CPX trailer comparison round robin test data analysis

One of the methods to determine the influence of the road surfaces characteristics on the emission of noise by road traffic is the so-called Close Proximity (CPX) method, which measures the noise emission of the tyre-road contact in the near field of a sound radiating tyre. These measurements are executed with CPX measurement trailers. Experience in the Netherlands and in other European countries has shown that CPX measurements may suffer from a relatively large measurement uncertainty. In order to quantify the actual measurement uncertainty for the Dutch CPX trailers and to develop guidelines for further reduction of the measurement uncertainty a round robin test was held in the Netherlands in 2008. In 2011 this investigation was repeated and enlarged by the participation of three CPXtrailers from other European countries.