K 240 Monitor to DF modification

[Adda]

Well one of the cables broke off while looking inside my phones so I had to take it all apart to fix it and I shot a pic in the process, here you go.
Had to fix it by reusing solder from a broken PSU but it works

It seems my earlier observations was not accurate so it's all for the better.

 

[Shoewreck]

I bet in real life the drivers look almost identical - both light gray. What year is yours? My Monitor was purchased in 2004.

I see some wax/epoxy/sealant on the back of driver. It seems like they started with a bassier driver, then tuned it for the exact target response.

 

[Adda]

Quote:

Originally Posted by Shoewreck /img/forum/go_quote.gif I bet in real life the drivers look almost identical - both light gray. What year is yours? My Monitor was purchased in 2004. I see some wax/epoxy/sealant on the back of driver. It seems like they started with a bassier driver, then tuned it for the exact target response.

To the best of my knowledge my DF's where bought in 1986 while the model was still new, my dad bought used and in very bad condition a few years ago, he never used them though so I took them over.
I'm not sure about the date though but their condition told me they had many years and very heavy usage behind them.
Everything that could deteriorate had done so, pads, foam everything and they had a bad smell too.

I guess it's a smart design choice with all those holes, it makes it easy to fine tune them.

 

[Shoewreck]

I've reiterated the mod. Aluminum tape has been replaced by bitumen, pieces of felt were inserted into breathe slots. The mod was more successfull than desired. Absolutely no bass now - it rolls off below 200Hz, so I'm planning a step back later. Treble is very DF-like, so felt (or foam?) damping is the way to go, one just has to be more accurate.

 

[CptKlotz]

Hi everybody,
 
The sealed "bass hole" on the DF's capsule is very interesting indeed.
 
This is the very same thing the K 280 service documents specify:
 
http://www.akg.com/mediendatenbank2/psfile/datei/78/k2804055d247f35e1.pdf
 
One of the two capsules is to be sealed with wax while the other one is to be left open.
 
I have an older K 240 Monitor (the one that has the Sextett baffle but white and black dampening material on the holes. While I think it's a very good headphone, I always noticed a slight hump in the mid bass. Since I'm a "neutrality fanatic" I always wished it wasn't there even though it wasn't too offensive.
 
I've now sealed the capsules' hole next to the red wire with hot glue (carefully applying it, so it just seals the hole and doesn't go into the capsule) and I think the bass is "tighter" now while the very low notes are still there, much like the K 280.
 
Could it be that this is 90% of the reason why DF's have a more neutral bass range? It sure is similar to what I noticed with the K 290 (both capsules open) compared to the K 280 (one capsule sealed).
 
In this thread, it seems as if early DF had the same baffle as early Monitors, including the black and white dampening material:
 
http://www.head-fi.org/forum/thread/442491/k240-photo-guide-sextett-to-monitor/45
 
 
In the official AKG forums, the tech support guys stated that "In the high frequencies both headphones are sounding equally"
 
(sorry, but I don't seem to be able to post a working link. It just leads to the forums start page, so just search for the phrase here: http://www.akg.com/site/powerslave,id,40,nodeid,40,board,3,_language,DE,country,DE.html).
 
While "high frequencies" could be interpreted as "treble", I rather believe that what they meant is "from the midrange upwards".
 
 
So... do I now basically have a "DF" or some weird kind of unholy evil AKG from Frankenstein's headphone lab? Sadly, I don't have the "real thing" to compare, but from what I read so far and compared to my other phones, this may be pretty close to it.
 
 

Kind regards,
Stephan
 

 

[CptKlotz]

Hi everybody...
 
today I got my hands on a K240M which seems to be a newer model since it doesn't have the Sextett-style baffle with damping material over the holes but the baffle with smaller holes and a different kind of (less dense?) damping stuff over them.
 
In fact, it looks exactly like the "DF" baffle in the "K240 photo guide" thread (not 100% sure about the damping material though since it seems to be pretty worn off in the "photo guide" thread but quite intact on the model I have here).
 
Right now, it looks to me as if you can't tell Monitor and DF apart by looking at the baffle since the supposed "early Monitor" baffle seems to show up in DFs as well and the "DF" baffle seems to have been used in Monitors as well.
 
