GB/T 4980-2025 in English

1. Principles for establishing the reference body

The reference body needs to envelop the main body of the compressor and the main noise radiating parts, ignoring non-main radiators (such as handles, connecting pipes, etc.). For special models such as screw compressors, the reference body size needs to be determined by referring to the diagram in Appendix C.

2. Specifications for measurement point arrangement

• Basic measuring points: 9-point method (4 side surfaces + 1 top surface + 4 top corners)
• Additional measuring points: When the A-weighted sound pressure level difference >9dB or the reference body size >2m, increase to 17 points
• Simplified conditions: When the difference between the 9-point and 5-point measurement results is ≤1dB, it can be reduced to 5 points

3. Background noise correction

Correction value K₁ calculation formula:

K₁ = -10lg(1-10^-ΔL_p/10)

Wherein, ΔL_p is the difference between the measured value and the background noise. When ΔL_p>15dB, no correction is required.

Test Environment Selection Priority

1. Semi-anechoic chamber (ideal free field)
2. Outdoor venue meeting K₂≤4dB
3. Indoor space where the reverberation field affects the direct sound field

Instrument Calibration Requirements

Total standard deviationσ_tot = √(σ_RO² + σ_omc²)

Wherein:

• σ_RO (reproducibility deviation): A weighted ≤1.5dB (see Table 1)
• σ_omc (operation and installation deviation): usually 0.5dB

Special Note: For low-speed reciprocating compressors, it is recommended that σ_omc be 2dB