Checkout the PDF posted by the author,
elantraelite, of the topic:
FD Speaker Replacement - Detailed Guide - found by "tweeter" in the Custom Google Site Search
Page 5 onwards is about tweeters -
page 6 shows added wiring leading from a crossover up to the tweeters.
I assume it was done because the wiring
isn't there. Instead of being it is there - just not connected to anything and/or a cross-over (that could be possible - if a crossover was built into the door speaker itself and only installed in i30s with the tweeters).
I also assume removing the blank triangle plate will be the same as with the tweeter plates (without needing to disconnect wires) - description here regarding (tweeter) plate removal...
HOW TO: Remove and replace i30 side mirror including it's housing - slight different method give here just above the last image in the post
External rear vision mirrorPossibly the best, and quickest way to know, is take the blank out and see if there is a 2-contact connector (of some sort) there - if no one can advise.