Lightweight steel floor systems, utilizing typical bay sizes while supporting few non-structural elements, are prone to disturbing levels of floor vibration due to walking excitation. Even though design criteria exist to assess and avoid this problem, decisions based on cost are often made to construct a floor that is prone to excessive vibration. These floors are very difficult to fix by conventional means without great disruption to the occupants. Active control, using a velocity feedback loop and a proof mass actuator to deliver the force, has proven to be a very effective repair with little disruption to the occupants. Perhaps the greatest barrier to wider implementation of this repair technique is cost. To keep costs down while obtaining the best performance possible, it is important to understand the dynamic behavior and interaction of all the elements. This paper explains the important parameters in designing an active control system. Then specific hardware is described and utilized in implementing an active control system in an occupied building.