I recall hearing about this technology 50 years ago. Two ultrasonic speakers each producing a very directional beam, then at the point where they cross (and only there) it generates an interference pattern of audible sound.
There was no overt nefarious intent of MK controlling people. The declared use was in places such as museums - you could stop to look at an exhibit and hear a soundtrack giving you info about it. But the people at the next exhibit even if quite close by would not be disturbed by hearing yours.
Then again I don't recall ever hearing this actually in use in a museum anywhere so yes maybe the sekrit squirrels did steal the tech for their own use and ban it everywhere else.
I recall hearing about this technology 50 years ago. Two ultrasonic speakers each producing a very directional beam, then at the point where they cross (and only there) it generates an interference pattern of audible sound.
There was no overt nefarious intent of MK controlling people. The declared use was in places such as museums - you could stop to look at an exhibit and hear a soundtrack giving you info about it. But the people at the next exhibit even if quite close by would not be disturbed by hearing yours.
Then again I don't recall ever hearing this actually in use in a museum anywhere so yes maybe the sekrit squirrels did steal the tech for their own use and ban it everywhere else.