The dual M5s, a load of 3 Ohms and slightly less, brought the 1500 to its knees but not before 112 dBC was measured 12 feet away. I can't tell you what that sounded like because I had muffs on but I know crossed to a sub at 80 Hz, I can take the M5s to 105 dBC before I detect squirreliness.

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