I stumbled upon infra sound and it's effects on humans a while back. It is very interesting stuff.
Infra sound and its uses as a weapon and its effects on humans are well documented.
It is said Hitler used infra sound to illicit anger in crowds.
http://www.lowertheboom.org/links/oi...us_weapon.html
Depending on the pitch, infrasound can cause physical pressure, fear, disorientation, negative physical and mental symptoms, explode matter, incapacitate, and kill. For example, in World War II, Nazi propaganda engineers used infrasound to stir up anger in the large crowds that had gathered to hear Hitler. The result was a nation filled with anger and hatred.
http://schizophonia.com/installation...esis/index.htm
Other physiological changes that occur include chest wall vibration and some respiratory-rhythm changes in human subjects, together with sensations of hypopharyngeal fullness (gagging). The frequency range between 50-100Hz also produces mild nausea and giddiness at levels of 150-155 dB, at which point subjective tolerance is reached. At 150 to 155 dB (0.63 to 1.1 kPa); respiration-related effects include subcostal discomfort, coughing, severe substernal pressure, choking respiration, and hypopharyngeal discomfort.
Some police cars are being outfitted with ultra sonic sirens which I think is a bad idea.
http://www.noisefree.org/video/bostonglobemay08.php