Cooling fan noise test and the best way to reduce fan noise

Cooling fan noise test

The commonly used volume definition method in physics is the sound pressure volume, in dB. However, when defining the amount of fan noise, it is more appropriate to define the noise power emitted by the fan. Generally, the general fan noise unit is Db(A).

Noise test method: According to ISO 3744, ISO 3745, ISO 7779, CNS 6753, JIS 8346 test specifications. The fan is placed in a silent room with a background noise of less than 15 decibels, and 1 meter away from the noise meter. After the fan is running in free air, measure the suction surface of the fan and pass the sound collection noise test to provide fan users with some guidelines. For reference, to reduce fan noise to a minimum:

1. System Impedance. The range between the air inlet and air outlet of a chassis accounts for 60% to 80% of the total system impedance. In addition, the greater the airflow, the higher the noise. The higher the system impedance, the greater the airflow required for cooling, so in order to minimize noise, the system impedance must be minimized.

2. Air flow is disturbed. The turbulence caused by the obstacles encountered along the airflow path can cause noise. Therefore, any obstacles, especially in the critical air inlet and outlet areas, must be avoided to reduce noise.

3. Fan speed and size. Since high-speed fans produce more noise than low-speed fans, you should try and choose low-speed fans as much as possible. A fan with a larger size and a lower speed is usually quieter than a fan with a smaller size and a higher speed when delivering the same air volume.

4. The temperature rises. In a system, the air volume required for cooling is inversely proportional to the allowable temperature rise. Allowing a slight increase in temperature rise can greatly reduce the required air volume. Therefore, if the restrictions imposed on the allowable temperature rise are slightly relaxed, the required air volume will be reduced and the noise will also be reduced.

5. Vibration. When the weight of the entire system is very light, or the system must operate in a certain manner, it is particularly recommended to use soft insulation equipment to avoid the transmission of fan vibration.

6. Voltage changes. 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 The design of each part of the fan will affect the noise level. The following design considerations can achieve noise reduction: the size of the winding core, the design of the fan blade and the outer frame, and the precise manufacturing and balance.

Attach basic knowledge of noise

Decibel (decibel) referred to as dB

We all know that Bell invented the telephone in 1876, but the important thing is that he discovered that our human ears respond to sound intensity in a logarithmic form, which roughly means that when the intensity of the sound increases to a certain level, the human hearing will It became less sensitive, which allowed the logarithmic unit to be used to represent the characteristics of the human ear. In memory of his discovery, it was named Bell.

Bell is ok when used in long-distance calculations, because the Bell unit is too large for practical applications. When we use it for small signals, we have to subdivide it by tenths as a unit, just like you are using When the meter wants to measure a small voltage, it will automatically broadcast it down and cut a grid similarly, this is decibel (decibel), from the English word decibel is (tenth), (decimal) is decimal, abbreviated as deci, change deci +bel becomes decibel, and this has the abbreviation dB. Note that the d in front of dB is lowercase and the B behind it is uppercase. What is the definition of the noise unit dB(A)? Are there dB(B), dB(C)...etc. What are the differences in the applications of these units? According to the interpretation of noise, dB is decibel (decibel). The A in () represents the weight, which is weighted in the audible range of the human ear at 20-20K Hz. In (), B is very rarely used, C represents the measurement of machinery and equipment, G represents ultra-low frequency, and D represents aviation noise. These are all differences due to the different feelings of sound. The most common is (A ).

The human ear has different sensitivity to different frequencies, which brings out the concept of weighted sound level. Taking the "A" weighted sound level as an example, the sound pressure level value will be reduced according to the formula before the low frequency and high frequency sound pressure level values ??are added together. The unit of the value obtained by adding the sound pressure level values ??together is decibel (A). Decibel (A) is more commonly used because this scale can more accurately reflect the human ear's response to frequency. Louder noise has a higher decibel/decibel (A) value. For weaker noise, the decibel/decibel (A) value is lower.

The sensitivity of the human ear to sound depends on the frequency of the sound. For sounds from 2,500 Hz to 3,000 Hz, the human ear responds most sensitively, while it is less sensitive to low-frequency sounds.