As you know Wayne, I have purchased some Altec 811b horns for the 4pi Theatres I am building. In searching through the Pi Forum archives I found where you had posted this:"The PSD2002 sounds excellent on the Altec 811 with the same crossover used in the Theater four π speaker. You can really consider the whole kit to be a good second source to Altec components for the Model 19 loudspeaker, but swap the polarity of the HF driver."
Why the polarity swap?