  It is well-known that the perturbations of Schwarzschild black holes are
governed by a wave equation with some effective potential. We consider
perturbations of a gas in a tube called Laval nozzle, which is narrow in the
middle and has a sonic point in the throat. By equating the wave equation in a
Laval nozzle of an arbitrary form with the wave equation of spin-s
perturbations of Schwarzschild black holes, we find the exact expression for
the form of the Laval nozzle, for which acoustic perturbations of the gas flow
corresponds to the general form of perturbations of Schwarzschild black holes.
This allows observation, in a laboratory, of the acoustic waves, which are
analogue of damping quasinormal oscillations of Schwarzschild black holes. The
found exact acoustic analog allows to observe also some other phenomena
governed by the wave equation, such as the wave scattering and tunneling.
