A transformer comprising at least two phase windings, each phase winding having coil turns around a coil axis, said transformer being adapted to transform voltage at a predetermined frequency, when said transformer is operating, said transformer is excited by a mechanical load having a main frequency corresponding to said predetermined frequency multiplied by two and having vibration modes, wherein the combination of load and vibration modes results in a vibration of said transformer, said transformer having a set of vibration modes, each vibration mode having a vibration mode frequency, wherein at least one main contributing vibration mode of the set of vibration modes is the vibration mode resulting in the largest acoustic power, of said vibration modes, when the transformer is excited by said load, wherein the at least two phase windings comprise at least a first type of phase winding and a second type of phase winding, each of the first type of phase winding and the second type of phase winding comprising a plurality of winding portions comprising at least a first winding portion and a second winding portion, the first type of phase winding comprising a first winding portion having a first winding portion stiffness and a second winding portion having a second winding portion stiffness, wherein a stiffness difference between said first winding portion stiffness and said second winding portion stiffness of said first type of phase winding is such that the acoustic power is minimized at said main frequency, wherein said first winding portion of the first type of phase winding has a first winding portion stiffness, as seen along said coil axis, and said second winding portion of the first type of phase winding has a second winding portion stiffness, as seen along said coil axis, said first winding portion stiffness being different from said second winding portion stiffness, and wherein the first winding portion of the second type of phase winding has the first winding portion stiffness, as seen along said coil axis, and said second winding portion of the second type of phase winding also has the first winding portion stiffness, as seen along said coil axis, and wherein the transformer comprises three phase windings arranged along a second axis (x), and wherein one first type of phase winding is arranged centrally, between two second type of phase windings, or the transformer comprises three phase windings arranged along a second axis (x), and wherein one second type of phase winding is arranged centrally, between two first type of phase windings. wherein the at least two phase windings comprise at least a first type of phase winding and a second type of phase winding, each of the first type of phase winding and the second type of phase winding comprising a plurality of winding portions comprising at least a first winding portion and a second winding portion, the first type of phase winding comprising a first winding portion having a first winding portion stiffness and a second winding portion having a second winding portion stiffness, wherein a stiffness difference between said first winding portion stiffness and said second winding portion stiffness of said first type of phase winding is such that the acoustic power is minimized at said main frequency, wherein said first winding portion of the first type of phase winding has a first winding portion stiffness, as seen along said coil axis, and said second winding portion of the first type of phase winding has a second winding portion stiffness, as seen along said coil axis, said first winding portion stiffness being different from said second winding portion stiffness, and wherein the first winding portion of the second type of phase winding has the first winding portion stiffness, as seen along said coil axis, and said second winding portion of the second type of phase winding also has the first winding portion stiffness, as seen along said coil axis, and wherein the transformer comprises three phase windings arranged along a second axis (x), and wherein one first type of phase winding is arranged centrally, between two second type of phase windings, or the transformer comprises three phase windings arranged along a second axis (x), and wherein one second type of phase winding is arranged centrally, between two first type of phase windings.