Here’s an article about a sophisticated type of advertising which uses hypersonic sound:
New Yorker Alison Wilson was walking down Prince Street in SoHo last week when she heard a woman’s voice right in her ear asking, “Who’s there? Who’s there?” She looked around to find no one in her immediate surroundings. Then the voice said, “It’s not your imagination.”
Indeed it isn’t. It’s an ad for “Paranormal State,” a ghost-themed series premiering on A&E this week. The billboard uses technology manufactured by Holosonic that transmits an “audio spotlight” from a rooftop speaker so that the sound is contained within your cranium.
Hypersonic sound technology is discussed by Jonathan Moreno in his book Mind Wars (which I reviewed back in January). It uses sound waves that have been compressed into narrow beams which can then be projected to a specified location. The sound thus carried is audible only to the person or people within the targeted area, but not to anyone else.
The projected sound is “contained within your cranium”, as the article says, because the beam actually consists of two separate sound waves, which merge when they hit an object, so that the pressure of the air surrounding the object (i.e. a person) to reproduce the sound.
Such technology is ideal for, say, audio guides in museums: a description of each exhibit could be projected to the appropriate area, so that only those people standing within a defined distance of the exhibit can hear it.
Hypersonic sound also has miltary applications. The U.S. Army is developing long-range acoustic devices for the targeting of messages during crowd control, and in noisy environments such as military aircraft. And high intensity acoustics can be used as a non-lethal weapon: a sonic bullet painful and disabling, causing loss of balance and vomiting when heard.
Serious ethical issues are raised by some of the potential uses of hypersonic sound, because the projected messages are imposed upon people against their will, and could perhaps be used to subtly manipulate behaviour.