Reunited grunge band join Bruce Springsteen and Paul Simon in headlining London festival
Singer will follow Soundgarden's European run with four solo shows
Singer covers Led Zeppelin and John Lennon on forthcoming LP
Frontman says he wishes he'd stuck with piano lessons at an early age
Kim Thayil says band want new songs to 'excite them'
Singer chats about progress of band's first studio album in 15 years
Reformed US band are working on first studio album in 15 years
Reunited grunge band ready to hit the studio
'Live on l5' is out on March 21
Guitarist Kim Thayil says band have been working on new material