OK, forgive the length but I could use some guidance here.
I have been tweeking the settings on my wife's pioneer head unit that was recently installed into her car with the Hertz ECX165speakers, image dynamic sub, and zapco amp. I wasn't really happy with the way the car shop had set things up.

The question I have is in regard to the settings for the subwoofer crossover. There are two options in the head unit to adjust the crossover.

One is labeled High Pass Filter, selectable options are 50 hz, 63hz, 80 hz, 100 hz, 125 hz. According to the manual it states "When you do not want low sounds from the
subwoofer output frequency range to play
from the front or rear speakers, turn on the
HPF (high pass filter). Only frequencies higher
than those in the selected range are output
from the front or rear speakers."

I have found that setting this to 80 hz sounds pretty good, but 63 and 100 hz weren't bad either. (the shop had set it to 125 hz and the front speakers had too much high end and basically sounded thin). I assume this is like the typical crossover frequencies which can be selected from my denon receiver?

The other option is just called the "cut off frequency" and the selectable frequency options are the same as the HPF option. The manual states "When the subwoofer output is on, you can adjust
the cut-off frequency and the output level
of the subwoofer.
Only frequencies lower than those in the selected
range are outputted from the subwoofer."

I set this to 100 Hz. The shop also had this set at 125.

I think I know that I need to set the cut-off frequency above the HPF frequency selected or I could be eliminating a frequency range from playing altogether. However, what would be an appropriate setting for the cutoff frequency if the HP was set to 80 HZ? 80? 100? 125? Does setting this higher than the HPF frequency result in "Double Bass" in the overlapping frequency range?

The two crossover settings are on page 26 and 27 of the manual:
http://www.pioneerelectronics.com/StaticFiles/Manuals/Car/DEH-P5100UB_OperationManual1208.pdf

Any clarification or input that anyone can provide would be greatly appreciated.

If it is of any importance, the frequency range for the Hertz speakers is listed as 60HZ-23KHZ, but the graph shows a drop off a little lower than 100hz. link with speaker info here:
http://www.hertzaudiovideo.com/Doc/pdf_ecx165.pdf
Also, I thought this was kind of neat: The Hertz speakers have a tweeter that can be rotated to "aim" the tweeter to various locations. This is kind of neat because the speakers are about knee level in the door, but sound like they are at ear level with the way the tweeters were oriented during installation.

Thanks,
David

It seems to me the the sub out only affects the sub. Then the high pass will only affect the other speakers. I would think if you set these to the same frequencies you should be good. I can't imagine this is a brick wall filter so both the sub and the mains will be covering a little above (the sub) and a little below (the fronts) a bit of the selected frequency.

David, so that's the way that Pioneer unit accomplishes bass management. The High Pass Filter rolls off the speakers below the selected frequency and the "cut off frequency" rolls off the sub above the selected frequency. Consistent with home audio practice, both should be set to the same frequency for the smoothest blend(unless you want the overlap that you mention for "double bass" to some extent). From the frequency response shown for the speakers, 80Hz should work well as the crossover.

OK, thanks for the quick responses and clarification. I will set both to 80 hz for now and do some more comparison later.