K240 Studio history

[Axure]

About three weeks ago I bought the K240 Studio earphones and I think it is a great product.

Now, I'd like to learn more about these phones. The technical details of this model can be easily found on the AKG website, but my search for information about its evolution was fruitless. What particularly interests me is the design. I have read somewhere on the web that the way 240s looks didn't change much from previous products of this line for 20 years or so. Of course, I'm not saying there's anything wrong about it - quite the contrary, actually. One of the reasons I chose these earphones (apart from great sound and comfort) was its serious appearance that doesn't pretend to be modern, cool or hip.

I would be grateful for any information about the history of K240S and its predecessors. I think this might be interesting not only to me, but also other users that are emotionally connected to their audio equipment . So I hope my question will not only satisfy my own curiosity but might also turn into an official article that will help to promote your products.

[Axure]

I kindly ask someone from AKG Acoustics to respond to my question.

[Axure]

Gosh, I must say I am disappointed. This is one of the most read threads among the recent ones and yet I am the only one who posted. AKG doesn't want to say a few interesting things about their product... Maybe they just don't need us clients, hmm?

[audioburg]

Hi,
Please excuse the delay in our reaction. The K240 has a very long story, thus I am just doing a research in order to give you a detailed anwser. Please allow some more days for it.

[Axure]

Wow, I didn't expect that. I'll be waiting, thanks!

[audioburg]

Hi, finally here you are:
The first K240 was introduced in 1975. From its design it looked similar to the K240 models we know from current production. Only the metal rings over the ear cups were of silver colored polished aluminum and the inner headband was perforated. Like in the recent version K240 Monitor a 32mm driver was used but it was surrounded by 6 passive radiators. Each radiator consisted of a membrane attached to a perforated disc covered with carefully selected acoustical friction material. Conventional circum-aural headphones often have a resonance peak in the upper bass region followed by a more or less significant bass roll off. The result: an unnaturally sounding boomy bass. The resonant frequency of the passive radiators in connection with the relatively high friction of the damping material behind these membranes effectively influences this irregularity in the frequency range.

In the region of the bass boost the membranes become transparent to sound waves and thus reduce the air pressure in the coupling cavity between capsule and ears. In that way the bass boost is leveled out. Below this boost-frequency the membranes block the sound waves and the roll-off is compensated. This acoustic principle was invented by Dr. Goerike, co-founder of AKG.

The first K240's had a four core cable and were available in two connector versions. One had the standard 6,3 mm stereo jack while the other carried a 5 pin connector according to the German DIN standard. This plug was known as Wuerfelstecker (Wuerfel = dice) because the 5 pins were arranged like the dots of a dice. The advantage was that the connector could be plugged into an amp or TV set in two directions. One caused the internal speaker to be turned off, while in a 180-degrees turned position both speaker and headphones were on. For this trick it was necessary to have all four terminals of the headphone drivers connected to the plug.

In France the K240 was named K242 for marketing reasons and during the first years of it's production.

Headphones with the same working principle as the K240 but with individual design were built by AKG for Philips (N6330), Saba (H200) and Uher (W774 and W775).

Although the first series of the K240 were a great success, there were certain discussions among the experts at AKG if the same effect as achieved by the passive radiators could be reached or even surpassed by a different design possibly less critical in production. This brought the introduction of the K241 where instead of the passive radiators only various sound ports covered by acoustically resistive material were used. The dynamic drivers were surrounded by apertures closed by carefully selected friction materials with various values of perviousness related to the acoustic impedances of the outer ear. The K241 was introduced in 1979.

Soon after the introduction of the K241 it's principle of the variable acoustic resistors – patented by AKG – was applied to the K240 as well and replaced the passive membranes.

In 1984 AKG introduced the K240DF, acoustically equalized to the diffuse sound field.  The K240DF refers to such a sound field present in a reverberation chamber using third-octave filtered pink noise and measured in the close vicinity of the ear drum with a measuring probe. The work of the IRT - Institut für Rundfunktechnik (Institute for Broadcast Technology) in Munich proposed a standard for headphone-monitoring calling for the diffuse field equalization of monitoring headphones coming closest to loudspeaker monitoring, because there existed no current IEC or CCIR standard for such a system. Especially at times, when program material is exchanged between stations internationally and the monitoring facilities may vary it looks extremely sensible to exclude the varying acoustical parameters of the different monitoring rooms and refer to standardized headphone monitoring when comparing program material.

The K240 Monitor as made from 1984 to 2006 was based on the K240 without passive membranes but with the ear related resistive sound ports. It's earshells were decorated with gold colored metal parts and a three core cable with universal 6,3/3,5 mm (1/4" and 1/8") plug was attached.

In 1997 when AKG celebrated it's 50th anniversary the "K240 Jubilee" in limited edition was made. Acoustically a K240M, it had different nameplates and came with a booklet with a short history of AKG.

In 2002 the 'Studio' Series of headphones was launched. A newly developed capsule with low impedance makes these products especially suitable for portable equipment. The cable is easily detachable. The first series had a minijack connection while from 2003 on a miniXLR-connection between earshell and cable is used. In the same year the closed version of the K240 Studio called K 271 was released.

[Axure]

I'm sorry I'm replying only now - I've read the story the day you've written it.

Thank you for assembling the facts. It is great to know about the long heritage these headphones have.

On a side note, a friend of mine has already bought one pair of K240S after a single encounter with my set. And another one eyes them each time we meet - I can see he's growing to a purchase decision  . And he hasn't even listened to them yet!

[clevermouse1984]

An extra question:
The earliest K240 seem to have two versions, one with perforated headband, the other with ordinary headband like the K240DF`s. Are there two different models? Or they`re all just called "sextett"?

Thanks for answering.

best regards

cm1984

[audioburg]

The new headband w/o holes was solely a design change of the headband itself.

[Axure]

Here's a link to an image I've found on the Head-Fi forums. It is an amateur photograph of four different 240 models:
K240 Sextet, K240 DF, K240 Monitor, and K240 Studio: http://img179.imageshack.us/img179/4110/k240seriesih2.jpg

Edit:
And here you'll find a couple more photographs
http://www.head-fi.org/forums/showthread.php?t=118116

Edit2:
Maybe AKG Acoustics would like to post a couple of high-quality photographs of older models of the 240 series? Just to balance the impression these crappy photographs may have made ;-)