I have an FBX-10 in a 1.5 ft poerted enclosure tuned to 35 hz with only 100 watts to each coil and just had it rta'd at a local shop......134 db.
My official review:
Excellent SPL sub, gets very loud wuth little power.
sound quality, not too bad. maybe it's my setup, or the amp, but bass is not smooth or lifelike, rather more in-your-face, and just plain LOUD!!
OVERALL a 7 out of ten stars