Dynamics and speed.Efficency is there also. Sure a horn will not hit the 30s, but if it can hit the 50s there is just so much more there than a vented cab ( we are talking low Qts drivers here). I have started a new project in running some sims in a loaded low Qts driver in a MLTL. IMO and from what i have seen in the sims is that by loading a driver in the form of a filter chamber/throat and installing it into a MLTL is that greater SPL can be produced without breakup and still hit the low frequencies and at the same time provide for a cut off at a point (still working on this) so that the upper harmonics of the TL action have less effect so stuffing can (possibly) be eliminated.
It still probably wont have the dynamics of a horn though. Although with a Flare at the end it appears to lessen ripple and may provide for more apparent dynamics. Dynamics is something i cant sim at the moment.
ron