When set to 80hz, it does not "cut off", as Ken mentioned there is a slope or pass-off to the sub. 80 hz is very low, most music never touches 80hz. Below 80hz, the sound starts to become non-directional and the sub is best suited to move more air.

The 80's actually do very well down into the lower frequencies if your receiver allows you to set a seperate crossover for them, try 60hz for music.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85