im guessing the OP meant take the wire from a car sub and make a 3.5mm jack plug on the end to stick in to a headphone socket, possibly on a car stereo or on a home stereo, or mp3 player, dunno which.....
you could do that...wouldnt do bugger all tho im guessing....lol...you need to amplify the signal before it gets to the driver....or did u mean a car sub with a built in amp? in which case it might have some sort of phono input, in which case you can get a 3.5mm to phono adaptor...but unless you split this off to some midrange and tweeters as well, all you are likely to get is low end stuff.....you'll be missing most of the music....