With their frontman’s unending smile and feel-good hits like “Two Princes,” it seemed the good times would never end for roots-rock band The Spin Doctors. Then, as they used to say on “Behind the Music,” things took a turn. Lead singer Chris Barron was diagnosed with vocal paralysis, and doctors said he might never sing again. But Barron would beat the odds and begin playing again after a strict diet coupled with physical therapy. The struggle left him with a solo career and a compelling narrative arc that attracts calendar editors. The smiling starts Saturday, Dec. 8, at 9 p.m. at Capital Ale House. $8-$10. 780-ALES. S