Hi Bill. Please read the

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**Quote:**

My question is this: how will the resonance of the slot be affected when one side of the slot is 18mm and the other side is 12 mm? Will we end up with a resonant frequency somewhere between the two?

That's actually a really interesting question, and to be honest, I don't know the answer. I'm not aware of any research that has been done on that, but it's a fascinating question.

The issue is this: The "slug" of air trapped in the gap between the two slats is actually what resonates here. It's the "mass" that moves in and out, sort of like a piston, vibrating in sympathy with a certain tone. It's the mass of that air slug that defines the resonant frequency. With normal slats that measure the same thickness, that slug is uniform and relatively easy to calculate. In fact, it's not just the slug itself that moves: it also affect the air just outside, pushing and pulling on that such that it also joins in, so there's a "mouth correction factor" that is applied to the calculated mass of the slug, usually estimated at roughly 20% extra. But with slats of different thickness, it's not clear to me how you would calculate the mass of the slug, nor how you would calculate the mouth correction. You MIGHT be able to estimate this by taking an average dimension, half way in between the thicknesses of the two slats, but I'm not sure how valid that is. And since Helmholtz resonators usually have a fairly high Q, I'm not sure how much that would be affected either. Another way of looking at it might be to just pretend that your slot wall is actually a perf panel, an use the open percentage equations, instead of the Helmholtz equations. Once again, I'm not sure how valid that would be, considering the asymmetric hole geometry.

You might just have to experiment, and see how it really performs!

Sorry I can't be more help than that!

- Stuart -