Many bass guitar players are now choosing active pickups for their bass guitars.  An active pickup has a small pre amp built into the guitar and requires a battery.  This active pickup allows for greater control over the EQ of the bass frequency giving a smoother, thicker, and fuller sound.  This thicker, and more powerful sound is especially good for rap and dance music where the bass plays a very large part of the overall song.  The passive bass guitar pickup consists of a magnet and a coil of wire.  The passive pickup gives the bass guitar a raw and lively sound.  This pickup will give greater dynamics.  When you pluck your guitar string softly you will get a very quiet sound and when you really hit hard on your bass guitar string you will get a very loud sound.