Stereophonic sound is a method of sound reproduction that creates an illusion of a multi-directional audible perspective. This effect is most often achieved by using two or more independent audio channels through a configuration of two or more loudspeakers.
From 1940 to 1970, the progress of stereophonic sound was slowed by the technical difficulties of recording and reproducing two or more channels in synchronization with one another. The economic and marketing issues of introducing new audio equipment. A stereo system cost roughly twice as much as a monophonic system.