¼ wavelength...90°phase difference... not a big deal? Well I guess that is a matter of opinion which is fine. I know I could not find a way for such a thing to match up to a mid in a high quality system. Maybe for PA work. How would you match up such a large discrepancy? Would really like to know that one. A new trick for me to use in problem cases, cool! 
sumaudioguy,
90° at 200hz at a normal -20dB (or greater) levels is no problem what so ever. This assumes a sub driver with a very low Le, and a normal receiver 120Hz xover. It will effect things with the magnitude of a fraction of a dB at most.
Most drivers begin rolling off on their own above 80Hz due to higher Le, so most can add another +4dB of loss easy.
This has nothing to do with a mid driver.
The sub will act as a true monopole throughout its intended passband. No (extra, IE non-room) phase issues. As long as ka<1 there will be no issues.
90° at 200hz at a normal -20dB (or greater) levels is no problem what so ever. This assumes a sub driver with a very low Le, and a normal receiver 120Hz xover. It will effect things with the magnitude of a fraction of a dB at most.
Most drivers begin rolling off on their own above 80Hz due to higher Le, so most can add another +4dB of loss easy.
This has nothing to do with a mid driver.
The sub will act as a true monopole throughout its intended passband. No (extra, IE non-room) phase issues. As long as ka<1 there will be no issues.
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Thanks for that explanation and how you would make a crossover that suits you. Appreciate that. The steep crossover could be replaced by a FIR filter while your at it using some form of DSP.
-24dB per octave has never worked for me because of all the lost information from the center terms not appearing in either output. Yuk to me but others seem to find this just fine. Also that -24dB octave means something like another -180 degrees at the crossover point so how is the result of the Sum from the mid to the woofer every going to line up it time? Well I guess the mid could be +6dB at the crossover or it could also be out of phase with the signal 180 degrees so in energy the mid and woof line up perfectly. But then there is that issue mentioned above now with 360 degrees of phase shift in the two octaves around the crossover point. Again, this may be fine with others but yuk to me.
The FIR filter would work fine and if that what you mean I must agree, -3dB at 120Hz and -60dB at 140Hz all with out phase shift in the pass band. Yes a good idea and must agree with you that would work fine. Not so with IIR filters.
-24dB per octave has never worked for me because of all the lost information from the center terms not appearing in either output. Yuk to me but others seem to find this just fine. Also that -24dB octave means something like another -180 degrees at the crossover point so how is the result of the Sum from the mid to the woofer every going to line up it time? Well I guess the mid could be +6dB at the crossover or it could also be out of phase with the signal 180 degrees so in energy the mid and woof line up perfectly. But then there is that issue mentioned above now with 360 degrees of phase shift in the two octaves around the crossover point. Again, this may be fine with others but yuk to me.
The FIR filter would work fine and if that what you mean I must agree, -3dB at 120Hz and -60dB at 140Hz all with out phase shift in the pass band. Yes a good idea and must agree with you that would work fine. Not so with IIR filters.
Now we are moving away from polar response phase issues into crossover issues which are a separate topic.
The xover I posted was the default for most all receiver/pre pro units. (It also happens to be the LFE channel bandwidth top end.) That is why I posted it. Using defaults he would be fine. If he used the 100Hz from the OP 200Hz would be +/= 24dB even better.
I would personally never use a mono sub with redistributed content above 80Hz when SQ is a factor.
The xover I posted was the default for most all receiver/pre pro units. (It also happens to be the LFE channel bandwidth top end.) That is why I posted it.
Using defaults he would be fine. If he used the 100Hz from the OP 200Hz would be +/= 24dB even better. I would personally never use a mono sub with redistributed content above 80Hz when SQ is a factor.
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