One interesting point on the 411 cores I purchased from Fleebay and that I supplied to Bill. These had the pleated black goo surrounds that are the hallmark of many other Altec woofers. I'm relatively sure they were factory original cones/surrounds since I discussed this with Bill before the work was done. He confirmed the "correct" surrounds for the 411 are foam half circle. As I recall, he did not remember any 411s with factory folded surrounds but his discription of the cones and spiders were consistent with the 35 year old cores I supplied to him for the rebuild.

I guess the weird part about this is the motors are a ceramic magnet and not alnico units. I would have thought if the early "problem" woofers had the folded surround but the factory changed the surround to a foam unit to cure the problem in later factory runs, that those units would be alnico not ceramic motors.

As I rememberm, the 411s first came out in the early 1970s and the ceramic magnets did not start appearing until the early 80s; right?