INTRODUCTION The assessment of transmission loss (TL) in the automotive industry is required for the quantification of transfer of acoustical energy through the body or treated body of vehicles. Most of the time, the knowledge of the transmission loss is necessary at component level, because it is directly related to the acoustical performance of the corresponding acoustic part, which is covering this part of the body, and for which it is necessary to set the individual acoustic TL targets. The main examples of such so-called “acoustical components” are the dash insulator covering the firewall, or the floor insulator including the carpet covering the floor structure. This component approach makes sense from the point of view of industrial automotive parts, but is also adapted to the practical methods for assessment of the transmission loss. For obvious reasons, it is more practical to measure the transmission loss of a component isolated from its vehicle environment and inserted into a framed setup between two coupled rooms, because it fits in such a way the theory of TL through a baffled partition. In practice, such measurements require the knowledge of the incident as well as the transmitted sound power measured in two coupled rooms. Such rooms are either reverberant to create a diffuse sound field, in which the sound power can be easily measured by means of microphones, or anechoic or semi-anechoic, in which the free field incident/radiated power can be measured by means of intensimetry technics. Those measurements are performed according to international standards ([ 1] and [2]) either on flat sample setups, or on cut-outs of components like the dash of a car. When measurements are not possible due to time constraints, or physical components simply not available, the simulation is used for TL evaluation, allowing comparing in a fast way different design variations or material modifications against FE Simulation of the Transmission Loss Performance of Vehicle Acoustic Components at Low and Medium Frequencies Rainer Stelzer and Theophane Courtois Autoneum AG Ki-Sang Chae, Daewon SEO, and Seok-Gil Hong Hyundai Motor Company ABSTRACT The assessment of the Transmission Loss (TL) of vehicle components at Low-Mid Frequencies generally raises difficulties associated to the physical mechanisms of the noise transmission through the automotive panel. As far as testing is concerned, it is common in the automotive industry to perform double room TL measurements of component baffled cut-outs, while numerical methods are rather applied when prototype or hardware variants are not available. Indeed, in the context of recent efforts for reduction of vehicle prototypes, the use of simulation is constantly challenged to deliver reliable means of decision during virtual design phase. While the Transfer matrix method is commonly and conveniently used at Mid-High frequencies for the calculation of a trimmed panel, the simulation of energy transfer at low frequencies must take into account modal interactions between the vehicle component and the acoustic environment. After providing a brief review of the established approaches for TL simulation at LF, the article will present a new FE methodology for TL simulation and introduce the advantages of “in-situ” TL simulations by means of fluid-structure FE calculation. In a first step, results are given on bare flat plate as well as bare vehicle structures, in comparison to the results of mass law representations. In a second step, it is shown how the simulation of insulation trims by means of poro-elastic FE can be used to assess the TL of in-situ trimmed vehicle components. On one hand, the FE simulation of the in-situ TLs highlights the limitations of the Transfer matrix method at low frequencies. On the other hand, it is shown that, as far as only the Insertion Loss (IL) of the insulation treatment is concerned, the transfer matrix method can be used in a broader range toward lower frequenc