1)10 out of our 12 PS15's (first version, not R2) have a big dip around the crossover frequency between the woofer and horn as shown in the pics.
2)I then experimented with reversing the polarity of the woofer which removed the cancellation at 1 Khz, but the phase response no longer matched up with a PS15 that measures good which told me something else was going on.
3)So, I figured something might be going on with the passive crossovers. I switched the crossovers between a PS15 that measures good and one that measures bad, and the problem followed the crossover unit.
4) Does anyone know what could go wrong in so many crossovers to cause this before we go through the trouble of sending all of them to nexo to fix?
1) 10 out of 12 appear to have the polarity reversed on the HF.
2) Reversing the woofer's polarity would make the phase response 180 degree off from the "normal" woofer. You can easily determine the woofer's polarity with a 9 volt battery "click test", + voltage to the + terminal should make the cone go away from the magnet. Normally one reverses polarity of the HF driver to correct a "hole" in the crossover region.
3) The difference between the crossovers could as Ivan suggested be due to a problem capacitor, or component changes between crossovers.
4) Some HF diaphragms can be installed "upside down" in relation to the compression cover, resulting in reversed polarity, which could have happened at the factory or if re-diaphragmed.
Art