"Micro Cooling Fan" to increase the distance between the vanes, when the bit stream to reduce the impact of interference effects than wake speed changes faster blade acts as a sound barrier will decrease with increasing distance. Thus, at least three parameters that affect the size of the interference noise: leaf blade shape radiation area "Micro Cooling Fan" velocity waveform (ie blade loading), the distance between the columns and the blade as the sound source. Very small pitch may have two acoustic impact. If the "Micro Cooling Fan" vanes on the rotor blades interference field established pulsation makes the bucket into a sound source, and the vanes are sound barrier.