Indie rock’s most incorrigibly happy band may have finally found something to frown about. When the 20-plus-member rock orchestra and choir the Polyphonic Spree invades the Manhattan Center’s Grand Ballroom on Friday, gone will be the members’ trademark flowing gospel robes and the band’s defiantly upbeat musical sunshine, which owes as much to “Jesus Christ Superstar” and “The Electric Company” as it does to ELO, Wings, and the Beach Boys. In their place will be new uniforms — Chinese Cultural Revolution-like plain black work suits and a sound no less symphonic but decidedly less saccharine.

An eight-minute mash-up teaser of the band’s latest album, “The Fragile Army,” due June 19, reveals a band possibly embracing the underbelly and cracks in its perpetual glee. If so, it’s exactly what the Polyphonic Spree needs to do right now.

The band’s story is one of emotional necessity. When the Spree made its debut in 2000, its ecstatic, almost childlike music was in part shaped by tragedy. The Dallas-based band was formed around the core group of vocalist-songwriter Tim DeLaughter, bassist Mark Pirro, and drummer Bryan Wakeland. The three were previously in the Dallas rock outfit Tripping Daisy, which scored a minor alternative-radio and MTV hit in 1995’s “I Got a Girl.” Tripping Daisy was effectively disbanded when guitarist Wes Berggren died in October 1999 from a drug overdose.

As the surviving trio laid low in Dallas for the ensuing winter, song ideas coursed through the Mr. De-Laughter’s head. Nothing definitive, merely melodies and sounds that needed a number of different instruments — cello, French horn, flugelhorn, flute, harp, organ, piano, trombone, violin — and many voices. So he started recruiting people who played those instruments to improvise around his ideas. In July 2000, an opening spot for Granddaddy opened in Dallas, and a 13-member outfit called the Beginning Stages of the Polyphonic Spree made its first public appearance.

The group soon swelled to 24 members and recorded demos in the fall of 2000. Those demos became the Spree’s 2003 debut, “The Beginning Stages of …,” whose 10 songs — dubbed “sections” — were best experienced as a single piece of symphonic happiness. The album opens with a ruminative piano, cello, violin, and flute quartet that slowly builds to a tidal wave of melody as more instruments enter the tune. Mr. DeLaughter swims into the melody with the easygoing first line, “Have a day, celebrate, soon you’ll find the answer,” and soon what sounds like a church-full of voices has joined him in singing these defiantly optimistic, almost reverential lines.

“The Beginning Stages Of …,” along with the band’s storied appearances at 2002’s South by Southwest festival, established the Spree’s cultish reputation. And the word “cult” was often taken at face value. Dallas is only 90 minutes up Interstate 35 from where David Koresh based his Branch Davidians in Waco, where Robert Tilton built his Word of Faith Family Church, and was ground zero for the subculture known as Church of the SubGenius in the 1980s and ’90s. The very of idea of 25 smiling, robed young people touring together in a bus and creating wildly euphoric music sounds suspiciously like a cult on paper.

Journalists and fans never really took the “cult” tag too seriously, but through three years of steady touring, the band’s perpetual cheeriness did start to feel forced and insincere. By the time the band’s 2004 sophomore effort, “Together We’re Heavy,” emerged, stagnation had settled in. Despite being a much better recorded, produced, and arranged album than the debut, “Together We’re Heavy” felt like treading water. The individual songs — still called sections — were stronger, thanks to Mr. DeLaughter’s realization that he didn’t have to use every instrument on every song. And the lack of instrumental clutter created better dynamics, making the highs and lows land with greater impact — especially on gems like “Hold Me Now” and “Two Thousand Places.”

The Spree’s biggest problem was that the world wasn’t the same as it was when “The Beginning Stages” was recorded in 2000. Only the pharmaceutically maintained and delusional can hold a bulletproof smile in the face of anything. The big albums of 2004 — Kanye West’s “The College Dropout,” Green Day’s “American Idiot,” Modest Mouse’s “Good News for People Who Love Bad News,” Arcade Fire’s “Funeral” — were disgruntled and anxious, at odds with the Spree’s devotion to the sunny side of the street.

That started to change with the 2006 EP “Wait,” a five-song teaser of the group’s new direction. The music is still larger than life and overwhelming, but Mr. DeLaughter and company have finally turned to exploring more than just unencumbered joy. The band turns in a riotous, noisy cover of Nirvana’s angry, anti-social anthem “Lithiuml”; on “I’m Calling,” the Spree turns its considerable power to something modestly bittersweet and even conflicted, with Mr. DeLaughter admitting, “Today my heart is like an empty room,” before conceding that “If I can’t stop this feeling, now, that’s alright.”

Nothing on “Wait” is going to be mistaken for nü-metal angst or hardcore doom, but even the slightest diversion from the Spree’s usual up-with-everything norm makes the band feel all the more approachably human. And that’s exactly how it sounds on the anarchic, blaring, and busy mash-up teaser of the new album. Granted, it’s impossible to get an accurate read from eight minutes of stitched-together musical snippets, but it sounds as if Mr. DeLaughter and the Spree have looked around at the world and realized that it’s very, very hard to be overwhelmingly positive, a confession the band desperately needed to make if it ever hoped to feel pertinent again. Don’t expect something as opportunistic as a political protest album from “The Fragile Army,” but as the band’s costume change suggests, sometime you have to do hard work before you can let loose and celebrate today.

The Polyphonic Spree will perform Friday at the Manhattan Center’s Grand Ballroom (311 W. 34th St., between Eighth and Ninth avenues).