Acoustic foam results

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David Cooke

New member
Just curious if anyone has any extensive experience with acoustic foam. My space is currently treated with a combination of 14 (4x8x6") broad band absorbers (roxul mineral wool) 2 (8x4) fiberglass broadband absorbers and a combination of 2" 4x8 roxul panels and 2" 1x1 pieces of acoustic foam for early reflections/flutter and after moving my mix position around and tesing in rew the results aren't nearly what I was expecting. :( The decay times have improved but the nulls are still pretty harsh. I realize my space has its limitations but I'm not here to complain about the room I'm just curious if anyone has any graphs preferably waterfall that would display a room treated with cheap acoustic foam. I'm not trying to defend foam but I have yet seen a fair shootout between a room treated with foam vs other velocity based absorbers sq ft being equal. I'm really curious as if all things considered like angle of incidence and the speed of sound changing as it goes through the material if foam wouldn't work better in the real world than on paper or atleast not as bad as the claims. I'm no acoustician but from my experience and research porous absorption in general doesn't seem to be as effective as what most people around here claim for low frequencies. That is until you add a membrane to it like most commercial products (gik/ realtraps) or even using owens corning with frk. I'm not saying that fiberglass or mineral wool traps don't work or don't help at all because they do but my question is apples to apples is it really THAT much better than foam?
 
Firstly, a well treated room typically employs absorption, diffusion, and redirection. Not absorption alone.

All one really needs to know about absorption is what frequencies it affects. Thinner, denser materials are only going to absorb higher frequencies where thicker lower density treatments work across a broader spectrum of frequencies (broadband absorption).

An entire room fitted with thin foam only is going to sound unbalanced in that its only addressing higher frequencies. Not recommended.

So, a treatment that affects frequencies from 200hz-20k (12" Pink Fluffy) is better than one that affects 800hz-20k (2" foam). By affects, I mean a absorption coefficient of 0.8 and greater.
 
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is it really THAT much better than foam?
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The two don't serve the same purpose. Foam tackles high end sparkly stuff. If you're talking broadband / low end peaks and nulls, foam isn't even going to show up.

Well, if you were using 6" thick open-celled foam with the same density as mineral wool, it might...
 
I don't mean to sound rude but did you guys read the post in its entirety? I'm not debating how a SCULPTED 2" or even 4" piece of foam works and I understand the concepts even though to throw the tern "density" around is wrong because what is important is gas flow resistivity. My question is does anyone have any graphs or results to show an equally treated room with foam vs with fiberglass/rockwool or even cotton. I understand the science and i'm not arguing foam is better what i want to see is a real world test of a space treated with an equal amount of foam vs rockwool/oc whatever. NOT a test of is a 2" sculpted piece of foam better than a 2" piece of oc703. Does such a test exist? And i mean true comparisons not one of commercial traps with membranes or fiberglass with frk.
 
Massive Master said:
The two don't serve the same purpose. Foam tackles high end sparkly stuff. If you're talking broadband / low end peaks and nulls, foam isn't even going to show up.

Well, if you were using 6" thick open-celled foam with the same density as mineral wool, it might...
Click to expand...


Thats what I mean. And i understand and agree but i was curious to actually see with my own eyes some graphs of a room treated with a great deal of foam. I doubt i will due to cost but i think to even try to tackle low end in a small cube room like so many on here (8x8x8") with plain jain porous absorption is unreasonable. I'm curious as to how things play into the results such as stud spacing, drywall, windows and ofcourse the different angles that come in to play when you measure an entire room.
 
