The idea of a group of classically trained musicians not playing strictly classical music is an old one. Yet it’s still one that’s trotted out as a selling point because, it seems, the classical world still isn’t sold on “new” ideas (even though, you know, it is). But in the age of mash-ups and the free-flowing eclecticism forged by the Internet, a string quartet such as Ethel follows a natural path in exploring its catholic repertoire. Like Bang on a Can, Ethel mixes the avant-garde and world music, improvisation and composition, and pop and folk to create almost mixtape-like albums and concerts. The New York City group sometimes toys with electronics, too, augmenting its supple string serenades with reverb, distortion, and other elements from contemporary music. Because really, that’s all Ethel is playing: modern-day music, free of restrictions, rules, or genres. Ethel performs at 7:30 p.m. at Atlas Performing Arts Center, 1333 H St. NE. $25. (Christopher Porter)

MUSIC

Dancey Long Island dream-poppers Twin Sister —-whose take on slick, slightly chilled disco is not at all grating—-headline at Rock & Roll Hotel with Ava Luna and prolific locals Bike Trip. $12. 8:30 p.m.

Local pan-Latin lounge dudes Empresarios perform for free at the Kennedy Center’s Millenium Stage. 6 p.m.

FILM

The Film|Neu festival continues: Joschka & Mrs. Fischer at 6:30 p.m. and If Not Us, Who at 9 p.m. at E Street Cinema.