On the irresistible Polaris, the Allstars diversify the driving, bluesy attack of their previous two albums. Fronted by Luther Dickinson, this freewheeling quartet brings the spontaneity of a jam session to its soulful tunes, with feel-good results. Dickinson is a deft yet unpretentious guitarist who evokes the sweet slide licks of Duane Allman on “Eyes” and channels Jerry Garcia’s spacey elegance in the country-blues delight “The One Thing.” The Allstars ignore boundaries, blithely shifting styles; the hybrid of psychedelia and hip hop on “Be So Glad” could easily seem contrived, but Dickinson and company make sure every note sounds genuine.