A really good question. I've never heard of an answer specifically. I did a search (which you
ve probably already done) but if you haven't here's what I found. (one is an article on the futility of trying to make a home stdio bedroom into a professionally sounding studio.) The last one has charts and graphs. You might find something in all of them.
Stop Worrying About Room Acoustics | The Recording Revolution
Acoustics treatment for a small home studio | Become a Music Producer
Acoustic Myths & Realities - Acoustics First - Acoustical Materials for Sound Control, Noise Elimination, and Acoustic Enhancement or Suppression
How to Soundproof: Acoustic Foam Does Not Block Sound » ASI BLOGS
https://www.google.com/search?q=tes...i4HADQ&ved=0CGEQsAQ&biw=1280&bih=611#imgdii=_
I think some acoustic engineers might think it doesn't matter enough to let it get in the way of your producing good recordings.
Good Luck,
Rod Norman
Engineer

David Cooke said:
Just curious if anyone has any extensive experience with acoustic foam. My space is currently treated with a combination of 14 (4x8x6") broad band absorbers (roxul mineral wool) 2 (8x4) fiberglass broadband absorbers and a combination of 2" 4x8 roxul panels and 2" 1x1 pieces of acoustic foam for early reflections/flutter and after moving my mix position around and tesing in rew the results aren't nearly what I was expecting. :( The decay times have improved but the nulls are still pretty harsh. I realize my space has its limitations but I'm not here to complain about the room I'm just curious if anyone has any graphs preferably waterfall that would display a room treated with cheap acoustic foam. I'm not trying to defend foam but I have yet seen a fair shootout between a room treated with foam vs other velocity based absorbers sq ft being equal. I'm really curious as if all things considered like angle of incidence and the speed of sound changing as it goes through the material if foam wouldn't work better in the real world than on paper or atleast not as bad as the claims. I'm no acoustician but from my experience and research porous absorption in general doesn't seem to be as effective as what most people around here claim for low frequencies. That is until you add a membrane to it like most commercial products (gik/ realtraps) or even using owens corning with frk. I'm not saying that fiberglass or mineral wool traps don't work or don't help at all because they do but my question is apples to apples is it really THAT much better than foam?
Click to expand...
 
David Cooke said:
I don't mean to sound rude but did you guys read the post in its entirety? I'm not debating how a SCULPTED 2" or even 4" piece of foam works and I understand the concepts even though to throw the tern "density" around is wrong because what is important is gas flow resistivity. My question is does anyone have any graphs or results to show an equally treated room with foam vs with fiberglass/rockwool or even cotton. I understand the science and i'm not arguing foam is better what i want to see is a real world test of a space treated with an equal amount of foam vs rockwool/oc whatever. NOT a test of is a 2" sculpted piece of foam better than a 2" piece of oc703. Does such a test exist? And i mean true comparisons not one of commercial traps with membranes or fiberglass with frk.
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Our point, or my point specifically, is that if you understand the properties of how the material in question performs, then you dont need a room fully treated with it to know how such a room is going to measure in regards to the effect the material will have.
 
There's a PDF HERE that gives the "differences", but no numbers.

The only numbers I could find were a single factoid from Insulation Institute that said, "It (rock wool insulation) can also absorb up to 25% more sound, with a Noise Reduction Coefficient (NRC) of up to 1.00, vs. spray foam and cellulose with a NRC of .75.6"

And this one minute video demonstrates the properties of diamond foam vs rock wool


Will that help? I know most of this information is on actual NRC vs frequency responses, but the info you're looking for doesn't seem to be there.
 
jim1961 said:
Our point, or my point specifically, is that if you understand the properties of how the material in question performs, then you dont need a room fully treated with it to know how such a room is going to measure in regards to the effect the material will have.
Click to expand...

Yes thats true but at what incidence? there haven't been an apples to apples comparison that i know of. As you have even stated at different thicknesses things absorb differently e.g fluffy pink stuff does well at higher thicknesses but oc703 probably works better on say a 2" panel. Again I'm not disagreeing i was just hoping someone would chime in and say "I treated my whole room with foam here are the results." Maybe its my lack of understanding here but there clearly aren't a lot of tests done by the average joe with foam. I was curious to see some. To say that 32 sq ft of foam is a waste compared to 32sq ft of rockwool is understandable but at the same point 32 sq ft of "fluffy pink stuff" might be even worse than both. If that was the only logic than we would all be using helmholtz resonators for our bass problems no?
 
