The brushless DC motors are normally built with rotor mounted PMs, which create the necessary back EMF voltage to produce a mechanical power. The shape of this back-EMF voltage is very important compared to the phase voltage supply one. Indeed, the electromechanical power is obtained by the product of the back-EMF and the phase current. Two possibilities are normally used to make the choice of the electronic supply. If the back-EMF is trapezoidal, the supply will be "block" (120 degrees, two-phase one mode) in order to produce a constant torque. If the back-EMF has a sinusoidal shape, the current must also be sinusoidal. Some companies are working on new electronic drivers in order to minimise the noise created by the electronic commutation in the winding. Indeed, with the "block" current, the whole harmonic spectrum is exited and generates audible noise unsuitable for the customers. The new generation of electronic drivers uses sinusoidal shape current in order to suppress the harmonics. With trapezoidal back-EMF shape motor, the noise cannot be totally avoided. This paper presents solutions to transform the back-EMF shape in order to minimise the harmonics only by changing the PM width. The stator is not concerned