The difference ( between the 2311 & the HL14-50 ) is that the HL14-50 is a fully realized horn flare ( from a technical perspective ).
The 2311 is a truncated horn ( some of the horn-bell is cut off ) giving the result of a tilted-upwards, HF response ( that is then attenuated downwards by the little slant-plates ).
All of JBL horns meant to drive into a slant-plate ( of some sort ) are of the truncated bell variety.
The HL14-50 is a nice horn & sounds very pure on its own ( with no 2308 mucking up it's imaging ).
If a person wants a slant-plate in front of it, it'll take 2 ( 2308 ) to fully cover the mouth opening ( plus some network working ).
PS; the HL14-50 is a very good buy & a good project horn to have available .