Xover frequency recommendation between a 4in driver to 8in. driver

[andy2]

I will be building a pair of speakers that will be similar to Troels "Illuminator-4"
Illuminator-4
but instead of the 6.5in. mid range driver, I plan to use only a 4in. driver to improve the upper mid range dispersion. The cabinet will be almost the exact dimensions as his speakers. In his speakers, he designed the xover at around 200Hz between the 6.5in. and 8in. , but that may be a little too low for a 4in. driver. Troels being a fundamentalist when it comes to sound so he thinks the lower point xover is more important than the upper mid range. His solution is to add an extra 4in. driver with his "Illuminator-5" Illuminator-5
but to me it may have an extra driver too many and I am not sure about how to integrate the sound with all those drivers.
So my question if I were to use a 4in. driver, given the cabinet above, which is a good xover point between a 4in. to a 8in. driver? Should I use a 5in. driver instead?
Thanks.

 

[Face]

Cross at battle step, which off the top of my head, would be around 400hz with those cabinet dimensions.

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[AllenB]

The 200Hz region is underrated IMO. Here is where you find the tactile feel, vocalists bumping their chin on the mic, footsteps and venue cues, breath sounds. In fact, there isn't any part of the spectrum you can annihilate and expect a good result IMO, only the tolerance varies.