Tonal noise is one of the main sources of noise generated by cooling fan module in automobile. The methods to decrease the tonal noise become more and more important with the popularity of automobiles and the demand for comfort increasing. Finding a quick way to predict the tonal noise in the early design stage will help the designer shorten the design circle and improve the efficiency. The traditional way, uneven spacing rotor blades, to modulate tonal components in noise spectrum by controlling factor “A” show positive influence in harmonic 2 and 3 (H2 and H3) but cannot work for harmonic 1 (H1) subjects to limitation of blade overlap as shown in the test result. Further step to modulate the stator vanes by adjusting parameter “χ” can attenuate the H1 dramatically based on “Venetian blind” theory of stator vanes. At last, the new cooling fan module design method to control tonal noise in design stage by “A” in rotor blade design and “χ” in stator vanes is reviewed and implemented in two cases of 7 rotor-blades & 6 stator-vanes and 7 rotor-blades & 8 stator-vanes. The experimental results agree well with the theoretical prediction.

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