Mary Bichner leads her band, Box Five, in a show last year at the Cloud Club in Boston’s South End. Box Five performs Sunday at Club Passim in Cambridge with Jaggery and Ginger Ibex. (Photo: Prehensile Eye)

Sunday is a good day for the merging of musical forms. It starts with a free pops concert and wraps up with a trio of bands that fuse rock with symphonic instruments. The mélange of musical styles have even forced the bands to come up with their own terms for what they do — “darkwave jazz” is a suggestion by Jaggery and “classipop” by Box Five.

First, though, is a staple of summer: a free outdoors pops concert by the Cambridge Symphony Orchestra. The orchestra, a 35-year old body of 70 volunteer musicians from around the city, performs at 3 p.m. at the park at Norfolk and Broadway in Cambridge. The selections include space-themed movie music, marches by John Philip Sousa and “The Little Girl with The Tree Branch” by Harold Farberman, narrated by WGBH’s Brian Bell. The rain site would be Area IV Youth Center, which is next to the park.

Five hours later the experimentation begins.

The Passim show includes Box Five, led by Philadelphia’s Mary Bichner, who says her music is all about “combining Mozart-inspired chord progressions and bratty Brit-rock hooks into a musical succotash.”

Her website biography explains a bit why combining these things would make perfect sense to Bichner:

Mary also possesses perfect pitch (the ability to recognize notes and chords by name simply by hearing them played), and synesthesia (a bizarre neurological condition which causes Mary to “see” splashes of specific colors when she hears certain pitches sounded).

But it doesn’t take synesthesia to combine classical instruments with rock, which may — combined with a tendency toward performance art and the inclusion of burlesque and cabaret elements — be the closest the area comes to having a “sound” or common theme. (Unless it’s the same “sound” being heard in musical scenes around the country.)

Jaggery, an experimental art-rock collective led by Mali Sastri, is keyboard driven and regularly incorporates harp, upright bass and viola. The version of the band taking the stage Sunday is a trio, like Ginger Ibex — a Cambridge band of piano, drums and six-string mezzo viola. The band’s bio:

One of Sharon Crumrine’s earliest influences was Beethoven, whose music alternately rocks the world or moves listeners to tears with its dark lyrical beauty. She was also deeply affected by the Romantic Classical composers (Schubert, Rachmaninoff), Impressionistic composers, Middle Eastern modes, tango and contemporary rock. Betty Widerski’s radically eclectic background (Classical gone Irish punk/rock/improv) and endless creative and technical ability on a wild variety of stringed instruments, plus some percussion added to the mix, gives Ginger Ibex a powerful yet lyrical sound that is truly unique.