Noctua NF-P12 120mm Fan
 

The Noctua NF-P12 is a great fan. Its combination of good
performance with low noise seals the deal. Noctua has delivered on their
company motto of producing "sound-optimised premium components" - this
fan is almost silent when used with the included ultra low noise
adaptor. In fact, it was near silent without even using any of the
adaptors! This may be due to the unique "vortex-control notches" on the
fan blades which apparently spread the noise spectrum of the fan out
over a wide range to make it sound less noisy.

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