Comparison of CPX systems with Round Robin Test

The CPX method (ISO/CD 11819-2) is regularly used for assessing the acoustic quality of road surface within the frame work of checking with compliance to contract requirements nd conformity-of-production. The reproducibility of the test procedure is investigated ith a Round Robin test in which 7 operators of CPX systems, coming from Belgium, Denmark, Germany and Netherlands, participated. All systems were constructed as two heeled trailers, both with and without enclosure. All systems performed tests with three different tyre sets. One of them was a reference set that was used by all systems. Tests were done on a series of five different road surfaces, comprising of dense, semi open and porous types. The analysis of the variances observed in the test results (ANOVA) learned that the repeatability of the test procedure (one standard deviation) is about 0.4 dB. The reproducibility of the system without the effect of differences in tyre properties is about 0.6 dB. When the variation in tyre properties is included a standard deviation of 0.8 dB resulted. These test results corroborate the estimated uncertainty given by the ISO/CD 11819-2.