U2's Bono admits the sound of their 'U2:UV Achtung Baby Live At Sphere’ show in Las Vegas wasn't "rock 'n' roll" enough to start with.

The Irish rockers have been having to drive their sound harder to get the distortion they are used to during their residency at the state-of-the-art, multi-billion-dollar immersive MSG Sphere at the Venetian, which sees gig-goers placed in a "360-degree sonic spectrum" where the sound is the same wherever they are sitting.

Speaking to MOJO magazine, the frontman said: "We didn't know if the building was going to work.

"There were engineers and builders and plasterers and people wiring stuff up right up to the very last minute.

"The first night was not as rock'n'roll as it needed to be.

"I mean, I'm relieved that the sound is as great as everyone says, but distortion is part of the language of rock'n'roll. You do need to drive the system a little hard. So we got that the second night. We got a bit more rock'n'roll, but there's more to go."

U2 have been performing their 1991 album ‘Achtung Baby’ in full alongside some fan-favourites at the high-tech venue.

The 'With or Without You' hitmakers recently surprised fans by bringing out Lady Gaga to duet on her mega-hit 'Shallow'.

The 37-year-old pop superstar had checked out the legendary Irish rock group's show at the Sphere with her boyfriend Michael Polansky.

And she returned weeks later, this time duetting with Bono and The Edge on her 2018 hit from her blockbuster movie 'A Star Is Born'.

The Grammy winner previously duetted with U2 on 'Ordinary Love' during the band's 'iNNOCENCE + eXPERIENCE' tour at Madison Square Garden in 2015.