Rotorcraft comprising: - a main rotor producing at least the lifting and even the propulsion of the rotorcraft. - at least one engine to rotate the main rotor with respect to the fuselage of the rotorcraft, - a main power transmission box, called PTB, to transmit a rotational movement generated by the at least one engine to the main rotor, and - an antivibration system arranged at the interface between the fuselage of the rotorcraft and a casing of the PTB, wherein the antivibration system comprises: - at least one absorber (10a-10d) comprising: ∘ an elongated rigid structure (11a-11d) extending in a longitudinal direction (Da-Dd) between a first end (12a-12d) secured to the fuselage of the rotorcraft via an articulation with at least one degree of freedom in rotation about a center and a second free end (13a-13d), ∘ an absorber mass (14a-14d) that is able to move in translation along a longitudinal axis (La-Ld) parallel to the longitudinal direction (Da-Dd) of the rigid structure (11a-11d), and ∘ motorised members (15a-15d) making it possible to control the displacement in translation of the absorber mass (14a-14d) along the longitudinal axis (La-Ld), - - at least one PTB suspension member comprising an elastic return means (20a-20d) that is designed to return the at least one absorber (10a-10d) to a central position, wherein the at least one absorber (10a-10d) is able to oscillate alternately about the central position following a rotational movement about the center, - at least one first accelerometer (21a-21d) arranged on the fuselage of the rotorcraft to measure in at least one direction the resultant vibrations to which the fuselage is subjected, - first input means to receive the measurements of the resultant vibrations, - at least one computer connected to the first input means to analyze the measurements of the resultant vibrations as a function of time, characterised in that the antivibration system comprises: - at least one second accelerometer arranged on the casing of the PTB making it possible to measure in at least one direction the dynamic excitations to which the casing of the PTB is subjected, and - second input means to receive the measurements of the dynamic excitations, and in that the at least one computer is connected to the second input means to analyze, as a function of time, the measurements of the dynamic excitations, wherein the at least one computer calculates a temporal phase shift (φ) between the dynamic excitations and the resultant vibrations, and to control the motorised members (15a-15d) as a function of the temporal phase shift (φ). - a main rotor producing at least the lifting and even the propulsion of the rotorcraft. - at least one engine to rotate the main rotor with respect to the fuselage of the rotorcraft, - a main power transmission box, called PTB, to transmit a rotational movement generated by the at least one engine to the main rotor, and - an antivibration system arranged at the interface between the fuselage of the rotorcraft and a casing of the PTB, wherein the antivibration system comprises: - at least one absorber (10a-10d) comprising: ∘ an elongated rigid structure (11a-11d) extending in a longitudinal direction (Da-Dd) between a first end (12a-12d) secured to the fuselage of the rotorcraft via an articulation with at least one degree of freedom in rotation about a center and a second free end (13a-13d), ∘ an absorber mass (14a-14d) that is able to move in translation along a longitudinal axis (La-Ld) parallel to the longitudinal direction (Da-Dd) of the rigid structure (11a-11d), and ∘ motorised members (15a-15d) making it possible to control the displacement in translation of the absorber mass (14a-14d) along the longitudinal axis (La-Ld), - ∘ an elongated rigid structure (11a-11d) extending in a longitudinal direction (Da-Dd) between a first end (12a-12d) secured to the fuselage of the rotorcraft via an articulation with at least one degree of freedom in rotation about a center and a second free end (13a-13d), ∘ an absorber mass (14a-14d) that is able to move in translation along a longitudinal axis (La-Ld) parallel to the longitudinal direction (Da-Dd) of the rigid structure (11a-11d), and ∘ motorised members (15a-15d) making it possible to control the displacement in translation of the absorber mass (14a-14d) along the longitudinal axis (La-Ld), - - at least one PTB suspension member comprising an elastic return means (20a-20d) that is designed to return the at least one absorber (10a-10d) to a central position, wherein the at least one absorber (10a-10d) is able to oscillate alternately about the central position following a rotational movement about the center, - at least one first accelerometer (21a-21d) arranged on the fuselage of the rotorcraft to measure in at least one direction the resultant vibrations to which the fuselage is subjected, - first input means to receive the measurements of the resultant vibrations, - at least one computer connected to the first input means to analyze the measurements of the resultant vibrations as a function of time, - at least one second accelerometer arranged on the casing of the PTB making it possible to measure in at least one direction the dynamic excitations to which the casing of the PTB is subjected, and - second input means to receive the measurements of the dynamic excitations,