SOMERVILLE, Mass. — On a rainy Saturday night here more than 100 revelers jigged to “The Smash-a-Bank Polka.” They chanted “Rise up! Get down!” and stomped their feet. Three members of a brass band used a homemade concoction of duct tape and rubber cement to set the ends of their trumpets on fire, then kept playing. Everyone cheered and sang. “Here’s to the bands in the streets!” they belted out, fists pumping in time with the drums. It was hard to tell where the politics ended and the party began at the Honk! festival of activist street bands, which ran for five days, starting on Thursday, in this Boston suburb.

Thirty-five ensembles — more than 670 performers in all — converged at this year’s event, a mix of grass-roots politics, homespun fun and punk edge. Most came from the United States and Canada, and more than 200 out-of-towners were billeted in volunteers’ homes. One group, the Pink Puffers, flew in from Rome and planned to stay in the Northeast for two spinoff festivals: Pronk! on Monday in Providence, R.I., and Honk NYC!, a four-night affair with less of a political bent that kicks off on Tuesday in Brooklyn.

For all the outward-facing spectacle, many of the musicians said they were most excited about seeing one another during what has become a conclave for brass bands marching to an alternative beat. Many groups share a do-it-yourself ethos and have formed in the past decade, when new nontraditional marching bands cropped up in New York City; San Francisco; Pittsburgh; Boulder, Colo.; Madison, Wis.; Greensboro, N.C.; Los Alamos, N.M.; and elsewhere. Knit together by Honk!, they now form a network that reaches overseas.

“It’s kind of a band jamboree, something we all look forward to,” said Matt Arnold, 39, a sousaphone player in the Rude Mechanical Orchestra, whose fists-up anthems fueled the impromptu dance party on Saturday. This marching band coalesced eight years ago protesting the Republican National Convention in New York. It has since played every Honk! festival, taking a break from an otherwise crowded schedule of picket lines, antiwar protests and, starting last year, Occupy Wall Street rallies.