Boyz II Men co-founder Wanya Morris took a tour of the Chelsea at the Cosmopolitan last week. He liked the room’s vibe. Or, more specifically, its vibrations.

“It’s a wonderful stage, it’s beautiful, and almost interactive to a certain degree,” Morris, a Las Vegas resident for nearly a decade, says during a phone chat. “There are some sort of hydraulics under the stage. When people dance, the stage actually moves and the floor moves.

It’s crazy. I have never seen anything like that inside a theater.” The Chelsea itself will help push-start the party when Boyz II Men play the venue Friday, Saturday and continuing Aug.

30-31. Among the predominant R&B groups of the all time, the original roster of Morris, Shawn Stockman, Nate Morris and Michael McCary brought the “Motownphilly” sound to the fore. The term referred to the guys’ Philadelphia roots.

More than 30 years after scoring their first No. 1 single, Boyz II Men’s chart success remains impressive. Their 1992 hit, “End of the Road” was No.

1 for 13 seeks and was the top Billboard single for the entire year. “I’ll Make Love to You” was at the top for 14 weeks, and “One Sweet Day” (a collaboration with Mariah Carey) followed by spending 16 weeks atop the charts. “On Bended Knee” took the top spot from “I’ll Make Love to You,” as Boyz II Men was the third act ever to replace its own No.

1 Billboard hit. In today’s Las Vegas, R&B “legacy” acts are burning up the stage and box.