Disclaimer: DON'T TRY THIS AT HOME, FERROFLUID IS SUPER TOXIC, FLAMMABLE, DIFFICULT TO WORK WITH AND LEAVES STAINS THAT CANNOT BE REMOVED!!!
Ferrofluid is a little bit like a liquid magnet, it reacts to magnetic field around it. You might have seen some amazing videos of it. I thought 'would it be possible to make it move to the sound?' After many hours of experimenting and trying out stuff I've built a massive electromagnet from a huge speaker and it works ;-) here you can see the results. I intend to use it at my live performances as a visualization of sound.