An apparatus for disrupting cells or viruses comprises a container having a chamber for holding the cells or viruses. The container includes at least one flexible wall defining the chamber. The apparatus also includes a transducer for impacting an external surface of the flexible wall to generate pressure waves in the chamber. The apparatus also includes a pressure source for increasing the pressure in the chamber. The pressurization of the chamber ensures effective coupling between the transducer and the flexible wall. The apparatus may also include beads in the chamber for rupturing the cells or viruses.