220V AC Cooling Fan how to achieve low noise

"220V AC Cooling Fan" disrupt airflow obstruction along the flow path and encountered turbulence 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. A "220V AC Cooling Fan" into the air and out of the enclosure range accounted for 60-80% of all system impedance between the air, while the greater airflow, noise is relatively higher. System impedance is higher, the greater the airflow required for cooling, so in order to minimize the noise, the system impedance must be minimized. Some cases, the weight of the whole "220V AC Cooling Fan" system is very light, or the system must operate in accordance with the provisions when some particularly soft isolated equipment recommended in order to avoid passing the fan vibration.