If this is true, the bass hole may well be the only difference and AKG pretty much exaggerated all the "equalized strictly to IRT specifications" stuff. It does sound more impressive than "we sealed the bass hole with glue", though, I have to admit
 
Practically, using the bass holes to tune the capsules is probably a very elegant solution because it allows you to tailor the same component to different responses by a very simple means.
 
Concerning the bass holes, I've noticed something. The hole next to the white lead seems to have fabric between the hole and the capsule's diaphragm whereas the hole next to the red lead seems to be completely open (you can see this if you shine a light at the capsule's diaphragm and look "through" the capsule from behind.
 
[Speculation]
Perhaps the completely open hole increases frequencies up to the lower mids whereas the hole covered with fabric only increases the response in the low bass (since the fabric filters out higher frequencies while it is "invisible" to the very low frequencies that have a much greater wavelength).
 
Maybe I'm on the wrong track here, but this seems to be exactly what closing the bass hole next to the positive lead seems to do. The low bass is still there while the mid-bass is tamed a bit.
[/Speculation]
 
 
I still think "DF-ized" Monitors sound better. I always found the slightly increased mid-bass a little tiring in the K240M and closing the bass hole seems to make the response much flatter. The low bass doesn't seem to change all that much since I still seem to hear the lowest frequencies just fine.
 
The weird thing is that this seems to increase the perceived "transparency" a lot for me. Apparently, the added "thump" of the Monitor obscures the midrange more than I would have thought.

 

[MDR30]

A most interesting thread! The AKG manuals describe the K240DF drivers as [size=11pt]DKK 32 + 22 (2058M0702), or in a few cases [/size][size=11pt]DKK 32 (2030Z0018). Those parts numbers are different from all the other K240 models. What intrigues me is the "DKK 32 + 22" description. The DF hardly had 2 x 2 capsules, so is the DKK 22 an alternative variation? It sure would be interesting to see a photo of the DKK 22 capsule.[/size]

 

[Adda]

There is at least two versions of the DF's, I have one with paper covering the holes in the baffle, all the pics around this forum shows a fabric version, but that just changed
 

 
Could it be that baffles is not the only variation to be found in DF's?
As far as I know, the paper version of the DF's is older then the fabric one, no one have been able to compare the two versions as far as I know.
 

 

[Adda]

Oh I hadn't seen those pics http://www.head-fi.org/forum/thread/442491/k240-photo-guide-sextett-to-monitor/45

That means we have no less then three variations.

 

[MDR30]

Does anyone know the difference between the DKK32 and DKK22 drivers?

 

[CptKlotz]

Being German, I strongly suspect that "DKK32" stands for "Dynamische Kopfhörer-Kapsel, 32mm" (dynamic headphone capsule with a diameter of 32mm).
 
Part 22 in the K240 service documentation is the baffle and DKK32 + 22a seems to imply that the DF capsule always comes with a special baffle when you order it.
 
This is strange of course, considering that DFs seem to have been made with both kinds of "Monitor" baffles.
 
The way things are, we can only speculate whether the Monitor and DF capsules are any different at all, they certainly seem to look identical (and for the record, so do the K270 and K280 capsules, except that they're 150 Ohms a piece and the K270 is supposed to have two different capsules and a different "bass resonator" for each kind of capsule per side).
 
My *guess* would be that this whole "22a" business may be an attempt by AKG to obscure the fact that the difference between both models is a drop of glue. Maybe not every customer would have appreciated the "elegant simplicity" of this solution (along with the price difference) and maybe they also wanted to make "reverse engineering" harder.
 
As I mentioned earlier, they didn't exactly make the "bass hole" business a secret with the K280 but then, there aren't different K280 models - it was just used to tune the two capsules on each side.
 
I really would like to talk to the guy(s) who designed this stuff

 

[12Bass]

Although it has been some years since I've compared K240DF with my K240M, my memory suggests that there is a bigger difference than just the character of the midbass response.  From what I recall, in addition to flatter bass response, the DF was also more open and extended in the highs.  My suspicion is that a change in driver porting would not be sufficient to explain such a difference.  I remember wishing to replace my K240M with a DF. 
 
On a side note, there's simply no comparison in detail between my K702 and K240M, nor do I think that the DF would come close to the same resolution of the new model.

