AVS Special Member
Join Date: Dec 2008
Location: L.A. - Lower Alabama
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I understand what you're getting at, and you may be absolutely right. My thought, however, is that if there is no propagation of the wave inside the riser, we will see a pressure differential at the opening. There will be a high pressure region at the boundary, and a pressure gradient across the insulation at the opening back to atmospheric. With no velocity component remaining the wave can't propagate into the riser and take advantage of the extra insulation there. That raises another question. How far does that gradient extend into the riser? If the gradient extends all the way to the next rigid boundary, then BINGO, you've got it nailed! However, if that's the case, why would covering the openings into the riser with insulation prevent it from functioning? There should still be a pressure gradient across the OC703 just as there is with regular old fiberglass.
Now, perhaps you are correct that there is some resonant phenomena going on here that I don't see yet. That's certainly an interesting thought, and I'm trying to see how the energy at one frequency can be "moved" to other frequencies by inducing a resonance in the cavity. I'll have to think on that a while.
Again, I really don't understand exactly how these things work. On the surface it seems simple, but when you get down to the details it seems to get complicated pretty quickly.