tips on building ported sub box.?

Question

this will be my second sub box i have built. 1st ported. 

its a 1200w kenwood sub 12 inch

Sealed - 35.4 litres, Ported - 42.5 litres - port diameter / length: 76 x 178mm

here is the reccomended stuff, what does this 42.5 litres mean? can someone explain this to me in STANDARD measurements. (i know its volume)

also, does the general shape of the box matter as long as it has the right volume and does port location matter?

N2Audio · Accepted Answer

google's search will do conversions, just type 42.5 liters to cubic inches...42.5 liters = 2594 cubic inches.

2594 = w x l x h, so plug in some logical numbers and see where you're at...

2594 = 20 x 14 x ?
20x 14 = 280
2594/280 = 9.26

So internal dimensions of 20x12x9.25 would give you the required volume.

However - you need to allow for sub and port displacement.  The sub is probably around .07 cubic feet and the port would be pi x r x r x l or 3.14 x 38 x 38 x 178
= 807080 sq mm or about 49 cubic inches.

Sub at .07 = 121 cubic inches

So recalculating volume you'd be shooting for 2594+170 or 2764

Again using 20x14
2764/280 = 9.9 deep

Internal dims 20x14x9.9 (I'd round it to 9.875 for easier measuring purposes)
With a port 3" dia that is 7" long.

"Ideally" the port and sub should be on the same face.  But I've always read it doesn't make much difference in practice.
Shape of the box doesn't matter.  Just the volume.

Anonymous · Answer

You need to get your box design first. Determine box size before displacement. And determine tuning frequency. For your first build I would just do a vented enclosure. Basics: Your box needs to be about 7 cubes before displacement, with 105 sq inches of port. If you want low rumbling bass then tune box to 30 Hz. For higher spl tune to high 30s.

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tips on building ported sub box.?

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