Hi,
Everybody thinks this way about crossovers--that the response from the M60s' woofers suddenly stops dead at 80 Hz and that by setting the front mains to Small and using a subwoofer you are somehow "wasting" the output of the M60's woofers.
It doesn't work that way. Every crossover has a slope, so the transition becomes gradual. The slope is expressed in dB per octave, thus an 80-Hz crossover with a 12-dB per octave slope would mean that the M60's woofers would be 12 dB down (-12 dB) at 40 Hz. That means that the woofers are still producing bass at 40 Hz, but at about half as much output as at 80 Hz. At 30 Hz, the output would be diminished some more, but you get the idea. . .the woofers just don't work as hard as normal (hence distortion is lower) and gradually turn over the really deep bass duties to the sub as the audio frequencies get deeper.
Crossover slopes are designed with either 6 dB, 12 dB, 18 dB, or 24 dB-per-octave slopes. We don't publish this information on the web site because neither Ian nor I nor Peter (our R&D director) want to get into protracted discussions over crossover design and slopes. What matters is the sound quality from the speakers--its accuracy, transparency and freedom from coloration and distortion, as well as its anechoically measured smoothness, especially throughout the midrange and upper octaves.
Regards,
