question about absorption coefficients

[mukiw]

just a quick question, i'm not particularly clued up about how you figure this out, so i apologise for my complete naiveness . i've been looking at http://www.bobgolds.com/AbsorptionCoefficients.htm

for example, on bob's page, roxul rht 40 goes from 0.15 @ 125 hz in a 1.5 inch thickness and 56kg/m3 density, to 0.26 at 2 inches, 0.62 at 3 inches and finally 100% absorption at 4 inches.

is it safe to say that any insulation that has around 0.20 absorption @ 125hz with a 1 inch thickness will have 100% absorption at this frequency by the time you get up to something between 4-6 inches thick?

thanks

[Glenn Kuras]

That would be hard to say but it is safe to say that straddling a panel that is 3 pound or more in the corner will.

[Ethan Winer]

Originally Posted by mukiw

is it safe to say that any insulation that has around 0.20 absorption @ 125hz with a 1 inch thickness will have 100% absorption at this frequency by the time you get up to something between 4-6 inches thick?

Probably, but understand that absorption data is only an estimate anyway. More here:

Alternative Test Methods for Acoustic Treatment Products

--Ethan

[avare]

Originally Posted by Ethan Winer

Probably, but understand that absorption data is only an estimate anyway.

A clarification. Absorption coefficients are valid for the environment they are tested in. As that environment changes, so do the absorption coefficients.

This is one of areas of acoustics where a seemingly simple question has a very complex answer, if the answer is completely correct.

I am not trying to put words in your mouth Ethan. I am trying to avoid the start of a huge misunderstanding due to a sincere simplification.

Andre

[Ethan Winer]

Originally Posted by avare

Absorption coefficients are valid for the environment they are tested in. As that environment changes, so do the absorption coefficients.

Yes, but my main point is the same material tested in three different labs will give three different results. Sometimes varying by quite a large amount, especially at lower frequencies. I've even seen negative absorption numbers reported at very low frequencies!

--Ethan

[mukiw]

thanks guys thumbsup