There is something else to consider. In some cases the crossover setting affects the low frequency extension of a sub. By setting it to its highest setting you can also end up cutting off the lowest frequencies. How can you tell for your sub? Good question. Test reports, when you can get them, really help. For two of my subs (older Velodyne Servo 1200's) it turns out that (from a 1990 Julian Hirsch review in Stereo Review) for a setting of 100 HZ the low extension peaks in the 35-50 Hz region and falls off sharply below that. But (and I am skipping a few settings now) at the 40 Hz setting the maximum is in the 25 to 30 Hz range, and is only down 2 dB at 20 Hz. Since I'm running true full-range speakers (flat to 30 Hz or lower) across the full front, a 40 Hz setting for the Velodynes (and operating the all of the fronts in BYPASS) gives me the smoothest and lowest low bass extension, whereas turning the setting all of the way up would cause me to lose a lot of the LFE material. If I end up losing some of the redirected "upper" bass from the surrounds (a 60 Hz setting on my 950), it's a tradeoff that I'm willing to accept. While I'm sure that not all subs behave this way, it's something to consider.
Jeff Mackwood
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Jeff Mackwood