A
decibel is a referenced logarithmic scale OR a ratio of two numbers. Saying "97 dB" doesn't actually mean anything until you put it against a reference.
A dB is a ratio of
power where dB = 10 log (P1/P2)
Through some math you can algebra
Ohm's law into a formula for dB where for
voltage (or force eg dB SPL) dB = 20 log (V1/V2)
Note that
power and
voltage/force use different multipliers.
If you lock P2 or V2 as a refernce value that's a dB scale.
The reference of dBV is 1 volt
RMS
So dBV = 20 log (V/1 volt
RMS)
20 log because
voltage uses a multiplier of 20. That allows you to turn any
voltage into dBV.
As a
point of interest, a dB is a
decibel. Deci as in 10.
In the 20s Bell Telephone worked with the Bel to measure
power loss over a mile of telephone cable. A Bel was simply log (P1/P2) but their numbers were always fractions so they put the 10 multiplier in and called it a
decibel.
I'm pretty sure that all makes sense.