My PCB speaker is very simple and works just like any other speaker.
Its main components are the magnet and a coil, in this case a flexible printed traces. The vibrations created from the coil pushes the surrounding air to create sound waves. I also tried adding a diaphragm to amplify the music. It also worked with a 1.6mm rigid pcb, having the magnet connected to the diaphragm.
Check out the full video:
I've noticed that stacking rare earth magnets generally doesn't actually increase the field strength in the direction you intended In some of my test cases, it actually was worse than a single magnet
Don't know the math as to why, but that was the observation.