in 24"x48" pieces, do design accordingly. If you can build the physical traps yourself, you'll save a lot of money, and some people just wrap the rockwool in cloth, no frames.
 
There's also Roxul Safe'n'Sound, which is what I used, but it only comes in 48" x 15" (wide) x 3" (depth) batts. It' not "floppy" but I think it needs to be framed for must uses, especially for mounting on a wall. They have a product called Fabrock (might have been Rockboard before, as it seems similar) that is in 2'x4' panels, and slightly denser (e.g., .65 vs .52 for 3" depth vs Safe'n'Sound at 125Hz) that probably is Ok to work with unframed, though mounting on walls is a potential problem, so I'd go ahead and frame it.

You should plan to add a couple "clouds" overhead. You'll definitely want to frame that if it's not rigid, and probably need to for mounting regardless.

I'd think about making the corner traps deeper, like 6" or 8", TBH. (Will you actually have 2 drummers going at once in that room?)

Nice drawing.

P.S. think about heavy "blocking" drapes for the windows & doors.
 
[MENTION=39487]mjbphotos[/MENTION] ok so no on the foam. Rockwool even turns out to be cost efficient here and more importantly, it seems to be a far better absorber. Most of the rockwool batts i find are 1m x 0.6m, 2in thick. Will check out Roxul. But the reason I wanted to frame them is so that I can leave an airgap of another 2 inches behind them. This should prove to be a more efficient absorber right?

[MENTION=196982]keith.rogers[/MENTION] nice job there! Roxul batts do look sturdy. Most of the rockwool I saw in stores here is the "floppy" one. And even the Fabrock series looks sturdy. It almost looks like a rock board. Are the "rigid" ones better at absorption? Or are the density/thickness/rigidity requirements different for bass traps and absorbers? Dont mind checking out the price for Fabrock if its worth it. Of course Safe n' Sound, 703 look like a safe bet.

Oh yes the ceiling and the drapes, will definitely treat the ceiling with a cloud of 2 batts to start off, and a 3 layer curtain I already have and see how the room sounds. Sometimes two drummers might play when my friend comes but that will only be jamming. Although the diagonal corner trap with a face of 3ft is giving me a depth (height of the equilateral triangle formed) of around 19 inches. Guess will have to play around with the depth to catch the problem frequencies better.

Thanks! found an online 3D sketcher called homestyler. That was fun. :)
 
... But the reason I wanted to frame them is so that I can leave an airgap of another 2 inches behind them. This should prove to be a more efficient absorber right?

... Are the "rigid" ones better at absorption? Or are the density/thickness/rigidity requirements different for bass traps and absorbers? ...
The air gap allows both sides of the panel to "catch" sound waves so, yes, it's more efficient. The size of the gap does matter. I think 2" is probably on the low side (though it's what I used simply because I was already in a pretty small space). The bass traps need a lot more space than that.

Rigid material is generally denser so you can get better results with a little bit thinner material, but you really need to look at the spec/data sheet for the specific product you are looking at.

When you start looking for the material, a lot of it may come down to what you can find locally, since the shipping can add up quickly. I wanted to use Rockboard, but wasn't having luck finding it and stumbled across one of the local Lowe's that seems to keep the Safe'n'Sound stuff in stock. Then it's relatively cheap if you don't have to pay shipping.
 
Hey these are the kind of sheets a local rockwool dealer presented me with. The only difference I see in the first 2 types of rockwool is that the 2nd can be purchased with a coating/ face, even though he said that its preferred for wall partitions/ceilings more that absorption inside a room. Maybe because it can come with a coating/face that provides thermal insulation. Apart from that, they are available in all densities and thickness. Which ones do I want for the corner traps, ceiling cloud and the side wall absorbers? Really appreciate the help and advice.

rockwool brochure1.jpgrockwool brochure2.jpg
 
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[MENTION=196982]keith.rogers[/MENTION] was indeed waiting for the seller to send me a data sheet of whatever he stocks. I have attached it above if you can spare some time to advice.

Will definitely decouple the panels atleast 2 inches from the wall, or more if mounting doesn't get too difficult.
[MENTION=7442]mixsit[/MENTION] Thought if I can get a continous thickness of 4inches instead of doubling the sheets, why not? Although I need to find out how much is the dealer charging for a 4in thick sheet. :p
 
Yes, you can either double up on the 2" or use 4" Either of the materials above looks good (I'd go with the unfaced). Some people like to use faced or a thin plastic membrane for their corner traps as it will reflect a small amount of high frequencies, but still let the low frequencies pass through to be absorbed.
 
Yes, you can either double up on the 2" or use 4" Either of the materials above looks good (I'd go with the unfaced). Some people like to use faced or a thin plastic membrane for their corner traps as it will reflect a small amount of high frequencies, but still let the low frequencies pass through to be absorbed.

Hey I am getting a good deal on the 4" slabs. 2$/slab. Although I was wondering if the solid looking boards on the 2nd page are any good for absorbing any spectrum at all? They look like the Fabrock series. And look easy to handle/install without a frame.

Was wondering myself if I should get the unfaced ones and put a thin reflective layer before finally wrapping it with cloth. Do you think a thin gelatin paper would do the trick, in case it is worth doing at all? Although I am not too sure about using glue to paste them on the rockwool slabs.
 
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