SOUND POLLUTION (NOISE)
The lowest sound level can be heared by human is 10-12 W/m².

This phenomenon can be explained as follows:
Sounds at human ear are summed logarithmically more than linear.
Unit "Bel" is developed to measure the sound level depending on this fact. but since it is not best suits for practical
usage, sound level is stated as "Decibel" actually which expresses pW/m² value as exponents of 10.

Although sound pressure measurement is performed by full spectrum analyse, sometimes, it is needed to determine
a particular noise by measurement of sound pressure within a specific frequency range.

As summary, four main characteristic of sound wave are:
- Sound pressure is amplitude or magnitude of the sound.
- Sound gap is determined by the fluctuations in frequency of pressure wave.
- Sound waves are diffused away from the source
- Sound pressure decreases by the distance from the source.

Some equipments used in noise control:
- Vibration absorbers.
- Sound absorbing link accessories.
- Sound absorbing booths.

Example calculations:

Example 1:
Total noise level is 90,4 dBA when two machines with noise levels of 80 dBA and 90 dBA operates at the same time.

Example 2:
If a machine raises the noise level to 85 dBA from 80 dBA background, the specific noise of this machine is
calculated as 83,4 dBA.