Re: missing a trick
South Korea is a pretty small country (about the size of Illinois) yet they have a very strong emphasis on nuclear power generation. Given this is a military operation, I don't think energy use is at the top of the priority list. As for signal cancellation, they can mitigate this with speaker placement to make the sound difficult to counter-phase as well as applying some constantly-shifting effect on the raw recording to keep it coming out slightly different. Not only will this reduce the ability to record and rephase the sound, but subtle tonal variations have been known to play havoc with people's heads.
Biting the hand that feeds IT
