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Governmental regulations regarding exterior noise emitted by motor vehicles vary throughout the world. A vehicle which is compliant in one market may not be compliant in another market. In this case, a production North American class 8 truck was being prepared for sale overseas. The requirement to meet European Union (EU) pass-by regulations as tested per the EU standard meant development of a production feasible package to substantially reduce noise emissions without changing any fundamental design or operating parameters of the truck. The development testing was done on a chassis dynamometer in a hemi-anechoic chamber without any specific pass-by noise simulation software. Efforts to develop a reasonably accurate correlation from lab to track, use of acoustic beamforming for source localization and package design iterations leading to a final successful package are discussed.

The reduction of full acceleration truck pass-by noise conforming to Type ECE-51 regulation (Reference 1) was predicted in a hemi-anechoic chassis dynamometer chamber with microphone arrays and compared with actual test track results. This gave a close match to the track data, with both showing a 4 dB reduction in the A-weighted overall noise level after identical acoustic treatments were applied. Noise control materials were selected to perform as acoustic barriers and absorbers. These were optimized by analyzing the 1/3 octave spectra, determining dominant frequency bands, in critical source locations and engine speeds, and using combinations that dissipate or contain energy well within those bands. With the truck being stationary while tested, important source locations could be quickly identified both subjectively and with localization tools such as Beamforming.