Once a year every year for the past two decades, brah-rock institution Dave Matthews has ditched his backing band for a couple weeks in favor of getting his acoustic thing on with Tim Reynolds, the fellow guitarist who convinced him to start his first band. This year is no different. What is different about Matthews and Reynolds’ two-night billy-flippin’ stint at McCaw Hall is where the money ends up: anywhere you want. In a unique partnership with charity clearinghouse JustGive.org, the duo are rewarding ticket-purchasers with $150 to shower on the do-gooders of their choosing. After the last chord is plucked and the final marching ant noted, JustGive expects to clear a cool million. Which should give you the requisite cover — “Hey, it’s for charity” — needed in case you feel guilty about dropping three-figures on a guy who just named his last album Big Whiskey and the GrooGrux King. CALEB HANNAN

Mon., Dec. 6, 7:30 p.m.; Tue., Dec. 7, 7:30 p.m., 2010