myfipie wrote:Just so I understand what you are saying about this kind of panel. Basically you would build it the same way as EW wood panel trap but leave the back open to space it off the wall to what ever frequency you want? If that is right how you do know how to space it to get a curtain target frequency?
Sorry I did not mean to label that panel, but found it funny that I was reading Rods book about Hybrid panels just about at the same time I read your post.
Glenn
Glenn,
A panel trap for me can be a lot of things.
It can be mounted in between studs which are also used to mount standard absorption, which then are covered by continues fabric, hence you can't recognize or see them. It can be panels laid/mounted between the bottom flanges of I or H beams, it can look as the Ethan plans. It all depends. John also referred to an application he described here.
How to know?
First calculate it as good as possible theoretically, where by definition for closed panels I start from the wall MSM formula as entered in that Bob's thread, I adjust it listening to my belly knowing much more than I do, and depending on the situation. I ONLY should use the traditional formula (Everest and others) on very heavy walls, NEVER on drywall.
I take care that I easily can adjust things. Hence if I don't integrate some standard posibility, I mount it temporary in a way I can easily adjust things until happy with the results.
I once tried to aim for about 32 Hz (if recalling correctly) and then gave up, because once it was tuned correctly and damping high enough, it hardly absorbed anymore (was a costly, time consuming experiment).
And I have the advantage of doing narrow band sound AND vibration measurements, but with single walls, which I have more experience with here than double walls you can also see it with narrow band sound measurements on the other side of the wall too (DIP in isolation)**.
Hence you measure it with whatever and however it's practical.
I easily can imagine that with pure sinus tones scanning the relevant frequency range you can find it back as well.
It's like playing a sweep in a living room. Once you hit the resonant frequencies of different objects they start rattling/vibrating. Only with a sweep you don't know exactly the frequency (passing through).
In DSSF3 sits a very extensive signal generator with some fun possibilities.
In the freeware version a lot of function stop working after 30 days but the signal generator remains functional (is meant as freeware).
http://www.soft32.com/download_13520.html
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** For triple leaf systems the TL method is too uncertain too my taste (not enough experience with.
The first time I was confronted with the TL behavior of triple leaf systems by adding an additional layer on the outside of a wall was between '80 to '84 somewhere (can't remember exactly).
I helped people from a company called Agglorex which produces this bonded foam. The idea was to start using it as resilient skin walls to be glued to existing walls (hence the only connection is the foam itself).
There are also mineral wool versions of this principle.
The logical test back then was to check also (note that brick walls are standard here in private housing) how this should behave on drywall to improve TL (offices and utility buildings are made a lot here with non-load bearing drywall as separation). There I was first confronted with this strange triple wall behavior. In general the curve remained comparable with some dips at certain frequencies and others a bit better.
Overall it became worse. But the traditional behavior one could expect from a theoretical stylized mechanical MSMSM system was far from recognizable.
But the conclusion was: Don't do it. It doesn't work in function of TL. But that behavior isn't that clear for walls.
This triple leaf system however does work nicely as the theory predicts on decouplers. I once worked for a factory which sold such decouplers mainly/often for elevator constructions (a lead block in between springs). It did what it was expected to do: Increasing high frequent insulation significantly, but it simultaneously increased the MSM frequency, which wasn't a problem since located far enough below the frequency of interest.
