Decibels - Inverse distance law

This is an empirical law that calculates the variations in dB_spl levels when distance from a sound source varies. If at d1 distance from a sound source we have a sound pressure level of dB_spl1, at a distance of d₂>d₁ we'd measure a sound pressure shown in the following formula:

Equation 3.4. Inverse Distance law 

Let's take a look at a simple practical example: if d1= 1m and at this distance from the sound source we measure dB_spl1=100 at distance d₂=2m we'd have a sound pressure equal to:

Equation 3.5. Application of the inverse distance formula 

From this simple example we obtain an easy, useful empirical rule: every time we distance ourselves from the sound source, doubling our distance from it we'll have a decrease of 6 dB_spl, vice versa if we come closer to the sound source, halving our distance from it, we perceive an increase in sound pressure of approximately 6dB_spl. This rule is called the Inverse Distance law.