There are composers of classical music, and there are composers exploring the boundaries of the possible. Guess which ones are the focus of “Re: Sound,” a festival of new and experimental music presented by Uncommon Sound Cleveland. That’s right. The latter. Attend even one of the festival’s six concerts Thursday, June 6-Sunday, June 9, at the Bop Stop at the Music Settlement and several local galleries, and you’re guaranteed to hear something new. Something previously unimagined, unknown or untested.