Great answer. I didn't find that video. All the charts in the world don't beat hearing the real sound.
Rod Norman
Engineer
 
David Cooke said:
Yes thats true but at what incidence? there haven't been an apples to apples comparison that i know of. As you have even stated at different thicknesses things absorb differently e.g fluffy pink stuff does well at higher thicknesses but oc703 probably works better on say a 2" panel. Again I'm not disagreeing i was just hoping someone would chime in and say "I treated my whole room with foam here are the results." Maybe its my lack of understanding here but there clearly aren't a lot of tests done by the average joe with foam. I was curious to see some. To say that 32 sq ft of foam is a waste compared to 32sq ft of rockwool is understandable but at the same point 32 sq ft of "fluffy pink stuff" might be even worse than both. If that was the only logic than we would all be using helmholtz resonators for our bass problems no?
Click to expand...

Your argument seems to be that we need test results of how a bicycle tire on a dragster will perform to confirm it wont work very well. Every paper and valued opinion on absorption that I have ever read specifies that absorption should be broadband. Given thin foam (most foam in general) is not broadband, I fail to see what test results would yield that is not already known or predictable.
 
Foam is broadband. You seem to have a problem accepting that. I agree on all points that for economical reasons fiberglass/wool is probably better. Ok the air is clear there is no debate. My point is what is the difference between foam and fiberglass and how big is it like for like. My feelings are that it may be overstated...a lab test that says 12x12x1" (thats what 2" foam really is) is inferior to a 48x24" oc wrapped in fabric big surprise thats not the discussion the discussion is a room say 19x11x8 covered in 200 sq ft of 4 inch foam how big is the differrnce between that and the same with fiberglass instead. most labs (that ive heard of) don't test much under 100hz because they aren't equiped to do so also most tests ive seen don't test over 4khz. This was a debate a while ago between wood floors and cement that stated they were acoustically the same. You seem to be saying that acoustic foam is
Completely invisible to lower frequencies whether it be 1" or 100" thick.
 
Primacoustics lists several "pro" studios that use their product, but it's almost always 4" pyramid (runs about $250 for 6 2'x2' panels) and QRDs. That's a lot of OC703! If you're looking at building a pro studio, with expensive stuff, in a perfect anechoic chamber...this might be a better solution, but from what I've seen of the pictures of these studios, they combine the stuff with 4" rock wool and corner traps anyway. So is the main value of foam traps not really trapping, but diffusion?
 
I always enjoy reading this from Ethan Winer: Acoustic Treatment and Design for Recording Studios and Listening Rooms

RE: Ethan: He has had more than 70 feature articles published in computer and audio magazines including Mix, PC Magazine, EQ, Electronic Musician, Audio Media, Computer Language, Microsoft Systems Journal, IBM Exchange, Strings, Keyboard, Programmers Journal, The Strad, Pro Sound News, prorec.com, Recording, and Sound On Sound. He now heads up RealTraps, manufacturer of high performance acoustic treatment and also hosts the EQ Magazine Acoustics Forum at the MusicPlayer web site.
 
The purpose wasn't to debate it was to have a reference . I have read through as many bbc articles as i could find as well as Ethan (realtraps) and Glenn's (gik) articles and with auralex selling as much foam as they do I'm surprised there aren't people here posting graphs of their rooms. I would still like to see someone comparing a whole room with foam compared to the same room without and with something else strictly porous no membrane. The nature of frequencies below the schroeder frequency is a lot different than higher frequencys that is my only debate... someone laying a 12" piece of foam accross the floor and measuring it isn't taking that into consideration. But anyways what of the test data from riverbank that if im not
Mistaken both auralex and gik both use? Its no doubt that gik's/real traps products work better but to call foam useless seems to be an understatement. And like i said doesn't gik and realtraps both use membranes? I'm pretty sure they aren't just wrapping/framing oc703 and slapping their name on it. Can't defend foam too much but I do think its silly to just say foam is complete garbage especially on a site called HOMERECORDING.com.
 
I cant say that GIK or RT are using membranes on anything but you do make a point in regards to Foam.
Foam is efficient at certain frequencies as you state.

I believe folks here see the low-frequency issues to be of higher importance primarily due to its existence in a standard designed room in most houses which most of us record in.

My big AHA moment in all of this was to equate sound-waves with thermal energy.
That made a big difference as to how I look at absorption.
 
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