Leave your formalwear in the closet and your evening gloves in the box. If you’re planning to see the National Symphony Orchestra this week, you can do so in an atmosphere much more casual than the Kennedy Center’s Concert Hall. For its fifth annual “NSO In Your Neighborhood” series, small groups of orchestra members will perform at venues throughout Penn Quarter and downtown. On most evenings, the area empties out by 6:30 p.m., when all the office workers head home, but organizers hope concerts at nearby venues like Woolly Mammoth Theatre Company, Sixth & I Historic Synagogue, and the Smithsonian American Art Museum will persuade curious listeners to stick around for an extra hour. For its kickoff at The Hamilton, violinists, violists, cellists, and bassists will join percussionists for a lively introduction to chamber music. These community-based performances often feature surprise collaborators, so shake off that stiff orchestra posture and enjoy the cozier setting. The National Symphony Orchestra performs at 8 p.m. at The Hamilton, 600 14th St. NW. Free. (202) 787-1000. thehamiltondc.com.