The original top model from AKG unfortunately weakens on many levels. A pair of headphones can be as great as you like, but if they don't fit properly to the head due to a lack of hinges for horizontal adjustment, or the ear pads are too thin and the ears touch the inner plastic grille, or the suspension headband is too weak, the sound can still be as good as you like - the headphones are put away after 10 minutes. This is exactly what is present with the K340. I have made some modifications to improve the wearing comfort, but I demand that from a manufacturer itself - in 1979 the heads were not different than today (in terms of shape).

I own the model with gray drivers, so it is a "bass heavy" version, while the others (red and black) are also often described as that, or at least as "neutral". The green version is referred as "bass light". My test combination can be seen in my signature.

And yes, the bass is good in quality and quantity, reaching below 40 Hz and producing a pressure that electrostatic drivers could never do on their own. And yes, the electrostatic drivers reproduce a great amount of detail, including fine detail. They are never intrusive, bright or metallic, instead the high frequencies are very pleasant to listen to. Combined together in the AKG K340's cabinet, it sounds like this: As if you actually put good speakers in a laundry room with tiles on the walls. Unlike other models from the time (explicit the K240 Sextett), the K340 are not brightly tuned, also the soundstage is extremly wide and large. However, this combination makes everything sound hollow, synthetic and washed out, as if there was a big veil over everything. Everything sounds wrong, out of phase, not homogeneous in itself, every driver playing separately for itself. After half an hour I had a headache because of this, the brain tries to permanently compensate the obviously audible delay between the electrostatic and dynamic driver.

So the K340 had to be modified. Rewired the entire headphone, the dynamic driver is thus directly connected, a cable from the dynamic driver then leads to the PCB, instead of first to the PCB and then to the dynamic driver. This solved the "out of phase" problems, the sound image is much more homogeneous. Other ear pads also immediately help the headphones in terms of sound as well as comfort. I also removed the inner grille, this made a big difference. For more details feel free to look at my posts.

Connected to a rather darkly tuned OTL tube amp, the slightly modded K340 suddenly becomes great fun. I admit, I was initially very disappointed with the headphones and didn't understand what they did better than a K240. But now I understand what people mean that these headphones can easily compete with today's models. I won't say it's better than the 500€ price range, but it attacks them with its very interesting unique presentation.

Important: Here the mid production Sextett (MP) is described. This is recognizable by white passive membranes, but with orange plastic behind and a orange colored driver. The early production (EP) has everything in orange, the last production (LP) everything in gray/white. I assume for the review that you have already taken a closer look to the headphones. The test configuration can be found in my signature.

The AKG K240 is rough, aggressive and forwarding, while always exciting. Localization sticks close to the head, everything on an axis between right, left and center - nothing is far away. The AKG points out things that even more expensive headphones (linear tuned Audeze LCD-2C as comparison) present only subtly and quietly, while the K240 leaves out finer details. But the AKG is smart: The music is not reproduced correctly because the frequency response is treble dominated, while it sounds like there is more detail, but in combination with the very "direct" sound characteristic, the most basic details are simply louder.

The strengths are the reverberation, the resonance of instruments and the transient reproduction - this makes it so incredibly realistic to listen to. In every recording you can hear how big the recording room was, whether there was a lot of echo in the room or not. All hiss, hum and crackle are unforgiving represented. In live recordings you can hear the audience bumping glasses or moving chairs. The audience is suddenly louder, where this was still in the background with other headphones. To reproduce this at such a high level requires far more money. The AKG dissect the music, there is no other way to write it.

It's not the best headphones I've ever heard, also I would say that it is beaten pretty fast in the 300€ price range in terms of details and pure spatiality. But the AKG is able to make me put down the high-end headphones and get into listening with the AKG, simply because it's so special.