There you answer me that you could do more or less a M2 ... subjectively, I did not feel any advantage to listen to this one ... but well, it was in a very different room.I've built enough speakers now, to know the design is relatively simple to make, using drivers and construction at least equal to the design.
And frankly, the box as is, could easily be improved by taking it active, and ditching the passive xover.
It could be bi-amped, using FIR processing to further smooth out the frequency response. A linear phase xover could be used to play with xover orders and frequency hoping for better polar optimizations. While at the same time eliminating any phase rotation or group delay above the bottom end rolloff.
For the bottom end, where the bass-reflex design is almost surely being protected from potential overecursion below port tuning frequency by a high-pass filter, I would add frequency dependent processing that doesn't put a hpf in place until there is a risk of over excursion.
This would significantly reduce bottom end group delay / phase rotation, and still protect the speaker. Make it more like sealed.
I'm sure the IKEA effect is real....and i'm sure i've no doubt suffered from it, and no doubt will occasionally continue to suffer from it, on some of my more exotic build/experiments.
But not on this guy we're discussing...it's a really simple speaker
On the other hand, I do not doubt the excellence of your level but it would be desirable, it seems to me, to have a little more humility towards the engineering of JBL ...
To make a copy/paste of the existing is one thing, to conceive and imagine a new thing is another.