O-Line uses a line of five custom-designed HF dome tweeters, with a spacing of only 0.83” (21mm) between each device. Such small spacing relegates high frequency vertical sidelobes to outside the audio band.
Compare this to using off-the-shelf 1” (25mm) dome tweeters. Sidelobes as loud as the main (red) lobe appear at frequencies as low as 8kHz; well within the audio band!