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Old 26th June 2006, 12:41 AM   #1
Tenson is offline Tenson  United Kingdom
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Default Closed sub box

Hi guys,

I am going to be building a pair of closed ‘subs’ that I would like to be good up to 400Hz. I have got a pair of Eminence Magnum 12” drivers which sound excellent right up to 1.3KHz so that should not be a problem. I also have a digital crossover so I can EQ the roll-off that will occur in a closed box.

Basically I wondered if you have any tips for box construction? Are non-parallel walls something to use in a sub or does it not matter because of the huge wavelengths? Should I just go for something simple like ¾” MDF with a matrix or other bracing inside and heavy acoustic filling?

I was planning to try aluminium honey-comb for the box but my funds are running out so I think its going to be MDF for now
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Old 27th June 2006, 03:20 AM   #2
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3/4 mdf, paralell walls dont matter, and shelf bracing is good!
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Old 27th June 2006, 11:26 AM   #3
Tenson is offline Tenson  United Kingdom
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shelf bracing? I was thinking maybe some 2"x1" pine fixed across the back of each panel.

So there isn't really nay clever tricks to sub box building? Just make it strong!

What is the best way to damp the rear output? What type of meterial?
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Old 27th June 2006, 12:03 PM   #4
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Shelf bracing is best IMO but you can get good results from rib braces like you propose. As for filling, bonded acetate fibre (BAF) wadding used for furniture and bedding stuffing is good, easy to work with and cheap. Don't pack it too much though.

Bear in mind that your fancy digital EQ will be useless if you 1) haven't the power to feed the subs and 2) want more SPL than the EQd subs can give. For a PA-type application vented is 99.9% times the winner.
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Old 27th June 2006, 12:14 PM   #5
Tenson is offline Tenson  United Kingdom
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What is shelf bracing?!

How much is too much filler? I thought the more the better really with a closed sub.

I am not using it for PA stuff, so the SPL will be alright. It should manage around 95dB at 20Hz.

Thanks
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Old 27th June 2006, 01:12 PM   #6
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Shelf brace is literally as the name implies, a shelf inside the cabinet with holes or cutouts to keep the airflow up.

Just stuff the sub loosely so it's not compressed. If you overstuff it it's no longer stuffing it's just dead space reducing volume.
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Old 27th June 2006, 02:46 PM   #7
Tenson is offline Tenson  United Kingdom
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Hmm I find that hard to believe. Surely at the wavelengths we are talking about, something like a solid lump of rockwool would be a very efficient absorber, not just dead space. It is, after all, the type of thing many bass traps are made from! I can understand what you say if it was a midrange driver though.
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Old 27th June 2006, 02:54 PM   #8
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Bass traps are not packed solid.
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Old 27th June 2006, 02:59 PM   #9
Tenson is offline Tenson  United Kingdom
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Yeah they are - http://forum.studiotips.com/viewtopic.php?t=535

Even the foam types are foam all the way through. Maybe it would be best to completely fill it with foam rather than fibre stuffing?

I'm not meaning to disagree with you, it just seems that surely the best solution with a closed box is to absorb as much as possible. Maybe I am wrong.
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Old 27th June 2006, 03:29 PM   #10
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There's packing full, and packing solid which is what I was trying to differentiate between.
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