Virtual surround is an audio system that attempts to create the perception that there are many more sources of sound than are actually present.
In order to achieve this, it is necessary to devise some means of tricking the human auditory system into thinking that a sound is coming from somewhere that it is not.
Most recent examples of such systems are designed to simulate the true (physical) surround sound experience using one, two or three loudspeakers.
Such systems are popular among consumers who want to enjoy the experience of surround sound without the large number of speakers that are traditionally required to do so.
For virtual surround to be effective, the room should be both physically symmetrical about the perpendicular to the line between the speakers, and the absorbing characteristics of the left and right walls.