Vibro-Acoustic Source-Path-Receiver approach to Identifying and Troubleshooting in an Agricultural Tractor Mode Coupling Issue

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. Data are also presented in support of the interpretation of the noise generation mechanisms and to validate countermeasures focused on source and path sensitivity reduction strategies, such as frequency shifting and mode decoupling by use of lumped masses and ¼ wavelength tuner.