Mark, there is no "crossover" in the sub; as I pointed out to Em, it's just a low pass filter which rolls off the sub above the set frequency, but has no effect on the speakers, even if they're connected through the sub. A very few subs have a separate high pass filter on speaker level outputs to the mains, fixed at 100Hz or so, but that has nothing to do with the frequency control on the back of the sub.

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Enjoy the music, not the equipment.