Help me with my car audio sub enclosure

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Hi everyone, I came here for help on building an enclosure for my new sub which i'm putting in my car. I don't think my amp matters but I will provide what kind it is just in cause. It is an mtx thunder 4250D. My sub is a 12" Type S Alpine (SWS-1241), see link below for specifications from the alpine site. I would like to know if I should build a sealed or ported box, and what the measurements for everything/some things should be. If you could help I would appreciate it very much. My manuel says that the recommended sealed box volume is .8 - 1.7 feet cubed. Please help. Thanks!

Here is the link for the Alpine specifications: (you might have to copy and paste it if it doesn't all appear on one line)
If you haven't built any/many enclosures before you may want to start with a sealed one. There is very little you can do wrong that way (provided it IS actually sealed:)). Car subs generally rely heavily on the vehicles transfer function to boost the real low frequencies anyways and if you have a small car you can usually get away with a fairly small sealed box and still get nice low extension. If you're looking for nice smooth response go sealed. If you need a little more kick you could consider a ported box. But I'd just go with as big of a sealed box as you're comfortable putting in your car up to the recommended 1.7 cu ft.

As far as measurements of the box itself you'll have to post some more info regarding maximum dimensions where you'd like to put it in your car. i.e. if in a sedan you may have 38" between the shock towers and 14" in height. From that we could determine how deep the box needs to be to get your desired volume.
More info

Ok, I know I put car, but for right now the sub is going into my parents van until I get a car which might be a couple months. So as far as the size of the box, it can be quite big, but keeping it to a limit, I don't want the whole van filled by the sub. I am a beginner with building boxes but my brother said he would build me one (he's built a couple) and he asked me to find out all the dimensions from the net, but the problem is that I'm having problems finding all that stuff and understanding it. He wants to build a ported one because we have all the materials because our dad is an electrician so everything is easy to come by.

This is a real quick and dirty comparison. I suggest you download WinISDBeta to play around some more with it. But basically I simulated a 1.7 cu ft sealed and ported enclosure (tuned to 36 Hz). The yellow curve is sealed, green is ported. As you can see you're -3dB @ 40Hz sealed and -3dB @ ~33Hz ported. The main advantage (or dis if you don't like it boomy) to the ported box is the large gain centered around 55 Hz. Personally I prefer the sealed response but to each his own. If you listen to lots or rock/rap you may want to tune the ported box even higher. WinISD isn't perfect but it'll put you in the ballpark as far as box size, port diameter/length and roughly what you can expect from the box. But keep in mind that the low end will be boosted lots when in the vehicle so you don't need it to be ruler flat. A nice steady drop off is desireable generally.


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1 cu. ft. sealed. i think Jason has it right.

also try this.....

take a 3 or 4" dia port about 4-5" long. stuff the port with polyfill. stcik port into sealed box. if yo dont like it cover port with wood.

the stuffed port might sound good fo you. I took 2 x 12" Pioneer subs in 2 x 1 cu. ft. boxes and did this and it sounded great in my sedan (OPEL ASTRA). You have to experiment.

I call this technique Short over damped Tranmission line.

I did the same thing in my car with a Kenwood 10'' sub. I did the box for the sealed dimension and I have added a port for a specific tunning freq. After experimentation, I have prefered the sealed box. Sealed box are smaller so it is a good advantage in the car especially if your wife is using the car for shopping. They usually need a big trunk. Big box = very low WAF. :)
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