How to choose a subwoofer for your car audio system (to place in the trunk of your car)

This instructible will give an idea of how to choose a suitable subwoofer/s for your ride. This has a lot of information regarding selection of your beloved 'woofer. I have a lot of friends who have taught me a lot of stuff about sound systems, as well as magazines and internet articles, which have developed my knowledge heaps as of late.
I hope this helps you people unsure about what to get. Enjoy.

Step 1 Your car

Firstly you need to have an idea of what car your subwoofer/driver is going into, because the size of the car and amount of space will directly affect the size and/or amount speakers you can install. If youre like me, you wont have a car at the moment, but it wont stop you if you have a little knowledge about cars (I didnt have a car at the time of writing, but I had a very good idea of one that I wanted).

Comments

[buddton]

pretty helpful, i didn't know a few things hear and there but quite helpful.

[3VIL G3NIUS]

QVC (quad voice coil)?
18" 21" 22" 24"? heck even 32 (not recommended because of extreme suckage)
square? round?
bandpass (4th order? 6th order?) horn? 1/4 wave T-line? 
a couple-a missed things but oh well.

nice 'ible

[nmesis_02]

thanks for the comments, but bandpass boxes and the like are too hard to understand for AV-novices, which are who this 'ible is aimed at.

[3VIL G3NIUS]

 oh this is for noobs :-P. Your welcome :-)

[jhig]

Don't forget that you really need to match the sub impedance with your amp!

[surfturf]

How is that done? Just bought a used base cone to use in a portable soundsystem.. What should I look for? What happens if something's totally wrong?

[pyper]

In my experience car audio is pretty much 4ohms across the board, to the extent that most things (drivers or amps) don't even bother specifying the impedance. Low impedance better suits the low voltage / high current power available in the car.

[3VIL G3NIUS]

 quality gear is 2ohm, 1ohm or sometimes 0.5 ohm (no subs are 0.5 amps can be stable at this though)
what kinda stuff doesnt have a rating? 
true about it being better though.

[nmesis_02]

a lot of this info is, or seems to be, aimed at people who have a basic knowledge of automotive audio systems, and while there are a lot of good things mentioned in these comments, they may not be applicable to everyone. Despite this, there isn't much the internet won't have. That's how i learnt everything! thanx for the comments peeps.

[slimguy379]

i had a ported box and the handles can be screwed off, i unattached them, and in the end re attached them seal boxes hit so much harder. also i feel that installing a sound system is not difficult, its work but not worth paying someone t do if you can do it yourself. ik there are many HOW TOs on this site about installing subs, please if anyone is going to do this please install it yourself, save money, get knowledge, and the satisfaction of being able to do it yourself. but nothing against your way, decent knowledge here thanks for the time to do the instructable.