In my high school physics class the other day the teacher botched an example problem involving sound level (decibels). 1. The problem statement, all variables and given/known data A single sound source produces 105 dB at a distance of 5.0 m. How far away must the observer be to not hear this sound at all? 2. Relevant equations 3. The attempt at a solution The reference intensity I0 is the lowest intensity a human can hear, 1 x 10-12 W/m2, so when the source is far enough away its intensity will be equal to this. The intensity of a sound falls off as 1/d2, so after substituting the information in the problem the equation above can be rewritten as follows: In this equation, d0 represents the distance to the sound source that produces the reference intensity and d is the distance to the original source, 5.0 m for this problem. When this is solved for d0, the result is 177828d, or about 890 km. This can't be right! What happened? Thanks in advance for your help.