I remember doing a physics problem over 30 years ago but I can't remember enough to do it again. The only reason I remember it is that it seemed like it would be so useful when I had teenage kids. Funny how the brain works sometimes. Got teenagers now. We were working on acoustics. If I remembered correctly the problem used the threshold of hearing and distance. The idea was to calculate the distance to stand away from headphones playing music such that if the volume at that distance was just at the threshold of your hearing than the volume would be safe if you put the headphones in you ears at that volume. I'm sure there are all sorts of assumptions and problems with so simple of a model but I would like to know how to do it anyway. Anyone know the answer?