The present study demonstrates the use of a transportable anechoic chamber for conducting microphone free-field calibrations with lowest levels of uncertainty. A dedicated transportable anechoic chamber (make SPEKTRA, Germany) of internal volume of 2 m³ completely lined with wedge-shaped absorbers is utilized for free-field calibrations in the frequency range of 125 Hz–20 kHz using the substitution method as per the IEC 61094-8 standard. The study has identified the usable working space inside a free-field chamber using the inverse-square pressure law, and the deviations from the inverse-square law of the free-field chamber are quantified. The measurement uncertainty of ± 0.36–0.52 dB (k = 2, 95% confidence level) is evaluated in the frequency range of 125 Hz–20 kHz and is validated in a bilateral comparison. The application of Monte Carlo simulation approach in the evaluation of measurement uncertainty in microphone free-field calibrations is also demonstrated.

中文翻译：

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麦克风自由场比较校准中的测量不确定度

本研究表明使用可移动消声室进行麦克风自由场校准，具有最低的不确定度。内部容积为2 m ³的专用可移动电波暗室（德国SPEKTRA制造），其完全衬砌成楔形吸收体，用于采用IEC的替代方法在125 Hz–20 kHz频率范围内进行自由场校准61094-8标准。该研究使用平方反比压力定律确定了自由场室内的可用工作空间，并量化了与自由场反平方定律的偏差。测量不确定度为±0.36-0.52 dB（k = 2，95％置信水平）在125 Hz–20 kHz的频率范围内进行评估，并在双边比较中得到验证。还演示了蒙特卡罗模拟方法在麦克风自由场校准中测量不确定度评估中的应用。