# Distance law sound level

where are the limitations of the distance law? Can I calculate a sound from the free field back to the near field?

For example: If I have an impulse sound which is 80 dB loud at 2m. Is it than 118 dB in 0.025m (calculated)? If this calculation is not possible, how much decibel would it be instead approximately?

• I'm confused about where you got the 118 dB estimate from, so I don't know if it is reasonable or not. The distance law I recall (still not valid here) is 3 dB down per doubling of distance, which would yield $80+3\log_2(2/0.025)\approx99dB$. What distance law are you referring to? Commented Mar 2, 2018 at 20:25
• It depends on how accurate you want to be. If you are OK with a $\pm5$ dB uncertainty, then sure, go with 118 dB (you will probably be a little high in your estimate). If you want to be really accurate, you need to know a lot more about the problem. Commented Mar 2, 2018 at 20:34
• Two points. (1) The far field is an average of the near field details, and so parts will be louder than the far field will suggest and parts will be quieter. Thus, as mentioned in the post you sent, the levels will vary widely. The graph you showed is just a schematic and should not be used for calculations. Also, I pulled the $\pm5$ dB out of my head, trying to give you an idea of what is happening - I don't know what the uncertainty really is. Commented Mar 5, 2018 at 12:44