AKG D12 repair attempt...
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raketenmann
Well-known member
I know you commented on another post, but the information there is not accurate. In my experience, every AKG D12 has a bass chamber, regardless if there is a tranny or not. Sure, the tranny sits inside the bass chamber, but there is still a bass chamber behind it. so the part underneath the capsule itself is both: bass chamber and transformer housing. But yes: THERE ARE SOME OEM D12's that have such a big transformer that the bass chamber is stuffed so much the low end isn't as good as on a standard D12. As far as I know this can only be found in Norelco, Philipps and probably some other OEM D12's.
There's also a Version of the D12, called the Echolette Top12 that doesn't have a transformer, not even the bigger housing underneath it. The bass chamber there sits at the back of the capsule and even if it is way smaller, it delivers the same low end as the regular AKG D12 design.
Actually, I can't confirm if all the D12's over the years really had the same specs, but I would say they were pretty close in the low end, with or without a tranny in the chamber.
@panman you are the expert and can probably say, if they all sound sort of the same (if in fully working condition).
Yup, definitely. But we don't know how you got that eq curve. With a sine sweep? It is not so easy to get accurate results with that method...
raketenmann
Well-known member
Just a regular older D12: both a stepup tranny from 60Ohm to 200Ohm AND a bass chamber, all in one housing. Your low end loss has nothing to do with the chamber neither the tranny.Looking at 1 photo one would say there is a bass chamber, looking at the other they built the transformer into it
So maybe it!s a smaller chamber?
If you are about to ask questions like that, I assume it is your first D12 you put your hands on? How will you know that your diaphragm is aligned (which you said you did). I tried to do this work on a lot of D12's and was never able to do it. To realign a deformed diaphragm you need a hot air dryer, otherwise there's no chance. Probably you could replace the paper shims under the diaphragm mounting ring to get more "headroom" for the diaphragm to resonate and putting it into the correct distance to the resonator cap - but this is just guesswork if you don't know how it needs to look like.
Like I said, after putting my hands on a large amount of D12's I gave up and just pass them to @panman to do this work and stick with repairing more easier mics.
You certainly improve the sound, but to get it "up to specs" is an art.
StereoSteve
Member
It is for sure my first D12
By realigning i ment that as described earlier in this thread i was able to get way more low end by loosening the 6 screws and moving the diaphragm a bit. Even loosening was already a big difference. I started with the red graph!
Because i wasn't able to get more bass tan the blue graph i posted earlier, i was wondering if this version of the D12 simply didn't have more bass as s2udio suggested. Hence my original question if this was possible, without bass chamber.
I realize that putting the mic to specs is not in my ability, but i can try to improve it. In the first place i want to learn.
The way i measure is sufficient for my goal i think, if the bass response goes up i will know? I measure at my listening position, the yellow graph is the freq response with an omni at the same position. The D12 is lacking a bit of bass, to say the least
Thanks for your input!
By realigning i ment that as described earlier in this thread i was able to get way more low end by loosening the 6 screws and moving the diaphragm a bit. Even loosening was already a big difference. I started with the red graph!
Because i wasn't able to get more bass tan the blue graph i posted earlier, i was wondering if this version of the D12 simply didn't have more bass as s2udio suggested. Hence my original question if this was possible, without bass chamber.
I realize that putting the mic to specs is not in my ability, but i can try to improve it. In the first place i want to learn.
The way i measure is sufficient for my goal i think, if the bass response goes up i will know? I measure at my listening position, the yellow graph is the freq response with an omni at the same position. The D12 is lacking a bit of bass, to say the least
Thanks for your input!
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dmp
Well-known member
If you follow the method using a signal generator to drive the diaphragm, it's pretty clear when you have the diaphragm aligned without any interference. If you started with the red (-45dB @ 80Hz), and improved it to the plot from yesterday (-13dB @ 80Hz), I'd expect the signal from the generator cleaned up a lot. Is this all true? Can you sweep 20-100 Hz and hear a clean sound produced by the mic?
raketenmann
Well-known member
I tried this method befor with no success. I don't saye that it can't work, but it is not the whole story. The question in the first place is: Why is a diaphragm not aligned? It is because of magnetic dust that has been on it for many many years. The dust deformes the diaphragm. Sometimes you see clearly, sometimes you don't or it even deformes it in a concentric way, but still: the "headroom" is no longer available, you need to get thicker paper shims underneath it or correct the form with a heat air dryer.
