Acoustical Design of Vehicle Dash Insulator

The acoustical performance of a vehicle dash panel system is rated by the noise reduction, which is calculated from the sound transmission and absorption characteristics. A typical dash insulator consists of a steel panel (vehicle body panel), a porous decoupler and heavy layer in the form of sandwich construction. The use of dash panel is to block engine noise from entering into the interior cabin. In the present study the transmission loss of dash panel has been evaluated in reverberation chambers and the sound absorption of dash panel has been determined in impedance tube. This paper deals with improving over all sound transmission loss and shifting of the double wall resonance well below the engine firing frequencies by changing the decoupler materials such as felt and foams of different density and thickness and heavy layer mass per unit area. Numerical simulation of dash panel is also carried out for predicting sound absorption and sound transmission loss of different combinations. The simulation requires intrinsic properties of poroelastic and viscoelastic materials of dash panel. These properties are measured using standardized test rigs and inverse techniques. A parametric study is also carried out to check the effect of intrinsic parameters on sound absorption and sound transmission loss. Finally the simulated results will be validated with experimental results.