Noise cancelling rooms

You've heard of noise-cancelling headphones. This inventor (who developed THX sound amplification for theaters) is working on a system employing multiple speakers and amplifiers to achieve noise cancelation throughout an entire room. He explains it in this short video.

I always thought that producing an inverted sound wave could cancel noise at one fixed point in space, and it would be impossible to do for an entire room without an equal number of 'loud spots' as quiet spots scattered through the room where the noise was twice as loud as the background. But he seems to describe having accomplished this.