This paper explores the development of active sound transmission control systems for windows to achieve significant reduction in noise transmission. Several fundamental challenges need to be addressed in order to make the development of such noise blocking windows feasible. These include the need for a distributed actuation system that is optically transparent and the unavailability of a real-time reference signal that can be used by the active control system to provide advance information on the noise affecting the window. In this paper, a transparent thin film actuator (speaker) is developed for the control system, which consists of a piezoelectric poly(vinylidene fluoride) (PVDF) thin film coated with compliant carbon nanotube based transparent conductors on both sides. The developed thin film speaker shows excellent acoustic response over a broadband frequency range, and has the advantages of being flexible, transparent, extremely thin, and lightweight. To provide a time-advanced reference signal for the feedforward controller from a moving noise source, a small microphone array distributed around the home is used. A new noise source identification algorithm is employed, by which an appropriate set of microphones from the array can be chosen to provide a reference signal. Experimental results show that over 12 dB reduction in sound transmission can be achieved globally, which demonstrates the effectiveness of the control system in blocking sound transmission.