10dB is 10 times the audio power that sounds twice or half as loud. 20dB is the rise or drop per decade of frequencies of a single RC filter.
Frequency response is spec'd at -3dB which is half the power and is a noticeable but small decrease in loudness.
Whenever you are using the power values you use 10log(P2/P1) whenever you are using voltages it will be 20log(v2/v1).As u know P=vsquare/R(where v is voltage and r is the resistance).