Stereo Systems
Mono system does not provide many characteristics of the performance space to the listeners. These characteristics include perception of the volume (spatial perception), localization of different sound sources, the reverberation process and many others.

Stereo system illustrated in the figure provide or improve the special perception; localization of the virtual sound sources (located between the two loudspeakers); perceptions of the sound filed of the performance space, and frequency characteristics of the reproduced sound sources.

Stereo-Sound Listening Area
All the characteristics that are described in the stereo reproducing sound will depend largely on the position of the listeners with respect to the loudspeakers. The following illustration shows the optimum area for stereo listening. Area 1 represent the listening locations where preferences of the stereo system compared to the mono system is more then 85%. In this area the listener can locate all of the virtual sources of the sound stage along the line between the loudspeakers.

When the listener move farther off the line of symmetry the virtual sound sources move toward the closest loudspeaker as well and the width of the reproduced sound stage reduced. Consequently, the preferences of the stereo system drop. The listening area where the preference is 60-85% represent the location where the listener can separate fewer virtual sound sources (at least 3 group) on the loudspeakers line (Base Line).
The stereo-effect area can be increased in many ways. One is to minimize the shifting of the location of the reproduced sound stage when the listener moves off the symmetry line. This can be done in different ways, one of which is to aim the loudspeakers as following:

Multichannel Stereo Systems
Multichannel systems refer to the system that incorporate two or more transmission channels or recording process and more then two loudspeakers. These systems are widely used in the cinemas and the home theater. The major issue for these systems is the compatibility between these systems itself for different applications as well as the compatibility between these systems and the regular stereo or mono system. This is the reason why these systems started to be standardized just in the last few years.
The main configuration of the system for home theater is the 5-1 or 3-2 system illustrated in the following drawing. This configuration may be applied with different transmission system or recording process and it is independent of the coding formats.

Practically, room interiors may not be optimized for the loudspeaker layout and movement of some loudspeaker is needed. In this case, delay of some loudspeaker signals will be needed.