Acoustic attenuation structure provided with s-shaped cells having drained barriers and method for manufacturing same

An acoustic panel with resonators for a nacelle of an aircraft propulsion unit, the acoustic panel comprising acoustic cells adjoining one another in a plane orthogonal to an acoustic propagation direction of the sound waves in order to form a cellular core, each acoustic cell comprising an enclosure extending along a main axis parallel to the acoustic propagation axis of the sound waves and, inside the enclosure, at least one partial obstacle that extends from a wall of the enclosure in a transverse direction that is orthogonal to the main axis, said at least one partial obstacle comprising at least one edge rigidly attached to a wall of the enclosure and an internal passage that is off-centre with respect to the central axis of the enclosure parallel to or coincident with the main axis of the enclosure in order to increase the length of the path travelled by the sound waves through the acoustic cell, said at least one partial obstacle further comprising at least one drainage orifice,

• wherein said at least one drainage orifice is adjacent to an edge rigidly attached to a wall of the enclosure and has an elongate shape extending to the edge of the partial obstacle with which it is associated, the drainage orifice being laterally open on said wall of the enclosure rigidly attached to said edge with which the drainage orifice is associated.