Is it possible to extrapolate the loudness in dB (A or C) of a source at some distance given its loudness nearby?

As I recall, sound drops off at the cube of the distance. It's the cube, because the sound waves spread out in three dimensions.

So, if you double the distance, the sound will fall off by a factor of eight (2^3), which is 9 dB (or is it 18 dB? I always get confused between power and amplitude.)