The function of voice coil of loudspeaker

(1) When current I is applied to the voice coil in the magnetic gap of loudspeaker with magnetic field strength B, the voice coil will receive an electric power f = bli (L is the voice coil length), and the force direction is set according to the left-hand rule.
 

(2) When the vibration system including voice coil vibrates at the speed V, the induced voltage BLV will be generated inside the voice coil after the occurrence of the force, and its direction conforms to the right-hand rule and is supported by the original current direction. At this time, the voice coil is the initial actor and the acceptor of damping.