A lack of rap for a second straight year on the Projekt Revolution tour is circumstantial, according to Linkin Park's Mike Shinoda.

During a teleconference with reporters today (April 9), Shinoda said that in booking this year's tour, Linkin Park "didn't find the right rap groups to put on the show. There weren't many that we felt would mix well with everything. For this one, it's pretty much an all-rock bill ... but this is a really diverse bill as far as rock."

Shinoda said that rap is "not gone forever" from Projekt Revolution, and that "in the future we'll have more hip-hop artists back on the bill."

Besides headliner Linkin Park, this year's Projekt Revolution -- which kicks off a North American run July 16 in Boston after a one-off on June 29 in England -- features Chris Cornell, the Bravery, Ashes Divide and Armor For Sleep on the main stage and Atreyu, Hawthorne Heights, 10 Years and Street Drum Corps on the second, Revolution Stage.

Shinoda said there was interest in major hip-hop acts such as Kanye West, Lupe Fiasco and Gnarls Barkley but that "these groups were out on the road doing their own thing ... with other commitments going. I think if there had been a place for these guys to be on the tour, it would've worked out."

The British show, meanwhile, features Jay-Z and N*E*R*D.

Cornell and the Bravery's Sam Endicott, who were also on the call, joked about forming a "sub group" of different Projekt Revolution band members to bust rhymes during the days. Shinoda, meanwhile, asked Cornell if Timbaland, who's working with the former Soundgarden/Audioslave singer on his next solo album, might show up as a surprise guest at some point.

"I hope so," Cornell responded. "You never know."

While not giving away too many details about the new project, Cornell did say that he would "try to work in ... probably two or three new songs." He also said he's probably have a new single out by the time the tour starts but that at this point he's not sure what that will be. The album, he added, "will not be ready for release during the summer."