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# 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)

### 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

## Related Topics

### • Acoustics

Room acoustics and acoustic properties, decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation.

### • Noise and Attenuation

Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems.

## Related Documents

### Fans - Noise Power Generation

The sound generated by a fan depends on the motor power, the volume capacity, the static pressure increase and the discharged volume.

### Sound Power

Sound power from sources like fans, jet engines, cars, humans and more.

### Ventilation Systems - Acoustic Calculation Procedure

Acoustic noise calculation procedure HVAC systems.

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