Have you heard the one about the composer/sound theorist who teamed up with a slow-motion metal guitarist? There you go, looking for punchlines involving the two of them walking into a bar. But there’s no such funny business on Cylene II, the latest recording by François J. Bonnet, who’s the director of the French National Audiovisual Institute and records ambient music under the name Kassel Jaeger, and Stephen O’Malley, who dons the robes in Sunn O))). It sounds seriously heavy but also quite distinct from the electro-acoustic environments and congealed rock music that its makers have devised in other settings.