[Phys-L] sound intensity problem

["Anthony Lapinski" <Anthony_Lapinski@pds.org>]

I was considering this sound problem.. For a 100-W megaphone, how far
would you have to be so that it is barely audible (0 dB)?

I = P/A

Io = P/4pir2

With Io = 10-12 W/m2, the result is 2821 km = 1750 mi

This seems unreasonably far! I would think that the sound level would drop
off much closer, as we typically experience. Or am I
missing/miscalculating something?