John Sayers' Recording Studio Design Forum Archive

Hi all!
I'm working on a DIY acoustic project and I would like to add a few LF resonators to control some nasty room modes.
I read some forums on the internet and found the nice spreadsheet for calculating the resonance frequency for a slat helmholtz resonators here on this site.
But in the spreadsheet and even in some books that I have there's an assumption that the slats are going to be placed over a rigid wall.
I was wondering if I could make a wooden box that would have slats on its front side and place it along the wall. Will it function the same?
Here is a picture of what I mean:

This box is 34 cm deep, slats are 4 cm deep and 7 cm wide, slots are 2 mm wide. Resonance frequency, according to the spreadsheet found here is 72 Hz.
Please tell me if my direction is right.
Thank you!

I do not think you wil like the answer.

Thhe slats and box will act as a Helmhotz absoirber. Good. The back of the box against the wall will act as a membrane absorber with the tuning unknown. Bad.

Andre

Andre, thank you for your reply!
I didn't realise that the back of the box against wall could behave as a panel absorber. Now as I'm thinking about it, you're probably right. But such kind of "side-effect-absorber" would be (IMHO) quite inefficient, considering the air cavity behind the panel isn't sealed AND the back of the box is going to be considerably rigid (almost an inch thick). Am I right?

Martin

nixx wrote:But such kind of "side-effect-absorber" would be (IMHO) quite inefficient, considering the air cavity behind the panel isn't sealed AND the back of the box is going to be considerably rigid (almost an inch thick). Am I right?

No. The factors you detailed affect the resonance frequency of the membrane, not the efficiency. It will absorb quite well at its resonance.

Andre