1. The problem statement, all variables and given/known data The sound pressure level is 80db at a distance of 30 meters. What is the dBSPL at 60 meters? 2. Relevant equations My book has provided me the following formula: dBSPL = dBr-20log(di/dr) - but it has not explained what "di" and "dr" are. 3. The attempt at a solution I've been looking into this for about two hours, and I'm very confused by what I've read both in my textbook, and online. I understand the concept that Intensity = Energy / (Time * Area), and the concept that as sound travels further away from its source, there is an inverse square relationship between distance and intensity - but I do not understand how to write this out in a formula, or truly how this "inverse square relationship" works. My textbook has the following graph showing distance vs. intensity: 1m = 160 Intensity 2m = 40 Intensity 3m = 17.8 Intensity 4m = 10 Intensity but I can't figure out how they got there. Mainly, because if the formula is I = E / ( T * A), all I'm being shown is I and A - how do I solve this without knowing E or T? I'm very frustrated after spending about 2 hours on this. My textbook is useless at actually explaining this to me. I don't just want an answer - I want to understand this! From what I can gather, I may be correct, or totally off-base with the actual ANSWER to the problem. Either way, I still don't actually understand it. Using the formula above: dBSPL = dBr - 20log(di/dr), I think that it goes like this = 80 - (20 * log(di/dr)) = 80 - (20 * log(60/30)) = 80 - (20 * log(2)) = 80 - log2(20) = 80 - 4.3219 = 75.67 So - if the sound pressure level at 30m is 80dB, at 60m it would be 75.67dB.