+3 dB = twice the power (Power).
+6 dB = twice the amplitude (Voltage and sound pressure).
Depends on which acoustic theory you consider, whether a doubling of level, or a doubling of pressure causes a doubling of loudness. If going by pressure, a 6db increase would be 2x, and 3db 1.4x.
The 10dB is a widely accepted belief of loudness (by experimentation), but the 6dB (pressure change) is a recently studied one.
Edited by proton007 - 1/19/14 at 10:24pm