The Tower of Voices at the Flight 93 National Memorial was designed by Paul Murdoch Architects in collaboration with Nelson Byrd Woltz Landscape Architects. Completed as the final phase of the memorial in 2018, the structure stands 93 feet tall and serves as a "monumental musical instrument." It houses 40 wind-activated chimes, each uniquely tuned to represent one of the 40 passengers and crew members who lost their lives on September 11, 2001. The tower's construction involved sophisticated engineering to ensure the chimes would sound even in light winds (7–10 mph), using music theory to create a set of tones that connote both serenity and the dissonance of the tragic event. The tower is located near the memorial's entrance in Shanksville, Pennsylvania, and its "open" design allows the wind to flow through the structure, symbolizing the voices of the heroes being carried across the rural landscape.