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Fan noise by type: mechanical noise, pneumatic noise, electrical noise;
Noise testing environment and standards: Silence room ISO7779 standard;
ANSI - S10.12
The noise value is in dB (A), which is usually measured with a noise meter;
Source of noise
There are three main sources of fan noise: bearing friction and vibration, fan blade vibration, air flow noise.
1. Friction and vibration of bearings: they not only produce noise, but also affect performance and shorten the life of devices.
2. Vibration of fan blade: Generally, the fan blade made of plastic has a certain toughness and can withstand a certain degree of physical deformation. It will also vibrate in the process of pushing air due to force, but the amplitude is generally small.
The other serious vibration is caused by the uneven distribution of blade mass and the eccentricity between the center of gravity and the rotation axis.
3. Air flow noise: the flowing air will collide with each other, causing friction with the surrounding objects, the separation effect of blades on the airflow, and the pulse force of periodic air supply, etc., all produce noise.
The faster air velocity, the more turbulent the air velocity and the higher air flow noise, the acceleration will increase with the increase of wind speed.
Ordinary axial flow fans will generate flyback airflow in the gap between the fan blade and the outer frame, which will not only produce higher wind noise, but also cause an adverse impact on the air volume.
In addition, the noise of the same type of fan is proportional to the speed, the smaller the blade clearance, the greater the noise.
Criteria for noise reduction
1. System Impedance
The range between the inlet and outlet of a case accounts for 60% to 80% of the total system impedance, and the higher the airflow, the higher the noise.
The higher the system impedance, the greater the airflow required for cooling, so the system impedance must be minimized in order to minimize noise.
2. Turbulence
Noise is generated by disturbances resulting from obstacles encountered along the airflow path.
Therefore any obstruction, especially in critical inlet and outlet areas, must be avoided to reduce noise.
3. Fan speed and size
Because high-speed fans produce more noise than low-speed fans, try and choose low-speed fans as much as possible.
A large, low-speed fan, usually quieter than a small, high-speed fan, delivers the same amount of air.
4. The temperature goes up
In a system, the amount of air required for cooling is inversely proportional to the permitted temperature rise.
Allowing a slight increase in temperature can substantially reduce the amount of air required.
Therefore, if the limit on the intensity and allowable temperature rise were slightly relaxed, the amount of air required would be reduced and the noise would be reduced.
5. Vibration
In cases where the overall weight of the system is too light, or where the system must be operated in a prescribed manner, it is particularly recommended to use soft insulation to avoid fan vibration transmission.
6. Voltage variation
Voltage variations affect noise levels.
The higher the voltage applied to the fan, the greater the vibration and the greater the noise due to the increase in speed.
7. Design considerations:
Every part of the fan design will affect the noise level.
Noise reduction is achieved by the following design considerations: the size of the wound core, the design of the fan blade and frame, and the precise manufacturing and balance.
