Yeah, that's Andy Gradds' page. He posts here from time to time as "Andy G." That's a great article on large-format piezo tweeters (made to fit existing 1" thread-on compression horns). I don't think that particular article was on Andy's site last time he posted a link here, so thanks for giving us a "heads-up" about it.Like Gar said, the CTS website also has some very useful information. They've really done well to keep the original Motorola design popular, and to even extend their value by increased awareness of the device and excellent quality control.
And for the archives, I also have the original 1970's spec sheet for the KSN-1038 small-format horns from the original manufacturer, Motorola. You can find it on the π Speakers website at www.PiSpeakers.com/KSN1041.htm. Click anywhere on the page to get a large, hi-res view.