I acquired the JBL MP418SP some time ago with blown Crown amp. Repaired the amp, both channels functional. It's in the family room. Its fun to use it and on some tracks can prove its merit of being a prosub. I have read it operates between 38-150hz utilizing the lo pass filter in the amp. Is the driver not capable of dipping below 38hz by cabinet design or does the integrated amp have a subharmonic filter in the amps circuitry? I recently purchased a DBX 234 crossover to try to tame it. the DBX is currently set an indent or so below 70hz.

It does improve the sound of it being able to crossover at a lower set point. also can set amp gain at 2:00 and utilize gain control on crossover. Just acquired a 4645B and want to place this in the same room with the 418SP. Could use the second channel of the Crown amp in the 418SP but am assuming it will still play in the 38hz to whatever crossover point that is set on the crossover. if this doesn't satisfy then am thinking of dedicating an amp to the 4645B using the crossover so it can play below 38hz.