Then the first analysis of the mechanism of vibration. Probably there are several (friends can complement or challenge) is a magnetostrictive core cause, such as low frequency application materials such as iron, silicon steel in magnetostrictive materials when the frequency is relatively large, but when the design load is large, the core itself emits hysteresis stretching vibration of the frequency precisely in 20KHZ audio, reached a certain intensity, ears will hear. Or a ferrite core used in low frequency, because the design margin is small, close to saturation, the application rate is relatively low and frequency will occur this audio noise;

Second types of winding gap bonding is not solid, when power is larger or the load changes greatly, cause the winding line between the air and the occurrence of audio vibration. (vacuum impregnation, drying gradient is very important, should not form toothpaste effect, outside the paint dry, not dry, winding without bonding, the dielectric constant does not meet requirements. The distribution of capacitance change.

The third type is that the winding wire, the package and the core are loose. When full load or alternating load occurs, there is an audio oscillation between the winding and the core

Fourth kinds of distributed parameters, resonant voltage distribution parameters and audio signal resonance effect of a circuit.