Ambient alt-rockers Eroica hosted a CD release event at afterHOURS Thursday, without the CDs.

The band, comprised of Northeastern students Ben Gram, Ben Hoffman and Zivi Krieger , faced complications with shipping their 6-song EP, Hisen the Architect, to bassist Krieger’s house. Gram, a junior music major, said he was not discouraged by the lack of CDs.

“CD release without CDs?” he said. “What can you do? You can’t let it get to you.”

The evening’s main draw was a dramatic performance by Eroica. Band members took the stage to the sound of classical music, which they soon incorporated into their more standard rock. They maintained a serious demeanor during fun upbeat jams, then moved into a slower lullaby of a song. Middler chemistry and philosophy major Roberto Barberena Pelaez briefly took the stage to perform with the band on tenor saxophone.

Guitarist Gram explained Eroica’s lack of a vocalist.

“If there’s no lyrics, it can mean whatever you want it to mean,” he said. “It has infinite meanings.”

Gram, who often climbed atop the amplifier before jumping through the air with his guitar, was illuminated by a green light throughout the performance. When the lights went out, Eroica left the stage only to be beckoned by chants of “Eroica! Eroica!” before returning for an encore.

The four-hour show also featured performances by ambient-rock band Plastic Reverie, San Francisco progressive rockers We Be the Echo and experimental ambient band Irepress. About 110 students attended the event.

The evening’s first performance came from Plastic Reverie, the only band with a vocalist. Its set included “Crooked Spine,” the title track from their debut EP to be released June 25 at Bill’s Bar, “Only For You” and other displays of the band’s eclectic catalogue. Vocalist Marc Pellegrino, a junior music industry major, paid homage to the evening’s headliners between songs.

“This is a night to be celebrating Eroica and an absolutely bitching album,” he said.

Plastic Reverie, comprised of Pellegrino, junior music industry majors Tom Klodenski and Sean McDermott and senior music industry majo Chip Homer, has performed previously with Eroica, including at last fall’s Halloween show at afterHOURS. Bassist Klodenski said they are “good friends” with Eroica band members.

“We’re at the point where we both have our own albums. We have something to market now,” he said. “It’s good to see progress.”

We Be the Echo signaled the beginning of their performance with a megaphone siren. Bassist Myke Tokarz, who performs as Myke Stryker, proceeded to use the megaphone to communicate with the audience.

“It will be our pleasure to rock here tonight,” he said.

The instrumental band swept through four songs, featuring moments of heavy shredding, throbbing bass and dainty guitar riffs. Guitarist Graeme Nicholls gave an anthemic twist to Madonna’s “Like A Virgin” and the theme song from “Indiana Jones.”

We Be the Echo, named after words band members saw on a gravestone, formed after band members Tokarz, Nicholls and drummer Ilk Koskelo played together at an improvisation collective in San Francisco.

“I think we all come from different backgrounds,” Tokarz said. “Where we kind of cross over is that punk-metal type sound.”

Synthesizer player Jarrett Ring , of Irepress, said the band’s name reflects the “emotional release” of its music.

“It’s the opposite of repressing. Instead of keeping something pent in, you let it out,” he said.

Irepress’ performance featured a fusion of ambient, dance, rock and funk styles. During one song, the tapping of the cymbal shimmered over the crashing and soaring of the guitars. Students and band members alike head banged to the set’s heavier segments, and one of the more melodic songs featured a brief clap-along.

Irepress, comprised of Ring, bassist Shan Dav’eacute; , drummer Sheel Dav’eacute;, guitarist Bret Silverberg and guitarist Jon Dinapoli, are touring the East Coast and will return to Boston to perform at Bill’s Bar July 12.

Middler history major Kathleen Pendleton said her favorite part of the evening was Eroica’s performance.

“They just have a lot of energy,” she said. “They’re really fun.”

Senior theatre major Angelica Sirabella said she attended the show to see Plastic Reverie and Eroica.

“They were flipping awesome. I’m incredibly impressed,” she said. “It was the first Eroica show I’ve seen. I was not expecting that music to come out of those boys.”