I'm actually going to list this in contrast to CBredlow's - but like the blueprint in that answer, this isn't necessarily 'official' canon either, although, the two images below and their explanations are sourced as coming from a canon source (depending on your point of view)
Doug Drexler, the designer of Enterprise NX-01, was very generous in
giving us more insight into the design of the ship than I ever would
have hoped for. He describes the purposes of many not-so-obvious or
concealed details of the ship.
Symmetrical Warp Field Governor
From Memory Alpha:
'a symmetrical warp field governor located just aft of the saucer
section, that regulated the warp field shape that would otherwise
break apart at higher warp factors'