Fans - Noise Power Generated
Noise or sound generated by a fan depends on the motor power, volume capacity, static pressure and 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)
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 |
Related Topics
Related Documents
Tag Search
- en: fan sound noise level estimating
