A ferrofluid is a special kind of liquid that responds to magnetic fields. Originally developed in the ‘60s by NASA engineer Steve Papell to facilitate rocket fuel delivery in zero gravity, ferrofluids are made by suspending tiny nanoscale particles of ferromagnetic material in some kind of carrier fluid. Those particles are given a coating that keeps them from sticking together, which lets the ferrofluid flow uninhibited. The result is a dark, oily substance that reacts to nearby magnetic fields in interesting ways. Dakd Jung found what is likely the coolest application for ferrofluid when he used it to create a sound-reactive display for a custom Bluetooth speaker.
This device resembles any other medium-sized bookshelf speaker. It has a clean, white, minimalist enclosure that would look at home on Jony Ive’s desk. The exception is that ferrofluid display that is placed front and center, where the primary speaker driver would normally be mounted. That “display” is a round glass reservoir that is lit by LEDs and that contains a blob of ferrofluid floating in water. When the speaker is turned off, the ferrofluid just kind of sits there. But as soon as music is played, the ferrofluid bobs, explodes, and wiggles in response to the sound. It is a bit like a lava lamp, except the movement is faster and corresponds to the music being played through the speaker.
That sleek enclosure was 3D-printed, then carefully sanded and painted. It has three off-the-shelf speaker drivers, which are powered by a small amplifier and receive audio from a Bluetooth module. The ferrofluid was carefully poured into a round glass container that was given “special treatments” that prevent the ferrofluid from sticking to the glass. An electromagnet was mounted behind the glass container and controlled by an Arduino Nano board. The power going to that electromagnet corresponds to the volume in a specific frequency range. The desired frequency range can be set using a dial and is controlled by an MSGEQ7 module that is meant for filtering graphic equalizer displays. So if the dial is set to something like 150 Hz, then the ferrofluid will react to the bass in the music. If it is set to 4 kHz, the ferrofluid moves in reaction to the treble. This is a wildly creative use for ferrofluid and the speaker is completely mesmerizing to watch.