The Measurement Uncertainty of Single-Number Quantities for Rating the Impact Sound Insulation of Concrete Floors

The ISO standards defining the single-number quantities for rating of impact sound insulation will be revised in the future. In the revision process, a new quantity, impact sound reduction index R-impact, has been suggested by Scholl. The suggested revision means that the measured frequency range will change from 100-3150 Hz to 50-2500 Hz. The aim of this study was to find out how the measurement uncertainty of the suggested single-number quantity, impact sound reduction index R-impact, differs from the measurement uncertainty of the current single-number quantity, weighted normalized impact sound pressure level L'(n,w) defined at traditional frequency range 100-3150 Hz. The uncertainties of the indicator L'(n,w)+ C-I were calculated, too. Another aim was to study the uncertainties of the 1/3-octave band values of the normalized impact sound pressure levels L'(n). The measurement uncertainties were simulated with Monte Carlo method on the basis on 50 field measurements of concrete floors. It was shown that the measurement uncertainty of the single-number quantities depends on the shape of the impact sound spectrum and hence on the floor type. The measurement uncertainty of 1/3-octave band values does not depend on the floor type, which means that the uncertainty of the single number quantities is connected with the impact sound pressure levels that determine the value of the single-number quantities. The measurement uncertainties of both the 1/3-octave band values and the single-number quantities rise when the 1/3-octave bands 50,63 and 80 Hz are included in the rating, but the change remains so small that it does not prevent the measurements at the enlarged frequency range. However, if some alternative reference spectrum or reference curve will be used in calculation of a SNQ, the measurement uncertainty of that SNQ will differ from the present SNQs, which should be taken into account when alternative reference spectra are used.