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 ChamberReactive(DEC) Muffler with various combinations of placement of extended inlet and extended outlet. The approach isuseful in the acoustic analysis of Double Expansion Chamber Muffler for maximizing Sound Transmission Loss. Thepurpose of paper is to study the effect of extended inlet and extended outlet on transmission loss of Double ExpansionChamber Reactive Muffler with the help of numerical analysis as well as experimental analysis.