Reproducibility of the present and the proposed single-number quantities of airborne sound insulation

  • Hongisto V
  • Ker??nen J
  • Kylli??inen M
 et al. 
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Abstract

Background. A proposal for new single-number quantities (SNQ) for
airborne sound insulation was recently published by Scholl et al. The
proposed SNQs, R-traffic and R-living, are determined in the frequency
range of 50-5000 Hz. Their present counterparts, R-w + C-tr and R-w, are
determined in the smaller frequency range of 100-3150 Hz. There is
concern that the high reproducibility values of ISO 140-3 measurements
below 100 Hz could result in an increase in the reproducibility values
of the proposed SNQs.
Aim. The aim was to compare the reproducibility values of the proposed
and the present SNQs based on the results of a round robin test. The
second aim was to compare the SNQs and their reproducibility values
based on the pressure (ISO 140-3, 50-5000 Hz) and the intensity methods
(ISO 15186-3, 50-160 Hz).
Methods. The laboratory measurements used for this study were obtained
from a previously published interlaboratory measurement of a window. The
sound reduction indices were measured at each laboratory using both the
pressure method (ISO 140-3) and the intensity method (ISO 15186-3). The
present and the proposed SNQs and their reproducibility values were
determined from the interlaboratory data.
Results. The reproducibility values of the proposed SNQs were found to
be larger (i.e. larger uncertainty) than the reproducibility values of
the present SNQs when the pressure method was used. The reproducibility
value of R-traffic was unacceptably high, 3.6 dB, while it was 3.1 dB
for R-W + C-tr. Correspondingly, the reproducibility value of R-living
was 2.1 dB while it was 1.5 dB for R-w. The increase was due to the
inclusion of the measurement data in the 1/3 octave bands below 100 Hz
which had significantly larger reproducibility values than the higher
1/3 octave bands included in the calculation of the SNQs. The use of the
intensity method also resulted in slightly larger reproducibility values
for the proposed SNQs. However, the increase was small and the
reproducibility values of both R-traffic and R-living were approximately
2 dB.
Implications. It is suggested that scientific evidence for including the
frequency range 50-80 Hz should be significantly improved before
deciding that the low frequency measurements should be included in the
calculation of the SNQs. The practical disadvantages of the change may
be larger than the expected benefits.

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