In order to promote inside
noise assessment, they proposed a reduction of 21 dB(A) as a default
value to derive indoor noise levels from the outside noise
Consequently, the large variation
between study results has complicated comparative analysis.
To come forward with this issue, the development of a universal
noise assessment program for Europe (cfr. Harmonoise Project)
has emerged. This stresses the need for more research data on
comparative and methodological issues