GB/T 4129-2025 Active

This document specifies the acoustic performance requirements for standard sound sources, including: -- Time stability of sound power output; -- Spectral characteristics; -- Directivity. Time stability is defined by the repeatability standard deviation (see 5.2). The spectral characteristics can be verified in a semi-anechoic chamber or reverberation chamber according to the frequency band sound power levels specified in this document (see 5.4). The performance requirements for the directivity index can only be verified in a semi-anechoic chamber (see 5.5). This document also specifies the method for providing sound power level calibration data and uncertainties for sound sources intended to be used as standard sound sources under the standard meteorological conditions specified in Chapter 4. Although this method is typically performed in a test laboratory, this document is still referred to as a calibration standard. Although the sound pressure level measurements and distances associated with this method are traceable, in a strict metrological sense, the sound power level calibration results cannot be directly traced to national metrological standards. Test laboratories using this method do not need to meet all the requirements typically associated with calibration laboratories. Note: ISO/IEC 17025 specifies different requirements for the qualification of test laboratories and calibration laboratories. Laboratories testing standard sound sources according to this document typically meet the requirements for test laboratories, but not necessarily those for calibration laboratories. This document not only specifies a calibration method for standard sound sources in a free field above a reflecting surface, but also a calibration method for standard sound sources at different distances from the interface in a reverberation chamber. For a standard sound source positioned on a reflecting surface, the two different test environments are considered equivalent in the freque