How to reduce 220V Cooling Fan noise?

1, the system impedance: a "220V Cooling Fan" cabinet with a range of air inlet total system impedance between 60-80% air, in addition to the greater airflow, noise is relatively higher. System impedance is higher, the greater airflow needed for cooling, so in order to minimize the noise, the system impedance must be minimized.
2, disrupt airflow: spoiler along the path encounter airflow obstruction caused generate noise. Therefore any obstacles, particularly in the critical range of the air inlet and outlet must be avoided in order to reduce noise.
3, "220V Cooling Fan" Speed and size: Because of the high speed fan noise greater than the low speed fan, so you should try and use low-speed fan as possible. And a large size, low speed fan, generally, quieter than small size, high speed fan when transporting the same air volume.
4, temperature: one system, "220V Cooling Fan" required for cooling air flow is inversely proportional to the allowable temperature rise. Allowable temperature rise slightly increased, to a significant reduction in the required air flow. Therefore, if you impose the allowable limit temperature rise slightly relax, the required air flow will be reduced, the noise can be reduced.