Ihave 2 sony xs-gtx120Lw 12' going in a 04 honda civic. I want to build a box but do not have the specs for them subs in a ported box

it depends on the type of enclose you are building and number of drivers .. you can build them and share air space or build it to were neither sub shares any air space.. if you buy a prefab enclosure for your 15s what ever q logic or q power or any other manufacture choses to build a universal port or vent or sealed box will be just fine.
which type of enclosure are you looking for ..
port
vented
seal
isobaric

1.6 cuft to 2.5 cuft per subwoofer check out the sub boxes from qpower and there specs for 15"BASS15 3HOLE 40 1/8 x 21 x 21 x 17 2.5cuBASS15 4HOLE T 42 x 18 x 18 x 16 1/4 1.6cuqpowers specs from there website
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Here is the spec sheet for your sub.

http://www.crutchfield.com/S-6KjEsFcldcJ/p_158L1236/Sony-XS-L1236-Single-12-Sub.html?tab=features_and_specs

there is a web site that gives the equation

Try checking the specs on the amp. It might not be able to drive a 2ohm load. just a suggestion.

Hello bgl6176,

According to their specs, the L7's will work in a ported enclosure with as little as 3 CuFt and up to 6 CuFt. Usually with ported, bigger is better, so let's use the 5 CuFt per chamber. I'm assuming that you have room for a 10 CuFt box in the trunk? That's a big box? Almost half as big as a medium sized refrigerator. I hope you don't plan on putting your golf bags in there too. For 10.15 CuFt, a box will need to be 36X29X20, allowing 0.15 for the partition, sub, and port displacement.

To tune each chamber to 30Hz, you need a 4" diameter port 4.6" in length. Lots of custom builders use PVC and even ABS pipe for round ports. You can also buy "pretuned" ports from sites like www.partsexpress.com.

You'll have to measure the exact room that you have available and then adjust the dimensions accordingly.

Here's a link to a great site for calculating almost anything in box building and subwoofer related. You can use the old "multiply LxWxD and divide by 1728" and the other formulas too, but here you can plug the figures in and immediately see the results.

http://www.the12volt.com/caraudio/boxcalcs.asp#rec

Hope this helps.

you need to find out factory reccomendations for airspace and port size. Many people with lots of experience building boxes still fail to do this and build good quality boxes, but for the wrong speakers.

try a electronics store like jaycar? they have the specs for sealed and ported speaker boxes depending on size and watts

Try going to Alpine web site, I think they have box building program as well that you just input your sub models into and it gives you blueprints for various types of enclosures. I know Rockford has one and a comparative attachment to compare equipt specs. Or if you call Alpine headquarters you may be able to get info that way, I once sweet talked a rep @ a demo vehicle I met doing some car shows that turned me on to a senior rep @ Korbon Trading the owners of Rockford Fosgate and they gave me specs for a 5 stage band pass box for some competition subs that was more intricate and detailed than anyone before that could find me, Won me first place in spl. Matching your box specs to your subs is crucial and the best specs are often kept a secret for demo competition vehicles! So ask around with some competition guys or other top experts if your real serious about your boooom.

do you want the box ported or unported (holes or no holes) if you don't got a lot of room than you dont want a ported box. keep in mind the box has to have the correct amount of cubic air space or you could seize your sub... if you're building it make sure you use OSB board (oriented strand board) or MDF board(medium density fiber) your sub needs .7cubic feet of air space in an unported box

Sealed box and somewhat large if they are 12's I usually try to get 3 cubic feet overall internal dimensions and generally the inside dimensions will be 13" tall 32" wide and 13"-14" inches deep. with no divider and make sure the box is sealed. Personally I like to phase the speakers backwards. Gives the bass a little more rumble.