Speakers have a relatively simple design, yet they are borderline perfect at what they do, but how do they actually work?
Before we can appreciate how a speaker works, we have to understand the technical side of audio. Sound is a sense that our brains interpret from vibrations. So, in basic terms, there is not nothing between the source of sound and our eardrums. There are air particles that act as an elastic medium in a longitudinal manner by transferring high-pressure pockets to low pressure over distance. We interpret these vibrations as sound.
In order to create a device that carries sound, the primary function is the device needs to create disruptions in these high and low-pressure mediums.
And audio speakers do just that. A speaker consists of a motor that drives the speaker back and forth. The motor is attached to the speaker cone which carries the motion of the motor into pressure waves.
The motor is where the "magic" happens. The motor is made up of a heat resistant cylinder that has a coil around it, where electricity runs through in order to create an electromagnetic field. There is also a large magnet that sits at the back of the speaker which constantly pulls on the motor. When electricity runs through the motor, the motor will pull away from the magnet depending on how much electricity is transmitted through it.
The amount of electricity that runs through the motor determines the amplitude and frequency of the sound, where the frequency describes the number of vibrations per second. Higher the frequency the higher the pitch.
Our hearing ranges from a low base sound of 20Hz right up to 20,000Hz, the only problem is that not many speakers can deliver even close to what we can hear on the scale. So, different size speakers are usually used together in order to deliver a wide range of sound, such as an audio system that consists of "tweeters" which are small speakers that carry higher frequences and "sub-woofers" that carry lower frequencies.
Take a look at the video below by YouTube channel, Animagraffs, on How Speakers Make Sound.