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Building my first tuned trap (60hz). Any tips/guidelines?
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JLiRD808
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11th November 2012
Old 11th November 2012
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Building my first tuned trap (60hz). Any tips/guidelines?

Im about to go on a crazy read/research fest looking up how to build tuned membrane traps, but if anyone has a link, any images, tips, or suggestions to throw at me, I would be most GRATEFUL!!

I know there's a drawing floating around (think its EW's) with specs for 3 tuned traps at 3 diff frequencies and the dimensions needed to build them. I gotta try to find that and hope it'll help.

I have a bunch of 705, and from my general knowledge, I need to get plywood of a certain thickness and space it off the 705 a specific distance. The dimensions for the trap are about 34" x 30" and I can make it 6"+ thick <--- is that too small to do much though?

I used an SPL meter and ran low freq sweeps and found that there's A LOT of 60-67 lingering around the floor-wall corners flanking my desk, particularly on the left side. This is where I plan to place it.

THANKS!!!
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11th November 2012
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Check your local library for the "Master Handbook of Acoustics" by Everest. There's a cheat-sheet chart with plywood thickness verses depth aligned with frequency, as well as a formula for figuring it out. I don't have the book in front of me, but i believe it's in the 9th chapter (at least in the 4th edition it was the 9th)
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11th November 2012
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Originally Posted by AwwDeOhh View Post
Check your local library for the "Master Handbook of Acoustics" by Everest. There's a cheat-sheet chart with plywood thickness verses depth aligned with frequency, as well as a formula for figuring it out. I don't have the book in front of me, but i believe it's in the 9th chapter (at least in the 4th edition it was the 9th)
NICE!!! Thats exactly what Im looking for.
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11th November 2012
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Make sure to take a glance or two at the limp mass bass absorber thread, as there is much relevant information. Also, you can get a feel for the tuning by tapping the soft part of your hand to the membrane and listening, or by placing a microphone inside or directly in front of the membrane.
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11th November 2012
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Originally Posted by OpusOfTrolls View Post
Make sure to take a glance or two at the limp mass bass absorber thread, as there is much relevant information. Also, you can get a feel for the tuning by tapping the soft part of your hand to the membrane and listening, or by placing a microphone inside or directly in front of the membrane.
This one?

Tim's Limp Mass Bass Absorbers
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15th December 2012
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Got the "Master Handbook of Acoustics" by Everest/Pohlmann (Pohlmann even emailed me to thank me...and we've had some quick discussions regarding this!).

I've got the specs that I need to build my resonant panel absorber, but still have some questions.

First of all, and I asked this in the huge limp mass thread but haven't gotten a response yet (they're arguing over Varitunes again lol), why would you use a limp mass vs plywood? Most guides mention plywood, but these people are all about limp mass. I assume as long as the density of the resonant surface is the same, it doesnt matter?

Love this gem from the limp mass thread btw! Thanks for steering me towards it OpusOfTrolls:



Also, how about LxW dimensions? I'm finding it hard to find out how BIG my trap would need to be to be effective.

THANKS!!
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15th December 2012
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The limp mass is used because it helps widen the Q and makes the trap more broadband.

You should build the trap no more than .5 * wavelength of the design frequency, roughly. Smaller works, but the performance is up for debate.
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15th December 2012
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Ahh nice thank you!!

I've been looking at plywood thickness, and according to this graph, 1/2" comes in at 22 oz per square ft or about 1 3/8lb per square foot. Having trouble finding the densities of MLV's to match though. Doesn't adding pink fluffy widen the Q also? Does making a tuned trap more broadband reduce its efficiency at its peak resonant frequency, or just absorb more AROUND the freq?



I've heard some people even use some kind of aluminum too??

THANKS!!!!
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16th December 2012
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Yes, widening the Q will usually result in less peak absorption, but if porous absorption is used, then some effectiveness is returned.

FWIW, if you insist on plywood, just take note that the density varies largely because of moisture content and irregularities of the wood itself.
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16th December 2012
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Quote:
Originally Posted by OpusOfTrolls View Post
...
FWIW, if you insist on plywood, just take note that the density varies largely because of moisture content and irregularities of the wood itself.
Yes, but you can get around this by weighing your wood.
If you're using a 2ft by 4ft sheet, for example, you weigh the sheet and divide by 8 (because there is eight square feet in the sample)
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18th December 2012
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Where do u guys pickup ur MLV or other limp mass then? I seem to only find 1lb or 2lb/sq foot stuff online. Admittedly, Ive been working a lot, and havent spent as much time as I'd like doing research :(

THANKS!
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18th December 2012
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I would use a harder backing on it or mount it directly to the wall. Also, not sure what tuning you are going to make but plan on building way more then 1 or 2.
See the following for some testing I have done.
GIK or Realtraps?
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18th December 2012
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How would this crappy huge baseboard affect mounting it to the wall? The depth would technically be uneven inside the cavity. The baseboard's like 1.25" x 7". I want to get down to the floor-wall corner (tons of resonance there) for sure.



In other words, I would have to cut the frame to fit for it to be flush....thats why I was thinking of just putting a plywood back on it and leaning it against the wall.

Thoughts? Thanks!
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19th December 2012
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Just a thought:
If you're going flat against the wall, you could make a block of wood the size of the traps, at the thickness of the baseboard (so it was essentially continuous) so you don't have to fiddle with notching and such? i dunno.. there has to be a better way.
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JLiRD808
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19th December 2012
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Hey thats not a bad idea, at least the depth would remain consistent. It would be all flush against the wall too.

Thanks...I'll look into it further
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19th December 2012
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That would work right up above it. You may just want to try it without and see what happens.
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