Metallica‘s Lars Ulrich has revealed that Lou Reed found the criticism of their ‘Lulu’ collaboration “difficult” to take.

Veteran rocker Reed teamed up with the metal legends to release the album, which is based around German dramatist Frank Wedekind’s 1913 play about the life of an abused dancer, in October last year. He later claimed that Metallica fans had threatened to shoot him because they had been so unhappy about the LP.

Ulrich, talking to the US radio station DC101, said that Reed had taken the criticism very personally and had been surprised at the negative reaction to the album.

“Obviously, it’s fantastic in 2012 that the internet gives everybody access to voicing their opinions, and I think it’s an incredible medium to communicate and to bring the world closer,” he said. “But obviously, as an artist, or somebody who is creating something, you’ve gotta be careful how deep you dive into what everybody’s talking about, because it could really screw with your mind. I’ve always been in a place where I’m pretty thick-skinned, so it doesn’t bug me that much.”

He then went on to add: “It was difficult for Lou Reed because he takes everything very personally. And I think he was very surprised. We told him all along: ‘Listen, there are some very, very, very hardcore metal fans out there that like everything pre-packaged in a particular little box that looks like this, and the minute that you slightly veer outside of that, then they have a hernia.’ And that’s fine – I’m fine with that…”

Metallica will play a headline slot at this summer’s Download Festival as well as a series of other large European shows, performing ‘The Black Album’ in its entirety, and are also said to be working on a new studio LP.