Everyone here realizes that while incredible output can be had from a tapped horn, the compromise is all of these have to be highpassed, IIRC, right?
If you are looking for incredible output at the expense of size and bandwidth, these tapped horns are THE ticket, bar none. Nothing else will get you that much SPL/watt. But if you are in the MKTheater, notnyt, JapanDave camp of ULF, you need to stay away from horns.
I am not discouraging anyone here, as I love lilmike's, OKWolf's, and Ricci's designs (I was privileged enough to be present for the first test of the F20!), and I use front loaded horns in my HT and living room. But anyone who is thinking of building one has to know that if you are after the 9Hz peak when The Incredible Hulk uses halves of a police car as boxing gloves, the horns are not the right tool.