acoustic processing device of the noise emitted by a turbojet

The invention relates to an acoustic processing device of noise emitted by a turbofan engine, comprising a primary cowl (26) comprising at an outer surface of an inner annular panel (100) of acoustic processing and a secondary cowl ( 28) comprising at an inner surface an outer annular panel (200) of acoustic processing arranged facing the inner panel. The inner and outer panels each comprise a central panel portion extending axially over a same predetermined length opposite to each other, the length of the central panel portions being between one-fifth and four-fifths of the total length (L) of the panels and the ratio between the acoustic resistances of the central panel portions being at least equal to 2.