Life safety. Acoustic vibrations (most important)

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Life safety. Acoustic vibrations (most important)

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15. ACOUSTIC OSCILLATIONS

Mechanical vibrations in elastic media cause the propagation of elastic waves called acoustic vibrations. The physical concept of acoustic vibrations covers both audible and inaudible vibrations of elastic media. Energy from the source of oscillations is transferred to particles of the medium. As the wave propagates, the particles are involved in oscillatory motion with a frequency equal to the frequency of the source of vibration, and with a phase delay depending on the distance to the source and the speed of propagation of the wave.

Propagating in space, sound vibrations create acoustic field. The distance between two nearest particles of the medium oscillating in the same phase is called wavelength, i.e., the wavelength is the path traveled by the wave in a time equal to the oscillation period. The speed of wave propagation depends on the density of the medium in which it propagates, the distance from the wave source and a number of other factors.

The human ear perceives and analyzes sounds over a wide range.

Pitch determined by the frequency of oscillation: the higher the frequency of oscillation, the higher the sound. The volume rises much more slowly than the intensity of the sound waves. The minimum threshold values are in the range of 1-5 kHz. The threshold of hearing in humans is 10 dB at a frequency of 1000 Hz, at a frequency of 100 Hz the threshold of auditory perception is much higher, since the ear is sensitive to low-frequency sounds. The pain threshold is considered to be sound with a level of 140 dB, which corresponds to a sound pressure of 200 Pa and an intensity level of 100 W / m². Sound sensations are evaluated according to the threshold of discomfort.

Ultrasound does not differ from an audible sound, but the frequency of the oscillatory process contributes to a large attenuation of oscillations due to the transformation of energy into heat and is classified as low-frequency (1,12x10⁴ - 1,0x10⁵ Hz) and high-frequency (1,0x10⁵ - 1,0x10⁹ Hz); according to the method of propagation - to air and contact ultrasound.

Infrasound is also an area of acoustic oscillations with a frequency below 16-20 Hz. In production conditions, infrasound is combined with low-frequency noise, in some cases - with low-frequency vibration.

The biological effect of the impact of acoustic vibrations on the human body depends on the intensity, duration of exposure and the size of the body surface exposed to vibrations, and is expressed by a functional violation of the organs and systems of the human body.

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