Need your opinion SB Acoustics SW alignment

Thanks for the great explanation!

So, if I understand correctly I should use a sloted port with a AR of at least 9:1 (which dials it back to 270mm x 30mm) that it will give me higher air speed... or use a rounded port which is more effcient (friction wise).

Both cases are not ideal because they have long ports with a bend.

When modelling in WinISD, dual 3" rounded port gives me similar performance than the sloted port, better yet when appling a HP @21Hz, air speed dials back to 18 m/s @ full power (250W)...

So, the final question is... sloted port with a 9:1 AR with air speed around 22 m/s or dual 3" rounded port with 18 m/s air speed, both with a bend.
 
You're welcome!

No, less than [<] 9:1.

Correct, though critically damping the vent ameliorates it as it's slowing down the vent mach.

Dual vents have additional losses Vs a single large one, so have to be longer for a given tuning, hence short of larger flares than sold commercially, any gain from them can be negated if not longer; so you're on the right track, just need to make it a lower AR and at the bend, triangulate it as the excess volume [Vb] in its own little acoustically triangular corner only acts as a source of bend damping.

I assume AkAbak can accurately enough sim it, but otherwise tuning will be whatever it is unless others have more experience with tweaking duct bends.