Hello here's a notion that's been knocking on the back door of my brain for some time but never done .
Using a low power 555 timer and a maybe a 3 volt gated MOSFET to drive the pizeo speaker .and a hollow wooden box could you use a string or tuning fork type connected to a small neo and a wire wound toroidal core .one... could you drive it to create energy being in the box it acts as a sound wave guide .what about 100 would they run if everything in resonance ?. Using low frequency and a large tuning fork with a slide bar make a difference ?. What do you think ? I saw in popular science a guy who made a fan about six inch's like a computer fan the blades were made out of pizeo material it was 10 times more effective than a normal fan ..it ran on a tiny hearing adid battery !! So I'm going with pezio speaker . a violin string is tunable . how about many moving each a neo ?.