A droplet generator for a continuous stream ink jet print head comprising : an elongate cavity (13) for containing the ink; nozzle orifices (7) in a wall (10) of said cavity (13) for passing ink from the cavity (13) to form jets, said nozzle orifices (7) extending along the length of said cavity (13); and actuator means (3) disposed on the opposite side of said cavity (13) to said wall (10) for vibrating the ink in said cavity (13) such that each said jet breaks up into ink droplets, in operation of said generator a standing wave being present in the ink in said cavity (13), characterised in that the cross-sectional area of said cavity (13) varies along its length in a manner so as to tailor the form of said standing wave in the cavity (13) such that each said jet breaks up into ink droplets at a respective predetermined distance from said wall (10) of the cavity (13).