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"...a "magnetic acoustic device" or MAD that can broadcast a targeted beam of sound for a more than mile. At close range, the sound from these devices can be terrifying and painful."

Designed to emit sound as an irritant

These produce certain high or low, partially audible frequencies which cause humans to experience nausea or discomfort. The use of these frequencies to incapacitate persons has been used both in counter-terrorist and crowd control settings.

The possibility of a device that produces frequency that causes vibration of the eyeballs — and therefore distortion of vision — was apparently confirmed by the work of engineer Vic Tandy[citation needed] while attempting to demystify a ‘haunting’ in his laboratory in Coventry. This ‘spook’ was characterised by a feeling of unease and vague glimpses of a grey apparition. Some detective work implicated a newly installed extractor fan that, Tandy found, was generating infrasound of 18.9 Hz, .3 Hz, and 9 Hz — which, combined, generate a frequency of 0.56 Hz.[dubious — see talk page]

In 2005 CNN reported that the crew of the cruise ship Seabourn Spirit used a long range acoustic device (LRAD) to deter pirates who chased and attacked the ship[1]. Its actual efficacy, however, has not been established.

At higher energy levels, a subsonic shock wave is powerful enough to do damage.[citation needed] The possible effects have been the subject of much speculation. See [2].