The Air Force Academy’s A cappella group In the Stairwell went all ‘Sing Off’ at a White House holiday reception Dec. 8, 2011. Didn’t get your invitation? Check out In the Stairwell in action. Don’t miss the cadet that gets his human beat box on in the beginning. Doug E. Fresh would be proud. [youtube]http://www.youtube.com/watch?v=qNt72iwPdpY&feature=related[/youtube]