# calculating absorption coefficients



## adam12 (Feb 9, 2010)

I have purchased three different materials: a high density rock wool, owens-corning 703 and 705. I have also acquired a measurement mic and downloaded room EQ wizard. I am planning to put together these materials in different combinations of 4" panels and compare measurements (for example, 4" rock wool vs. [2" rock wool/1" 705/1" 703], etc). I'm certain I can handle the tests and comparisons, but I would like to be able to make comparisons with other products or materials that I don't have.

My questions:

When people publish absorption coefficients, are these based on a set of standard practices in testing and measurement?

If so, where can I find guideline information?

If not does anyone know of any other relevant online resource that I should take a look at?

Can I calculate absorption coefficients using Room EQ Wizard for my test measurements?

 Thanks in advance for any input!


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## bpape (Sep 14, 2006)

It is done to a standard, with minimum sample sizes, covering of edges, in an echo room, with a mic that rotates around the room to minimize modal issues.

Bryan


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## adam12 (Feb 9, 2010)

I see. That seems to be well beyond the scope of my project.

However, is there somewhere that I can read more about those testing procedures?

Is there perhaps a way to calculate absorption coefficients of these different combinations from other published coefficients?


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## bpape (Sep 14, 2006)

Riverbank Labs is one of the oldest labs around. There might be something on their site. There are also ASTM specs that define the sample sizes, how things are to be mounted, etc.

If you just want to do a comparison, you can do that easily enough as whatever room and setup you use will be the same for all samples. It's the comparison of those results to lab numbers that won't match up.

Bryan


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## adam12 (Feb 9, 2010)

Cool. Thanks for the info!


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## owlfan12000 (Jul 2, 2007)

I think you can find what you are looking for by downloading the spreadsheet from this web page - http://www.whealy.com/acoustics/ControlRoom.html

The 9th tab in the sheet has values for over 300 materials and the source of the data. The last tab label acknowledgments has some links to the sources.


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