OK, generic backloaded horns (BLH, aka scoop bins) designed for midbass 'slam' and not much else. Makes visceral kickdrum hits though. Anyway, not really suitable in your app as I understand it.

21" square x 42" high o.d. makes enough Vb to even go sealed if you prefer, which considering they will be ~up against the wall may work best, though tuning them to ~Fs or a little lower is worth trying. Anyway, it gives you some tuning flexibility.

GM