Have you heard the Audio Spotlight?
boston.com
boston.com
It's a great device, (as Joe Pompei told us) there are some misconceptions people have when they read about the device:
1. The audio spotlight does direct most of the audio sound at a point, but sound does spill over to off-axis listeners, so even if it's not pointed directly at you, you'll hear the audio (but at a greatly reduced level). You couldn't really use this to direct a beam sound to one person in a crown and expect no one else to hear it. But in a kiosk setting (for example) the spillover would be acceptable.
2. The video isn't quite right, but the technology doesn't work by using constructive interference or beat frequencies. It takes advantage of the non-linearities of ultrasound propagating through air to convert the ultrasound into audible sound. One side effect of this process is that the sound has to propagate through enough distance for the non-linearilities to have an effect (I think the minimum distance for it to work is around 6-10 ft, but it actually works best at large distances of 20ft or more). This isn't something you could put on your desktop and have it work. You can read Pompei's thesis about the technology here: http://dspace.mit.edu/handle/1721.1/7987
3. By no means does it produce high-fidelity audio, it's maybe FM quality at best. Similarly because of the wavelengths involved, the Audio Spotlight can only produce upper mid-range and treble, no bass, so it won't be replacing normal loudspeaker in applications where audio quality it key. But again, it works perfectly fine for any number of other applications.
Overall, it's a nifty product and actually quite affordable. It's worth taking a look at if if you have an application that can benefit from having directed audio.
If it's really beaming ultrasound then I suspect it relies on constructive interference to produce audible sound.
The proper information is here:
http://en.wikipedia.org/wiki/American_Technology_Corporation
It's fun for practical jokes or making the neighbors think their house is haunted. I'm not sure how this guy is getting credit for this.