Sound Transmission Loss through Front of Dash and Instrumental Panel

The subsystem of front of dash (FOD) and instrument panel (IP) is a critical path to isolate the powertrain noise and road noise for vehicles. This subsystem mainly consists of sheet metal, dash mats, IP, and the components inside IP such as HVAC and wiring harness. To achieve certain level of cabin quietness, the sound transmission loss performance of this subsystem is usually used as a quantifier. In this paper, the sound transmission loss through the FOD and IP is investigated up to 10kHz, through both acoustic testing and numerical simulation. In the acoustic testing, the subsystem is cut from a vehicle and installed on the wall of two-rooms STL testing suite, with source room being reverberant and receiver room being anechoic. In the testing, various scenarios are measured to understand the contributions from different components. The numerical simulation is based on statistical energy analysis (SEA) because deterministic methods have difficulty to predict the STL up to 10k Hz due to problem size. Good correlations are obtained for all the scenarios. From the investigation, the contribution from different components to the overall STL performance is evaluated and ranked. Taking advantage of the correlated numerical models, design changes which are not feasible or easy to be measured are studied. As an example, in the “virtual” design changes related to the IP components, the influence from IP skin and leakages are checked.