here's a bit of history for the "vintage AKG geeks" around here.
I like the good old K 270 and K 280 a lot and I was interested in their history, so I asked AKG for some details.
The kind folks at AKG clarified some things for me and since this may be interesting for some people around here, I translated their response for you:
The questions I asked were:
-What were the design goals of the K 270 and K 280 headphones? Why was the twin capsule arrangement chosen and are there benefits to it apart from lower distortion and higher maximum sound pressure levels?
-What kind of mareket was the K 280 meant to appeal to (home users or rather recording studios)? What role did the K 280 play in AKG's lineup of high quality headphones?
-When was the K 270 introduced and why did AKG choose to make a closed-back headphone on the basis of the K 280 as opposed to the current K 171/K 172 models which are based on K 141 / K 240 technology?
-Some people believe that the "Playback" model of the K 270 sounds better than the "Studio" model which has the auto-mute feature. Is there any reason to believe the two models perform differently, given that they use the very same parts execpt for the micro switch which should not make any difference?
-Are the spare parts that are no longer used by current models (e.g. DKK32 capsules) still produced or is there a limited number of them in stock?
Here's the response from AKG:
The design goal of the K 280 was to develop a headphone that was capable of reproducing high sound pressure levels with a minimum of distortion. To this end, two transducers were arranged in a way so they focused the sound directly on the entrance of the ear canal. The doubled cone area was responsible for a much better sound quality that was free of distortion.
The headphone was popular with recording studios and home users alike.
The K 280 was introduced in 1987 and the K 270 followed a year after that.
The design goal of the K 270 was to create a closed-back headphone with a sound that is as balanced as possible. Based on the K 280, the K 270 used different acoustic tuning of the capsules which was achieved by using different bass resonators and cavities to achieve this aim.
The headphone was equipped with an automatic mute switch that has no effect on the sound quality whatsoever.
All spare parts for the mentioned headphones are still available.
The original (German) discussion is available here: http://www.akg.com/forum/index.php/topic,3754.0.html