Decibels are logarithmic with a base of 10. I've been told before that two car horns are not twice as loud as one car horn. Rather, it takes ten car horns to be twice as loud, because of the log10 nature of decibels and our perception of sound.
Why does our perception of sound intensity have a logarithmic base of 10, instead of 6, 1.234, or any other real number greater than 1? That is, why doesn't it take 6 (or any other real number greater than 1) car horns to be twice as loud as one? It seems kind of arbitrary to me that 10 is the magic number.