is building a ported sub box very hard?

If your going for boom outside the car I would go with a bandpass box.Youll miss a few freq. from that of a sealed box but the bass will be loud. A couple of good things about bandpass are : speakers inside so know1 messes them up by kicking etc.,the bass, and last you dont need as much power to pump your speakers. If you want the ported box its going to be bigger than your sealed. Your speakers should have box requirements. The box is the main thing. You can take an old paper woofer put it in the right box and it will hit. Ive done it to show people.

Depends on the sub... Large ported enclosures tend to be better for the lower end. However, there is much more to building a ported enclosure then that. You have to take into account the subs T/S parameters and use a subwoofer enclosure program for best results when making a ported enclosure. You should look at your manufacturer's recommendation for enclosure size. This will be the best bet if you are new to building ported enclosures. Putting your subs in an incorrect enclosure (wrong size/tuning frequency) can damage your subs or make them sound horrible. Make sure all your measurements are correct and you build to the correct design. Good Luck!!!

It is going to be fairly difficult to design a ported enclosure if you have no prior experience. Actually building it though will not be that hard IF you know what you are doing. As long as you make the enclosure just like the plans then you will be fine.

Ported enclosures are greatly effected by any build or design errors. If you make any mistakes it will be appearant when you listen to your subs.

A bandpass enclosure is going to be even harder yet. Plus it will be MUCH worse if you make a mistake.

Good Luck!!!

standard ported box is not so bad. you have to use the speaker with lower Qes (like 0.25-0.45) and use some good program - like LSPLab demo. It is speaker box simulator, so you can play with it. add some speakers and try to make some imaginar ported boxes, change its parametters and see what happens with frequency range, linear excursion etc. The frequency range should be "flat" and alt the low frequency end fall down.

well actually it is very complicated with at least calculating the port size/width(usually at least 4 inches diameter)

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

theres a site that has a calculator to do all the work for you as long as you have the inputs, good luck