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making a subwoofer box...

Old Nov 12, 2008 | 04:58 PM
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Default making a subwoofer box...

I'm making my first subwoofer box from scratch. The specs for my subwoofers call for 1.5 cubic feet. The box is going to have 2 subs, side by side pointing forward and slightly up under the rear glass like a partition. Would it be best to separate the box or leave it open between the 2 subs (2 combined 1.5 cu ft boxes or 1 big 3 cu ft box)? Gonna be a sealed box.
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Old Nov 12, 2008 | 05:45 PM
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You have a few options.

With a single chamber box, two subs will be fighting internal air pressure. You could wire one sub out of phase causeing the subs motions to rienforce eachother. This will give you deep booming bass especially at very low frequencies.

With a dual chamber box and both subs wire in phase, you'll have tighter bass and good bass drum reproduction.
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Old Nov 12, 2008 | 07:18 PM
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Dual chamber it is, then. Does the shape of the box matter much, as long as it's some sort of quadrilateral and has the right internal volume?
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Old Nov 12, 2008 | 07:42 PM
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If you wire one sub out of phase, you'll very likely have little to no bass at all.

Combined or separate, doesn't really matter much. Individual chambers leads to higher box strength if that matters to you. Shape is not very important.
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Old Nov 12, 2008 | 08:41 PM
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Kale's right. You absolutely do NOT wire subs with opposing polarity, especially in the same enclosure space.

Separate internal volumes are almost always better, and in your instance a single larger enclosure with a separating partition would be the best way to go. The partition stiffens the box panels reducing efficiency losses through panel vibration.
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Old Nov 13, 2008 | 11:53 PM
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dual chamber and polyfill
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Old Nov 14, 2008 | 01:17 AM
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Polyfill is that fiber you fill the box with, right? Does that stuff really work? Seems like it'd just rob air volume.
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Old Nov 14, 2008 | 08:26 AM
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Polyfill slows down the soundwaves which has the effect of a larger accoustic chamber...When I purchased my Infinity sub, they actually specified using polyfill in the box...
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Old Nov 14, 2008 | 11:41 AM
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Originally Posted by Gideon's_Test
Polyfill slows down the soundwaves which has the effect of a larger accoustic chamber...When I purchased my Infinity sub, they actually specified using polyfill in the box...
You are correct

Don't cram it your box with it though, just enough to fill it. If you put too much in your box it will start to rob airspace.
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Old Nov 14, 2008 | 11:56 AM
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The accepted ratio is one pound of polyfill per cubic foot of airspace. Anything more precise requires test equipment to verify the target Qcb.
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Old Nov 14, 2008 | 08:35 PM
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Originally Posted by Gideon's_Test
Polyfill slows down the soundwaves which has the effect of a larger accoustic chamber
If I'm building the box to the specific size recommended, is there any advantage to having this effect of a larger chamber?
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Old Nov 14, 2008 | 10:47 PM
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Originally Posted by carnut101
If I'm building the box to the specific size recommended, is there any advantage to having this effect of a larger chamber?
Yes. The sound waves are absorbed by the poly fill. It cuts down on vibration and resonance. I'll save you the thermodynamics and fluid mechanics equations and just tell you to follow Spkrboy's recommendations. He's right on target.

Ultimately... the larger the chamber, the lower the frequency that the box can play, effectively. Some boxes sound "okay" with zero poly fill, but all of the ones that I have built seem to sound a bit more 'smooth' when the poly fill has been added.

Good luck.

Mark
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Old Nov 15, 2008 | 12:20 AM
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Originally Posted by carnut101
If I'm building the box to the specific size recommended, is there any advantage to having this effect of a larger chamber?
Ideally, consult your subwoofers reccomended airspace and shoot for somwhere between the sealed and ported box volume.
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Old Nov 15, 2008 | 01:19 AM
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the polyfil makes the woofer think its in a bigger home!! Or its "PFM" Pure F_____ Magic,
Either way get sum from wally,, 1 lb per cubic foot is right on (see other post) good luck
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