The "sonambient" works are recordings made from his sound-emitting sculptures.
They're really cool-looking objects in and of themselves, the records, and the music can veer from largely silent to clanging and loud. I own three of them, myself, and am not sure I personally need all of them, but they sure are nifty. The records' value has ebbed and flowed over the years, partly because sealed copies keep being magically found, but whatever. A complete sealed set of the original records is up on eBay right now, in fact.