 

[CptKlotz]

The tech support guys in AKG's forums have stated that the Monitor and DF are identical in the mids and highs - which seems likely, given that the diaphragms seem to be the same. The voice coil is *probably* also the same since they're both 600 Ohms (I know that this doesn't prove anything in a scientific sense).
 
It's possible that they're in error, of course.
 
These days, AKG's headphone forums seem to be pretty much abandoned by the support guys and I find myself answering questions even though I'm just a hobbyist.

 

[MDR30]

 
Quote:

Being German, I strongly suspect that "DKK32" stands for "Dynamische Kopfhörer-Kapsel, 32mm" (dynamic headphone capsule with a diameter of 32mm).
 
Part 22 in the K240 service documentation is the baffle and DKK32 + 22a seems to imply that the DF capsule always comes with a special baffle when you order it.
 
This is strange of course, considering that DFs seem to have been made with both kinds of "Monitor" baffles.
 
The way things are, we can only speculate whether the Monitor and DF capsules are any different at all, they certainly seem to look identical (and for the record, so do the K270 and K280 capsules, except that they're 150 Ohms a piece and the K270 is supposed to have two different capsules and a different "bass resonator" for each kind of capsule per side).
 
My *guess* would be that this whole "22a" business may be an attempt by AKG to obscure the fact that the difference between both models is a drop of glue. Maybe not every customer would have appreciated the "elegant simplicity" of this solution (along with the price difference) and maybe they also wanted to make "reverse engineering" harder.
 
As I mentioned earlier, they didn't exactly make the "bass hole" business a secret with the K280 but then, there aren't different K280 models - it was just used to tune the two capsules on each side.
 
I really would like to talk to the guy(s) who designed this stuff

Thanks for clearing this up CptKlotz - good work.
 
Let me return to my initial ponderings about the capsule/driver where I suggested that the AKG XXL driver (used in present K14x and K24x models as well as the K530 and possibly other AKG mid range headphones) started its life as the 27,5 mm driver of the 1984 K3 headphones. The XXL driver has been criticized in another thread because of its small size, which I think is unfair.
 
These compact long-through driver designs, including the original DKK 32 of the K140 from 1974, (as opposed to the larger, flatter drivers of the K400-K701 series) were probably the best dynamic designs of their day, and the only ones still in production in one form or another. "Old-fashioned" some people say, and that is not wholly untrue, but it also says something about the enduring qualities of the original design.
 
 
 

 

[CptKlotz]

Hi,

I found your picture of the K3 driver but I had difficulties finding the actual headphone. This thread at least links to a picture: http://www.head-fi.org/forum/thread/471404/akg-rare-k-specimens.

Even AKG doesn't seem to have it in its product archives. Is the "K3" a slightly modified / renamed model, maybe for some markets where the original name wasn't appropriate or available?

What makes you think it has anything to do with the XXL capsule? To me, it looks quite similar to the DKK32, with slightly different dimensions and shape.

The XXL capsule on the other hand has quite a different diaphragm design. Instead of the diagonal "ridges" in the surround, it has rectangular elevations. Maybe this, together with the "varimotion" (variable thickness) technology is a way of dealing with unwanted resonances and cone break-up.

Actually, I'm not sure what makes the new capsule "XXL" anyway. The outside diameter seems to be almost the same as the old DKK32. The voice coil diameter is greater though, so maybe that's what the name refers to.

Some days ago, I got my hands on a K 171 S for a good price, so I couldn't resist buying it.

Being the geek that I am, it goes without saying that I also couldn't resist opening it. I noticed the 55 ohms capsules have a bass hole as well, which is on the center of the capsule's back. In the K171 (and K271, for that matter), there's a "bass tube" attached to the hole which leads to a cavity in the closed earcups, much like one of the bass tubes in the K270.

Since the "S" and "MK II" versions of K141, 240, 171 and 271 all use the same type of capsules, this makes me wonder if one could create a "K 240 S-DF" by closing or damping the bass hole.

I think the K 240 S isn't bad and with an amp that has a low output impedance it sounds quite similar to the K 240 M (with a high output impedance, the "S" is indeed quite bass heavy). I still prefer the bass response of my "moDFied" K240 over the "M" and "S" versions.

The K171 is, surprisingly, really nice, despite being recommended for "DJ mixing". I think it has a more neutral bass response than the K 240 S (sold mine to a friend though, so I can't compare directly).