The speakers send out low-level ultrasound from a node attached to a dish, and use a 30,000 Hz frequency (much higher than what the human ears can hear) to beam an audible wave to a specific point. When this high frequency wave interacts with the air, it breaks up into three different waves. One of these waves is normal sound that humans hear. The two other waves confront it and keep it in a focused beam, thereby making the sound audible in a narrow beam.

via Klang Ultrasonic Speakers Create Sound Only Where You Want It – Bornrich.