A & E is heavily promoting it’s new series about ghost investigations. The title of the series is Paranormal State.
Here in this image you will see a huge billboard which covers a six story building in New York. Who wouldn’t notice such a large billboard, especially if you could hear weird voices when you came near it.
If you notice the two black square looking things on top of the building, those are special speakers which use directional audio technology. These speakers make use of ultrasound waves to concentrate and direct sound in much the same way that lasers do with light.
The sound waves from these speakers can be controlled in such a way that only people within a certain area can hear the sounds. This has been described as making people feel like they were actually listening to the sounds through headphones! Very amazing stuff.
This appears to be the first commercial use of directional audio technology on a billboard.