why 3db

hi there
I have a very basic question..Why do we always consider 3 db bandwidth of the signal and not 2 db or 1 db ...
hope to get a reply
thanks

In the old days of lumped circuits, the 3 point was easy to calculate because it was where the magnitudes of the real and imaginary parts of the circuit impedance were equal. Also in the early days there could be ripple in the passband which was usually less than 3 dB.

The point where the power is only 50% of the inband.

Within this limit useful power is obtained & also some tolerence of non linearity is to consider

w=w(pole) i think if it was 2 dB then we would have made 2-dB BW

a power at that freq decrease 50% from center of freq , try to calculate ...Ex

1W
10log(1)=0 dB,

0.5W => 10log(0.5)= -3dB