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AKG K4 electret/dynamic classic PICS

post #1 of 14
Thread Starter 

 

AKG K4

Not much has been written about the fascinating electret/dynamic AKG K4, so I thought I’d share some of my findings.

 

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First off, this is quite an engineering feat. This headphone was introduced in 1983, I think, and of course it appeared in the wake of the Sennheiser HD414 and the successful Sony Walkman headphones, introduced with the portable cassette player in 1979. The market for small, portable headphones suddenly exploded. And when these slim, low-weight and good sounding headphones appeared – why use the heavy and clumsy headphones of yesterday? AKG realized that the size and performance combination was important. This was the first AKG mini headphone series and it included four headphones: the retractable 20 ohm K1 (inferiour sound), the 200 ohm dynamic K2, the dynamic “multi-diaphragm” 200 ohm K3, and the top of the line 400 ohm electret/dynamic K4.

 

AKG K4 close up.jpg

The voltage transformer. The plastic dish is silver painted, but I have also seen a chromed version.

 

The K4 is a beautiful design, planned in every detail, admirably executed. This tiny package includes a dynamic driver, the electret element and voltage transformer, and it’s still small and elegant. The style is somewhat straight and angular, and in my eyes quite appealing.

 

AKG K4 parts.jpg

 

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Review of the K4 in Gramophone, July 1983. Note that this is a silver version.

http://www.gramophone.net/Issue/Page/July%201983/89/828582/#header-logo

 

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AKG K4 headband different.jpg

There were also two types of headbands: one with a small "comfort pad" (upper) and one with a riveted cloth/weave band. Headband size adjustment is by the automatic and ubiquitous AKG elastic band, inside the headband itself.

 

It is one of three electret/dynamic AKG headphones, the others being the famous full-size K340 (introduced in 1978) and the less well-known K145. These constructions were probably triggered by the fact that AKG developed and produced their first electret microphones at the same time, and someone realized they could use that knowledge/production investment for their headphones as well. I guess they reasoned that elctrostatic/electret drivers produce less distortion and has better transient response than dynamic drivers.

 

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The electret driver on top.

 

AKG K4 dynamic diaphragm.jpg

 

Here you can see the ridges of the dynamic driver underneath.

 

The K4 is an open headphone, with foam pads and ventilated back. Just like the K340, the dynamic driver “plays through” the electret membrane, but the latter is much smaller on the K4.

 

So how does it sound? In short, the bass is full and midrange a bit forward, the treble somewhat rolled-off. Since the electret driver is smaller than the one in the K340, I guess it works in a more limited range – downward – than the K340 which according to some sources sets in at 3kHz [Edit: 4 kHz]. I suspect a (lower) treble dip at the crossover point of the dynamic and electret driver of the K4, which together with the “eager” midrange contributes to the perception of a softened treble. But in a sense this headphone is more honest than the bass and treble emphasized portable headphones common today.

 

However, there are remedies for this mild frequency imbalance, of the mechanic variety. First of all, the headband is too tight. With the small pads, this means too much pressure on the tragus part of the ear, which effectively closes the ear canal. All you need is a hair dryer to heat up and soften the headband, then stretch it a bit and let it cool in the proper position. There is a mile of a difference when the pads rest easy on the ear. Here are before and after shots of the distance between left and right earpiece:

 

AKG K4 tight.jpg

 

AKG K4 wide.jpg

 

Secondly, you’ll probably need to fix the earpads. The foam AKG used has deteriorated ages ago and replacement pads are not available. I renovated the original ones with an outer ring of dense foam, and a centre piece of acoustically transparent foam.

 

AKG K4 pads.jpg

 

This produced too much bass in my opinion (even though this was before the headband modification, so they might sound fine now), as did experiments with PX200 type pleather pads that fit nicely and look good but left me with a bass heavy, closed-in sound. Grado pads actually fit and sound very good, but are no winners aesthetically. Solution came with simple PX100 (or Portapro) foam pads. They need a small build-up of washer rings, I cut some out of synthetic chamois leather, glued them together with the pads on a plastic ring and then attached the pad assembly to the headphone with double sided tape. As many wise men have said before on these pages, the distance between ear and driver is crucial for the frequency response: closer to the ear = more bass, farther from the ear = less bass (and perceived treble level is lower/higher). I’ve now found a good balance that I don’t think can be much improved upon.

 

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The K4 has an open, appealing and surprisingly full sound with no major flaws. Resolution is good but not top notch, attack also good. It doesn’t show the cross-over oddities I’ve experienced with the K340 with quite audible crossover problems if you listen to female vocal recordings in mono.

