While it seems magical, the electrical circuit for a standard speaker is incredibly simple. When current flows through a coil on the speaker cone, it’s drawn towards a magnet. If that current is quickly modulated at the proper frequency, the cone vibrates and produces audible music. The magic fades a bit when you know how it works, but this plasma arc speaker created by YouTuber GreatScott! remains magical even after that veil has been lifted.
A plasma arc can be created by applying a very high voltage across two electrical conductors in close proximity. That plasma arc is what is created by a ignition coil and spark plug in a internal combustion engine. GreatScott! theorized that the same system could be used to cause the arc itself to emit sound if it were controlled in the same way as a speaker — just at a much higher voltage. To test that, he used an ignition coil from a scooter motor, which is essentially a transformer designed specifically to convert low voltages into extremely high voltages.
By reverse-engineering the ignition coil, he determined that the secondary coil released a high voltage when the low voltage of the secondary coil is removed and its electromagnetic field collapses. If he could just modulate that collapse with a PWM at the right frequency, the arc would produce recognizable music. Unfortunately, the scooter ignition coil wasn’t suitable because the impedance varied with the frequency. So, he replaced that with a transformer from a CRT monitor. That transformer was able to keep up, and GreatScott! had a speaker made from a plasma arc. The sound quality is bad and it’s horribly inefficient, but it is very, very cool.