Chris KornelisThe xx vocalist/guitarist Romy Madley Croft signs autographs after the band’s set at Sonic Boom on Friday, November 27.When a hyper buzzed about underage band called The Arctic Monkeys came through the old Croc in March of 2006 in support of their breakthrough, Whatever People Say I Am, That’s What I’m Not, lead singer Alex Turner held himself up with his mic stand and practically sleep walked through the band’s set. After the tour they lost bassist Andy Nicholson to fatigue. He never returned.The next night, The Subways, another British buzz band whose members were not yet old enough to buy a drink in town, started their evening at Sonic Boom, banged out a few cuts from their debut, Young For Eternity, and signed some autographs. Well, two of the three did. Weary drummer Josh Morgan wandered onto the streets of Ballard and left his bandmates wondering. I ran into Morgan before the show. To this day I’ve never seen anyone so exhausted. The band had to postpone their spring tour that year thanks to nodules on vocalist Billy Lunn’s vocal chords.When The xx — a trio of 20 year olds from London — took the stage for a free in-store performance at Sonic Boom this afternoon, the tour had already cost the band one founding member, Baria Qureshi. But there the three remaining soldiers were, playing cuts off the incessantly talked about self-titled debut.They sounded strong. Bassist (in instrument and vocal range) Oliver Sim wasn’t as clear as he is on record, but he was more expressive. His untrained vocals will be a force in years to come. The same can be said for the rest of the band if they keep on keeping on. What was most impressive about the set wasn’t the half dozen or so songs they played to a crowd that spilled out the door. It was the grins after the set, it was the band signing autographs, posing for pictures, and Sim empathizing with an underage fan who wouldn’t be able to make tonight’s show at Neumos. Sim can relate. They’re only letting him through the doors because he’s working.