Backstreet Boys 2013 AlbumWiki info
The Backstreet Boys have always prided themselves as a vocal harmony group and not a boy band.  In order to fight the boy band stereotype and the backlash from New Kids on the Block's lip-sync scandal in the beginning, they sing a cappella every chance they get.  The ad they answered in 1993 was for a singing group with "New Kids on the Block look with a Boyz II Men sound", and they aimed to have a white version of Boyz II Men.  "We were fans of New Kids, but were we really modeled after them? No. We looked at ourselves as Shai, Jodeci, Boyz II Men, the true vocal groups. That's who we listened to and who we really wanted to be like," Littrell stated in 2011.  The Backstreet Boys often employ polyphonic harmony, which sets them apart from many other singing groups. In choruses, Littrell, Carter, and McLean usually sing the melody with Dorough harmonizing above the melody and Richardson covering the bass parts.  During Richardson's absence, McLean and Carter together covered his part in choruses while Dorough took his solo parts.