Measurements:

Test Notes: Off axis and polars measured using a Celestion CDX1-1731  

Mic distance 1m, measurements gated at 4.5ms and are smoothed at 1/48 Octave.

Waveguide mounted freestanding on 3" diameter ABS pipe supported at the compression driver.

Final Notes:

Excellent uniform coverage over nearly 4 octaves, dispersion appears to come in close to 110 degrees.  The large roundover around the perimeter on this freestanding design prevents most of the diffraction ripples you would normally see on a horn with a hard edge termination. 

Narrowing seen in the top octave above ~14kHz is influenced more from the phase plug design/shape of the compression driver rather then the waveguide. This is true for most 1" horns/compression drivers as above that frequency the wavelengths become smaller then the exit of the driver.