DIY box for 4 12"s? - diyAudio
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Old 25th August 2008, 05:43 PM   #1
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Default DIY box for 4 12"s?

Well I was told to come to this forum, and ask how to figure out the specifications for building a box.

My old box was basically just a half-hearted failure, and I need to build a new one. I'm thinking building 2 box's would be best, each with 2 12"s in them. Ported of course lol.

Mikee55 was kind enough to give me some sites to help me out, but I don't completely understand them.

So I'll re-list all of the specifications that I know, and if you can help me that'd be cool, if not I'll just Jerry-rig something again.

Thanx.

Parameters
Fo (Hz) - 31.09
QMS - 4.25
QES - 0.38
QTS - 0.35
VAS (Litres) - 69.31
REVC (Ohms) Parallel - 1.6
SPL @ 1 watt/1 meter (dB) - 89.25
X-max Linear peak-peak (mm) 24
LEVC at 1k Hz (mH) 1.14

Ported
Vented (Cubic Feet) - 2.0
Vented to (Hz) - 41
3dB down point (-3dB Hz) - 37
Port Diameter (") - 4
Port Length (") - 15.5
Number of Ports - 2

Square Port Info
Port Area (Sq./in.) - 25
Port Length (") - 15.5
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Old 25th August 2008, 06:09 PM   #2
Did it Himself
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Well what do you want to know? You've got the box volume and port details right there.

The box details looks to be per sub, so you will need 4 cu ft if you put 2 subs in one box.

I don't trust that number of ports it's telling you, I think you only need one of that size per sub. Maybe I can check when I've got more time. If you do only need one port, then when you double up on the volume to 4 cu ft you will need to use 2 ports.
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Old 25th August 2008, 07:11 PM   #3
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Quote:
Originally posted by richie00boy
Well what do you want to know? You've got the box volume and port details right there.

The box details looks to be per sub, so you will need 4 cu ft if you put 2 subs in one box.

I don't trust that number of ports it's telling you, I think you only need one of that size per sub. Maybe I can check when I've got more time. If you do only need one port, then when you double up on the volume to 4 cu ft you will need to use 2 ports.

Well, I was criticized for the box size I made last time. I guess I had it too shallow?

I should've thought this out better, my bad.

Well, so I'm not wasting your time completely, how would I best brace each box so they will not flex?
Thanx.
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Old 26th August 2008, 01:13 AM   #4
pjpoes is offline pjpoes  United States
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the volume is what matters, not the dimensions. If you made the box to the correct volume, then the depth is fine. If on the other hand you didn't actually build a box to any particular volume, and thus it was less than 2 cubic feet, then you would have a problem.

As for bracing, you want to connect all the sides together, basically. One of the most simple and effective braces is simply a small piece of wood connecting the top to bottom, and side to side, forming a sort of cross shape. Cutting a board to fit the internal dimensions, then cutting 4 holes in it can give a similar appearance, but has the benefit of adding further bracing over a broader area for each panel.

Ok I just modeled that subwoofer based on the specifications you gave me. The box recommendation appears to be wrong, that will create a box with a pretty massive peak at the tuning frequency. Also, the port dimensions are incorrect for a 37 hz tuning in a 2 cubic foot box. That would tune it to 41hz, not optimal. In a 2 cubic foot box, for the best response, I would go with a 32hz tuning, which would mean 2 ports at 4" by 29.54" That will give you reasonably low port noise for most situations (Still not perfect mind you).

You could also do a pretty compact EBS if you wanted at 3.5 cubic feet and 25hz tunning.

sorry forgot to mention, thats per driver enclosure recommendations. Obviously you have to scale it up for 4 drivers. Is this for home or car? The specs on the driver make me think its a car subwoofer. In that case, the number of boxes doesn't matter, but if its for home, I would make 4 individual subs, not 2.

Ok just as an example here. If all 4 subs were in one box, you could make it 7 cubic feet and tune to 35hz. Then you would need, going with 4" ports, 8 of these ports to keep port noise reasonable, each one being 28.8" long, or so. Obviously at that point you might want to consider a slot port or larger diameter port. For instance a slot port of 6" by 18" by 26.62" would be a nice compromise port for this solution.
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Old 26th August 2008, 03:58 AM   #5
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Quote:
Originally posted by pjpoes
Ok just as an example here. If all 4 subs were in one box, you could make it 7 cubic feet and tune to 35hz. Then you would need, going with 4" ports, 8 of these ports to keep port noise reasonable, each one being 28.8" long, or so. Obviously at that point you might want to consider a slot port or larger diameter port. For instance a slot port of 6" by 18" by 26.62" would be a nice compromise port for this solution.

Thanks for the help, and yes it is for my car.

With a box that size (ported), I was planning on having a slot port. I trust your judgment far more than I do mine, and will figure out a box that will work well with the port size you gave me.

Thank you for you're help, and compared to other sites I would have to say I like this the best. People seem mature here and really willing to help others, not just poke fun at them.

I'll touch back when I get everything built and set-up!
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