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[Fan Basics] 6th Period

Fan noise and sound pressure level

For equipment used in quiet locations, fan noise is one of the important selection points. Fan noise varies depending on the layout of parts inside the equipment. In the sixth lesson, we will explain fan noise in an environment with no obstacles around.

What is fan noise?

Fan noise is measured in sound pressure levels, expressed in units of dB(A). (A) indicates the A-weighted sound pressure level. A-weighting is a value corrected to take into account the frequencies that humans can hear, and the correction value is specified by the JIS standard.

How to measure sound pressure level

The sound pressure level is measured in an anechoic chamber using a sound level meter placed 1 m from the fan intake surface. The fan is suspended in mid-air and measurements are taken with almost no obstacles around it, so the measured value is the sound pressure level at "maximum airflow."

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Sound pressure level relationship

Equation 1 expresses the relationship between sound pressure level and fan rotation speed, while Equation 2 expresses the combined sound when there are multiple sound sources.

Equation 1: Rotational speed and sound pressure level Equation 2: Multiple sound sources and sound pressure level

If you want to double the maximum airflow, you have two options: increase the rotation speed or add more fans. However, looking at the formula above, you can see that there is a big difference in sound pressure level. Therefore, if you want to keep the sound pressure level low, it is more effective to use two fans. Thus, adjusting the fan rotation speed and number of fans when designing the equipment can be considered as one solution.

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Supervised by: SANYO DENKI CO., LTD. Cooling System Design Department

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