9. Noise Reduction Strategies in High-Speed dc axial fans 12v Fan Design Axial cooling fans (https://axialfansupply.com), particularly high-speed or high-pressure models, are inherently prone to generating noise, which presents a significant engineering challenge in commercial and industrial applications[12][18]. Fan noise is broadly categorized into two types: rotational (tonal) noise and broadband (turbulence) noise[17]. Rotational noise is caused by the regular passage of the blades past stationary components (like motor struts or guide vanes) and is heard as a distinct tone, related to the Blade Passing Frequency (BPF)[17]. Broadband noise is caused by random flow turbulence, such as air separation from the blade surface, tip vortex shedding, and turbulence in the incoming air[17]. Modern noise reduction strategies focus heavily on manipulating the blade geometry[4][17].