Why silencer reduces engine noise ?

Due to Exhaust Gasses in Engine lots of noise produced. Silencer are installed within the exhaust system of most internal combustion engines, although the Silencer is not designed to serve any primary exhaust function. The silencer is engineered as an acoustic soundproofing device designed to reduce the loudness of the sound pressure created by the engine by way of acoustic quieting. The majority of the sound pressure produced by the engine is emanated out of the vehicle using the same piping used by the silent exhaust gases absorbed by a series of passages and chambers lined with roving fiberglass insulation and/or resonating chambers harmonically tuned to cause destructive interference wherein opposite sound waves cancel each other out. An unavoidable side effect of muffler use is an increase of back pressure which decreases engine efficiency. This is because the engine exhaust must share the same complex exit pathway built inside the silencer as the sound pressure that the silencer is designed to mitigate.