The purpose of an exhaust silencer is to reduce engine noise emission. An engine without a silencer will create an unbearable amount of exhaust noise in our environment. Noise is defined as unwanted sound.
Sound is a pressure wave formed from pulses of alternating high and low pressure air. In a combustion engine, pressure waves are generated when the exhaust valve repeatedly opens and lets high-pressure gas into the exhaust system. These pressure pulses are the sound we hear. As the RPM of the engine increases so do the pressure fluctuations and therefore the sound emitted is of a higher frequency.
All noise emitted by an engine does not specifically come from the exhaust system. Other contributors to engine noise emission include intake noise, mechanical noise and vibration induced noise from the engine’s body and transmission.
The industrial silencer has to be able to allow the passage of exhaust gasses whilst restricting the transmission of sound.