Sonic and ultrasonic weapons (USW) are weapons of various types that use sound to injure, incapacitate, or kill an opponent. Some sonic weapons are currently in limited use or in research and development by military and police forces. Others exist only in the realm of science fiction. Some of these weapons have been described as sonic bullets, sonic grenades, sonic mines, or sonic cannons. Some make a focused beam of sound or ultrasound; some make an area field of sound. Although many real sonic and ultrasonic weapons are described as "non-lethal", they can still kill under certain conditions.
Sound recordings have been used as a weapon to confuse the enemy in battle, as part of psychological warfare, and as a means of torture. Culturally inappropriate music has also been used to discourage teenagers from loitering in civilian settings. For example, the metro trains in Melbourne used to broadcast classical music over the stations' loudspeakers to discourage mischief.
Extremely high-power sound waves can disrupt and/or destroy the eardrums of a target and cause severe pain or disorientation. This is usually sufficient to incapacitate a person. Less powerful sound waves can cause humans to experience nausea or discomfort. The use of these frequencies to incapacitate persons has occurred 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 while attempting to demystify a “haunting” in his laboratory inCoventry. 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, 0.3 Hz, and 9 Hz.
A long range acoustic device has been used by the crew of the cruise ship Seabourn Spirit to deter pirates who chased and attacked the ship. More commonly this device and others of similar design have been used to disperse protesters and rioters in crowd control efforts. A similar system is called a "magnetic acoustic device". 'mobile' sonic devices have been used inGrimsby,