Experimental Investigation of Low-Frequency Noise and Vibration in a Bus

The low-frequency noise effects passenger comfort causing headaches, tiredness, and pressure on the eardrum. The mid- and high-frequency noises of an automotive vehicle can be easily attenuated with passive methods. The passive method involves the usage of fibrous or porous acoustic materials for sound absorption. But the reduction of low-frequency noise with passive methods is difficult. Hence the noise must be reduced at the source. The present work is related to the root cause identification of low-frequency noise and vibration in a bus. After the analysis of vehicle interior noise and vibration data acquired in static and dynamic operating conditions, it is identified that 30-40 Hz is the main problematic noise frequency band. From the component vibration data and modal testing results, it is concluded that unbalance in propeller shaft and resonance in the upper berth structure are the sources of this low-frequency noise. This is also confirmed with both acoustic and vibration operating deflection shapes (ODS) analysis carried out at vehicle interior.