to the left and right respectively of the figures in reference now to fig1 we have diagrammatically illustrated an aircraft turbojet engine including in its upstream portion a fan 3 provided with vanes 5 and in its downstream portion the engine 7 strictly speaking comprising as known in itself its compression 9 combustion 11 and propulsion 13 stages around the fan 3 and the compression stage 9 is a fan casing 15 defining a cold air stream 17 with the engine 1 upstream from this casing 15 and situated in the extension thereof is a tubular member 19 frequently designated by u201c shroud u201d which is part of the nacelle designed to surround the turbojet engine 1 more precisely this shroud 19 constitutes the inner face of the air intake of the nacelle as was indicated in the preamble of this description in all of the figures of this invention this shroud 19 is illustrated in the form of a structure having acoustic absorption properties such as a honeycomb structure indeed such a structure is generally used to reduce the energy of the sound waves emitted by the turbojet engine 1 and the fan 3 one will however bear in mind that the present invention is in no way limited to a shroud 19 having such acoustic properties one will also note that in all of the figures of the present invention.