I've had those for a few years now, Bootman. They were the top of the line AKGs close to 20 years ago. I picked up a used pair awhile ago from a classified on AudioReview. My son fell in love with them and I got him a pair this past year......from another classified. I paid $80 for one and $100 for the other.
The construction is exemplary. They are very sturdy with a self adjusting mechanism in the headband. They are not light, but they are extremely comfortable. The ear pads are leather and are circumaural, completely surrounding the ear. These things look professional. They have a single-sided flat coiled cable (10 feet) that has a 1/4 inch plug.
How do they sound? The soundstage is very
large.....to my ears, these present a better "out of head" experience than the Senn HD-600s. The sounds seem to emanate from well beyond my ears. The sound is also very
smooth.......no harshness whatsover........zero fatigue factor. I can't tell you how many times I fell asleep on the couch with these things on. The highs are well-extended, but the bass is not as pronounced as either the Senns or Grados I have. The mid-range, for my taste, is recessed and somewhat distant. Since I've been seduced by the Grado sound, just about everything else sounds flat and distant to me.
They are very difficult to drive, as they have a 400 ohms impedance. I've tried them with the Creek OBH-11 and the MG Head DT. Strange as this may sound, they sound best out of the headphone jack of my Carver receiver. Why? I have no idea, but they do........richer, fuller sound all-around. The bass is tighter and the midrange becomes a bit more forward, which is what I like. All my other 'phones do better with a dedicated headphone amp. Strange.
According to the literature from AKG:
"The K-340 headphone surpasses even the most elaborate electrostatics in transparency and accuracy. It has deeper and more precisely defined bass than is available from the most expensive loudspeakers. Every detail of the sound is clear and natural, and the acoustic image is better localized than any other headphone available."
In summary, I think these are very flat, neutral headphones with a large soundstage. I prefer Grados.