Pros: Unique soundstage and imaging, outstanding mids, lightweight and portable, inexpensive at this point in time
Cons: Requires an above average amp, elastic bands need replacement or mods as do older ear cushions
I've owned these headphones since I was a teenager. After all these years the headphone still sounds great. Made originally in Austria in the mid to late 70's these headphones have had several variations: early, mid and late. My sextet is the LP version.
Do not judge the quality of these headphone by the sound out of a normal headphone jack, unless it is a well powered vintage receiver headphone jack. At 600 ohms they need power. In comparison they are more difficult to drive than my Beyerdynamic Tesla T1. The T1 is more efficient with a similar 600 ohms. I am currently driving these with a combo Meier Daccord and Meier Corda Classic.
Strengths: Mids are outstanding as good as any headphone I've ever heard. Light and comfortable with updated cushions. The cushions are still made for the updated version of the K240. The K240 is not made in Austria anymore but the updated cushions work just fine with the vintage model. Isolation is fair as the cushions block out sound better than a Grado SR80i but not as well as closed headphones. Imaging and soundstage are like no other as a central speaker uses six unique sound reflectors to separate sound in ways often heard with more expensive headphones. I feel these headphones are best with Rock. Instrument and vocals are out front, with sound presentation and audio separation. Older Rock as well as modern rock sounds fantastic. Tom Petty "I Won't Back Down" and Muse "Supermassive Black Hole" equally resonate despite the lack of heavy bass. The detailed sound in the mids makes up for areas that could be better.
Weaknesses: Little Bass and lacking much in the way of transparency, these headphones are more consistent with Grado coloration which frankly from my perspective is not all bad. This vintage phone often requires minor mods or replacement parts which are cheap. Inefficient at 600 ohms if not properly amped it is easy to think that these headphones are broken. The high end of the audio spectrum is present but definitely not emphasized. The construction on these vintage phones are outstanding inside the speaker components but the main body is hard plastic, chrome, and rubber.
For the current price these headphones are cheap if under $150 or in great condition $200. With minor modifications and amplification these headphones sound great.
I packed these Headphones away for several decades. I tried the old AKG's on inferior amps and jacks and believing they were broke I simply packed them away. Little did I think they still worked, let alone sound so amazing. The good folks on the vintage thread helped me realize what I had ignored for years and with about $30 worth of minor mods I brought these old headphones back to life.
The LP sextet with the white reflectors. Given the 30 years they have been gathering dust they still sound great. This speaks to the original construction quality that went into these Austrian made headphones.
The LP version note the silver AKG on the headband. Some people prefer this version of the AKG while others prefer the EP or MP versions. Since I've never heard the other versions I hesitate to offer an opinion. I would definitely recommend the AKG sextet--Grado'd AKG thread. This is the main AKG sextet thread, a vary serious detailed thread that goes into levels of detail I only humbly scratch at.