Decibels - Decibel in the audio field

The quantity we come across most frequently is dB_spl (spl: sound pressure level) which is defined as follows:

Equation 3.2. dB_spl 

where P₀ is the reference value for atmospheric pressure and is preso pari at 0.00002 Pa= μPa (pressure is measured in Pascals) which is considered as sound pressure above which the human ear begins to perceive sound.

Let's take an example. The value 20 μPa Pa is a reference value for sound pressure in an environment where there is absence of acoustic waves.

This means that a 20 μPa sound pressure level doesn't exert any sound pressure perceivable by the human ear. Vice versa a sound pressure level of 10Pa generates a certain number of dB_spl which equals the following result.

Equation 3.3. Calculation of a sound pressure 

If we were to read the formula from a different angle we could say that a sound pressure level of 114 dB_spl corresponds to an acoustic wave that develops a pressure level of 10Pa. The following figure illustrates some typical sounds and their intensity measured in dB_spl:

Typical dB_spl values