A vertical soap film, freely suspended at the end of a tube, is vibrated by a sound wave that
propagates in the tube. If the sound wave is a piece of music, the soap film ‘comes alive’: colours,
due to iridescences in the soap film, swirl, split and merge in time with the music (see the
snapshots in figure 1 below). In this article, we analyse the rich physics behind these fascinating
dynamical patterns: it combines the acoustic propagation in a tube, the light interferences, and the
static and dynamic properties of soap films. The interaction between the acoustic wave and the
liquid membrane results in capillary waves on the soap film, as well as non-linear effects leading
to a non-oscillatory flow of liquid in the plane of the film, which induces several spectacular
effects: generation of vortices, diphasic dynamical patterns inside the film, and swelling of the
soap film under certain conditions. Each of these effects is associated with a characteristic time
scale, which inte…