Decibel question? Why is there a ratio in the Db equation?? what does this ratio represent? i thought decibels represented sound, such as a lawnmower, why does there have to be two sound/powers?? please help!

Question

anonymous · Answer

$$\frac{ P_{2} }{ P _{1} }$$ is the ratio im talking about

vincent-lyon.fr · Answer

Bels and decibels being a logarithmic scale, you need a reference power (non zero) that you call 0 on the logarithmic scale.
P1 is usually taken as 10E(-12) W/m²

anonymous · Answer

I'm currently writing a project on the decibel equation and its graphic applications, but i'm corresponding it to sound, such as music (70 decibels, for example). what would be my units in the ratio? and how can i explain this ratio in my project?

vincent-lyon.fr · Answer

70dB mean that the surface-power received by the mike or your ears equals
$10^{-5}$ W/m²

Solve : $70= 10\lg \Large \frac{P_2}{10^{-12}}$

anonymous · Answer

oh ok i understand that it's just that I don't know what P2 and P1 will be.

anonymous · Answer

what will they be?

vincent-lyon.fr · Answer

They will be the two powers you want to compare.

P2 is ten times as big as P1 will become : P2 is P1 + 10dB
P2 is a hundred times as big as P1 will become : P2 is P1 + 20dB
P2 is a thousand times as big as P1 will become : P2 is P1 + 30dB   etc.