Speaker
Description
The CPX method uses two mandatory microphones and up to four additional (optional) microphones to assess road surface noise. The microphones are positioned around a reference tyre and record noise generated at the tyre–road contact. However, the overall noise levels may vary depending on the number and placement of the microphones. This raises the question of whether the currently mandatory microphones are sufficient for the proper assessment of low-noise surfaces.This paper presents noise levels measured by all six microphones on conventional and low-noise surfaces of different ages. Microphones located along the tyre (Nos. 1, 2, and 3) recorded nearly identical values for both surface types. In contrast, differences between microphones 4 and 5 were already evident for low-noise surfaces. The measurement from microphone 5, located at the trailing edge, is strongly influenced by void content. The largest difference, up to 2.5 dBA, was observed on the newest surface.