crossover design for dipole rears

This isn't a car audio question but I trust and respect the pro's on this forum so here's my project.  I'm building rear surround speakers for home audio and have decided on using the dipole type for my older Pro Logic receiver.  This pair of speakers will each have a small woofer and tweeter on front and back in a mirror image arrangement.  I need some guidance in building a crossover for each of them.  I already bought the woofers and am looking at getting the tweeters.  The ports are already purchased.

Parts list:  woofers (4)  .........  Tweeters (4) _(besides low cost, selected for their small size)..........  ports are 1" x 4", to be cut, and the crossover components will also come from PartsExpress.  From what I've read about the ProLogic receivers, the sound to the rears is a limited frequency response of about 100 Hz to 8000 Hz, and my Yamaha amp gives each speakerbox 20 watts @ 8 ohms.  The THD is relatively high to the rears compared to the main and center speakers, so high quality components wouldn't be needed here.....and so I think this is a good way to try making crossovers for the first time.

DYohn told me recently that I should reverse polarity of the opposing sides, and highpass the front speaker at about 250 Hz , so I have purchased caps for a first order highpass.  I will need to purchase the rest of the components for the crossovers.  The diagram below shows an example of a second order crossover.   I used that as a guide for my working-model diagram below it which includes the second set of opposing speakers.

C3 represents the 250 Hz highpass filter.  I bought  these caps so that I could parallel two to each front woofer for a total of 160 uF to highpass at 250 Hz at 4 ohms.  The crossover should be at 3500 Hz.  I need to kow this stuff:

1  Would  the crossover work as shown in my diagram?

2  Can I put the 250 Hz highpass where it shows in the diagram?

3  Can I use one crossover for each speaker box (as shown)?

4  How do I determine the final impedance of the speaker box with these speakers?  And how does the crossover affect the final impedance?

When I started this, I thought I would get by using only the woofers, but their range is only to 5000 Hz.  That's why I bought them as 4 ohm woofers to be series-wired to an 8 ohm load.  Now I don't know how adding 6-ohm tweeters and a crossover will affect the total impedance.

5  Do I figure crossover values on the total of the series-wired speakers, such as at 12 ohms for the tweeters, and at 8 ohms for the woofers?  I already figured C3 at 4 ohms because it affects only the front woofer.

Haemphyst, thank you for the input.  In the diagram you show, first with the tweeter:  it looks like I should just series-wire the rear tweeter to the tweeter shown?

This is a rough outline of the dipole arrangement:

Okay, thanks.  I'll change the values on the bottom one (rear woofer) to L3 and C3, and reverse the configuration so that the coil is in parallel and the cap is in series.

On the middle bandpass figure (front woofer), is the order of components shown correct, then?  The cap C2 is before the coil L3. 

Looks like you guys are getting this one hammered out.  Like I said, the Xover design can be tricky...  :)

A couple of points: If the speakers are in phase, it is a "bipole" system.  Bipoles are very good in AC3 or 7.1 side fill systems with lots of side ambience.  Wiring them out of phase is what makes it a "dipole."  Using true dipoles is really only satisfactory with Dolby Pro Logic (or older) surround systems.  My suggestion for keeping one of the woofers highpassed at about 250Hz in relation to the other creates a modified dipole, where one woofer operates as a monopole below the high pass frequency.  Its bass information will not be diffused and will remain in phase.  This is more satisfactory with modern surround schemes that include more direct program information in the rear channels.  But I agree, try it both ways and see what works best.  Also, you don't necessarily need two tweeter; lots of folks build dipole bass systems and mount one tweeter only.

Here's an interesting and very powerful calculator for dipole bass systems.  Here's a good crossover schematic for a THX certified dipole system.