Sound can be defined as an undulatory perturbation of any type of elastic matter (gas, solid or liquid). This means that sound does not exist in the vacuum.

Audio monitors and most of loudspeaker sets must be positioned distant from the walls.

No, most people believe that just by using traditional sound absorbing materials (typically the polyurethane or melamine sponges, but also the classic and most economic egg crates) the room will sound