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The standard ISO/IEC 17025:2017 on the proficiency of testing and calibration laboratories requires that these laboratories shall apply procedures for estimating the uncertainty of their measurement results. In this work, analysis of the uncertainties of the airborne sound insulation measurement parts and their impact on the combined uncertainty in 1/3- octave frequency band with different thickness (4 mm and 100 mm) sample have been studied. Uncertainty is an unavoidable part of any physical measurement or prediction process. The total measurement uncertainty model contributes several different partial uncertainties, which are evaluated by the method of type A and type B. Regarding sound insulation measurements, the car body structures of modern trains have been formed of extruded aluminium panels (4 mm thickness, sample 1) and noise barrier structures (Sandwich structure) has been formed of gypsum board and noise barrier material (100 mm thickness, sample 2). Their acoustic properties, particularly the sound transmission loss, have an important influence on the interior acoustic environment. The Sound Transmission Loss (STL) of sample 1 & 2 are measured in the CSIR-National Physical Laboratory, through the measurement of the octave band levels in the reverberation rooms to meet the standard requirement (ISO 10140: 2010 Part II recommendations). Acoustic measurements were obtained with calibrated building acoustic analyzer (B & K Type 2270 with BZ-7229 software). A sound has been generated using the Omnidirectional sound source (B & K Type ZC-0032)) between 100 to 4000 Hz. It has found that the STL of sample 1 and sample 2 is increased with increasing the frequency, and 4 mm thickness sample has low uncertainty in STL measurement as compared to 100 mm thickness sample.
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