I'm trying to work out what is causing a broad 10 dB dip in my response at around 60 Hz. Is there anything I could try that might give me some insight? I'm not sure if this is useful information or not but I have noticed that, at the main listening position, if I reposition the measuring mic closer to the ground, the dip becomes less pronounced. In fact, placing the mic on the ground at the MLP, the dip becomes completely filled in and is in fact now a peak. (Also, moving the measuring position to an adjacent seat, the dip is also much improved.)
I don't know that much about optimizing bass and hence any comments will probably be very helpful.
Some extra information: my crossover is at 80 Hz. I have tried the trick involving varying the sub distance but it didn't improve things much.