Denver sound artist Jim Green, whose best-known public art includes a playful installation under a block of Denver’s Curtis Street and the train calls at Denver International Airport, died on Wednesday in Florida at age 75. Green was a prolific and highly collaborative artist, friends and colleagues said, pushing the boundaries of art with playful, subversive pieces that surprised and delighted anyone who encountered them. Hyoung Chang, The Denver PostTravelers who ride the train at Denver International Airport — and that’s most of them — have for decades heard artist Jim Green’s work “Train Call,” which features playful sounds and recognizable voices.