Sound in a Box

Sand on a ringing plate gathers on the lines that stay still. The same happens in 3D. Here a glass cell 1 cm across holds water and plastic beads, and a transducer underneath fills it with ultrasound at one of its resonances, a standing wave. The acoustic radiation force pushes each bead onto the mode's still surfaces, its nodes (the Gor'kov potential; H. Bruus, 2012).

The cube's modes ring at f = (c / 2L)·√(l² + m² + n²), the round flask's where a spherical Bessel function's slope is zero at the wall: about 75 to 370 kHz, so you hear each one eight octaves down. Tap to ring the chosen mode; tap again to swirl the water.

Or play a song, a built-in tune, or sing: the music's pitch is scaled up to the cell's ultrasound modes, and the nearest rings. Bead colors picks one color, a palette, a flag's colors, or colors by height or by distance from the center. “What are these modes?” in the Splash tab explains each mode. Files stay on your device.

Made in Splashery. Its code is MIT.