Distance and loudness
For a point source, the intensity decreases as the inverse square of the distance. Thus if a source of sound is twice as far away, its intensity should decrease by a factor of 22 or 4. How much will its intensity measured in dB decrease?
I(dB) = 10*log(1 x 10-6 / 10-12) = 60 dB , and
I(dB) = 10*log(1/4 x 10-6 / 10-12) = 54 dB.
(Notice that 4 is two 2’s, so the decrease is two 3dB’s for a total of 6 dB.)