A nozzle where the sector into which noise reduction is sought (the direction of populated areas) has a moving lip, driven by actuators in an oscillatory, periodic or sinusoidal motion, around the mid position, to and from the axis, so as to cause the shear layer to become more irregular and turbulent, thus enhancing scattering effects on the sound of internal sources, including back reflection into the jet, widening the directivity pattern and spreading the acoustic energy into a broader spectrum, so as to reduce the acoustic energy transmitted in these sensitive directions; the nozzle lip may also be corrugated, undulated or have vortex generators, in the sector over which noise reduction is sought. In all other sectors, for which noise radiation is of no concern, even if enhanced, the nozzle lip is smooth and fixed, leading to a thin shear layer, across which sound is more easily, so that acoustic energy exits from the jet in these harmless directions. The active nozzle need only be actuated at times when noise reduction is needed, e.g. a take-off and landing; at all other times, when noise reduction is not needed, e.g. in cruise flight, the nozzle is not active, i.e. is fixed in the mid-position, to save actuator power, and wear and fatigue of moving mechanisms; also, this position, minimizes any thrust loss or increase in fuel consummation, in cruise flight.