Yesterday I shared with you what a single tweeter looked like. If you'll recall, it was anything but smooth and flat.
But we don't listen to tweeters alone. Our systems use both woofers and tweeters in the hopes of reproducing flat sound.
Here's a response curve from Stereophile's review of the YG Anat professional monitor.
The blue line represents the output of the woofer, the red, the tweeter. Together they present a pretty flat response from 70Hz to 20kHz.
Note where the blue and red lines meet. This, of course, is the crossover point and, depending on how well the designer managed to pull rabbits from hats, will hopefully add together in the right places to present an even response to the listener.
You see the difficulty faced by speaker designers. There's little to be done with all the wiggles, bumps and dips of this response—and frankly, this is pretty good.
Imagine if this were an amplifier, the bottom end handled by one approach, the top end by another, the two hopefully meeting in the middle.