# Sound dissipating

1. Sep 13, 2008

I am not a physics student, although i have taken grade 11 physics :P, but i do have a general question to do with sound. My question came from this. There is suppose to be a rock concert about 4 Km away from my house. How many dbs would the concert have to produce in order for it to be barely audible (around 30 decibels) from my backyard at a tempterature of 25 degrees celcius (not sure if that matters for the distance sound can travel). So i guess what I am looking for is some sort of equation to measure how sound dissipates? Any help would be greatly appreciated, sorry if my question is lacking some key elements, let me know if you need more info.

2. Sep 14, 2008

### tiny-tim

Welcome to PF!

Assuming there's nothing in the way, it's an inverse-square law … the sound is 100 times quieter if it's 10 times further away … but some frequencies travel better than others (I don't know the reasons for that).

But remember two things …

i] houses and so on in the way will lessen the noise (so will mist)

ii] decibels are a "logarithmic" scale, not a linear one …

10 dB mean 10 times as loud, 20 dB means 100 times as loud …

so 10 times further away means 20 dB,

100 times further away means 40 dB …