12 alpine type r’s box .

Okay, i am having trouble deciding sealed or ported, and then the size. I used crutchfields recommendation for a sealed, and they came up 27 x 13 x 13. (Two subs, two chambers, 3/4 MDF) The subs are gonna take up most of the box volume. Does this sound right?

Next, i would also like to make a ported box, tuned to 33 hz, dual 2" ports, the box will need to be 35 x 15 x 15.  Now, is the port tuning as simple as just cutting the tube to the proper length, and putting it in the box? I am gonna put them in the front, below the subs on the left and right of the subs. Basically, this is my first ported box, i've alweays done sealed, but i hear that the 12" type r's sound the best in a properly built ported box.  as far as sound, i mostly listen to deep music, usually 45 hz and below. Most of the time around 30-20 hz though. Any suggestions will be helpful, as i would like to have my box designed before i get the subs on the 5th.

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Disturbin' Tha Peace

two 2 inch round ports are WAYYYY to small...I'd do atleast two 4 inch ports per woofer

i tried two 4" ports, and then the calculator says some obscene number, like 42 inches. my box is only 15" deep. I could use one 3" port. That works, but any bigger than 3", and the calculator gives me a length that wont fit into my box.

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Disturbin' Tha Peace

okay, i guess what i am asking is: are the sealed box dimensions wrong? or do they sound right?

And: are ports as easy to do as just building the box to specs for ported, and then cutting the tube to the proper length and putting it in the front of the box?

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Disturbin' Tha Peace

build a slot port and have it bend inside the enclosure

3 inches is too small...for ported I'd do 2-2.5 per sub net

Here is the skinny on the ported box questions that you have posted.
If you are going to build a generic box like the type that Crutchfield or Alpine or anyone ells tells you to build, your best bet is to cut and install the ports as specified by that resource. Port volume like box volume has a sweet spot that is critical to its design. You can change the port diameter for instance and then calculate the new length for that same tuning frequency, but in doing so you change several parameters of your box other than the tuned frequency. Some examples are: cone displacement vs. frequency curve (including 3 db down point), achievable SPL, Vent velocity, impedance curve, power consumption vs. frequency curve, phase vs. frequency curve, and group delay not to mention port resonances that you may not want. All of which have a huge effect on how your box will perform. In short if you are willing to spend the time to experiment with various port volumes (diameter and lengths) go for it, but if you want the best chance of a good result the first time stick to the design that was designed by an educated audio engineer.

The alternatives are to have someone with many years of experience optimizing and constructing (not just playing with share ware programs) actual boxes help you come to an educated decision.
Or even better have a real pro plot the cabin gain of your vehicle and test the parameters of your actual drivers, then post that info here and you will get several valid designs to choose from.

Regardless of what avenue you choose, this will require you to either absorb some knowledge of speaker design in order to make a decision or just trust the first Joe that responds to you.      

I would like to also add that in my opinion the alpine type R is a great sub and performs the best in a ported box. SPL, deep articulate bass, efficiency, and transient response are all better in a ported box. The draw backs are that it is larger in size and will require you to do more homework. If you want a small, easy to build box that will give you good sound and mediocre output, go for the sealed box.

And last but not least the type R subs have gone through generation changes, so be sure that any information that you receive about box design applies to the production date of your particular subs.