Strutt|Input Data|Empirical|Fan inserts sound power levels into the active row of the worksheet.
The total sound power has been calculated using the formula:
`L_W = 20log_10 P + 10log_10 V + 40`
Where,
`P` is the fan total static pressure, Pa
`V` is the fan volume, m3/s
Octave band sound power levels have then been calculated by adding spectral corrections as follows:
| Fan Type | 63 Hz | 125 Hz | 250 Hz | 500 Hz | 1 kHz | 2 kHz | 4 kHz |
| Axial | -5 | -5 | -6 | -7 | -8 | -10 | -13 |
| FC Centrifugal | -2 | -7 | -12 | -17 | -22 | -27 | -31 |
| BC Centrifugal | -7 | -8 | -7 | -12 | -17 | -22 | -27 |
| Propeller | 0 | -1 | +2 | -5 | -9 | -10 | -17 |
| Mixed Flow | -12 | -11 | -10 | -10 | -13 | -17 | -22 |
Blade-pass frequency is calculated is calculated as: BPF = (rpm*number of impeller blades)/60. With this option selected, 5 dB is added to the octave band containing the BPF and 3 dB is added to the octave band containing first harmonic.
References: