In this post, I’ll show you a plasma speaker I made many years ago in fact, over 13 years ago. I originally saw this on Instructables and thought it was really cool so I decided I would make one myself. Unlike a traditional speaker which moves air with a diaphragm, a plasma speaker makes sound by utilizing a high voltage electric arc to move air.
The way this circuit works is by creating an oscillating signal(carrier frequency) that drives the flyback transformer. Then the audio signal from the phone is added to the carrier frequency by modulating it which makes the electric arc emit it as sound.