Infrasound

What happens when the frequency sound is less than 16 Hz? Such fluctuations are infrasound. Perfectly spreading in the water, infrasound helps whales and other marine animals navigate in the water column. Hundreds of kilometers - for infrasound is not a hindrance. The infrasound affects the person in a peculiar way. Somehow in the theater for the play about the times of the Middle Ages ordered the famous physicist R. Wood (1868-1955) a huge organ pipe, it seems, in 40 m long. The longer the tube, the lower the sound it produces. Such a long pipe was supposed to make a sound no longer audible by the human ear.

The infrasound affects the person in a peculiar way. Somehow in the theater for the play about the times of the Middle Ages ordered the famous physicist R. Wood (1868-1955) a huge organ pipe, it seems, in 40 m long

A sound wave in 40 m length corresponds to a frequency of about 8 Hz, this is half the lower limit of hearing height. And when they tried to use this pipe at the play, it turned out to be embarrassing. Infrasound of this frequency, although not heard, but closely approached the so-called alpha rhythm of the human brain (5-7 Hz) and caused people a sense of fear and panic. The spectators fled, arranging a crush. In general, these frequencies are dangerous for humans. There is an opinion that the wind, reflected from the long waves in the ocean, can give rise to infrasound, which has a pernicious effect on the psyche of people. Thus, sometimes explain the mysterious disappearance of people from ships in the ocean, in particular Bermuda Triangle. They fell into a panic, they said, and fled the ships...

Infrasound obeys the general laws that are characteristic of sound waves, but it has a number of features associated with the low frequency of vibrations of the elastic medium: the infrasound has much larger oscillation amplitudes, compared to acoustic waves of equal power; infrasound much more extends in the air, as its absorption in the atmosphere is insignificant; due to the large wavelength for infrasound characterized by the phenomenon of diffraction, as a result of which it easily penetrates into the premises and envelops obstacles that detain audible sounds; Infrasound causes vibration of large objects due to resonance. Due to this, infrasound finds practical application in determining the place of strong explosions or the position of the firing gun. The sounds of explosions, containing a large number of infrasonic frequencies, are used to study the upper layers of the atmosphere, the properties of the aquatic environment.

Infrasound occurs when earthquakes strike lightnings, in strong winds (infrasonic aerodynamic noise) during storms and hurricanes.

Tools