A method of mixed mode operation of an internal combustion engine includes the steps of controlling a homogeneous charge combustion event timing in a given engine cycle, and controlling a conventional charge injection event to be at least a predetermined time after the homogeneous charge combustion event. The head stack assembly includes an actuator assembly and a plurality of transducer assemblies. The box includes a casing having an internal space, and a box side terminal arranged in the casing so as to be in close contact with the casing. The generally planar surfaces of the patch elements are generally coplanar.