The sparks generated by the coils are the only things producing the sounds.

A YouTuber, Nerdist, recently released a video of two Tesla coils playing Toto’s hit song, “Africa”. He explained that this is not merely a lightshow and that the coils are literally the only elements producing any sound. There are no speakers involved whatsoever. Thanks to some fancy science, phase, pulse width, and firing frequency, the coils are able to reproduce the classic song after being carefully callobrated.