The music that you hear is coming from the sparks that these two identical high power solid state Tesla coils are generating. There are no speakers involved.
The Tesla coils stand 7 feet tall and are each capable of putting out over 12 foot of spark. They are spaced about 18 feet apart. The coils are controlled over a fiber optic link by a single laptop computer. Each coil is assigned to a midi channel which it responds to by playing notes that are programed into the computer software.
These coils were constructed by Steve Ward and Jeff Larson. Video was captured by Terry Blake.
What is not obvious is how loud the coils are. They are well over 110dB If you look at another You Tube video which is from a different angle, you can hear the echo off the building and get a better idea of how loud it is.