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.
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.
| 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 | 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
| 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
-
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
-
Fan AMCA Classification
Fan classification established by AMCA. -
Fans - Efficiency and Power Consumption
Power consumption and typical efficiencies of fans -
Noise from Machines - Enclosures and Sound Pressure Level Reductions
Barriers and enclosures to reduce noise sound pressure levels from machines. -
Noise generated by Fans - Blade Pass Frequency (BPF)
TheBlade Pass Frequency noise generated by a fan can be very intense and varies with the number of blades and the rotation velocity. -
Noise generated in Air Ducts
Estimate noise generated by air flow in ducts. -
Noise generated in Blade Dampers
Sound power noise generated by blade dampers in ventilation systems. -
Octave Band Frequencies
The octave and the 1/3 octave band frequencies. -
Sound - Ls - Exposure Level
The EPA Sound Exposure Level - Ls - describes the noise from a variable source. -
Sound Power
Sound power from sources like fans, jet engines, cars, humans and more.
