In a dynamic loudspeaker, the voice coil is a winding of wire around a cylinder that is attached to the main part of a speaker. The voice coil is inserted into the 'gap' created between the magnet and pole piece of a speaker magnet assembly. When current travels through the wire, it generates a magnetic field that causes the speaker to move against the permanent magnet. The alternating current in the voice coil causes alternating magnetic fields to form which interact with the permanent magnet to cause the speaker to move back and forth producing sound.