Two Vintage AKG Headphones: K240 Sextett and K340 Electrostatic Dynamic Page 2

These mint-condition AKG K340s are new old-stock, fresh from the box with about 15 hours of play time on them.

The AKG K340 Electrostatic-Dynamic
Rythmdevil's Notes - I bought these NOS (new old-stock) from Germany they only have about 10-15 hours of use. They fit a bit loose on my noggin, so I added some felt spacers to force the cups to swivel to their max (they don't swivel enough, an obvious flaw to an otherwise brilliantly engineered headphone), and I also put foam spacers in the earpads to make them thicker on the bottom. I didn't notice any changes to the sound because of this, it just seemed to help them keep a better seal. They have to original earpads. I tried some newer ones, and they seemed to offer a smaller soundstage because they aren't stretched as big. No other mods have been done.

I think they are a great combination of warmth and speed that is quite unique to the hybrid design. Soundstage is great, imaging is great, and the treble is clean, smooth, and natural. Their faults IMO are a slightly bright top-end that doesn't seam terribly integrated with the rest, and a gap somewhere in the FR, or just something strange or missing in the upper mid-range area between the vocals and cymbals. I know the stat tweeter only produces the higher frequencies so this really cant be due to the crossover, but I can't help feeling that the dynamic driver starts to roll-off and then the FR picks up again with a slight peak. This may be amp dependent though; I haven't heard them on enough amps.

Tyll's Notes - The K340 is a very unusual design that uses both a dynamic driver and an electret (permanently charged electrostatic driver). I have measured a couple of modified versions of these cans, and you can find additional technical information about the AKG K340 on this page.

I had troubles with my treble before with the K340, and I had them again. I listened a bit more carefully this time as rythmdevil spent some time describing his experience with the treble. Again I found the highs too strong with the K340, but not as objectionable as last time. It might have just been the day, or maybe that they're virtually brand new, but I thought these sounded markedly better than the K340s I've previously heard.

The highs didn't seem quite as strident as the other K340s, but I did hear something which may be similar to rythmdevil's comment above, "Their faults IMO are a slightly bright top-end that doesn't seam terribly integrated with the rest..." I heard some things in the mid-to-high treble that was quite good; I thought the cymbals were quite well defined and natural in character. But the treble didn't seem to integrate well with the spectrum of sound lower in frequency. To me, it seemed the highs were closer in space than the rest of the instruments.


Click on graphs image to download .pdf for closer inspection.

Raw frequency response measurements show modest variation with position indicating reasonably good seal. Compensated FR shows somewhat typical of the era "n" shape response from 10Hz to 1kHz, with relatively poor bass extension. There's a very deep and narrow notch in the frequency response at about 1300Hz. I've not seen a notch like this on any other headphone I've measured except for the other two K340 headphones I've measured; I suspect it's some sort of destructive interference from the two drivers interacting. On the other hand, the electret is said in an AKG ad to have the crossover set at 4000Hz with a 6dB/octave slope, which makes it sound like there shouldn't be a problem at 1300Hz. It's a mystery. Frequency response is quite uneven above 1.3kHz, and highs above about 6kHz are maybe 3-5dB higher in level than I would like.

30Hz square wave shows poor bass extension but proper phase.

300Hz square wave is VERY strange, as is the impulse response. I really think we're seeing a time delay between the two driver elements with the electret's high frequency energy coming in before the main drivers lower frequency energy. I'll talk to this math geek I know who might make some proper sense of it.

THD+noise plot shows a headphone that's having a bit of trouble playing loud, and I think I heard them getting grungier sounding as I turned the volume up. The isolation is fairly good at -12dBSPL broadband (100Hz-10kHz). Impedance is 350 Ohms with a big spike at 10kHz --- probably an interaction with the electret transformer/crossover network.

At 670mVrms to reach 90dBSPL the K340 is a little more efficient than the K240, but you still won't be using it off your iPod.

I think it's really cool to look at these vintage AKG phones and see too what great lengths they went as AKG moved forward in headphone design. It seems to me they were quite successful in some ways, but at the expense of falling short in others. I had a quick listen to my Quincy Jones Q701s and thought they trounced the K340, and bested the K240 in clarity and articulation. But the early production Sextett had a more relaxed and warmer sound that I would prefer in the long run for listening pleasure.

Good luck finding one though.

Index to rythmdevil's cool headphone photos.
Wikiphonia page for the K340 and K240 series including the Sextett.
AKG Page to download some Sextett ads.
Head-fi member reviews here, and threads here, here, and here.


inarc's picture

Thanks for the reviews. I'm personally very interested in AKG's current and former high-end headphones.

Armaegis's picture

I've gone through a pretty healthy share of headphones, even trading away those I liked for the sake of curiosity, but through it all my Sextett was one of my first acquisitions and I don't see myself parting with it any time soon. Paired with a Bottlehead Crack OTL tube amp, it's just happy juice for my ears.

On a semi-related note, my next project is to transplant a SFI 120 ohm ortho driver into a Sextett shell. Unfortunately this requires fitting a 40mm driver into a 35mm enclosure... so a dremel may be involved.

