The acceptance criterion of any vehicle in terms of user comfort invariably depends on the vehicle interior noise and vibration characteristics. The levels of sound energy and structural excitation inside the vehicle compartment measures the amount of annoyance in terms of quality and comfort. For vehicle interior noise abatement and noise treatment, it is desirable to quantify the noise sources by determining the sound power contribution from each vehicle component/panel, acoustic leakages inside the vehicle, body panel vibrations, gearshift lever and steering wheel vibrations. Many a times, it is necessary to arrive at benchmarks or targets for the various sources of noise in order to refine the systems.
The present paper describes a methodology for interior noise source identification and its analysis for benchmarking. Two different vehicles of the same class but of different makes were compared and evaluated for interior noise and vibration levels. Intensity mapping of the complete interior of both the vehicles was carried out and compared. Similarly, the vibration and sound pressure levels were measured and compared at selected locations and at anti-node points. The effectiveness of the firewall, silencers and engine mounts were also checked and compared. The sound intensity measurements at stationary condition with different engine speeds inside the vehicle helped in computing the sound power from different vehicle panels, and identifying sources and their contribution. The correlation between pressure and vibration levels of different sources with acoustical and structural transfer paths were studied. The modal behaviour of the acoustic cavity and the structural panels were studied using finite and boundary element techniques, to predict the sound pressure levels at selected locations and the contribution of different vehicle panels. This provided benchmarking - sourcewise, acoustic as well as structural and system noise-engine, firewall, different panels, silencers, etc. enabling to set individual system targets.