A poorly designed horn will "honk".
A designer must pay close attention to the propagation of the wave front from the diaphragm of the speaker driver, through the throat and out of the mouth of the horn.
If it is not designed well or terminated correctly, it will create HOM's (higher order modes) or internal reflections.
These internal reflections create aberrations in the time domain of the loudspeaker which may or may not be visible in typical frequency response measurements.
Just because a horn costs a lot of money, or has a large following behind it, does not mean it is a well designed horn.