What is 3 dB?

Answer 1

3 dB is a way to describe the amount by which power increases when it doubles.

1 dB = increase 26%

2 dB = increase 58%

3 dB = double

4 dB = 2.51 times

5 dB = 3.16 times

6 dB = 4 times (3 dB + 3 dB = double double)

7 dB = 5 times

8 dB = 6.31 times

9 dB = 8 times (3+3+3 = double double double)

10 dB = 10 times

Similarly

-1 dB = decrease 26%

-2 dB = decrease 58%

-3 dB = halve

-4 dB = decrease 2.51 times

...etc...

The equation is:

dB change = 3 log2 ( final power / initial power )

Edit:

The more "official" equation used to compute a decibel Gain/Loss when comparing power values is this:

GdB = 10*log10(Pout/Pin)

Where GdB is the gain in power (if the value is negative, it means loss)

and Pout is the power level seen at the output

and Pin is the power level seen at the input

Also, 0 dB means no change in power.

Note: If you're measuring an amplitude (like a Voltage or Current value), then the decibel equation increases by a factor of 2:

GdB = 20*log10(Pout/Pin)

So, to double an amplitude, a 6dB increase would be required.

In other words, take the values at the top of this answer, and double the left side of the equation, and that's how it works with amplitudes.

Lastly, it's important to understand that when multiplying in the linear world, you are adding in the decibel world. If you double a power level 2 times (e.g. 10 watts -> 20 watts -> 40 watts), you are multiplying 4 fold, but you are increasing by 6 dB (3dB + 3dB = 6dB).

BUT if your talking about audio (sound) 1db is the smallest change in sound volume the human ear can detect.