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Advice on building some SPL sub boxes

acarmody

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Ok so my local WOW is having a comp in a month and I want to build some SPL boxes for the comp. I have two 12" Kicker L7s, and they are getting 700wrms each. I was thinking about 3 cubic foot for each sub (including port) using 25mm MDF.

Slot ports are easy enough to build but what are the advantages/disadvantages to a round PVC port? My dad will be constructing the boxes and hes quite good with woodwork.
 

acarmody

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I should also add that I have 100cm wide, 40cm height and 65cm depth, in the boot to play with. Also I would prefer two single boxes as a single dual box would be way too heavy to get out to get to spare tyre.

EDIT: Ok I have worked out that a box 480mm X 400mm X 615mm = 3.003 cubic feet, close enough. And that's outside dimensions using 25mm MDF.
 
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sweefu

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Is that 3cu.ft net or external volume? Might be worth shooting holdenboy a pm mate he's an expert with everything SPL

Though from a glance, and my short time with spl i would say that those boxes will be a bit big for the 12" L7's

And i know you will want alot of good woodglue/fibreglass resin to seal up the box well.
 

acarmody

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3cu.ft is internal volume, not taking the port into consideration. As for the size, Kicker has a 4.2cu.ft box as there maximum size for these subs. And I'll make sure I get a sealant around all joints.

Also I was thinking would using dowels to hold the port wall in work? This way I could just take the top of the box off and swap the port size for everyday use.
 

holdenboy

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For your VX i take it?

If so, 3cu.ft. per sub before displacement should be fine.

You wont be chasing every last 0.1db, so a slot port per box should be fine. Try to get a decent sized port in (atleast 5 x 40cm anyway). Im not too sure on how you mean "using dowels to hold the port wall in"?
If you think it'll be strong enough to not leak air and be easy to swap ports etc, then no problem. Just for insurance, put a strip of that foam weather tape etc onto the two pieces.....SPL is all about over engineering ;)
 

acarmody

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Yep definitely intending for that foam stuff that usually comes with subs.

I think I will ditch the dowel idea, because each hole would have to be absolutely perfect, screws are easier, they make there own holes.

As for the port it will be 35cm high, outside box dimension is 40cm high and I'm using 25mm MDF. So 35cm high, and is there any particular rules to width and depth or......? Since it will be taking away from the volume of the 'enclosure'.
 

holdenboy

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Have a look at this calculator,
You may have to register to use it though?

It'll tell you if your port dimensions are bad ;)

I'd probably tune the boxes to 30-35hz daily, then shorten them up to around 40hz for SPL.
 

acarmody

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OK, I'm getting there. If I build a box that has outside dimensions of 480mm x 400mm x 620mm, using 25mm MDF, then I get a box that has a volume of 3.03cu.ft.

So my box volume is 2.5cu.ft, my port displacement (including wall) is 0.45cu.ft, my woofer displacement is 0.087cu.ft, and the two 3"x3" brace triangles equal, 0.005cu.ft, so in total that equals 3.037cu.ft, close enough.

Now my port will be tuned for 40hz, so the port is going to be 2.5" (64mm) wide by 13.78" (350mm) high, by 17.12" (43mm) long. This is for the 2.5cu.ft box volume.

Can't make them any bigger or I wouldn't be able to get the damn things in the boot. Man these will weigh a ton.
 
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acarmody

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27760501.jpg
frontandside.jpg
 

ToMMMaY

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dont port it

Ports sound better in the car but unported kills it outside :D
 
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