By definition, an octave is a doubling of the frequency. 20-40 hx = 1 octave, 40-80 hz = 1 octave, so the range of 20hz - 80hz is 2 octaves.

I doubt you can break your M60's unless you feed them clipped signal.

I think the main advantage of crossing your speakers over at 80 hz is to relieve the strain on the amp (deep bass requires much more power than higher frequencies), not on the speakers.

Hpe this answers your questions.

Mark

"Shoot, a fella could have a pretty good weekend in Vegas with all that stuff"