Sound Power Measurement of Tyre/Road Noise Using the Close-Proximity (CPX) Trailer Enclosure

The present paper reports a new methodology for measuring the sound power level (SWL) of tyre/road noise, using a modified Close-Proximity (CPX) trailer enclosure. Specially designed diffuser panels are implemented to cover the absorption materials on the interior walls and ceiling of the CPX enclosure to create a reverberant chamber. Through numerical simulations, the optimal reverberant chamber design, which holds the least acoustic resonance and most uniform acoustic energy distribution, is determined to guide fabrication. The SWL of a reference sound source (RSS) is determined first. The sound pressure level (SPL) distributions inside the reverberant chamber with the RSS switched on are then obtained under static conditions and road tests. The relationships between the SWL of the RSS and the SPL it produces inside reverberant chamber with various RSS inputs signals show great consistency with theory. Using the linear regression of SWL with respect to spatially averaged SPL reverberant chamber obtained in static condition, the total SWL and its spectrum at a specific vehicle speed can be deduced from the captured SPL information inside the chamber during road tests with the RSS switched off.