Buying used: how old is too old?

My Seas Thors sound EXACTLY as they did when I bought them back in 2004.
Richard Gray advised me on upgrading the Millennium tweeters , which i did, and was a big mistake, = out $700,
Richard tested the old ones on his ohm tester and found a tiny miniscule fraction of a ohm off,,so I bought a new pair, Out $700 as they sounded exactly like the old ones. I since dumped the Millennium tweets at 1/2 price and will never ever go back to dome tweeters, I use a FR/PS for mids Far superior to all dome tweets. Like the one you have in your speakers.
So old vs new, = same speaker. 

A guy just bought a pair of Infinity Delta Gamma's for 150 bucks, he's posted on audiokarma. How's that for a deal!

My oldest loudspeakers are from the 1920s I have drivers that are about 90 years old that are still working well. But that being said avoid modern loudspeakers over 15 years old unless they are horn-based designs. Standard dynamics used ferrofluids in VC capacitors that drift after 15 years and rubber or foam surrounds that rot. The oil in ferrofluids dries up leaving Metalic particles in VC. Sure this can be repaired but unless you want to do so consider newer loudspeakers or those made before 1970. 

Three years ago i bought a pair of 17 years old dynaudio contours 3.3 for 1200 euro. They sound much but much better as the new dynaudio contour 60 i also own. The 14 years old genelecs i have sound better as the new dynaudio contour 60. Wait wait wait!!! The almost 40 years old bose 505 worth 300 euro sound way more natural and fun and big as the new dynaudio Contour 60. It’s not my personal opinion. And you save health by getting speakers which are already burned in!!! For my dynaudios Contour 60 it was 500 hours which can take one year in normal disappointing listening sessions. Good luck!

Its a complicated area with aspects of both failure and obsolescence. Paper drivers and surrounds degrade in speakers, but boxes and (well made) crossovers ought not. You really need to look at the materials since in speakers it is very much a materials issue.  I have three primary sets of speakers - one set ~ 27 years old, two about 15 years old.  All work like new - but these are very expensive and made from the best materials. I also had some big brand speakers (incurring mid-line Boston Acoustics) that literally crumbled to dust in about 10 years.
In electronics the major failure modes are tubes (let’s not go there) and electrolytic capacitors. We’ll push aside really old technologies like wax and paper. Paul Carlson can rant for hours on those, and does.Transistors and resistors will last longer than you.


As to obsolescence, i have 30+ year old (preamp/amp/related all solid state) designs ( and prototypes) that are, IMO, 100% current. Yea i did some re-capping but fortunately i also over-built them those years ago. I suspect old designs by Nelson Pass, Andy Rappaport, and others still sound awesome. Of course, Andy’s might catch on fire btu that’s the cross we bear. :-)

In the mid-fi area the level of general performance has risen greatly, similar in cheap CD players and cheap DACs. OTOH some old, "great" DACs hold up will iff and only if you add a modern, low jitter front end. Sadly the Schiit EITR didn’t accomplish that very well, so I DIY’d it.