Ferrofluid is a lot of fun to experiment with. There are already plenty of magnetic fluid kits that you can interact with using a strong magnet. This 3D Printed Ferrofluid Bluetooth 5.0 Speaker is also worth a look. It is designed to dance to the beat of your music.
By converting music to electrical signals, it is possible to control magnetic fluid. This speaker has a rotary knob that lets you adjust the rhythm. This is not only a speaker but also a sound visualizer. It has a 3000mAh battery.