Originally Posted by Jens Eklund
... I need to think about the best and most accurate methods to measure and compare absorption of perforated panels and “corner traps”. ...
There's some info regarding low frequency absorption coefficients
at the RPG's Modex[TM] Plate
page, paragraph "Absorption". I am not able to run a large impedance tube but I've been using the second option -- "... special approach monitoring the decay times of the lowest axial modes in a 5x4x3 m room, with and without the sample present on one of the opposing surfaces..." -- successfully for some time now (in a different sizes room), see postings