Fan cover design for 220V Cooling Fan impact

Shield "220V Cooling Fan" on, in addition to the fan blades to prevent users from being wounded, but the fan itself has a protective effect. But we all know that there is more or less the fan shroud will bring "220V Cooling Fan" wind decreased and increased noise and other side effects, but few people will go to pay attention to these problems. Low speed noise test, then the high speed noise test, while no shroud "220V Cooling Fan" noise as 55dBa, substantially the same test results after the installation of the shroud and the low speed, the best of the three still Wire , Mesh and Swirl, the bottom is still Turbine, an increase of 29.1%, the noise value of 71dBa.