The industry standard reference volume is 85dB (right guys?) And this is the level most people calibrate their speakers to. The reasoning behind this is that movie studios that produce the DVD movies also master their discs at this level. The easiest way to calibrate your speakers is by purchasing a Radio Shack SPL meter. They come in digital and analog versions, both of which work well.
One problem with calibrating your speakers and sub that high -- especially if you find 85db too loud and you never listen at that volume -- is that the sub will sound too soft when you listen at lower volumes.
What I did was adjust my speakers to the most comfortably loud level I ever listen to and calibrated to there. I think it ended up being somewhere around 70 - 75dB. That keeps my sub from sounding too soft even when listening at lower levels.
