Localization of Heavy Truck Pass-By Noise Sources Using Acoustic Beamforming

In a recently completed National Cooperative Highway Research Program project, acoustic beamforming was used to localize and identify noise sources on heavy trucks operating at a variety of highway sites. The 20 sites were located in California and North Carolina and represented various pavement types and truck operating conditions induced by flat, uphill, and downhill sites, as well as low speed acceleration. Over 1,200 trucks were measured. For each truck, acoustic contours of source regions were produced and analyzed. For all trucks, the loudest source region was at the tire pavement interfaces. A secondary source region was typically identified as being associated with engine and powertrain extending up to about 1 meter above the pavement. Noise from elevated exhaust stacks was identified only rarely. Less than 5% of the trucks had any indication of noise radiated from exhaust outlets. From the contours, profiles of sound level as a function of height were produced for each site. These were normalized to the average sound level at the tire pavement interface for the specific site. With this normalization, the average profiles from each site were found to be quite consistent despite the differences from site-to-site. The results of this study are summarized.