Arcos and colleagues stretch soap films across boundaries of different shapes and drive them acoustically. Because the film's normal modes obey the same wave equation as a quantum particle confined to a two-dimensional region, the visible patterns are direct analogues of the wavefunctions of integrable and chaotic billiards.
The striking result is scars: narrow bands of high amplitude that trace the classical periodic orbits of a chaotic boundary, which show up in the films and, the authors note, are visible even at low frequencies. That makes an effect usually seen in numerical simulations into something you can photograph on a bench.
For a studio working with high-performance bubbles, this is the most useful thin-film paper we know: it treats the film as a resonator with a boundary condition rather than a fragile surface, and it makes the case that the shape of the frame is the real instrument. Published in the American Journal of Physics in 1998; this arXiv copy is free.