I gotta agree with Mayhem. If anyone were to look at that woofer response and suggest to you that you should spend 100+ for it and expect to cross it over above 2khz, most designers would say no way. The tweeter response is much worse at another $100. I doubt anyone whould buy those two drivers were they sparate, with that kind of response at that price level, crossed where they would have to be crossed. These are horrible looking on axis responses. I believe first arrival sound should be first on the priority list and that means excellent on axis response should be a top priority. Why is anyone willing to sacrifice that first arrival sound quality in favor of a bit higher sensitivity and the ability to play to an unrealistic, ear damaging, peak spl levels? I wonder why you don't see Geddes using coaxes in his Pro driver/constant directivity solution? As Mayhem said, it can't be a good thing to have a constantly moving waveguide or a waveguide whose design is secondary because it has to act as a driver first. To me, there is so much compromize in the design of the coax, as can be seen by observing BOTH drivers responses, that it swamps any possible benefits it may have and compromizes the design of both drivers. So you end up with two very substandard driver responses just so that you can make them into a coax? I don't get the attraction, personally.
There is a reason why MT or TM is predominant, because it works. You can use a pro midrange, which is pretty flat out to 4khz. The SB29 Ring radiator tweeter looks to be have a sensitivity in the 93-94db range and very good low end performance, flat down to 1khz, for a nice diver overlap. Mated with a pro woofer you should be able to get in the 92-93db range, depending on applice BSC, have very low distortion and be clean at all but insane levels, IMO.
If you want to increase the low end output of the dome tweeter, potentially increasting its power handling, increase directivity and create some pattern control above 3khz or so, you can mount the tweeter (less flange) from the rear of the baffle in a shallow waveguide. A DIY waveguide, at 3/4" deep with a 3/4" roundover you can get a boost in the range of 4-5db at the centered around 3-4khz and get some directivity benefits etc. Even Geddes admitted that if he were to use a dome tweeter, he would mount it in a waveguide.
Below is a study of the Peerless HDS in various depths of shallow DIY waveguides, but first is a pic of the final WG mount (in Lexan and wood, with open baffle mid, not suggesting that for this project
). The waveguide is created by nothing more than a 1-5/16" forstner bit and a 3/4" roundover bit, so it easily doable by most DIYers. With the tweeter flange removed, you can decrease the CTC distance of the mid to tweeter which improves vertcial polar response. Put the waveguided tweeter on a sloped baffle and you can align or come close to aligning the tweeter and mid AC in the vertical plane as well.HDS mounted Flush: 0-15-30-45-60º1/2" deep WG, 1/2" roundover: 0-15-30-45-60º1/2" deep WG, 3/4" roundover: 0-15-30-45-60º3/4" deep WG, 3/4" roundover: 0-15-30-45-60º3/4" deep WG, 3/4" roundover, with 1/2" deep 45º chamfer after, sharp edges sanded round by hand: 0-15-30-45-60º3/4" deep WG, 3/4" deep 45º chamfer, sharp edges sanded round by hand: 0-15-30-45-60º