Sound is the result of vibrations that travel through a medium like air or water which can be heard when they reach the ear of a person or animal. Sound results from sudden contact of high energy level gases (pressure, speed or heat) with low energy level gases. The loudness depends on the scale of swiftness and magnitude of the transition. If these vibrations can be reduced, then the resultant sound will also be less. Silencers in guns, motor vehicles and jet engines apply the principle.
When a gun is fired, it produces superheated and pressurised gases. The exploded gun powder creates hot gases and these gases propel the bullet from barrel. The crack of a gun is caused by the bullet crossing sound barrier and the rapid release of high pressure gases. These gases from the barrel when escapes into the open, it causes dramatic vibrations in environment creating the loud sound of gun blast. If these gases can be slowed down, there will be less noise.
Silencers work by regulating the transition of high energy level gases gradual and smoother. A silencer basically consists of two chambers: an expansion chamber and a number of baffles. The expansion chamber permits the hot gases to expand and become cooler. The baffles are made of metal. They results in further deceleration of gases by causing the gases to swirl around. They also absorb the heat from gases. The cooler, low pressure gases released from the barrel to the open result in slower vibrations and thus reduce the sound. The silencer of a gun also ensures reduced recoil, more accuracy and fewer disturbances to nearby people. How do we hear sound?