Ordinary "Waterproof Cooling Fan" use a certain number of blades, and dispersed the angular distance between each other are equal, such a fan is usually manufactured in accordance with industry standards, the purpose is to reduce the noise. But the problem in "Waterproof Cooling Fan" blade rotation frequency (BPF, blade pass frequency), the pressure waves can cause harmonic frequency. The main source of noise in the PPF (pole pass frequency) of the shaft portion noise. Apple's design avoids these problems is to control the sound through the blades of unequal distribution of dispersed arrangement of the spectrum. "Will"Waterproof Cooling Fan"noise when rotating dispersed to a variety of different discrete frequencies go, serve the purpose of reducing the noise in the BPF tone makes the user feel from hearing the noise becomes smaller. Let the fan blades in the distribution unbalanced state, and maintain a balance of the impeller, can play a very good noise reduction effect. "