How Do Speakers Work?

posted by Margaret Potagal

As a teenager in 2022, my life is full of music. Everyone is constantly in earbuds, blasting BlueTooth speakers, and basking in finally being able to listen to our own music in the car. Music is everywhere all the time, and I for one have taken it for granted. Could you imagine what life was like before we could listen to music whenever we wanted? When parties weren’t pulsing with extra base? Well before the invention of Edward Kellogg and Chester Rice’s 1925 dynamic driver many of the ways we enjoy music today were impossible. And can I just point out how cool speakers are? They can reproduce any sound you want just by plugging in a box or putting some little devices in your ears. How is that even possible?

I decided to do some research on speakers to see how exactly they work. And oh. My. Goodness. This is probably one of the coolest things I have ever learned about. Okay so first of all they use pretty much solely high school physics, right? You’ve probably heard about sound waves and how vibrating at different frequencies pushes air around and such. That’s how speakers work! Except the actual way the vibrations are produced is mind-bogglingly complicated and simple at the same time.

Here’s a diagram of a speaker:

a current is sent through the voice coil which produces an electric field that interacts with the magnetic field of the permanent magnet attached to the speaker. The parts depicted here are:

The cone and the dust cap (the parts that move air and produce sound)
The spider and the surround (also called the suspension, these are the parts that hold the cone in place while still allowing them to move)
The magnet and the voice coil (the parts that interact to convert electric energy into motion)
The basket
The pole and top plate
And finally, the frame that mounts everything together

Like charges repel each other and different charges attract. As an audio signal is sent through the voice coil and the musical waveform moves up and down, the voice coil is attracted and repelled by the permanent magnet.

This makes the cone that the voice coil is attached to move back and forth. The back and forth motion creates pressure waves in the air, also known as sound waves. Here’s a cool little animation to show a speaker in action:

And here is a real-life picture of an old radio from the back:

For high frequencies, speakers must move very quickly. For low frequencies, speakers must push a lot of air. This is why tweeters (high-frequency drivers) are typically small domes and woofers (low frequency drivers) are usually large cones.

We hear 10 octaves (20hz-20kHz) that is a very wide range (for comparison, we can only see less than one octave of light). It is a lot to ask for a speaker to reproduce such a wide range accurately. and it often takes 2 (woofer + tweeter), 3 (woofer +mid range+ tweeter), 4 (sub +woofer +mid range + tweeter) drivers to produce this wide range well.

So now the next time you listen to your headphones, or blast music in your car, you get to think about how cool it is that a magnet, some electricity, and a wire moving back and forth are reproducing your favorite songs whenever and wherever you want.

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