Renee McMahonWatch a slideshow of Sunday at Bumbershoot, featuring Sera Cahoone, Common Market, Vivian Girls, and the Yeah Yeah Yeahs.Who: Sera CahooneWhere: Starbucks StageWhen: 5 p.m.One of the best things about Sera Cahoone is that even though she’s technically a solo artist, she plays like a member of the band–not as if she’s the band all by herself. This also means she writes music that is strong enough to carry sound past the edge of the stage and into the hundreds of crowd members. (The Old 97s had trouble doing this Saturday night; they play a similar kind of country-tinged rock, and their songs sounded hollow and sparse in the wide-open Memorial Stadium.) Even when Cahoone played the lilting, quiet “Couch Song”–which she prefaced by telling the audience she was “going to mellow it way out for you guys”–it sounded like a country symphony.