Why is the volume measured as db in AV amps? What does say -20 db mean?

Answer 1

Because it is a seriously mind boggling system.

The decibel (dB) is a measure of the ratio between two quantities. It is a "dimensionless unit" like percent. Decibels are useful because they allow even very large or small ratios to be represented with a conveniently small number (similar to scientific notation). This is achieved by using a logarithm.

Logarithms are just hard.

Answer 2

To explain it in simple terms...a dB reference is more accurate, a level of -20dB would indeed be -20 below max volume. It does throw people off, most people are used to the 0 to 10 scale. Don't lose any sleep over it, it is simply a different scale.

Answer 3

I would suspect that the reference is to the maximum volume setting of the amp, which would be 0db. -20db means that the setting is 20db below maximum. What is not clear if these units are voltage db or power db; I would guess power db, in which case the formula is

db = 10log(set pwr/max pwr)

Then -20 db means set power is 1/100 of max power [log(1/100)=-2]