Soundproofing is any means of impeding sound propagation. There are several basic ways to reduce sound: increasing the distance between source and receiver, decoupling, using noise barriers to reflect or absorb the energy of the sound waves, using damping structures such as sound baffles for absorption, or using active antinoise sound generators.
Acoustic quieting and noise control can be used to limit unwanted noise. Soundproofing can reduce the transmission of unwanted direct sound waves from the source to an involuntary listener through the use of distance and intervening objects in the sound path (see sound transmission class and sound reduction index).
Soundproofing can suppress unwanted indirect sound waves such as reflections that cause echoes and resonances that cause reverberation.