A sealed box rolls off at twelve decibels per octave with a clean transient response. It reaches less deep for the same volume, but its gentle slope blends well with room gain.
A reflex enclosure gains roughly half an octave in the bass for the same driver. In exchange the slope steepens to twenty-four decibels per octave below tuning, and the driver is left uncontrolled under that point.
The choice therefore depends as much on the room as on the driver. In a small listening space, boundary reinforcement often compensates for the shallower reach of a sealed box.
A third route exists: the passive radiator, which replaces the port with an unpowered diaphragm. Behaviour stays that of a reflex design, without air noise or a length of tube to fit inside the cabinet.
It costs more and the moving mass has to be matched precisely to reach the intended tuning, which is done by adding weights and measuring.
Room gain changes the arithmetic. In a small room the boundaries reinforce the bottom octave enough that a sealed box measuring shallower in free air can end up flatter at the listening position than a reflex design tuned low.
There is also the matter of what happens below tuning. A reflex cabinet unloads the cone there, so a subsonic rumble on a recording produces large excursion for no output. A high-pass filter a little under the tuning frequency removes the problem and costs nothing audible.
