Panel Muffler

Enclosures and acoustic damping to help quiet them.

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Rory B.
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Panel Muffler

Post by Rory B. » Thu Oct 28, 2004 1:27 pm

Inside my school bus back in high school, I remember that the roof had an inner layer with a piece of sheet metal with holes drilled in it like modder's mesh. Between that layer and another layer, there was a layer of some type of damping material, like open-cell foam or fiberglass or something. It had the effect of greatly reducing the sound inside the bus, the sound of many little voices yelling and screaming. I am wondering, would it be possible to build such a layer on the inside of a case panel? And would its sound damping effects be effective enough to eliminate sound before it can escape the case?

Rory B.
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Post by Rory B. » Tue Nov 02, 2004 4:54 pm

so much for that...

Bluefront
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Post by Bluefront » Tue Nov 02, 2004 10:59 pm

Ok....I'll respond to this. I have seen double-layering of metal panels used for noise reduction, specifically on exhaust manifold shields on autos. Two layers of steel, spot welded together in many places, with an air space of maybe .050 thou between the sheets......

This technique works very well. But just how do you propose to incorporate it in a computer case?

Straker
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Post by Straker » Tue Nov 02, 2004 11:48 pm

two different ideas, sheet metal with a gap between the layers would be pretty easy to do in a PC case though, actually... hmm.

if this is all it takes, you wouldn't need to weld it even - just cut sheets to line your case two layers deep, and separate them with washers or so. only really easy way to actually attach them to the case, though, would probably mean taking the case apart, bolting the sheets/plates through the case, then re-riveting it.

Bluefront
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Post by Bluefront » Wed Nov 03, 2004 2:16 am

IMHO....the welding together of the two formed steel sheets seems to be the key here. Other attachment methods might work. I am not an expert in this subject, but it looks like the different sized areas between the spot welds create sound potential areas of different frequencies, that tend to cancel each other out.

I am also not sure how this would work on a flat panel. But if you drop one of these welded shields on a hard surface, you only get a dull knunk, rather than the noise you would expect. :)

And if you place the shield over a running engine's manifold, the noise reduction is quite dramatic.

Straker
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Post by Straker » Wed Nov 03, 2004 11:47 pm

hmm, that makes sense too, i was just figuring it'd (bad analogy alert) sort of work like a double-paned window. harder if the welds are necessary, i think with a flat panel you'd just end up with two pieces stuck together with practically no space between them, unless the process of welding itself sort of crimps/stresses it enough that the sheets spread apart at the points farthest from the welds.

Bluefront
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Post by Bluefront » Thu Nov 04, 2004 3:15 am

Actually there are dimpled areas in the panels where they are welded, which hold the two panels apart, giving the small gap between the two metal sheets.

These shields on a manifold also function as heat shields, lessening heat transfer into the engine compartment. How the sound blocking, and the heat blocking interact with one another is unknown to me. :?

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Post by Tibors » Thu Nov 04, 2004 2:12 pm

I've seen double panels like Rory B. describes. (Which I think is completely different from what Bluefront writes about.) IMHO the function of the panel with holes is just protecting the damping material between the panels from mechanical damage.
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Bluefront
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Post by Bluefront » Thu Nov 04, 2004 3:24 pm

If memory serves me, there was a thread some time ago that talked about "quiet" steel. It was actually a metal sheet made from a layering process that promised noise reduction. Haven't heard anything more about it though....

hvengel
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Post by hvengel » Thu Nov 04, 2004 7:30 pm

Ford is using the ¨quite¨ steel for the firewalls of F150 pickups. They talk about it in the F150 advertisements.
Hal

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