number of blades determines number of spaces, but its the trailing edge of the blade that makes the noise

primes are 3, 5, 7, 11, 13, 17 etc

heres why.


take an 8 blade fan, it will generate frequencies at multiples of 8, 4, 2, and 1

a 12 blade fan will generate frequencies at multiples of 12, 6, 4, 2, 3, 1

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