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)
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.
Room acoustics and acoustic properties, decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation.
Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems.
The sound generated by a fan depends on the motor power, the volume capacity, the static pressure increase and the discharged volume.
Sound power from sources like fans, jet engines, cars, humans and more.
Acoustic noise calculation procedure HVAC systems.