A performance by Improvox may be wild or reverent, quirky or soulful, but never the same twice. Spinning music on the spot singers Kathy Slack, Martin Swinger, Matt Loosigian, Fred White and Deb Hensley on Sunday, April 11, will present a cappella music — from Bobby McFerrin’s soulful version of “The 23rd Psalm, to a spunky presentation of “Old Blue.” Audience members may be invited (never required) to offer melodic ideas, word prompts and even their own voices to help create music on-stage or off. Tickets to the 5 p.m. concert at Nordica Auditorium on the University of Maine at Farmington campus are $6 for adults, $5 for seniors; free for children under 16. No advance tickets. For more information, call 778-3722.