Piezo horn crossoverCounting from the tweeter, I added a 8 ohm serial resisor, this does not affect the resistance in the working range 2-20 kHz but protects the amplfier against low impedance way higher up in frequency. I then added a 8 ohm resostor across the driver to get a 8 ohm resistance. With this setup I could try different capacitors to see if I could equilize the the lift arount 4 kHz and get a flatter frequency response. I tried the horn with no crossover at all, then adding a 3.3 µF cap, a 2.2µF and finaly a 1.65µF.
This is how the responses turned out