We must be going insane, because this surely terrible idea in theory is actually pretty impressive in execution. At a recent show at San Diego’s Balboa Theatre, Chris Cornell sang an acoustic version of Metallica’s metal classic “One,” but it wasn’t just any ol’ stripped-down rendition. The Soundgarden singer took it a step further, offering up James Hetfield’s lyrics but setting them to the music and style of U2’s own song of the same name. Cornell’s new favorite equation: “One” plus “One” equals awesome. Or think of it as “One cover 2 rule them all. Hopefully Cornell will bust this one out when he comes to the Citi Performing Arts Center Shubert Theatre in Boston on Friday, November 15, as part of his ongoing solo acoustic tour that touches on his entire career — and according to this recording, some added treats. Tickets are still available.