Need to make a custom box for a 12 inch sub, how big should it be? Should I port it or not? Thanks

Depends on the room you have, the music you listen to, the power you have going to sub & the sub parameters itself.

For most part a sealed box has more tight (less boomy) bass, smaller encloser, requires more power to reach same db's as a ported box.

Without knowing the sub itself, its impossible to come up w/ an accurate enclosure.

1 cubic foot is normal for a 12,,,, but you should really check with the mfg,,, as they can differ

Exactly true. and the CI needed is pretty specific and important to get right. Also you can't just port a sub box if the sub requires non-ported and vise/versa.

if you get the brand/part number any car stereo place should be able to give you the size box it needs. for a 12 it is usually between 1 and 1.5 cubic feet. dont forget to compensate for the speaker sticking into the box. if you dont have enough room to make a big enough box, some dacron fluff can 'fool' the box into thinking it's bigger. a sealed box will be much tighter than a ported. also make sure you seal the seams and the speaker, even a very small airleak can wreck the sound.

If you're building the box yourself a trick I was taught is to mix wood glue with the left over saw dust from building the box. Mix the two and paste it to the box creases(inside). Makes a wood paste like welding.

The sub is a Hifonics and the amp is a JL Audio 500. Thanks for the help.

Call a Hifonics dealer. They'll tell you right over the phone what the CI need to be and if they can be ported or not. I would go with no port though. Like others said, tighter more solid bass with enclosed box.