Acoustical properties of styrofoam?

[ThomasT]

Hi,

since many people with no acoustic knowledge think that styrofoam (styropor) is good for acoustics, I beginn to wonder what are its actual acoustical properties. Ege crates are measured already to show its uselessness, but styrofoam seems not.

As everything it should have an acoustic effect. It is slightely compressible so it should provide a kind of low frequency absorbtion. An it reflects highs of course.
So you could ask, what sound has a completely damped cold storage inside?

Just academical interest.

Thomas

[Soundman2020]

Interesting question! I'm looking to see if there is any research papers on this, with real numbers, but not finding much.

Something interesting I did find is a comment on the web site of a company that deals a lot with styrofoam, saying this: "Acoustical characteristics for this or any closed-cell foam insulation are nearly non-existent."

http://www.ta-inc.com/newshtml/green.htm


The way I understand it, this is because of the gas flow resistance characteristics. In order for a material to absorb sound effectively, air needs to be able to move through it, and experience a certain range of resistance. Since styrofoam is closed-cell, air cannot move through it at all: it has practically infinite gas flow resistance. This is why it isn't any use at all for most acoustical purposes. That's not to say that it has no effect on sound: obviously it does have some effect. It's just that the effects aren't useful for acoustics.

That said, it sure would be interesting to see what kind of behavior it does actually exhibit in real acoustic testing!

I wonder if Ethan or Eric or someone else has ever tested it properly in a lab?

- Stuart -

[Ethan Winer]

I wonder if Ethan or Eric or someone else has ever tested it properly in a lab?

I sure haven't because of the expense, but it's not difficult to do a home-made test. If I were going to test Styrofoam sheets I'd find an empty bedroom and use Room EQ Wizard before and after, being careful not to move the microphone between tests. Then I'd look at the RT60 reverb time graph with and without the styrofoam in the room. That won't give hard data in sabins, but it will show how little effect that material has. If you have the same number of panels made of rigid fiberglass and test those in the same places, there's probably a way to derive sabins for the Styrofoam knowing the absorption of the fiberglass.

--Ethan

[ThomasT]

A more serios question come in mind: What about building QRD diffusors with styropor/styrofoam?

[Ethan Winer]

^^^ That's what RPG uses for some of their diffusors. Though I suspect the plastic they use is much more rigid and dense than the usual flimsy flaky stuff you find at hardware stores for thermal insulation.

--Ethan