1、 Preparation before testing
-Environmental requirements for anechoic chamber
-The anechoic chamber needs to have a suitable cutoff frequency, generally requiring the sound absorption coefficient of the wall to be above 99% (the reflection coefficient of the semi free field is above 95%, and the cutoff frequency is 125HZ, which can be specially designed and extended to 150HZ according to requirements), in order to simulate the free field or semi free field space, reduce the interference of reflected sound on the measurement, and make the measurement results closer to the actual noise situation emitted by the product.
-The anechoic chamber should have a low background noise environment. Within the testing frequency range, the sound pressure level of the background noise should be at least 6dB lower than the sound pressure level of the tested IT product's sound source, preferably as low as 12dB or more, to avoid the influence of background noise on the accuracy of the detection results.
-Placement of IT products
-Determine the placement method based on product characteristics, taking into account the weight, bottom structure, moisture resistance, and special requirements for the ground (such as electrostatic sensitivity) of the product. Some IT products placed directly on the ground may affect their performance or cause damage, such as some precision electronic components that may be damaged if exposed to moisture, and electrostatic sensitive components that come into direct contact with the ground may be disturbed by static electricity.
-According to specific testing standards and purposes, certain acoustic tests may require the product to be located on a specific support structure to avoid ground interference with the accuracy of test results. Even if the product is allowed to be placed directly on the ground, specific support frames or washers may be required to ensure product stability, prevent vibration, and maintain a certain distance from the ground, especially for products that require measurement of bottom noise emissions.
2、 Operation during the detection process
-Noise characteristic analysis
-Spectrum analysis: Determine the frequency components of IT product noise. The frequency distribution of noise may vary among different IT devices. For example, a computer CPU fan may produce noise within a specific frequency range. Spectral analysis can accurately identify these frequencies and analyze the sources of noise, such as fan rotation frequency, electromagnetic vibration frequency of electronic components, etc.
-Time domain analysis: Obtain waveform information of IT product noise. By observing the shape, amplitude, and other characteristics of the waveform, we can further understand the characteristics of noise, such as whether there are intermittent noise spikes, which may indicate intermittent faults or unstable working conditions of certain components within IT products.
-Choose appropriate measuring instruments
-Sound level meters are usually used to measure the sound pressure level of IT products. A sound level meter can accurately measure the intensity of sound and simulate the human ear's response to different frequency sounds based on different weighting networks (such as A, C, Z weighting, etc.). When detecting IT product noise, A-weighted sound level is usually used to measure the degree of impact of noise on people.
-According to the accuracy requirements of the test, more precise acoustic measurement instruments may be used, such as acoustic analyzers, which can provide more detailed acoustic parameters, such as octave band analysis, sound power level measurement, etc., which are more useful for comprehensively evaluating the noise characteristics of IT products.
3、 Analysis of the results after testing
-Comparison standards
-Compare the test results with relevant standards, for example, for IT products such as computers, there may be industry established noise standards or international and national standards (such as ISO standards, GB standards, etc.), to determine whether the product's noise is within an acceptable range.
-Analyze noise sources and improvement directions
-Analyze the source of noise generation based on the detected noise frequency, waveform, and other information. If the specific frequency noise generated by a certain component is too high, such as the high-frequency noise generated during hard disk reading and writing, then optimization of the component can be considered, such as replacing better shock-absorbing materials, improving the design of the cooling fan, etc., to reduce the overall noise level of the product.