Low frequency absorber minimum placement distance-Acoustics Forum-Acoustic Fields Forum

Hi Denis,
Hi everyone,

I read and listen to a lot of videos about lower frequency absorption . And different sources seem to have contradictory statements (or at least, confusing statements).
I also noticed the depth of your ACDA absorbers is 1/16 of the minimum absorbed frequency. For example ACDA -12 has 100% absorption down to 50Hz and its depth is 16″ = (c/50Hz)/16
And Carbon Panel absorbers are even thinner. CP-10 depth is 10″ = (c/40Hz)/32

Now, I’m puzzled regarding the quarter wavelength rule and low-frequency absorber ‘s placement. So, assuming the waveform displayed in the illustration below is corresponding to the ≈95% absorbed frequency:

http://www.chicoree.fr/pub/aco…..fusion.jpg

Which of (1), (2), (3) or (4) is the correct and minimum distance between the source, the absorber , and the wall?

FWIW, I’m considering the case of a voice recording room, with a lavalier mic attached directly to the talent. So I’m mostly concerned by the sound wave that bounces back to the source position or its close neighborhood.