1. Sources of audible magnetic noise

Magnetic noise (also known as electrical noise, electromagnetic noise being reserved for the field of electromagnetic compatibility, whose spectrum far exceeds the audible range) can be defined as the audible noise generated by the magnetic forces present in the asynchronous machine, which are themselves produced by currents. This is not the case with permanent magnet synchronous machines, where magnetic forces are not zero, even in open circuit. More precisely, magnetic forces cause the machine yoke to vibrate at audible frequencies (from 20 Hz to 20 kHz), and these vibrations are transmitted to the ambient air through the yoke, generating airborne noise. The surface area of the flanges is generally too small to make a significant contribution to the machine's acoustic radiation, and only in special cases, such as rotors or stators with inclined notches, are the flanges subjected to magnetic...