Final Notes:

As with the other 1.4" Waveguides/horns the top octave dispersion is determined largely by the driver phase plug design and partially by throat angle match-up which is why it gets really wonky and you see large variations with different drivers.

Another well performing horn by Marcel Batík with good loading and well controlled directivity.  There is a small amount of waist-banding seen in my measurements around 2 kHz but that range will depend some on the diffraction from the baffle/enclosure design.  The 4" radius foam covered sonotube roundovers on my test jig won't exactly match what you will see using them on a hard baffle with smaller roundovers.