I was reading an Autoweek article on the Alpha Romeo Brera, and came across some details about the sound system used in the car. It has a system called "Picasound" which has no speakers! (in the traditional sense). The system "directly stimulates air molecules to produce sound, and typically uses less than 10 watts for optimal performance. Developed by ATAO Luxemburg, based on patents by French researcher Pierre Piccaluga.
Amazing - the air itself serves as the "speakers". The writer describes the sound as "pouring forth from everywhere. Kind of freaky, but good freaky".