# Sizing of wood panel traps



## hjones4841 (Jan 21, 2009)

Ethan's website discusses wood panel traps as being effective at bass frequencies, but I don't see information regarding size of the panel vs. effective frequencies. Is the rule "as big as you can make it"? Is there guidance on panel sizing in Everest's book? What about the relative performance below 80-100Hz vs. a fiberglass or mineral wool trap of 6-8" thickness, spaced out from the wall?

Thanks.


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## bpape (Sep 14, 2006)

There is a formula available to calculate where the depth of the sealed cavity and the mass of the front membrane determine the center frequency. Those will usually work around 2 octaves and be pretty reflective at pretty much everywhere else. 

The overall size of each of the panel traps will slightly modify the center frequency due to changes in the relative stiffness of the entire assembly, but it'll still be in the ballpark.

Bryan


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## cinema mad (Jan 28, 2007)

From my understanding These traps usualy are for A narrower bandwidth as such can be built to deal with very low frequancy absorbtion and fine tuning in A narrow bandwidth, can be built to absorb lower than A 6" thick "fiberglass" substraight BroadBand type panel can be built to ...

As Bryan has pointed out Everest's master handbook of Acoustics 4th Edition has the mathematical formula to calculate and build to the spec you want....

Cheers....


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## bpape (Sep 14, 2006)

Correct. Like I said, they're usually pretty good for about 1.5-2 octaves. They're broader than a Helmholz resonator but narrower than a 'soft' absorber.

Just be very careful tuning them too low. They can actually generate resonances of their own. Trying to tune them to 25-30Hz is difficult at best. Besides needing a relatively deep cavity, the mass of the front membrane becomes so great that the efficiency drops pretty fast and you end up needing a lot of them to do the job.

This is not saying they don't work - they do. They have their place in the proper applications.

Bryan


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## cinema mad (Jan 28, 2007)

Bryan, If you wanted to fine treat very low feq room modes, what would you say would be the best type to use Helmholz ??...

Interesting point you made about issues tuning these type traps to low...
Cheers...


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## hjones4841 (Jan 21, 2009)

Actually, I was thinking about absorption of the 26-27Hz mode in my room, so perhaps it would be more trouble to build and tune it than it would be worth. 

After my original post, I saw more info on Ethan's site showing 2'x6' or 2'x8' vertical panel traps. No mention of the tuning of those, but it would make sense that size range would be needed for way down low. 

Ethan also said on his recording forum that if you cannot fasten them very tightly to the wall, then the panel trap is not for you. I don't have wall space for more than one of that size, so I suppose that I will stay with the broadband type.


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## bpape (Sep 14, 2006)

Jason

The best way to deal with very deep room modes is via placement of subs and seating properly to avoid them. After that, potentially spot treat if possible with a membrane type absorber - assuming it doesn't also requie a more broadband approach in the same place to deal with other problems.

Harry,
That's very true. If the whole thing isn't completely rigid except for the front panel, you're fighting a losing battle as the efficiency will go out the window and the tuning will change.

Bryan


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## fredk (May 14, 2008)

Hmmm... With concrete walls I seem to have the ideal situation for panel traps. Do you suppose my landord would mind if I put a bunch of lag bolts into the wall? :dumbcrazy:

Brian. I are membrane and panel traps not the same thing? Basically a sealed space with a resonant panel/membrane covering the front. I have not been able to find much useful in tuning a membrane vs a ridgid panel.


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## bpape (Sep 14, 2006)

Somewhat the same but not necessarily. You can have panels which have a reactive membrane that are not over sealed cavities. Think of OC703 with an FSK face on it. You get the reflectivity in the highs and you get somewhat of a membrane effect in the 'hump' at a certain frequency but they're still broader in performance. In this case, it's more the makeup of the membrane and the stiffness of the material it's bonded to.

In the panel traps Ethan references, the membrane is not touching the insulation and is over a sealed cavity. This allows the air to act as the spring but is much narrower in usage and reflects much much more. 

Bryan


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