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March 16, 2010 6:44pm UTC

Acoustic Analysis 6dB drop not observed

Hi all,

I am modeling a simple membrane in free space using the Acoustic-Structure interaction. The membrane is fixed at the edge and driven on the bottom surface. The membrane is 40 mm diameter and 19 um thick. I have modeled a 3d symmetry model and have also tried the 2d axi-symmetry model. There are two models, one with the membrane by itself and the other the membrane sitting on a baffle. The outermost boundary is modeled as infinite using radiation condition. I am looking at the SPL at certain distances from the membrane as a result of a harmonic analysis.
For the model with the membrane on the baffle, I am observing an expected 6 dB drop in the SPL with doubling of distance. When I remove the baffle, the SPL drops 12 dB, which I cannot explain. Can anyone point out the error in the model or the modeling scheme?

Thanks,
Mihir

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May 3, 2011 4:41pm UTC in response to Mustafa Kavasoglu

Re: Acoustic Analysis 6dB drop not observed

Hi Mustafa,

I think the problem is with the domain not being perfectly infinite. One of the things that I did was to completely separate the front and the back domains i.e. create the model of the membrane with the baffle. Then create the air domains on the front and back separately starting from the end of the baffle. This way the only interaction between front and back is through the membrane. This seemed to help my model and now I see a 6 dB drop as expected.

Try it and let me know if it works.

Mihir

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