I have made vortex cannons with my kids before. The most fun were the large ones made from trash cans. Add in a smoke machine and it is even better. Anyone that has not seen these just search “vortex cannon”.
I just saw this:
I had never thought of using a speaker as the membrane to fire the shot. It seems like it should work great and I could see adding a 2-axis aiming system using some servos and have a remote control unit for even more fun. Maybe add a small vaporizer for the smoke source.