I've had the bass light version of these headphones for 5 years and always wondered how the bass heavy one sounds. And so I bought one. The serial number was 13XX. It looked like new, no any signs of use whatsoever, like it was made not 20 years but yesterday. But from the first seconds of the test track there were obvious rattle sounds as mentioned in this thread before. So I took it apart and the glue that was used to keep the driver and the plate together was in a horrible condition. I barely pull the diaphragm and it came unstuck on one of the edges. So, I used the glue method introduced by hrklg01 http://www.head-fi.org/t/57805/history-of-the-akg-k1000/180#post_10593906 . And It was improved drastically but not completely. Now I think that almost every old pair of the К1000 is some way affected by this problem (that guy for the Flagship battle tried 7 pairs).
A few years ago there was a thread where Fitz took some pictures of the drivers and differences between but now unfortunately they're all gone. So I decided to take a few photos if someone is interested. Left is 1xxx, right is 8xxx.
As you can see, first, the plates below are totally different. Also there is a difference in the material of the driver. The later version is more transparent and the pattern of the bubbles is different. In addition to it the coating on the early is smoother.
At the right corner you can see the grid with two holes. They keep the driver plate and the rotary part of the headband together. On the early pair AKG used the glue instead of it.
The back of the driver also is not the same. First of all, the opening of the old versions is a little bigger. There are overlaps on the round basket. Another important difference is the voice coil on the early pair is not protected in any way, and it's very easy to tear it. So, if you want to disassemble your pair, you need to be very careful. On the later version is not a problem because is conected from the front.
The difference in the sound is also very obvious. You don't need even to compare them side by side.
First of all, actually, it's not the bass. The most striking difference is the medium and high frequencies. The later pair is much brighter. Sometimes it's a plus. When you listen to it quietly it sounds much more emotional and it seems more detailed. But if you want to listen louder it can become harsh and very bright.
Second, The early pair has much more bass. It's still as a matter of fact not "bass heavy". But the difference is significant. Maybe 3 or even 6 dB.
But while taking pictures I barely touched the foam disk and the dent appeared. It's obvious that the foam is too old and maybe it's another cause of the rattle because it's not always the same. Sometimes using the same test track I can barely hear it in one ear or another and sometimes it's quite strong and obvious. Maybe small foam particles get into the air gape.
You described a method for replacing the foam but I have a few questions.
To repair of a K1000:
As Karl wrote, a K1000 driver last for long time. However, the foam placed inside the center of the driver migh age... It did not on my very old prototype, but I did never place it on the sunlight... Foams are typically aging on light....
If small foam particles get into the air gap of the transducer, I guess it will cause some rubb & buss when driving strong.
To repair this I suggest first:
1) to check with AKG's service about their possibilities and not at least about guarantee
2) to open the basket carefully - may be there is already know hoe in this formum for this?. Then to ged rid of the inside foam carefully by any sharp plastic device like a plastic knife. (Careful! Do not skratch the very thin coil wire!!!!) Then to blow very strong to the air gap while fixing by hand the membrane. (do not worry - no danger at all)
3) Place a new 80ppi PU foam quite loose inside the center hole and fix it with just a bit of white glue.
This repair instructions are without any guarantee of my side of course!
To check the driver again, apply 25Hz AC slowly till the maximum dispalcement. If you do not hear any distortion in the far field before the hard contact of the membrane, th driver will be ok.
You haven't mentioned how thick should the foam disk. And I don't understand from the pictures how the foam disk is held up. There is no ledge or something to put the disk on. And the glue you described earlier (Ponal Wasserfest) is ok to do it?
And also I'm not sure how to cut a smooth round piece of foam. Do you have any suggestions? Sorry, many questions.)
Of couse not.) I think it's in the museum of AKG or something. I only found the pictures.)
Edited by qazxsw80 - 12/2/15 at 6:16am