The major source responsible for noise pollution is internal combustion engine. These engines areused for various purposes such as, in automobiles, locomotives, and in various manufacturing machineries. In an engine,the exhaust noise and the noise produced due to friction of various parts of the engine share maximum contribution tonoise pollution. Muffler is a device used to reduce noise within the exhaust system. It is arranged along the exhaust pipefor the purpose of noise attenuation. The paper describes the acoustic Analysis of Double Expansion Chamber Reactive(DEC) Muffler with various combinations of placement of side outlet. The approach is useful in the acoustic analysis ofDouble Expansion Chamber Muffler for maximizing Sound Transmission Loss. The purpose of paper is to study the effectof placement of side outlet on transmission loss of Double Expansion Chamber Reactive Muffler with the help ofnumerical analysis using COMSOL Multiphysics.