I've had my Thors 18 yrs,, no issues, except the foam diaphrams in the Millennium's diintergrtaed,, so replaced,, still my tech guy tested them, and suggested replacing at $300/each,, the speakers were not is use but 8 of the 18,,and not loud, nor much R&R, mostly classical,, so lightly used.
This gives you a idea of when to change mid wteeters,, midwoofers are perferfect,,except my cat long ago scratched 2 mids so recently i myself replaced the 2 surrounds, very easy to do.
just added new high tech xovers,, so a good speaker over say 10 yrs old, recommend replacing mid tweeters and also upgrading xovers.
Hope that helps.
This gives you a idea of when to change mid wteeters,, midwoofers are perferfect,,except my cat long ago scratched 2 mids so recently i myself replaced the 2 surrounds, very easy to do.
just added new high tech xovers,, so a good speaker over say 10 yrs old, recommend replacing mid tweeters and also upgrading xovers.
Hope that helps.