Dayton Audio produces a 1″ polyamide compression driver and several threaded horns.

The combination compression driver with horn is very efficient.  I estimate about 105 dB at 2.83 vRMS / 1 meter based on the measurements, which matches the manufacture’s specs.  Thus all testing is performed at -15 dBW.  The frequency response has a gentle roll-off of about 2 dB / octave until 12 kHz.  Then it drops off more quickly, and shows resonant behaviors.

The distortion curve is quite surprising.  It is completely dominated by second order harmonic distortion!  Reportedly second order harmonic distortion is the least offensive.  I’ll need to build something from this and find out how it sounds.  Recommended cross-over is 1.6 kHz, and that looks about right provided the slope is 2nd order or better.