Very good speakers with a sizeable cult following that considers them far superior to normal "chinless cone-tragic dome" modern speakers. They are built to a very high standard of parts and construction.
They are NOT PA speakers but intended for high fidelity use. Compared to a conventional modern speaker expect less extension at the bottom and top but superior midrange, FAR superior dynamics and better clarity and "life".
Many EV fans will start with a SP-12 used fullrange and then using a building block approach later add dedicated tweeters and/or midranges. EV encouraged this approach and made the add on drivers, horns and crossovers available.
You go with these you're entering a whole different world, get ready to buy a nice tube amp too.
Don't worry, a nice little 12 watt EL-84 amp will make them go to town, they're very sensitive speakers.
I wouldn't expect age to effect them----I've recently used Altec, EV and JBL speakers made as long ago as 1957 and they sounded fine and certainly better (IMO of course) than 99% of the things talked about around here. Note too that true point source old-school coaxial and fullrange drivers can float a spooky, three dimensional image that few speakers can match.
http://archives.telex.com/archives/EV/Speakers/EDS/SP12 & SP12B EDS.pdf
http://archives.telex.com/archives/EV/Speakers/DIY Manuals/Marquis DIY Manual.pdf
