Music System (BGM)
Background music is not stereo, but monophonic. This is because stereo requires the ability to distinguish the direction of the sound source and have a sense of depth. Background music, however, does not know where the sound comes from without paying attention to it, and does not want to be perceived as the source of the sound, so that the BGM system speaker requires that the source be concealed, while the volume is relatively light, so as not to affect the two person-to-person speech as the principle.