SAS's picture

The odd behavior at 1300 Hz could be a resonant mode of the driver or enclosure. You probably noticed a spike at the same place in the distortion measurement. The Ultrasone PRO 2900 headphones have some similar behavior just beyond 2 kHz. Such a narrow valley shouldn't be obvious when listening to most material, because most material just won't hit that narrow band. For the AKG, it lies around the third or fourth harmonic of the vocal range.

It would be interesting to do an FFT or CSD plot of the impulse response data. Send me the file if you want it done.

rhythmdevils's picture

Thanks for measuring these Tyll! Why do you think the Sextetts had trouble sealing? They are big circumaural pads, I'd think they would seal just as well as any other circum headphone.

Tyll Hertsens's picture
Not really sure. The dummy's ears are a bit stiffer than regular ears, so that can be a difference if the cup isn't deep.
Kool Bubba Ice's picture

The 240 are a true marvel.. No headphone connects me to the music like the Sexetts.. These with my DAC1 & HR2 was utter bliss with a type of emotional response I never encountered before. & I auditioned & owned some mighty fine headphones.. K1000/SA5000/K340/701/HE6/DT48/DT880/DT990/HD650/HD600

amateriat's picture

My very first headphones (1976-77) were in fact, AKG K240s, because the space I was living in was a tad awkward for fitting anything but the tiniest loudspeakers. Wonderful fact, when I wore out those 'phones (took a handful of years, but they got used most days of the week), I tried out a pair of the then-new K340s, HATED them, and exchanged them pronto for another set of K240s. (Never got the sound of the 340s - my ears picked up a weird sonic signature, along with what I felt was rather anemic bass response vis-a-vis the 240s. Definitely wasn't worth the extra chunk of change for me.

Even after briefly auditioning K701s not long ago, I still think the K240s are the best thing AKG made, or makes.

- Barrett

CptKlotz's picture

This is great stuff. Thanks to Tyll and rhythmdevils!

I can't help but be amazed at the performance of the Sextett that was designed and built almost 40 years ago. Its performance seems to rival modern designs which is mind-blowing.

The K 340 seems to be a bit of a mixed bag and the K 240 might actually be the better headphone from an "objective" point of view.

I really like my vintage AKGs...

My first serious headphone was a K 290 Surround (always used for stereo, though). It's essentially a K 280 with more bass due to different tuning of the drivers' bass holes). I passed it on to my father when I got an actual K 280 which I prefer.

I have a K240 Monitor that I have "moDFied" by plugging the capsules' bass holes as it is done on the DF (I'll probably order "real" DF capsules to see if I can see a difference apart from that). I think it was good when it was a "Monitor" (a little mid-bassy, though) and now that it is a "bastard DF", it's really great. Very transparent and neutral sound. People used to typical HiFi equipment would probably call it "bassless" :-)

When I get my hands on DF drivers, I could probably rig up some cables to run an impedance test... I can't do acoustic measurements, though.

Seeing a Monitor a DF and possibly a moDFied Monitor measured would be very interesting indeed.

The K 240's little brother, the K 141 Monitor isn't bad either but not as comfortable which is why I don't use it that often. It has less treble (and less bass compared to the K 240 Monitor) than the K 240 which is probably a matter of HRTF and/or taste.

I really like the K 280. It has a little more bass than the "DF" but it's still what I'd call neutral. The highs seem to be a little rolled off compared to the K 240 and the K 280 actually sounds a bit more like my monitor speakers in the highs. Hard to say which phone is closer to the "truth". Overall, it's a fairly accurate and non-fatiguing phone that can put out insane levels if properly amped.

Seeing some measurements of this unusual design would be pretty interesting.

The K 270, which I also have, is basically a closed K 280 that uses differently tuned bass ports for each driver. I dug up the old HeadRoom review on the Internet Archive and I think it was treated pretty unfairly back in the day. I think it's similar to the K 280 and has a pretty honest sound. The K 280 has nicer mids though (probably because it is half-open).

The old measurements of the K 270 actually show pretty large differences between the channels which points to some kind of manufacturing defect in the cans.

I have also noticed that this headphone really needs a good seal or the mids will sound hollow and honky. For me, the K271 velours pads with some additional padding underneath work best.

I'd really like to see some new measurements of a K 270 because I really think it's quite good.

I've actually bought a K 702 some weeks ago and while I think it's very, very good, I think the "DF" and the K 280 still hold their own pretty well in comparison.

I'd like to get my hands on a K 500 and a K 501 to compare to the K 702 but the prices on eBay are just crazy :-)

I'd send in some of my phones for measuring, but I live in Germany and I wouldn't really like to send them around the world.

Keep up the great work, though!

Kind regards,

baten's picture

I have AKG K240 late production sextett's, probably the exact same as Tyll used in this review. I have to agree with what's been said above. There's no headphone where you can get a.. connection with the music like with the sextett's. At head-fi they're described as "grado'ed" AKG's. At +- $100 these are a steal. For me, this is an end-game set-up. Decent DAC, decent amp and sextetts. The next upgrade would be in the $1000.

n32d's picture

Thanx for nice measurements for k240 monitor. Anyway, it seems that sensitivity measurements of K240 Monitor are too good. Result is about 6dB better than in actual product specification (SPL = 88dB/mW.)