Ported box

Alpine SWR-1242D (TYPE R)

does those measurment look right i think i had a number wrong

hahah, okay were getting somewhere but it sounds like you need to have a local shop build you a box....but just for shiggles heres some key points...

1.)  3.4 ft^3 is way too much airspace for one type-R 12"...Around 1.5-2.0 should be in the range...

2.) 44inch Port...*chuckle*....

3.) 33.5 x 17 x 26 is DEFINATELY not 3.4 cubic feet.  Correct me if im wrong anyone but isnt that somewhere around 7ft^3...?

That's not particularly the box-building aid that I'd recommend you try to use.

You can make the port opening much smaller for two of these Alpine subs, and with that smaller opening there will be a much shorter port length.  Alpine published a box-building guide here, but doesn't seem to show published specs for that sub, for some unknown reason.

The net volume you show is about right for two subs.  You want the tuning to be at 30 to 36 Hz, with each sub getting about 1.7 to 2 cu ft net.  And like I said, minimize the slot port opening so that you are not building 2 cu ft of port into the structure.  If you have a link to the published specs, show it. 

Oh, here it is...I was looking in the wrong place.  http://www.alpine-usa.com/images/products/documents/OM_SWR-1242D.pdf

Your best bet is to do this:  build each chamber of the box to the specs set forth in the pdf document.  Each sub gets its own chamber and its own port, although the subs may still be wired together electrically.  The box dimensions are laid out including port opening size and length.  Use the specs as described under "optimum vented box".

If you are getting stuck figuring material (MDF) requirements, you should lay out your design on paper.  Figure the measurement in inches of each panel that will be a part of the enclosure.  You are calculating total square inches that you need, and you know that one sheet of MDF is 8 ft X 4 ft (4600 square inches).  Be sure to allow for cut waste when you lay out your cut plan.