I listen to DVD's at around -18 and my speakers are Axiom M80ti's. It's loud, but not blow me out of the living room loud.

-30 to -20 doesn't seem out of the ordinary.

Axiom M80ti
SPL in Room 1w/1m(dB): 95 dB
SPL Anechoic 1w/1m(dB): 91 dB