ballpark way to measure bass trap absorption

[Ethan Winer]

That won't work because bass waves go right around relatively small objects such as a 2x4 panel. There is a method for self-testing absorption, and it's described in detail in my Audio Expert book. The short version is you put the absorber against a rigid reflecting wall, put an omnidirectional microphone a few inches away from the center of the panel, then play the tones of interest from a speaker that's at least a few feet away from the wall pointing toward the wall. Then do the same without the panel. You can calculate the absorption from the dB difference with the panel and without.

--Ethan

The Acoustic Treatment Experts

[ludwigvanlee]

Hey Ethan, I tried it out, thanks for the recommendations.. it worked like a charm!

[Glenn Kuras]

Ethan I generally test a room with product and without, but what is the calculation you use after you test?

[Ethan Winer]

Originally Posted by Glenn Kuras

Ethan I generally test a room with product and without, but what is the calculation you use after you test?

Testing with REW is great to get a visualization of the change, but it doesn't give actual absorption in sabins. This formula is from the Decibels Excel spreadsheet that comes with my book:

FIXED(1-(POWER(10,-B46/20)^2))

Cell B46 is where you enter the dB difference between the SPL levels at the microphone with and without the absorber against the wall.

--Ethan

[bastawa]

nice subject, i'll try to measure my 2 bass traps. i bought them few years ago from thomann.de and they never seemed to work.
btw. what kind of absorbtion should i expect from 1mx0,6m wooden basstrap?

[Glenn Kuras]

Great info ethan

[Ethan Winer]

Originally Posted by Glenn Kuras

Great info ethan

The rest of the spreadsheet has all sorts of useful stuff like that.

--Ethan