Aolean harp! I'm planning a workshop for kids around this now: build the harp & resonator however you like (two flower pots with a piece of fishing line in between for example -- more ideas here: https://www.homemade-dessert-recipes.com/aeolian-harp.html) then add a contact mic to the resonator and do some simple digital processing (delays and phase shifts) on the waveforms to demonstrate signal arithmetic and the basics of acoustics.