The 2011 champions of NBC's "The Sing-Off" show off their harmonies on the Billboard Hot 100's No. 1 song.

After winning NBC's a capella competition "The Sing-Off" in late 2011, Pentatonix has kept on racking up victories.

The Arlington, Texas, vocal quintet – Scott Hoying, Kirstie Maldonado, Mitch Grassi, Avi Kaplan and Kevin Olusola – soared onto the Billboard 200 at No. 14 the week of July 14, 2012, with "PTX: Volume 1." The set marked the highest-charting a capella title since Bobby McFerrin's "Simple Pleasures," featuring his Billboard Hot 100 No. 1 pop culture smash "Don't Worry, Be Happy," rose to No. 5 in 1988.

"Volume 1" includes reinventions of recent hits including Nicki Minaj's "Starships," Gotye's "Somebody That I Used to Know" and fun.'s "We Are Young." It's the same mix of contemporary covers that helped Pentatonix win "The Sing-Off," on which it made over such songs as Katy Perry's  "E.T.," Kanye West's "Love Lockdown" and David Guetta's "Without You."

In the video above, the group offered its take on Macklemore & Ryan Lewis' "Thrift Shop," featuring Wanz, in a recent visit to Billboard's New York offices. "We were super-inspired, so it only took us about two days" to devise the arrangement for its version of the Billboard Hot 100's current No. 1 song, the group explained.

Pentatonix's new video is a collaboration with violinist (and recent Chart Beat Meet & Great spotlight artist) Lindsey Stirling, a cover of Imagine Dragons' "Radioactive," the original of which has topped Alternative Songs for seven weeks and this week bounds 15-7 on the Hot 100. The reworked "Radioactive" has garnered 775,000 YouTube views, while Pentatonix's official YouTube channel has drawn an astounding 63 million views.

Pentatonix wraps its current headlining tour on May 11 in Seattle. It's preparing its second album, expected later this year.