P7__Electromagnetism A cone which has a coil of wire wrapped around it which is connected to an AC electrical supply. A permanent magnet is placed inside the coil of the wire. As current passes through the coil it generates a magnetic field which interacts with the magnetic field of the permanent magnet which creates a resultant force (via the Motor Effect which causes the cone to move in and out (due to AC) which pushes air in font of it to create sound waves. You can increase frequency of sound by increasing frequency of AC and amplitude of sound by increasing the amplitude of AC.