Percussionist Carolyn Koebel, one of West Michigan's most in-demand musicians, has released at least ten albums, with various groups, in the last three years. One of her favorite collaborators is Elden Kelly, a guitarist with a love for improvisation that equals Koebel's own. They'll perform both improvisations and composed songs for the final concert in the "Cool Concerts" Series, Wednesday at 8 pm at the First Baptist Church of Kalamazoo.