A repurposed 45m long spanning floor of a concert hall was found to be particularly prone to excessive vibrations during some music events and these were resulting in significant complaints from a nearby attached restaurant. Initial measurements by Full Scale Dynamics found a low fundamental frequency which was easily excited at resonance by the 2000 strong crowd. The use of props, beam stiffening, and Tuned Mass Dampers were all considered but ruled out for costs and the scale of modifications needed to achieve the required reductions in response. A novel active mass damper system was left as the only feasible technology. Full Scale Dynamics designed, supplied and commissioned this system as the first of its kind in the world, in collaboration with Gerb and Anco Engineers in the USA. This involved six electrodynamic actuators, 9600kg of moving mass and the development of unique algorithms to ensure robust and reliable performance throughout the most lively of concerts. Typical reductions of 40% were observed following successful commissioning of the system.