Acoustical sound measurement of SUNON fans is made in anechoic room with
background noise less than 15 dBA. The measured fan is running in free air
with a microphone at a distance of one meter from the fan intake.
Sound Pressure Level (SPL), which is environmentally dependent, and Sound
Power Level (SPL) are defined as following :
= 20¡ê P¡þPref and SWL = 10¡ê
- P = Pressure
- Pref = A reference pressure
- W = Acoustic power of the source
- Wref = An acoustic reference power
Fan noise data is usually plotted as SPL against the octave frequency
bands. The following provides an indication of the effect of dBA changes
- 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
- 60 ~ 80 dBA Loud
- 80 ~ 100 dBA Very Loud
- 100 ~ 140 dBA Deafening
The following five guidelines provide fan users the best approaches in minimizing
- 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.
- 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.
- 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.
- 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.
- 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.
- 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