I will assume there is some language barrier here and/or I didn't explain above clearly enough.
So I'll try to explain my thought process a little better.
I should have also stated that I was looking for comments about why this would or wouldn't work. To expand my understanding.
Yes, I generally understand the region and purpose for cardioid in these speakers.
This (cardioid) is achieved passive (via the side slots)?
If so, the rear LF drivers are only there for only for LF, it's not to achieve cardioid response (in the 100-500hz range).
But my understanding on some speakers that are actively achieving cardioid via using the rear drive as cancelation in this range.
If my understanding of a)how these achieve cardioid is correct and b) looking at the near field driver the MF and HF can cover from 80~100hz and up.
Then these speakers could be made without the LF drivers. And the LF area could be covered by subs.
This would reduce the size and cost of the speakers. And move the LF to subs which are likely less expensive than the LF portion of this speaker and have better flexibility for placement in room.
I believe you are correct. The DD has a crossover frequency of 100hz lr4, and if you look at the sonograms, it becomes omnidirectional at that frequency.
The LF drivers are essentially subwoofers in a small sealed enclosure.
Cardioid bass is a thing, especially in PA systems. There is some evidence that different bass dispersions (dipole, cardioid and Omni) interact with rooms differently but in practice the room is always the dominant variable so you might as well use the Lignment with the greatest headroom, which will never be cardioid or dipole.
You may look at the genelecs to see another approach to a small cardioid enclosure although now that I think about it, I don't know how they work exactly.
The inclusion of subs for the DD is driven by the a few factors. One is that the processing on board enables pretty sophisticated bass integration. The other is that without the subs, this would be a very underwhelming speaker. Even with an 8 inch driver, that woofer is being asked to do quite a lot, and the design arguably only works due to the quality of that driver. If you asked that woofer to also handle bass it wouldn't have enough output and the distortion levels would go from acceptable to bad.
I don't think we're going to see affordable cardioids any time soon unfortunately. Fundamentally it will always be a 3 way active system with a lot of driver excursion, a lot of power, a very complex cabinet in a speaker with less dynamic headroom than you would otherwise get with bass reflex. Obviously the performance is spectacular but it's not as cheap as putting a cardboard tube in a box.