An acoustic absorber cell (1) for mounting on a turbojet wall in contact with a fluid flow, the cell (1) having a resonant cavity (2) presenting a wall (30) having at least one orifice (4) associated with a neck (5) having a tube (51) extending inside the resonant cavity (2) and projecting from the wall (30). The neck (5) also having a tubular ring (52) coaxial with the tube (51) and movable relative to the tube (51), and the cell (1) includes electromagnetic actuator (6) for moving the ring (52) along the tube (51), and controller (7) for controlling the electromagnetic actuator (6) and configured to control movement of the ring (52) along the tube (51) as a function of the operating speed of the turbojet between at least first and second positions defining respective first and second resonant frequencies of the resonant cavity (2).