To mark the place in Pennsylvania where the fourth plane went down on 9/11/01, architect Paul Murdoch and his team designed the Tower of Voices, a 93-foot-tall open-air structure with 40 specially designed and tuned aluminum chimes, one for each passenger and crew member. Carolina Miranda talks to Murdoch and others about the incredible technical and aesthetic (and, yes, political) challenges that building the memorial posed. – Los Angeles Times