  In this paper, it is shown that in interaction with an oscillating bubbles
cluster the fluid becomes inhomogeneous. The radial variation of the acoustic
refractive index of the fluid generates an acoustic lens with spherical
symmetry. When the focal length of the lens associated with the bubbles cluster
is equal to the length of the position vector then the bubbles cluster behaves
like a dumb hole. Unlike the properties of a bubble, the cluster, by
compression under the action of attractive internal forces, can shrink its
radius to become a dumb hole.
