In a audio equipment, electricity flows into a coil of metal wire wrapped around (or in front of) a permanent magnet. The changing pattern of electricity in the coil creates a magnetic field all around it that pushes against the field the permanent magnet creates. This makes the coil move. The coil is attached to a big flat disc called a diaphragm or cone so, as the coil moves, the diaphragm moves too. The moving diaphragm pushes air back and forth into the room and creates sound waves we can hear.