I would like to fight a resonance with a Helmholtz absorber in a room with a volume of 97 cubic meters.
I'm building a home theater in a room that's 9.2m long (11 x 3.3 x 3.2).
In the beginning I had a disastrous reverberation. With self-built broadband absorbers, I have achieved a linear reverberation of approx. 250 ms - 350 ms in the range from 150hz to 20khz.
But, since the broadband absorbers are hanging, I have now a resonance peak at around 35hz.
(The reverb is clearly audible playing a sine tone in the frequency.)
My idea was to set up an additional bass trap in the other corners of the room or to build a Helmholz absorber.
Here is my calculation for a Helmholz absorber (actually a multi-layer absorber)
(This is no standard helmholz resonator with a defined volume and one hole!)
Question: What volume or area should such an absorber have?
I have a massive old beech wood panel with about 150cm x 80cm that I could use as a back. The volume would then be 0.48 cubic meters. (180 x 80 x 40)
If I can believe the little information that can be found on the subject, then that could already be too much.