During CES 2000, ATC, devlopers of the technology were demonstrating a prototype, truly bizarre! go to
ATC for more info.
The guy was holding what looked like a rectangular paddle (table-tennis bat size) with loads of tiny transducers on it. With it, he would scan the audience in front of him and unless directly pointed at you, you didn't hear a thing; you could even sense it going from one ear to the other. This with being at least 3 metres away from the device.
He would then point the thing at the ceiling and walls and you would swear that's where the sound came from.
Sound quality was very poor to say the least, very tinny with no bass or lower midrage at all but the point was made that the technology can be made to work.
I have been wondering about the effects of ultra-sonic sound at fairly high levels around you continously, though (as it works by the intermodulation components between two carrier frequencies somewhere in 40k range).
There's also an English company who claim to have speakers for surround sound applications doing the same thing. I forgot the name, couldn't be bothered to wade through loads of Google hits; I have the information somewhere, will dig it out.
Cas.