A speaker consists of one or more magnets, called voice coils, which are mounted at the narrowest part of a cone(s). The cone may be made of paper, cardboard, or Kevlar. When the amplifier receives a signal, it amplifies it, creating current. The current causes the magnet to move, which distorts the cone. When the magnet relaxes, the cone returns to its original shape, after a few oscillations. The cone moving back and forth compresses the air in front of it, causing a wave to travel away from the cone. That wave is the same frequency as the signal the amplifier received.