Picked up a used SVS PB10 ISD on Craigs. Used a frequency generator and the SVS has strong output down to 20hz and then nothing under 18hz, must have a low pass filter. The TSC 250 sitting on top isn't as powerful as the SVS, but is very good down to 25hz and then rolls off real real quick. I like using them stacked and the U571 depth charge is like a new movie with the SVS connected. First time having two subs connected at once and I like it a lot . I plan on moving the TSC around to other locations to see if I can improve the overall frequency response in my livingroom. One thing of interest is The SVS auto on requires more volume than the TSC to turn on.