Active Noise Canceler

No, not headphones. How do you cancel out a hammer drill? Take a noise source, you could put sensors around it - in 3 dimensional symmetry and sense the noise. Then, further downstream, put audio sources that will generate an out-of phase version of the noise so as to cancel it and make it not audible outside the sphere of the cancelers. But, noise contains energy and, if you don't hear the noise outside of the sphere - it means that the cancelers absorbed the noise - so where did the energy go? The transducers you're using to generate the out-of-phase noise are somehow absorbing energy. How does that work?