The pressure wave, produced by the rapidly expanding propellant gases is the only noise component that a suppressor can reduce. The suppressor reduces noise by two mechanisms. The first is it slows the release, through expansion and turbulence, of high-pressure propellant gases that we perceive as a "bang". The second is due to Newton's Law of Thermodynamics (Energy can neither be created or destroyed. It can only be converted from one form to another), where some of the kinetic energy of the noise impulse is converted to heat.