I just wish either Amir or Erin measures one of this...all of the fuzz, presumptions and speculations we are making up would clear up
Detailed
measurements of the 800D3 are available (all images are from there). The D4 should not behave much differently in comparison.
Excellent values for harmonic distortion and intermodulation distortion. The speaker's decay behavior is also impeccable. The maximum achievable sound pressure is excellent. There is not much to write about these points.
The crossover frequency of the woofer and midrange driver is unusually high at 500Hz and the distance from the lower woofer to the midrange driver is quite large, which creates a constriction in the radiation in the vertical direction.
The crossover frequency from midrange to tweeter is very high at 3.5 kHz, but works better than expected in terms of horizontal directivity.
The horizontal directivity taken as a whole is rather poor. I have drawn the course of the -6dB sound pressure limit (deviation in relation to the axis frequency response) here:
The 7kHz widening is caused by a dip in the axis frequency response and should not be a problem.
In the frequency range above 1.2kHz, the horizontal radiation is +-45°, which could almost be called narrow.
Quite bad is the abrupt change of the radiation at frequencies below 1.2kHz. Within one octave, the horizontal dispersion changes from +-35° (around 2.5kHz) to +-110° (around 1.2kHz) - but to be completely sure, one would have to look at the individual frequency responses.
The vertical listening area is very limited due to the high crossover frequency. Upwards, clearly less than 10° until the sound pressure deviates more than 6dB from the axis frequency response. Downwards it should be around 10°.
It would certainly be very interesting to have a look at the power response and PIR of this speaker.
Contrary to what is discussed here, at least the 800D3 clearly shows the behavior of a loudspeaker that is crossed at both crossover frequencies with fourth-order filters.
Due to the classic BR tuning around 270° phase rotation in the low frequency range (blue marked) and at the crossover frequencies at 500Hz and 3.5kHz each further 360° phase rotation (red and green marked), as one would expect for fourth-order filters.
Those who consider a low group delay important will not be satisfied by this speaker. Due to the crossover frequency at 500Hz and fourth-order filter, the group delay in the midrange will be unusually high.