Noise
Noise and
Loudness
Noise, which is typically
measured in Decibels (dB), is a measure of the energy or power emitted
into the air. Loudness is what a human being perceives.
There are three base
options for fans with their noise levels and relative loudness shown
below:
|
Fan Speed
Base Noise Levels |
|
|
At Distance (m)
|
|
Model
|
Speed |
SPL dBA |
5m |
10m |
15m |
|
4 Pole
|
1340
|
74
|
65
|
59
|
56
|
|
6 Pole
|
900
|
65
|
56
|
50
|
47
|
|
8 Pole
|
680
|
59
|
50
|
44
|
41
|
The noise of the fan is
changed significantly by its speed.
Effect of Speed
Reduction
Decibels do not directly
relate to the perceived loudness that a human being would experience.
Decibels are a logarithmic measure. In actual practice a reduction of
3dB halves the loudness. A 6dB reduction reduces the loudness to a
quarter and so on.
|
Effect of
Speed Reduction |
|
|
|
|
|
|
|
|
|
|
Noise |
|
Loudness |
|
Model
|
100% |
80% |
60% |
40% |
20% |
|
100% |
80% |
60% |
40% |
20% |
|
4 Pole
|
74
|
69
|
63
|
54
|
39
|
|
100%
|
33%
|
8%
|
1%
|
0%
|
|
6 Pole
|
65
|
61
|
54
|
45
|
30
|
|
14%
|
4%
|
1%
|
0%
|
0%
|
|
8 Pole
|
59
|
54
|
48
|
39
|
24
|
|
3%
|
1%
|
0%
|
0%
|
0%
|
Notes:
The effects of a change
in speed can be seen in the following: dB1 = dB2 + 50log10 (rpm1/
rpm2)
To find the external SPL
at a distance (x) metres from the unit use the following relationship:
SPL = PWL - (20 log 10 (x+.5)) – 8
|
