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NVH labs at Tier 1 and Tier 2 suppliers have in the past 15 years implemented testing techniques to validate the NV performance of their products. Validation tests are most often conducted to check compliance of the product to vehicle OEM specifications, less often to truly assess NV performance. Vehicle OEM specifications are sometimes outdated, narrow in scope and require lab-type of conditions, i.e. anechoic or hemi-anechoic environment, fixed microphone position and specific operating conditions. Tier 1 and 2 suppliers often find themselves in a situation in which they have to transport lab tests to the plant floor, as they are requested by their customer to ensure 100% shipped quality. In order to do so, they are faced with several technical and commercial challenges as vehicle OEM specifications often have no provisions for plant-floor boundary conditions and cycle time requirements.

As an agricultural tractor OEM was moving a new tractor model from development into production, an objectionable cab “boom” was identified that was not present in the preproduction pilot -level tractors. The cab boom was identified as a low frequency tone causing an increase of 7 (dBA) over the level in the pilot tractors, which was deemed unacceptable. The process used by the tractor OEM engineering team to address this problem has been widely used and refined in the automotive industry, but it is relatively new in the agricultural/off-road vehicle industry. This paper describes the source-path-receiver approach that led to identifying the exhaust tip as the source and the vibro-acoustic coupling of a windshield structural mode with an acoustic cab cavity mode as the path of the boom event.