I don't want to say its impossible, but the whole reason noise canceling works with headphones is that it's able to work in a very small area (the ear canal) to cancel out frequencies going to just that ear.

You could come up with some interesting speakers to cause cancelation (known as destructive interference) but as you'd walk around the room you'd get different blasts of different frequencies. It'd be quite wild!

A good discussion of it here:
http://discuss.fogcreek.com/joelonso...w&ixPost=71391