Burbly vintage synth sounds, repeated arpeggios straight out of mid-period Reich/Glass high minimalism, trippy light show, mellow vocals, closed-eyed audience members…for one night, TBA's late-night social hub The Works turned into That '70s Show when singer/composer/keyboardist Nick Hallett presented his multimedia Rainbow Passage. Only the incense and soft cushions were missing.

The gloopy atmosphere shrouded Rainbow Passage's underlying inspiration: "a popular diagnostic text by speech scientist Grant Fairbanks, containing every sound of the English language." At a workshop last week, Hallett led a dozen amateur singers in a section of his TBA piece, explaining his influences: a famous essay by cultural studies maven Roland Barthes, linguist Noam Chomsky, composer John Cage. He said he aims to express meaning via "paralanguage," using tone of voice and other nonverbal means rather than words' literal meaning. Hallett's goal in such "songs without words" is to liberate singers from relying on language to convey feelings and ideas, without requiring them to discard words altogether. The sounds in the "Cumulus" section, for example, came from the vowels in a passage about the physics of rainbows; listeners would never know that, but it makes a useful seed, like an artist who scrawls a hidden text that's then obscured by paint or another art form. Last night, Hallett left some room for improvisation, and the performers responded to each other with admirable sensitivity.

In fact, what really made this performance work were the collaborations: That psychedelic video and light installation came courtesy of Brock Monroe and complemented the music so smoothly I wished it'd been present for the whole show instead of just parts of it. Golden Retriever's Matt Carlson and Jonathan Sielaff contributed additional electronic layers and deep waves via that staple of avant-garde improv music, the bass clarinet. Portland's superb indie classical female vocal ensemble, the Julians, added their characteristically pristine siren vocals, avoiding overindulgence in Romantic vibrato in favor of a cleaner, early music approach. TBA favorite Holcombe Waller sang front and center for one segment. And Holland Andrews, from the evening's following act, Like a Villain, added her own voice and clarinet to a "duet" with Sielaff that might have been the show's highlight. The result was a warm bath of soothing sound and light.

Edge-seekers might have felt insufficiently stimulated, but for others so inclined, after a hectic weekend of scurrying around TBA, a soothing, late-night sonic soak seemed just the ticket, reminiscent of yet another '70s staple: the hot tub.