On the 500 & 600, 60dB/octave. By 110Hz, the drop is 10dB and by 150Hz, the drop is 30dB.

When I set my Sony sub's xover to by-pass (170Hz), I get a nice thump and slam. But when I set it to 80Hz, the thump and slam goes away. So it must have quite the hump somewhere north of 100Hz. The big problem with it (besides SPL) is a total lack of blending and transparency.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated