Hi,
A few summers ago, for an Axiom dock party, there were either three or four M80s strapped together and hoisted up in Ian's boathouse, which is open to the dock on two sides. The M80 array faced the open part of the dock, where everyone gathered. A local band played live, through the M80s, which were driven by two Yamaha professional digital amplifiers of 600 watts each, bridged, so I think there was either 1200 or 2400 watts into the four M80s. They sounded very clean and did not sound bright or aggressive.
The reason you have to use so much power to get really loud sound is two-fold: the M80s are not horn-loaded (which would make them sound aggressive and edgy, a la Klipsch) and outside there are no room gain and reinforcement effects going on. So it's almost like an anechoic chamber.
That's why outdoor rock concerts all use big horn-loaded speakers, because they can produce very high SPL levels and not require thousands of watts to do it.
The only famous rock band to actually try using domestic speakers for their outdoor concerts were The Grateful Dead, back in the late 1960s/early '70s. The Dead used multiple stacks of Acoustic Research AR-3a's (already a very insensitive speaker) powered by tens of thousands of watts. I was never a Deadhead, so I never got to hear the system, which they abandoned after a few trials because it was too cumbersome for touring and the power demands were unmanageable. It was likely a great sounding system because it didn't use horns, which really compromise fidelity.
Cheers,
Alan
