1. The problem statement, all variables and given/known data When the distance to a sound source is doubled, the noise level will be halved. Yes or no? 2. Relevant equations L = 10 lg(I/10-12) or L = 10 lg(I/l0) 3. The attempt at a solution my book used the first formula in another question and it used the second one in this problem. I know how to solve the problem but what I don't know is where 10-12 comes from. Because in the text where my book tries to explain sound they only write the first formula but then when they gave an example of a problem they used the second formula. Which is the real one and when do I use them?