That's a moderately tough nut to crack. Most of the noise canceling devices depend on eliminating a periodic noise. A waveform that matches the periodic form, but is 180 degrees out of phase will result in cancellation. A human voice speaking is not that kind of periodic waveform. A jet engine turbine or noise from a fan blade would meet the requirements.
A strategically placed microphone might be able to receive the audio waveform, transmit it electronically to get ahead of the wave front, then convert back to audio 180 degrees out of phase.
I Know its a Tough nut but it can be done. You must consider thier transmision will be the same transmision at a given time in the same wave lenght over and over. you can reverse phase it after you know the pattern which makes it all that easier, which begs the question... are they pre-recorded? If so then all the work is done because it can be done before hand and not rely on an incoming new message to re-phase just reverse phasing a known variable. If all the wave lenghts are known the enginering its already done... it all comes down to timing... a prerecored reverse phase in synch with thier transmision. echo effect may also work wont cancel the noise but will scramble the hell out of it! I'm not an engineer just a guy who spent lots of time playing guitar and listning to rock and roll. besides anything created by man can be defeated by man.