The San Francisco Art Institute Lecture Hall, up a steep, tree-lined and particularly Hitchcockian street in North Beach, has become a sound-art nexus in a city with more than its fair share of sound-art nexuses (nexi? nexes? nexum?). In the past year or so there, academic Douglas Khan (author of the superb Noise, Water, Meat) has talked about how radio was “discovered” before it was “invented”; artist Steve Roden has limned the commonality between his fragile music and his visual art; filmmaker Walter Murch (The Conversation) has talked about the craft of sound editing. M.C. Schmidt, of the duo Matmos, who is manager of the New Genres Department at SFAI, recently started hosting Thursday-night music events at the institute (among the guests: William Fowler Collins, Bevin Blectum and Thomas Dimuzio), and Saturday he took his series into the lecture hall for a sedate, hour-long set by fragile-sound experts Coelacanth, a collaboration between Loren Chasse and Jim Haynes, their slow-burn and anti-audiophilic noise given a fitting visual complement courtesy of filmmaker Keith Evans. Evans’ images of wiggling paramecium, of bent light and of nature in raw decline gave substance to the remote, intensely delicate sounds produced by Chasse and Haynes, who crouched in the near dark on stage as they performed. Their self-described mission: “operating the tools of an imagined science to explore the various possibilities for sound to originate from traditionally non-musical materials.” If you didn’t make the concert, there are MP3s from all three of Coelacanth’s records up at helenscarsdale.com, the web home of their record label (two each from The Chronograph, 2001; The Glass Sponge, 2003; and Mud Wall, 2004). Evans’ visuals don’t come along with the files. But if you close your eyes, the essence of decay will arrive in its own good time.