Broadband active vibration control of a rectangular plate representing a flexible wall of a thick Plexiglas container is experimentally investigated, for both empty and water-filled tanks, using five piezoelectric patches as control actuators. Preliminary dynamical analyses are carried out on the system in order to verify the influence of different water levels and different environment conditions (in particular, temperatures) on the system dynamics. Active vibration control is then experimentally applied to the plate with a single input–single output approach in the presence of broadband primary disturbance between 0 and 400 Hz, testing both filtered-x least mean square adaptive feedforward control and direct velocity feedback control. The time delay through the disturbance and control paths is measured.