Hi-pass and lo-pass filter points of 1000 and 2000Hz, respectively, make NO sense for a midrange dome. Maybe they're 100 and 2000?
The crossover point is not the frequency that the driver suddenly stops making sound, but the point where it is 3 dB down. It takes at least 10 dB for one sound to drown out another, so the useful range of that driver at 6 dB per octave is at least 500 to 4000 Hz. It is an unusually small range, but maybe the mid woofer and lower tweeter just didn't have enough musical overlap to work, so this dome is just bridging the gap. This is a range where many systems sound harsh, maybe because the drivers are working at the limits. By putting a dome here, maybe it allows the other drivers to work more comfortably. Are they Thiels?
They are Essence 10As. Yes I have asked but Dale keeps the specifics of his designs to himself. The owners material does say the crossover is 1st order and "This is the only filter that is both phase and amplitude coherent." Have owned the speakers for 12 years. Had them updated once. Have always been wondering about that 1,000 to 2,000 part of the crossover. These are my favorite speakers. I also like Vandersteen and Green Mountain. I know that just because the crossover points are far apart does not mean that it is 1st order but when it is this close can it be 1st order?
I don't see why not. 1st order just means the slope of rolloff is at 6db/octave, so the dirver is in fact operating over a greater range than 1000 -2000. That's the tough thing about 1st order crossover designs-- the drivers have to perform well over a much larger frequency range than they do in higher-order designs.
This is a 5-way design? I suppose that is one way to work around the demands of gradual slopes. Is this the same Dale who now makes the Intuitive Design products?
I know nothing about your particular speakers, but there's no reason it couldn't be a first order crossover with a very narrow range. I speculate, but the tweeter couldn't operate effectively below 1kHz (an octave below the midrange crossover point and only -6dB down in level using a first order design) and the lower midrange driver couldn't go as 4kHz, so the designer added a separate driver to span this frequency region. It could work, but it looks like you have three drivers with significant output in the critical midrange. Again, I know nothing about your speaker and I'm just speculating on an hypothesis.
As others have said the first order aspect of the crossovers has nothing intrinsically to do with the narrow range of the one driver, except that the designer evidently like first order crossovers and thought this implementation worked best with his drivers.
It would be just as unusual an implementation for Joseph Audio, with their steep slopes, to have a single driver with crossovers at 1k and 2k.