A study on the difference in noise reduction between rear and side microphone on CPX measurement method through sound absorption frequency analysis

The road noise evaluation method in Korea is based on the 'noise vibration process test standard' by the Ministry of Environment. In this evaluation method, the noise felt at the sound-receiving point is measured as LAeq. Recently, in order to clarify the noise measurement standards for low-noise pavements, an international standard (ISO11819-2, CPX method) was first introduced in the Porous Pavement Guidelines of the Ministry of Land, Infrastructure and Transport. According to ISO, CPX measurement method adopts side microphones as mandatory, and the rear microphone as optional. Due to the difference in location noise level is different, causing confusion in the road noise evaluation method. Researchers have published several studies in the past that the rear microphone is highly correlated with the equivalent noise level method based on the Korean standard. As a follow-up study to the above results, this study examines the characteristics and causes of the frequency spectrum of the rear and side microphones in the case of dense asphalt pavement and porous asphalt pavement and derives the results through frequency analysis of the sound absorption coefficient test to determine and to contribute improving reliability and institutional rationalization of the CPX measurement method.