Browsing Exhibit Builder, I saw an ad for www.holosonic.com, and thought I would post what I found here.
The audio Spot Light uses a 1/2" thick speaker (available in multiple colors!), which you can focus sound to one direct spot. They are used in exhibits and museums so that multiple tracks can be played in an area without the sound being overly cumbersome. While the price is certainly more than whats available in most sound designs - it could bring an interesting feature to theatre.