[sts9fan]

Why is gain measured in decibels?  Can someone explain the correlation between decibels and voltage?  My understanding is that with different speakers 1 watt will be at different volumes so what is the baseline?  Is it that no matter what your speakers output if there is a gain of 10 then it will be 10 greater then without the amp or pre?  A link to some articles would be fine.  I have been looking but have not found anything to my satisfaction. 
Thanks for humoring me

Kris

Edit: Mostly answered my own questions.  The definition of decibel helped.

[Bob Reynolds]

Voltage gain is defined to be the ratio of the output voltage to the input voltage. So gain has no unit of measure -- it is a pure number. A decibel is also a pure number derived from a ratio, but it follows a logarithmic scale. The logarithmic nature of a decibel makes the values manageable for audio. There's nothing magic about a decibel -- just convenience.

[JoshK]

gain in db = 20 x log of gain in voltage multiple.   like someone else mentioned, a convenience, but also related to the our hearing's scaling.