I used to work for a company that did certification testing on consumer and pro audio systems. They did work on the Performance series and I ended up with a prototype PC600 system. I recently took the system out of storage and found an issue with MF driver. By applying light pressure to the diaphragm you could feel/hear a "crunch" in the VC/gap. The VC DC resistance was in spec and an impedance sweep of the driver showed that there was some obstruction in the gap. I removed the surround, diaphragm and VC to find massive amounts of material in the gap. The VC was pristine. Looking at the residue under a microscope it appears that the plating on the pole structure as corroded and fallen into the gap. This appears to be an issue since this loudspeaker system was only exposed to home/office level humidity (average nothern california indoor environment).