Noise generated by Fans - Blade Pass Frequency (BPF)

The fan Blade Pass Frequency noise level intensity varies with the number of blades and the rotation speed of the wheel and can be expressed as

BPF = n ⋅ t / 60                         (1)

where

BPF = Blade Pass Frequency (Hz)

n = rotation velocity (rpm)

t = number of blades

Example - Blade Pass Frequency of Fan

If a fan with 10 blades rotates with 2400 rpm - the Blade Pass Frequency - BPF - can be calculated

BPF = (2400 rpm) ⋅ (10) / (60 s/min)

    = 400 Hz

Note that the energy in the sound may be very high and annoying for the surroundings, especially for fans with few blades.

Be aware that the Blade Pass Frequency may not be visible in charts common for fans and that fan noise in general is documented in octaves.