Noise generated by the motor running mechanical noise due to electromagnetic noise at high speed between the rotor and the stator generated, and the imbalance between the rotor and stator produced, but also includes generated when the motor cooling fan running aerodynamic noise noise was IF characteristics, peak between 125 ~ 1000H z.

Exhaust fan running noise. Shandong vacuum pump when the fan at high speed, friction between mechanical components and fan installation unbalanced rotating parts, consisting of mechanical noise and aerodynamic noise between the two parts of the blade and the air friction generated noise frequency peaks at 250 ~ 2000 H z between.

Exhaust noise. When powerful airflow generated when the fan at high speed forward movement in the air duct and the duct wall with friction and air flow through the vents, internal and external pressure imbalance generated aerodynamic noise, the noise frequency is concentrated in the 500 ~ 2000 H z between.

Since there is no specific room exhaust fan vents, all rely on the open door, window heat, there is no room for the inner wall of acoustic treatment, noise generated by the motor can not be effectively isolated. Fans do not have a special soundproof room, directly exposed to the outside, the noise generated by direct discharge, in order to effective noise reduction more difficult.