There is nothing simpler or more elegant in design than a loudspeaker. It makes use of some of the oldest laws of physics to reproduce sound, and since it's creation decades ago, basically hasn't changed at all.
The basic principals that speakers rely on are the rules of magnetism. We know that like charges repel, while opposite charges attract. The other thing you need to know is that when current flows through a conductor, a magnetic field is produced around the conductor. If you took even the most rudimentary high-school physics classes, you should be very familiar with these physical properties.
There are two important components in a speaker in terms of getting it to move. These are the voice coil and the stationary magnet. The voice coil is a winding of copper ( though aluminum is starting to become popular) that is wrapped around a circular drum called a voice coil former. The wire is insulated with a very narrow layer of varnish (or plastic) so that the winding is still one long conductor rather than just a conductive blob of copper. The ends of the voice coil wire is connected to the terminals on the speaker basket through what is known as tinsel leads. These are very flexible pieces of braided wire that allow electricity to pass.
The voice coil is suspended at the top of a large stationary magnet, centered on a plate of steel called a top plate. The magnetic field created by the magnet is focused on the voice by this metal plate, making it much more intense.
As we send electrical signals to the voice coil, it sets up a magnetic field around itself as the current flow through the wire. The magnetic field created by this current flow interacts with the magnetic field of the stationary magnet and either draws the speaker down towards the magnet, or pushes it away. That's the basics of how a speaker works.
Now, how does this produce sound? Attached to the top of the voice coil former is a cone (made of paper, plastic, aluminum or composite materials and sandwiches). As the voice coil moves up and down, it moves this cone up and down at the same time.
Ensuring that the voice coil and cone travel straight up and down is the spider and surround. The spider is connected at the base of the cone and the surround is at the top of the cone.
These are the basic components of a speaker. We'll look at some of the different designs and thermal control methods in another article.