Control of noise in the passenger compartment of the bus due to structural vibration

The design of the chassis with an appropriate structure is thought to be an efficient way for decreasing vibration and noise since chassis vibration is one of the key causes that generates noise in the bus passenger compartment. This study uses the Frequency Response Function Method (FRFM) and Modal Participation Method (MPM) to analyze an acoustic finite element model of a bus frame model THACO TB120S. To perform the noise radiation caused by the vibration of the bus frame structure, the chassis was triggered by a diesel engine. The bus engine has a six-cylinder, four-stroke, and in-line arrangement. The triggered frequencies from the engine were operated in the range of 1-100 Hz, while the maximum engine speed was 1900 rpm. The vibration of the roof array and the noise of the bus compartment was examined analytically at four locations on the bus structure. The results show that the performance of the bus structure with respect to the noise generation was significantly improved. The resonant frequencies of noise observed from analytic results are verified by experimental measurements in terms of sound pressure. The acoustic resonance in the bus passenger compartment mainly occurs in the frequency range from 15 to 70 Hz. The peak values of the sound pressure are significantly decreased when the roof modification technique was applied. An increase in the stiffness of the roof using the structural correction method could have a positive effect on noise reduction by approximately 60%.