How to Achieve Low Noise
How to Achieve Low Noise
Acoustical Noise Level
Acoustical sound measurement of SUNON
Fan noise data is usually plotted as SPL
fans is made in anechoic room with back-
against the octave frequency bands. The
ground noise less than 15 dBA. The mea-
following provides an indication of the
sured fan is running in free air with a
effect of dBA changes :
microphone at a distance of one meter
from the fan intake.
3 dBA Barely Noticeable
5 dBA Noticeable
10 dBA Twice as loud
Noise levels :
0 ~ 20 dBA Very Faint
20 ~ 40 dBA Faint
40 ~ 60 dBA Moderate
Sound Pressure Level (SPL), which is envi-
60 ~ 80 dBA Loud
ronmentally dependent, and Sound Power
80 ~ 100 dBA Very Loud
Level (SPL) are defined as following :
100 ~ 140 dBA Deafening
SPL = 20ʉP/Pref and SWL = 10ʉW/Wref
P = Pressure
Pref = A reference pressure
W = Acoustic power of the source
Wref = An acoustic reference power
How to Achieve Low Noise
How to Achieve Low Noise
1.System Impedance
As known, the area between inlet and outlet ports of a cabinet make up 60% to 80% of the
total system impedance. In addition, the greater the air flow is, the higher the noise level is.
The higher the total system impedance is, the more air flow is required to provide the necessary cooling. Therefore, system impedance must be reduced to the lowest possible level in
order to reduce noise to the least.
2.Flow Disturbance
Obstructions along the path of the flow of the turbulent air generated noise. Thus, obstructions, especially in the critical inlet and outlet area, must be avoided to reduce noise level.
3.Fan Speed and Size
Since a high speed fan usually generates greater noise than a low speed fan does, a low speed
fan should be tried and used whenever possible. Very often, a larger, slower fan is quieter than
a smaller, faster fan while delivering the same air flow.
4.Temperature Rise
Air flow is inversely proportional related to allowable temperature rise within a system. A
little change in the allowable temperature rise leads to a significant change in air flow
required. Therefore, if there is a little compromise to the limit imposed on allowable temperature rise, there will be a considerably less amount of air flow required. As a result, noise
is remarkably reduced.
In some cases, the system is light in weight or specified in some certain operating methods, a
soft and flexible isolator is highly recommended to avoid the vibration transmission.
6.Voltage Variation
Voltage variation affects the level of acoustic noise. When the higher voltage is applied to the
fan, the higher vibration is generated due to the increased RPM. Thus, the higher noise level
is generated.
7.Design Considerations
The design of every component of the fan affects the level of acoustic noise. Low noise levels
can be achieved by dimension of winding core, by design of impeller blades and housing and
by precision manufacturing and balance.
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