Uncertainty of sound insulation measurement in laboratory

Protection against noise is one of the six essentials requirements of the European Union
directive. In buildings airborne sound insulation is used to define the acoustic quality of walls
between rooms. However the evaluation of sound insulation /index/ is sometimes difficult or
even ambiguous, both in field and laboratory measurements, in spite of the fact that there are
some unified measurement procedures specified in the ISO 140 standards. There are problems
with the reproducibility and repeatability of the measurement results. Some difficulties
may be caused by non-diffuse acoustic fields, non uniform reverberation time or errors of the
reverberation time measurements. Some minor problems are also posed by flanking transmission
and the S/N ratio. The paper includes an analysis of partial uncertainties of the above
mentioned measurement components and their influence on the combined uncertainty in 1/3
octave frequency bands and the sound reduction index determined according to ISO 140-3,
using the uncertainty propagation law. All of the analysis and calculations performed in the
paper concern the conjugated reverberation rooms and measurement set-up located in AGHUST
Department of Mechanics and Vibroacoustics in Kraków.