Evaluation of close-proximity methods for tire/pavement noise measurements

摘要

An accurate and practical method to measure the influence of road surfaces on traffic noise using a close-proximity method is desired. The draft ISO standard for the CPX method specifies two mandatory microphones located 20 cm from the plan of the tire sidewall. One potential problem with this method is that evanescent waves in the near-field will be present for some frequencies of interest, which may overestimate the noise radiated to the far-field. Another close-proximity method, known as the On-Board Sound Intensity measurement methodology, uses one or two sound intensity probes located very close to the tire/pavement contact patch. This should eliminate the evanescent wave problem, but the result is dependent on the number and locations of the probes. In this study, near-field acoustical holography (NAH) is used with measurements of the complex sound pressure field at plane 10 cm from the side of the tire sidewall for several tire/pavement configurations. Processing the data using NAH, sound power through the measurement plane is calculated, as well as sound intensity and sound pressure, at the locations being used for two close proximity methods. Each method is then evaluated as to how well they correlate to sound power.