Directional sound is a technology that concentrates acoustic energy into a narrow beam so that it can be projected to a discrete area, much as a spotlight focuses light. Focused in this manner, sound waves behave in a manner somewhat resembling the coherence of light waves in a laser. When a sound beam is aimed at a listener, that person senses the sound as if it is coming from a headset or from "inside the head." When the listener steps out of the beam, or when the beam is aimed in a different direction, the sound disappears completely.
Marketers are investigating various possibilities of directional sound, such as sending messages to shoppers in specific areas without creating a cacophony throughout the store. In November 2006, Court TV used directional sound in a multimedia campaign promoting its "Murder by the Book" series in book stores. Motion sensors in front of advertising displays activated devices called "mystery whisperers." When customers stepped into range, they heard a thirty-second message. Here's an excerpt: "Hey you, over here, don't turn around. Do you hear me? Do you ever think about murder? Committing the ultimate crime? I do. All the time. I get paid to think about it. I'm a best selling crime writer..." The message goes on to explain the campaign and concludes by advising listeners that if they continue to hear voices after walking away from the display they should seek help.
There are many possible applications of directional sound, for example:
- People driving in a car could listen to different music without using headphones.
- One person could watch a loud television program while someone sitting next to them listened to classical music or enjoyed peace and quiet.
- A high-power sound beam could be directed at an assailant or fleeing criminal suspect, subduing that person while minimizing the effects on other people in the area.
There are at least two developers working on their own versions of directional sound. Elwood (Woody) Norris has created a version he calls HyperSonic Sound, the basis for a workable device produced by American Technology Corporation (ATC). F. Joseph Pompei developed his own similar technology, which he calls audio spotlight and launched his own company, Holosonic, while finishing his PhD at MIT.