NBC’s a cappella singing competition series The Sing-Off will return for a five-night second cycle in December with Nick Lachey back as host. The Sing-Off will premiere Monday, December 6  from 8-10 PM. Four 2-hour episodes will follow from 8-10 PM on December 8, 13 and 15 and December 20, when the series will wrap with a live finale. The Sing-Off, from Tenth Planet Prods., Outlaw Prods. and Sony Pictures TV, features 10 a capella groups competing for the $100,000 prize and a Sony Music recording contract. Also returning are celebrity judges Ben Folds, Shawn Stockman and Nicole Scherzinger. Last season, the four December telecasts of The Sing-Off averaged a 2.5/7 share in adults 18-49 and 7.3 million viewers overall. The reality show will preempt NBC’s regular programming on the nights which consists primarily of repeats that time of year.