There is this device I saw when I was a child at a big music store, that makes me curious.
It was meant to listen some CDs to try them out before the purchase. You stand under a bell-shape kind of "speaker" to hear the music, but as soon as you step out you aren't able to hear anything anymore.
I've been searching the net, but probably I haven't used the appropriate keywords because I didn't find anything. What's this device called, and how is does it work?
I'm interested in particular about the sound and how it's possible to transmit it only in a very limited area, and being able to hear it well only inside that little "circle"