You can’t move the horn to the centre unless you make the box wider or reduce the wall angle.
I don’t know how much the array performance is comprised if you do that.
The simple rule for arraying is ¼ wavelength spacing of the drivers centre to centre.
When you look deeper at the problem, the cone does not just radiate from the centre, it radiates from the whole surface. If we had square cones operating as a piston and they were close together then they would couple up to a much high frequency. To get that to work with round cones is difficult because the gap between the drivers on average is too much.
In practice there aren’t too many problems until you go past ½ a wavelength. In this case ½ a wavelength is 486Hz … so we are pushing things – but it seems to work and sounds fine.
The idea behind this box was to build a nice small powerful general purpose 60 degree mid high speaker that could operate from 80Hz up, but design it in such a way that it could be arrayed as two or three boxes a side and have fewer problems than any other general purpose box on the market.
What I did was pushed every thing as close together as I could to minimize these problems. I was thinking of putting a phase plug Nexo style over the 12” drivers, but I don’t think I will gain that much … may be I will try it latter.
If you increase the box size you may need to retune the box to a lower frequency to get a smooth roll off. You don’t want a resonant bump around the port tuning frequency.
