I was browsing ebay and came across this lot of 3 Altec 604B drivers. One of them has some ribs on the cone that the seller describes are "styrofoam cone stiffeners for improved cone breakup characteristics".

Was this a common thing to do? Does it work as described? I have heard of people stiffening a 604 cone with some kind of epoxy but I have never seen these ribs.

Another thought is I wonder how much these 3 604B will go for

3pcs. ALTEC 604B COAXIAL WITH N1000B CROSSOVERS | eBay

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