Noise is a kind of noise that makes people feel noisy and boring, and its degree sometimes varies with people's mood. But continuous noise will also pollute the surroundings. The causes of noise generated by general cooling fans can be divided as follows:

1. Noise caused by blade rotation

When the blade rotates, it will generate friction or impact with the air. High rpm exhaust fan, the faster the speed, the higher the frequency of contacting the air, and the sharper the noise. The width or thickness of leaves increases, which is more obvious. The frequency of noise is composed of multiple frequencies, which are related to the speed of the fan.

If the axial cooling fan is equipped with moving wing and static wing, the number of blades should be different to avoid greater noise resonance. However, whether axial flow fans or DC centrifugal fans, those with fast speed and high pressure will produce large noise.

2. Noise caused by vortex generated by blades

During the operation of the fan, vortex will be generated on the back of the moving wing, which will not only reduce the efficiency of the fan, but also produce noise. In order to reduce this phenomenon, the installation angle of the blades should not be too large, and the bending of the blades should be smooth. Do not suddenly change too much.

3. Noise caused by turbulence

When the air flows, if it encounters sharp obstacles, turbulence will easily occur. Although this turbulence is different from the vortex, it will also make the low noise exhaust fan produce noise, or high frequency whistling sound, which will also cause efficiency loss to the fan.

4. Noise caused by resonance with air duct housing

The joint between the air duct and the inner surface of the fan housing should be smooth to avoid roughness and tearing sound. Because the connected pipeline will produce resonance, the subtle sound will become louder, resulting in greater noise. In the design, sometimes the air duct can be covered with sound-proof materials to reduce the noise.

5. Noise caused by other than fan

In addition to the fixed noise of the fan itself, there are many noise sources, such as abnormal noise caused by insufficient precision, improper assembly or poor maintenance of the bearings. The motor also generates noise, some of which is caused by poor design or poor manufacturing quality control, but sometimes it is caused by the internal and external cooling fans of the motor. Gears and belts also generate noise due to friction. The noise generated by the resonance of other structures can not be ignored, which is sometimes caused by the imbalance of the body.