What kind of subwoofer should I get?

when i first got my car the sound system lacked bass, but i replaced my head unit and there was a major improvement because they put out more power and it is higher quality as well as the many equalizer it has. i recommend replacing your head unit first and you might be surprised at how it sounds, and if it is not enough then move up to a subwoofer, a bazooka tube might work for you, a little bass not to much but adds a lot of depth to the music.or if you feel it is necessary you can get a pair or a single ported 12in subwoofer with 300-600watts and you'll need earplugs