What factors are related to the noise of the cooling fan

The size of the noise is an important parameter of the cooling fan. Of course, we like the cooling fan with a lower noise. Then, what factors determine the noise factor of the cooling fan? The shape of the fan blade determines the air volume and at the same time the noise. The balance of the fan blades will increase the jitter of the cooling fan when it is running, and the jitter will also be louder. The accuracy of materials, such as ball bearings, oil-impregnated bearings, ICs, and shaft cores, will have a significant impact on noise. Unreasonable design of assembly structures, such as stators, bearings, magnetic strips, ICs, etc., will also produce noise.