Loudspeakers

Loudspeakers are devices that use a current to produce SOUND.

When connected to an ALTERNATING power supply, the ALTERNATING current creates a MAGNETIC FIELD around the coil which INTERACTS with the PERMANENT magnetic field.

This produces a RESULTANT FORCE which causes the paper CONE to MOVE.

ALTERNATING current means the DIRECTION of the current REVERSES back and forth. 

This means the DIRECTION of the RESULTANT FORCE also REVERSES back and forth which makes the CONE move backwards and forwards repeatedly to produce VIBRATIONS in the air which are SOUND WAVES.