Frequencies

	ULTRASOUND	Ultrasound is above the range of human hearing. Above 20,000 Hz. Dog whistles are in this category. Dogs can hear sounds at these frequency levels. In addition, studies on unborn children are studied via ultrasonic waves that are converted into real-time images.
	NORMAL HEARING RANGE	The human ear begins to detect sounds at around 20 Hz. It can capture sounds up to 20,000 Hz. Hearing is most acute at the mid-range level, 1,000 to 10,000 Hz. Human speech is mainly in the 1,000 to 4,000 Hz range.
	LOW FREQUENCY	This range is about 500 Hz and lower. Infrasonic sounds are included in the lower end of this category.
	INFRASOUND	Infrasound is generally classed as sounds below 20 Hz. Infrasound is generally inaudible to humans, unless at very high volumes. Even at very high decibels, infrasound will not be recognized as a sound. Infrasound is more commonly FELT. Infrasound is extreme bass.

The speed of sound through air, at a temperature of 0 degrees C. and 50% relative humidity = 331.6 meters per second!
Sounds consist of pressure waves. These waves of sound oscillate in the air. The number of oscillations (or cycles) that are made by a sound wave can be measured. The number of oscillations that a sound wave makes in one second is known as its frequency. Frequency levels are denoted by Hertz (Hz).

All noises have a measurable frequency. Some noises are composed of many frequencies, whereas some noises contain only a few frequencies. For example, an ambulance siren consists of a myriad of frequencies. This will remain relatively constant. However, the DECIBEL level may change, depending on where the ambulance is located in relation to the listener.

As a general rule, the more decibel levels increase, the more hazardous the effects seen on the human body, emotions, and hearing.

Today's car stereos are very powerful. They can be direct from the factory or installed in a boom car owner's garage.
Modern sub-woofers, and the amplifiers that give power to them are now capable of producing infrasound. All it takes is a CD with this type of extreme bass loaded onto it.

Boom car web sites and boom car owners have been known to pride themselves on their ability to produce this type of sound.

Infrasound can be deadly.

Infrasound has been tested and used by the U.S., and other governments, as a weapon.

Boom car drivers are truly audio terrorists.