Sound waves are vibrations of the air around us, which you can make just by clapping your hands or talking. Pitch is just the number of times the air vibrates per second. Higher frequency, higher pitch. Tesla coils are a combination of circuits that output thousands to millions of volts. That high electric field arcs up and out of the coil, filling the air with sparks and making it possible to light up fluorescent lights wirelessly. Certain types of Tesla coils, like the one used here, are putting out hundreds of sparks per second, with a rest between each spark. That’s already a lot like a sound wave. Each spark is pushing on the air and can create a sound. Change the frequency of the sparks and you get an equal frequency wave, hitting your ears like a note of music. The creators had to find a way to move seamlessly between frequencies to make the notes sound distinct, instead of just playing the whole scale.
Above, tesla coils “sing” the Inspector Gadget theme by ArcAttack, who were the first to use this technology in a live performance in late 2005. Watch more singing tesla coil videos at Know Your Meme. Related links: the tesla coil and Nikola Tesla, who invented it around 1891.