Fans - generated Noise Power
The sound generated by a fan depends on the motor power, the volume capacity, the static pressure increase and the discharged volume.
The empiric expressions below can be used to indicate generated Sound Power Level from fans.
Note! - Exact Sound Power Levels should be obtained from manufacturers data.
Sound Power Level - SI-units
LN = 67 + 10 log(S) + 10 log(p) (1a)
LN = 40 + 10 log(Q)+ 20 log(p) (1b)
LN = 94 + 20 log(S) - 10 log(Q) (1c)where
LN = sound power level from fan (dB)
S = rated motor power (kW)
p = fan static pressure (Pa, N/m2)
Q = volume discharged (m3/s)
Download and print Fan - Generated Sound Power vs. Volume Flow and Static Pressure chart
Sound Power Frequencies
Sound power level in the octaves can be calculated by adding the values below to the sound power level calculated in the expressions or diagram above.
| Decibels to add (dB) | ||||||||
|---|---|---|---|---|---|---|---|---|
| Fan Type | Octave (Hz) | |||||||
| 63 | 125 | 250 | 500 | 1000 | 2000 | 4000 | 8000 | |
| Centrifugal fan, backward-curved blades | -4 | -6 | -9 | -11 | -13 | -16 | -19 | -22 |
| Centrifugal fan, forward-curved blades | -2 | -6 | -13 | -18 | -19 | -22 | -25 | -30 |
| Centrifugal fan, straight radial blades | -3 | -5 | -7 | -7 | -8 | -11 | -16 | -18 |
| Axial fan | -7 | -9 | -7 | -7 | -8 | -11 | -16 | -18 |
Sound Power Level - Imperial units
LN = 90 + 10 log(s) + 10 log(h) (2a)
LN = 55 + 10 log(q) + 20 log(h) (2b)
LN = 125 + 20 log(s) - 10 log(q) (2c)where
s = rated motor power (hp)
h = fan static head (inch water gauge)
q = volume discharged (ft3/min)
Maximum Discharge Velocity from Fans for Quiet Operations
The discharge velocity from fans should be kept within certain limits to avoid noisy operations.
| Application | Maximum Discharge Velocity (m/s) | |
|---|---|---|
| Supply System | Exhaust System | |
| Sound studios, churches, libraries | 4 - 5 | 5 - 7 |
| Cinemas, theaters, ballrooms | 5 - 7 | 6 - 8 |
| Restaurants, offices, hotels, shops | 6 - 8 | 7 - 9 |
- 1 m/s = 3.6 km/h = 196.85 ft/min = 2.237 mph
ACMA Certified Sound Levels
| Certified Sound-Power Level (dB) | ||||
|---|---|---|---|---|
| Octave Band (Hz) | Fan 1 | Fan 2 | Fan 3 | Fan 4 |
| 63 | 117 | 113 | 120 | 101 |
| 125 | 118 | 116 | 113 | 98 |
| 250 | 109 | 111 | 111 | 107 |
| 500 | 106 | 106 | 107 | 120 |
| 1000 | 103 | 103 | 103 | 116 |
| 2000 | 97 | 98 | 98 | 114 |
| 4000 | 94 | 95 | 93 | 109 |
| 8000 | 92 | 92 | 88 | 105 |
