Millercarbon, you say it isn't a sub and that it is just another speaker, I want to make sure I'm not missing something here. The famed 128H woofer used in the JBL L150A speaker is still in the original speaker box where nothing has changed other than me disconnecting the mid and tweet, completely bypassing the factory woofer crossover and then adding a first order low pass crossover to the woofer. The 12" woofer with the 12" passive radiator in the factory 5 cubic foot massive box finds the -6db at 20hz with these speakers so they definitely go lower than most subwoofers on the market. If I disconnect my Sonus Fabers main speakers, the Classe' monoblock runs only the single JBL and it puts out so much bass I can clearly feel it in my chest and it fills the entire house with low bass. If I connect the mains back up, the bass sounds great...but just as good as the Sonus Fabers are by themselves. If I disconnect the JBL at that point, there is no noticeable difference in sound level or low bass extension. If I swap polarity on the JBL is also seems to be identical when added to the SFs...a whole bunch of nothing. That is why I was thinking it was my 1st order crossover network that was causing my JBL to be 90 degrees out of phase with my SFs.