Okay how's this?
One woofer is mounted right over the other now and the best response was obtained on axis with the front firing woofer. Green is the front facing woofer. Blue is the lower one, and red is the two together.
Because I am on axis with the front firing woofer and not dead center between the two of them, there is some cancellation going on in the 1.5kHz to 4kHz range but only a slight amount cause by a slight phase rotation. This is because the mic is slightly further away from the upper woofer. So it smoothed out the peak in the response of the front woofer. No notch filter needed.
Okay now how's this (below)? I added a .47mH inductor in line with the upper woofer to minimize how high it plays and to reduce upper frequency range interference a little. This time the light blue line shows them playing together.
Here is the response on a typical 10db scale like you see everywhere else.
Here is the horizontal off axis. Looks pretty smooth and consistent.
Here is the vertical off axis. As the mic moved up 4" per measurement you can see more coupling in the 1kHz to 3kHz range. Not too bad though.
Here are the impedance curves with and without the .47mH inductor on the upper woofer. Red is without the inductor and green is with it.
Another thought on this is that a rear firing ambiance tweeter could be added with a single small cap and resistor (adjustable) to give it back a little air. That will help with the over all sound since the top end is a little soft. It would also not effect the on axis response, just the overall in room response and balance. It will also lower the impedance in the top end and balance the impedance load.
These would be good speakers for a small untreated room, especially with the speakers placed well out into the room. They would create a pretty large sound field.