Mike,
Are you saying 20-30 years at or close to spec? That's not what I'd have expected.
If you pictured this as an X/Y graph, with the Y-axis measuring performance relative to spec, and the X-axis representing time, what I would have expected was a sharp upward slope initially during break-in, then a fairly level line going to the right gradually drifting back toward the X-axis as the cones age, maybe punctuated with a sharp drop with foam failure.
What I'm trying to figure out is whether there will be a gradual degradation in the audio qualities of the speakers, so gradual that it isn't noticed until you're visiting someone who has newer speakers. Then you wind up questioning if their speakers are better or if you have age and use-based degradation.
Just to get this straight in my head, can you clarify this?
Thanks,
-Bill