I don't know but there is quite a bit of dynamic range in the midrange as well. I suspect the loudest sounds and thus most power are in the bass region, but the dynamic range in the midrange is pretty large, too. Think ppp (quiet) to single instruments to full orchestra/band, for instance, and 20 dB change does not seem large. I have taken and seen 'scope shots of drum and cymbal hits where the peaks were easily 10 - 20 dB above the average without the kick drum in play.
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley