3-4 dB dip at crossover region: what should I listen for to hear it?

OP:  You are most welcome. 

Just, for the record, using a cheap SPL meter and frequency generator is so 1990s.  Get Room EQ Wizard with a calibrated mic (~$80) or OminMic and do it right. 

Alternatively, use your phone with AudioTools with something like the Dayton Audio phone mic

@erik_squires -- "What actually happens is that the ragged response makes some notes pop more than others, tricking your ear into believing it to be more revealing, and it is, but only in some ways."

Just an added comment -- I find that some speakers that are "impressive" on first listen -- those that make certain instruments or voices "pop" -- often turn out to be the most wearing to listen to over time.  I use unamplified live acoustic music as my personal reference when deciding if I like a particular piece of equipment, but recognize that lots of people listen for different characteristics, particularly if they are primarily fans of rock, pop, EDM, RAP or such.  But, that's the nice thing about this hobby, there is something for everyone. 

@mlsstl  You are not wrong at all. 

By the way, I'm not saying a juiced frequency response is necessarily something never to be done.  Between old Wilson's that had a similar crossover hole at ~ 2.4 kHz to the Dali's with the 2-3 DB extra treble lift, or the Dynaudio's with a W shaped response.  These speakers all have fans and listening habits which make them the ideal speaker.  There are also speakers and reviewers that have become enamored of certain colorations and call it neutral.  Ugh.

mlsstl’s comment dovetails with something I wanted to add. I use unamplified acoustic music as my "personal reference," too. I do like rock, even loud rock (e.g., Tool), but mostly listen to so-called "classical," and I play cello and acoustic guitar; my wife plays piano and my daughter violin. We hear live acoustic instruments in my audio listening space every day. We also sing, my daughter professionally.

Still, here’s a lesson of some kind, I think. I’ve got five pairs of high-end speakers, and two systems (one mostly for movies, in the library, and the main rig for music). Every now and then, I set up one—or even two—of the "extra" speaker pairs in my main listening room in such a way that I can fairly easily switch between them and my favored pair. And let me mention that my favored pair (Scientific Fidelity "Teslas" made in the late 1990s) are rare probably because Corey Greenberg in Stereophile killed the company with a very negative review when they first came out. One of the other pair are highly regarded Von Schweikerts, and another pair won all kinds of awards from Stereophile and other respected places, measuring flatter and with less distortion than any speaker at any price ever measured to that point in the anechoic chamber of Canada’s National Research Council (that’s a hint about its identity). However, of all my speaker pairs, it’s that last one I like the least. And remember: my ears are trained to prefer natural acoustic instruments in the very same acoustic space as my audio system utilizes.

So what’s the "lesson" here? Maybe that listening to recorded music is just a different experience from listening to "the real thing" (if that means: live acoustic instruments, voices, etc.). To the extent that this is true, measurements may actually be misleading—as they are for that speaker I just mentioned but didn’t name.