Question

You're at a concert at a distance of 10m away from the band and their sound level is 120dB. How far back do you have to move if you want the sound level to be 85 dB?
I tried using 85=(10/r1)^2, but this doesn't seem to be working.

Answer 1

Of course it does not work. dB has a special logarithmic meaning, and you need to apply that. Each doubling of the the distance changes the intensity 6db, so you want to have a change of 35db, so your answer ought to be near 6 doublings
10,20, 40, 80, 160, etc.

Use the log formula.

Answer 2

dB x distance^2 = K
120dB x 10^2 = 85dB X d^2
Divide both sides by 85dB
141 = d^2
11.874342087
You should sit 11.87 meters from the band for the sound level to be 85dB.