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)

Fan - sound power noise 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)

631252505001000200040008000
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.

ApplicationMaximum Discharge Velocity (m/s)
Supply SystemExhaust
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 1Fan 2Fan 3Fan 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

Matched Content

Tag Search

Search the Engineering ToolBox

- "Search is the most efficient way to navigate the Engineering ToolBox!"

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your SketchUp model with the Engineering ToolBox - SketchUp Extension/Plugin - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Translate the Engineering ToolBox!
About the Engineering ToolBox!

close