 These channels are "matrixed" from the standard surround channels; they are not discrete.Some matrix encoding surround sound systems use a single back center channel surround (Dolby Digital EX, Dolby Pro Logic IIx 6.1) or a back left and back right (Dolby Pro Logic IIx 7.1) speaker configuration.Often the standard surround channels are misconceived to be "rear channels" when they are in fact meant to be placed at 90-120 degrees.