Analysis of factors influencing the measurement result of the reverberant sound absorption coefficient under laboratory conditions

There are still discrepancies in the measurement results despite the standardized methods of measuring the sound absorption coefficient in the reverberation room. They appear especially in interlaboratory tests. The research used the method included in the EN-ISO 354: 2003 standard to determine the sound absorption coefficient. The subject of scientific research was to investigate the impact of measurement techniques (Maximum Length Sequence method and interrupted noise method for both T20 and T30 evaluation ranges), humidity in the test room, sample seasoning and sample fitting, and finally the influence of room variability on the measurement results. The tests were performed in two reverberation chambers. The study included two types of materials. Samples (1) made of identical pieces of mineral wool (ISOVER glass wool and ROCKWOOL rock wool) and (2) of fibreboard. Mineral wool was of different thicknesses. Among the measurement techniques, the smallest dispersion of the reverberation time results was obtained with the MLS -T30 method, and the highest differences in the results were caused by the test being performed in another room (reverberation chamber). There was no significant influence with the increase in humidity or the careful arrangement of the test sample from the components on the measurement result.