In wikipedia, I read the formula to convert a power ratio to db. This formula is :
10*Math.log10(power_out / power_in);
But, for the sound pressure, I read the formula is :
20*Math.log10(soundLevel_out / soundLevel_in);
I read in some places a reason : it is because the sound pressure, like the voltage, have to be squared in the ratio and this squared becomes a 20 instead of a 10. Ok, but why ?
When I want to double the sound "feeling", I was told I need to double my power amplifier so, I understand it's a question of power (with no squaring) and not a question of voltage, but it's wrong.
Who can help me to understand where does this square comes from ?