How long does it take a decent quality speaker to "wear out"?

Matthew:

The old production 5ar4's were a good investment (get them while you can).

I purchased the remaining stock of the Benji Frank eyeglass frames I wear (90% off closeout) and they are now unobtainable @ any price.

Though they are durable frames I'm down to 9 out of 11 pairs (hard on glasses).

DeKay

@dekay  , I remember you mentioning that back when I was inquiring about 5AR4s.  I am hoping that I am not as hard on rectifier tubes as you are on glasses.  

I own a set of DQ 10's.  Bought them from an electrical engineer.  They are still 100% original as far as I can tell with the exception of a re-foam  He told me they were never driven hard.  His wife wasn't too fond of them.  They sound fabulous.  Crossover looks original with the yellow DQ caps....

Eric gave a good technical answer above (and i agree). For some practical data points, i'll venture that i had a pair of Boston A40s in the basement where the surrounds turned to dust with minimal use an 10-12 years - fast.  One of my main pairs of speakers still in use, went into use in roughly 1994 and is played daily to this day - and appears every bit as good as the day i got them. They happen to have MB quart drivers with poly surrounds.  i do expect that how hard they are played, temperature, humidity and light all come into play as well.  but its kinda liek solid state electronics - aside from the electrolytic capacitors - their life is "nearly forever"

Ask a guitar player who owns an original "tweed" Fender amp from 1954 or so.