It's my understanding that you can do ANR over large areas, but it's not simple nor as effective as ANR in headphones, and is very frequency dependent. One system I've seen described has a number of sensors throughout the area and adaptively modifies the waveforms generated to create zones of cancellation, but I've no idea whether that's in production (or even proven to work!).
As an aside, work done on trying to apply ANR to aircraft ended up in flat speaker technology... from
http://www.edn.com/index.asp?layout=...cleid=CA438300:
"DML (distributed-mode-loudspeaker) technology began in the early 1990s as a research project of the United Kingdom's DERA (Defence Evaluation Research Agency), now QinetiQ. The research aimed to reduce the level of internal noise in military aircraft. As part of this research, DERA's scientists tried lining cockpits with high-stiffness sandwich materials but discovered that, rather than lowering the noise level, they increased it. As this effect might have significance for loudspeaker design, they filed a speculative patent. DERA itself had neither the resources nor the experience to develop this application, so it advertised for an audio-industry partner to license it."
The company that took it up, NXT, is
doing rather a lot with it.
R