Last week, the first heat of six took to the mics as they belted out hits from the 60s and today. Kinfolk 9 ended up getting the boot. One more team will join them as we continue toward $200,000 and a Sony Music contract.

But before we get into battle, let's feel the "Rhythm of Love" (Plain White T's) with tonight's six...

- The Collective; Nashville
- The Dartmouth Aires; Dartmouth College; Hanover, NH
- The Deltones; University of Delaware; Newark, DE
- North Shore; Boston
- Pentatonix; Arlington, TX
- Sonos; Los Angeles

First up...

7) DELTONES - They are "Friends first, singers second." That explains why they changed arrangements so much in the last two weeks. Will they find a winning combination to start the show off proper? The opening number in competitive play... "Edge of Glory" by Lady Gaga.

Well, when in doubt, stick with what's written. That's what this group does, as they sacrifice the "moment" for safety. The good: they are solid on the harmonies, and the soloist is pitch perfect. But there was a LOT that could've been done with that song to make it stand out from the original. As for the power level, if only the group vocal could match the intensity of the group choreo (which wasn't that good to begin with, but what the hell). Props to Lou for holding onto the drumbeat as long as he did. But overall, small step backwards.

8) PENTATONIX - They plan on doing "crazy things with their voices" this week, going from a basic Katy Perry last round to remixing Ke$ha's "Your Love Is My Drug".

My favorite song by Honor Society: "Here Comes Treble Again". Way too much top, and not enough bottom. The singers need some support. And when they don't have support... they end up pulling that remix stunt. Are we going to remember the tightness of the group? No, we're going to remember THAT, starting a little squirrelly with a cut-rate Blake Lewis impersonation, but bringing it together at the end.

9) THE COLLECTIVE - Last week, the 'net had them at the bottom of the power ranking, as the pro musicians made their obvious a cappella debut. Do they tighten it up tonight or stay on the course of mediocrity? They're going from the hot tub to the stage with "Rocketeer" by Far East Movement featuring Ryan Tedder. Can they pull it off with one member playing wounded (acute laryngitis).

Infinitely better. Although, and I'm speaking from 23 years as a vocalist, if you are playing wounded, and you are given the opportunity to fall back and recuperate while someone else takes the mic, you do so. I say this because of the solos, Rachael's (the one who saw the doc) was far and away the weakest. But we're starting to see a semblance of a group dynamic, and that is always a good thing. The arrangement was solid, the harmonies blended into each other, and the tones mixed into the timbre of the song.

10) NORTH SHORE - The doo-wop kings of the season are going to take a brave step out of their comfort zone. All they have to do is find a song that they can adapt their own brand to. Hard to do if you don't listen to the radio anymore. But they find their niche in... "The Lazy Song" by Bruno Mars.

Perfect song choice. The arrangement needed work. And you haven't seen performance until you've seen a bald guy in a La-Z-Boy doing the dougie. JUST SAYING. Anyway, they own the performance, and that's important.

11) DARTMOUTH AIRES - They established themselves as early favorites last week with "Higher Ground", but Michael's heart is elsewhere... with his sick mom. He's back in it, but will they win it with "Animal" by Neon Trees, a song that one member wasn't AT ALL familiar with before this week?

Again with the crazy college antics on the stage. They fit the song perfectly. As for the vocal, the dynamics are on point, the arrangement works, and everyone contributes their fair share. Picked up where they left off last round. Not bad when you consider they crammed for this performance.

12) SONOS - The tech-driven LA quintet has ditched the pitch pedals for a more natural sound, which exposed their weaknesses. Can they stomp them like they stomp the pedals, or will we hear the last of them after "Viva La Vida" by Coldplay? A natural bass is singing the solo. I'm afraid.

... the bass should've held the song together while a higher voice sang the lead. Shawn is right on, it was crazy "tinny", to the point of almost gratingly high.

Time to fire up the WABAC machine again. Destination: 1960s.

8) PENTATONIX - "Piece of My Heart" by Janis Joplin

Simple song sung simply, and made current by the group in the mixed-up arrangement, making up for the complete CF of the last round. And nice goof on the flugelhorn as well. You're back in the hunt with this. Now build off of it.

7) DELTONES - "You Can't Hurry Love" by the Supremes

Classic choreography, and a smart move to let the girls take this one. Among the best of the night thanks to spot-on performance and arrangement. I would've picked a better "copout ending" and watched the pitch, but I was feeling the performance with that.

9) NORTH SHORE - "Unchained Melody" by the Righteous Brothers

You almost want to call shenanigans since this is the only group that can REMEMBER the 60s. But they kill it.

10) THE COLLECTIVE - "Hold On I'm Coming" by Sam & Dave

Perfect example of a breakdown that works. But it falls apart by the end. Get lost in the performance, but don't lose yourself in the performance. Take it to the people, but keep some for yourself. Points to Kaleb for going into the false and pretty much taking us to church. And also... there's a rule when you're dealing with a minute and change for a performance... "Kill the damn dog already." But a nice step up from last round.

12) SONOS - "I Want You Back" by the Jackson 5ive

This group takes a normally upbeat song and goes to a dark, shadowy almost Gordon Pepper-like bizarro world. Inventive arrangement, but is it a little too much too soon? ... YES. You needed a goof on the original SOMEWHERE.

11) DARTMOUTH AIRES - "Pinball Wizard" by the Who

Sonos, take notes. That was a goof, complete with a goof on a pinball table. Of course, it helps matters that it's a classic song for a classic outfit. And Tar Heel Voices called, they want their arrangement back.

These six groups gave all that they had. But for one group, it will not be enough. Performance time is over... Decision time is now.

On the set list for NEXT week... North Shore... and the Dartmouth Aires! Joining them... Pentatonix and the Deltones!

This week's bottom two: The Collective and Sonos.

This week... we'll hear the swan song from... SONOS. Said song, in a bow to judge Shawn... It's Boyz II Men's "It's So Hard to Say Goodbye to Yesterday". And of course, Shawn can't watch.

GO GO POWER RANKINGS!

Power Rankings after Week Four (including ALL groups)
NORTH SHORE
DELILAH
DARTMOUTH AIRES
URBAN METHOD
AFRO-BLUE
DELTONES
THE COLLECTIVE
PENTATONIX
YELLOWJACKETS
VOCAL POINT

Next week, the last ten standing will sing as one as we move one step closer to a title. Big thanks to Joe Mello for his assistance in writing this recap. Signing off from the Sing-Off, it's Achordant #5 reminding you to support local and independent music!

To see this episode in its entirety, visit www.nbc.com/singoff.