Where Sound Comes From
Speakers are all around us, in phones, headphones, televisions, and music systems. They fill rooms with voices and music seemingly out of nowhere. An electrical signal goes into a speaker, and sound comes out the other side. But sound and electricity are completely different things. So how does a speaker bridge that gap and turn an invisible electrical signal into something we can actually hear?
Sound Is Moving Air
To understand a speaker, first remember what sound really is. Sound is a vibration traveling through the air. When something vibrates, it pushes on the surrounding air, creating waves of pressure that spread outward. When these moving waves of air reach your ears, you hear them as sound. So to create sound, a speaker needs to make the air vibrate in just the right pattern.
The Cone and the Coil
Inside a speaker is a cone, a wide, light, flexible part shaped a bit like a shallow funnel. Attached to the narrow end of the cone is a coil of wire, and that coil sits close to a permanent magnet. This arrangement is the engine of the speaker. When the cone moves, it pushes the air in front of it. The speaker's whole job is to make that cone move correctly, and it uses electricity and magnetism to do so.
Turning Signal Into Motion
The sound to be played arrives at the speaker as an electrical signal, a current that changes constantly in step with the sound. When this changing current flows through the coil, the coil becomes a magnet whose pull keeps changing. Because it sits near the permanent magnet, the coil is pushed and pulled back and forth, and it drags the attached cone with it. The vibrating cone pushes the air, creating sound waves that match the original signal. A microphone does the reverse, turning sound into a signal.
Source
This article was written using information from Wikipedia.