 

AKG K4 & D2.jpg

 

These little 400 ohm buggers are power hungry, even if a Cowon D2 manages to drive them to reasonable levels. But a good amp improves things…

The K4 is the aristocrat of portable headphones, now enjoying its old age as a vintage classic. A position it very well deserves.


Edited by MDR30 - 4/5/11 at 11:38am
post #2 of 14
Thanks for this! I'll add to this if I find anything else about them. There aren't very many people with these. About 7 here that I know of. Do you know how to open them up?
post #3 of 14

Thanks for the writeup on these little-known headphones!

post #4 of 14

Originally Posted by MDR30 View Post

The K4 is a beautiful design,

Most comments I've read around here consider it to be ugly tongue.gif
 

I haven't noticed phase problems on the K340. I'll test it right away, left me curious.

Edit: wow, you're right. Seems barely noticeable though.

post #5 of 14
Thread Starter 

I guess most people never held it in their hands...

post #6 of 14

Another piece of headphone history...

post #7 of 14

thanks for the review

post #8 of 14
Thread Starter 
Quote:
Originally Posted by Ishcabible View Post

Thanks for this! I'll add to this if I find anything else about them. There aren't very many people with these. About 7 here that I know of. Do you know how to open them up?


I left that uncharted territory for you, my friend. All you need is a steady hand, a small screw driver and equal amounts of curiousity, rashness and bravery.

post #9 of 14
Quote:
Originally Posted by MDR30 View Post





I left that uncharted territory for you, my friend. All you need is a steady hand, a small screw driver and equal amounts of curiousity, rashness and bravery.

Oh you...Haha I just got it open. Took me all of 5 minutes to realize the silver part was all one part. I'll take pictures later.
 

post #10 of 14

About a week late:

 

Okay why can't I post pictures.

post #11 of 14

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I just figured out how to embed pics here again. I have to click source twice or else it won't respond. Enjoy!

post #12 of 14
Thread Starter 

That transformer is a bit smaller than the one on the K340:

 

AKG K340 transformer.jpg

 

The electret driver kicks in at around 4 kHz on the K340. Note the descent after 12 kHz:

 

AKG K340 frequency response.jpg

 

I wouldn't be surprised if the K4 crossover frequency is even higher, but I'm sure people like kwkarth and others can draw the proper conclusion based on transformer size and resistor value. The electret driver seems to be connected in parallel with the dynamic driver, and with a system impedance of 400 ohms this implies that the dynamic driver is 600 ohms. However, the same size dynamic driver of the contemporary K3 is 200 ohms.

 

I made a brief comparison between the K4 and K340, and they're quite different even if they share the basic technical design.

 

Lee Ritenour / Rio - San Juan Sunset & Rainbow (GRP)

 

K340: Warm and clear, fine resolution. Buddy Williams highats sound realistic with plenty of overtones. The micro sounds of the highhat and the acoustic guitar (string and fret sounds, extremely dynamic string picking) are reproduced effortlessly. A slight "closed-in" sensation - it is a semi-open design after all.

 

K4: More midcentric, highs not as well defined and soundstage smaller and less precise. Highats sound a bit "dirty" and squashed. Bass full, but doesn't dig as deep as the K340. The latter, however, sounds a bit laid-back in a direct comparison. Some instrumental parts are clearar with the K4 which also has a more open sound.

 

Shostakovich Symphony No. 5, first movement / Haitink & London Philharmonic (Decca)

 

K340: immediately impressive resolution. Bass resonance of hall quite apparent. Strings sound similar to the K4, but with more sheen. Overall orchestral sound and portrayal very fine. There is some midrange colouration though, in the same vein as the K4.

 

K4: Surprisingly fine string sound, airy and delicate. The slight midrange peak (have yet to define at which frequency) still apparent, probably exaggerated by a lower treble dip. String decays and woodwind colour nicely reproduced, piano and brass too. All in all it's "flatter" than the K340.

 

Kraftwerk / The Mix - The Robots (EMI)

 

K4: Nice and punchy, ultimate treble bite missing. No problem what so ever to follow the bass lines. Good spatial definition.

 

K340: Nice and punchy, ultimate treble bite missing (but better than the K4). Bass lines stronger and deeper, but also flabbier (probably because of the extension downwards). More organic soundstage.

 

In the end, I find it very difficult to characterize the K4 - to fairly evaluate its positive and negative qualities. But I have patience and will give the K4 the time it needs to share its secrets with me.

post #13 of 14

Hmm, seems like I need to get a K340. Did you mass damp the K4?

post #14 of 14

I have a pair of these and they sound good. The foam ear pads do need to be refurbished. They are hard to drive.

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