If your 10" woofer is crossed over at 250 Hz then why would you be concerned with whats happening at 800+ Hz? thats between 12-30 dB below the reference level granted you're using either a second or fourth order crossover. Even then, depending on the driver, you may be fine running it higher.
Clean sound below 60 Hz means having the displacement to do it as well as not having them firing into the trunk at all.
Try a pair of these in the doors.
http://creativesound.ca/pdf/TRIO8.pdf
That ought to solve your midbass problem.
Bass = <40 Hz.
Midbass = 40-150 Hz
Midrange = 500-3000 Hz
Treble = >3000 Hz
Hole between midbass and midrange is because its HIGHLY debatable but one things for sure... midrange's often work in the 250-1000 Hz range. You'd be surprised just how high those frequencies are. Try listening to some test tones.
In car audio, the issue is, your woofer can only run up that high if its on axis, which it can't be. 250 Hz is a good goal for your midrange to midbass crossover.
