NBC has revealed the identities of the ten a cappella groups who will be competing on The Sing-Off's fourth-season holiday revival, which will premiere with a two-hour broadcast on Monday, December 9 at 9PM ET/PT.

As previously announced, Nick Lachey will be reprising his role as host of The Sing-Off, and Shawn Stockman of Boyz II Men and Ben Folds of Ben Folds Five will be returning as judges. In addition, singer and songwriter Jewel has replaced former The Sing-Off judge Sara Bareilles and will be joining the panel as a judge for the revival.

In a new twist this season, the bottom-two acts based on home viewers' votes each episode will face off in an "Ultimate Sing-Off" in attempt to knock out their opponent solely by the power of their voices. The bottom-two groups will sing the same song and one a cappella act will be eliminated from the competition at the end of each broadcast.

The Sing-Off will air as a "holiday strip" and run for seven episodes, with its two-hour finale airing on Monday, December 23 at 8PM ET/PT. The winning group of the season will walk away with a $100,000 grand prize and a Sony Music recording contract.

The Sing-Off originally premiered in December 2009 as a five-night event and became a weekly series in 2011. The series is coming back after having been off the air since its third season concluded in November 2011. NBC had announced The Sing-Off's revival in May.

The champions of The Sing-Off's third season -- a group called Pentatonix -- received the same recording contract with Sony Music but a larger cash prize of $200,000.

The Sing-Off is being produced by One Three Media, Outlaw Entertainment and Sony Pictures Television with Mark Burnett, Deb Newmyer, Sam Weisman, and Jane Mun serving as executive producers.

The 10 a cappella groups who will be competing on the fourth season of The Sing-Off and their NBC-supplied descriptions are as follows:

- Acoustikats, from Lexington, KY

This collegiate group has been serenading sorority girls all over the University of Kentucky campus, but now it's their time to make it on the big stage. With their southern charm they hope to win over America's hearts.

- Calle Sol, from Aguadilla, Puerto Rico

From the island of Puerto Rico, this group of six professional musicians has only been together for a few short months. Their Latin style is sure to bring a flare to the competition.

- Element, from New York City, NY

This all-female group brings a New York attitude to the stage. They all work day jobs and pursue their showbiz dreams in the concrete jungle during their time off. These powerful female voices hope to bring a buzz to the a cappella world.

- The Filharmonic, from Los Angeles, CA

This locally based group is made up of male Filipino singers. Their knack for '90s R&B, mixed with their Filipino culture, is sure to bring a new twist to the music of the past.

- Home Free, from Minneapolis, MN

This all-male group has already been on the road touring the country and the transcontinental journeys have made them all very close. Their years of performance experience add to their refreshing country sound.

- The Princeton Footnotes, from Princeton, NJ

A 50-year-old tradition is holding strong with this Ivy League group -- classically trained, perfectly polished and technically great. Although they stick to tradition, they also like to mix a modern flair.

- Street Corner Renaissance, from Los Angeles, CA

This soulful group put aside their dreams of becoming musicians to raise their families. Now it's time to shine. Their roots are in doo-wop and they strive to pay homage to this classic sound.

- Ten, from Dallas, TX

Many of these eclectic artists have experienced traveling with professionals in well-known bands. Their group leader brought them together. The gospel influence and impressive backgrounds produce a perfected sound.

- Vocal Rush, from Oakland, CA

The youngest group in the competition is a force to be reckoned with. They have won the high school a cappella groups' international championship two years in a row. Their pop and R&B influence are sure to put a spin on modern chart-topping hits.

- Voiceplay, from Orlando, FL

These three best friends have been together since high school and expanded their group to six, added the influence of a female voice. They toured the U.S. and ended up back in Orlando performing before auditioning for The Sing-Off. This pop-inspired group blends the male and female voices perfectly.