But still: good luck, probably you get a usable amount of bass out of it! Probably you are as close as possible just with realigning the diaphragm.
StereoSteve
Member
The generator trick i use only the last days, the red curve is from years ago when i bought the mic cheap
Now i can get a clean tone down to 90 something Hz. If i go lower it rattles.
Point is, these low clean tones come wit the diaphragm pretty loose, once i tighten the screws it's no difficult to go back to the red graph
What's the level of the tone you feed the mic? Maybe i'm overmodulating
Now i can get a clean tone down to 90 something Hz. If i go lower it rattles.
Point is, these low clean tones come wit the diaphragm pretty loose, once i tighten the screws it's no difficult to go back to the red graph
What's the level of the tone you feed the mic? Maybe i'm overmodulating
dmp
Well-known member
It is the way to know if the alignment is causing poor mic performance. Yes, there can be several reasons why it is not possible to get the diaphragm in a position that allows clean movement. The worst is a deformed voice coil or contaminants in the VC gap. But you will still be able to hear if the diaphragm cannot move freely at low frequencies with the method. The OP is questioning if the mic is getting full bass response - need to know if the diaphragm is moving freely.
I've had varying success for the reasons you list. Sometimes you simply can't get it in a position to allow clean movement. I've tried it on a D25, D12E, & D20. The D25 was successful, and I've been using it for years since as my primary kick drum mic. The D20 would not align to get a clean signal. The D12E would align and sound great but after a few months would lose it and need realignment.
For beginners I would strongly suggest trying to tweak the diaphragm into a 'clean' position before doing anything else. Sometimes it can take many tries. Removing the diaphragm and trying anything else is extremely difficult.
I've had varying success for the reasons you list. Sometimes you simply can't get it in a position to allow clean movement. I've tried it on a D25, D12E, & D20. The D25 was successful, and I've been using it for years since as my primary kick drum mic. The D20 would not align to get a clean signal. The D12E would align and sound great but after a few months would lose it and need realignment.
For beginners I would strongly suggest trying to tweak the diaphragm into a 'clean' position before doing anything else. Sometimes it can take many tries. Removing the diaphragm and trying anything else is extremely difficult.
dmp
Well-known member
Then it is a diaphragm problem. You can forget about the bass chamber stuff until the diaphragm is moving freely.
As low as possibly when you can clearly hear it. Start with the generator at minimum and slowly bring it up. Driving it too hard could damage it.
This is exactly the trick. With the screws loose it is fine, but when tightened, if it isn't clean, it isn't free. Try again, over and over. If you try 25 times and it it hasn't become clean, it is likely the VC can't find a position that works (either warped VC or contaminants). Try many times before thinking of taking the diaphragm off.
StereoSteve
Member
I will, it's tempting though Thanks for your input.
Another question, the 3 even smaller screws in the cutout of the diaphragm ring, what are they used for?
Thanks for your input.Another question, the 3 even smaller screws in the cutout of the diaphragm ring, what are they used for?
dmp
Well-known member
Further disassembly I think. It's been a long time since I worked on one. But you only need to loosen the ones holding down the diaphragm.
raketenmann
Well-known member
dmp
Well-known member
I don't think we are saying different things? Everything you list would present as a diaphragm problem. Above I said:
I am helping the OP stop worrying about the bass chamber, realize his diaphragm has a problem, and not go beyond that until trying the alignment adjustment many times. Taking the diaphragm off is a good way to make the mic unrepairable. If it is still unsuccessful many times, could then try a thin piece of paper to shim the dipahragm up. Taking the diaphragm off to try to clean or adjust the VC is extremely hard. It would probably be better to send to someone with expertise at that point.
raketenmann
Well-known member
I don't think we are saying different things? Everything you list would present as a diaphragm problem. Above I said:
And also: Yes: I said the same to the OP: standard tranny, standard bass chamber: the lack of low end has nothing to do with this. In most cases the D12 doesn't sound right it is a diaphragm problem. The magnet is so strong, the diaphragm so thin and so big, every bit of magnetic dust leaves a big impact on it. And all of the ones I opened had magnetic dust on them. On other mics as a Shure 57 or 545, also on Sennheisers (421, 409) the impact of magentic dust isn't that of a problem, but on a lot of AKG's it is.
And yes: to repair it it is very very difficult. So the man for the job is @panman !
No, that I didn't wanted to say (english is not my native language). I just try to explain, that a diaphragm problem in most cases can't be solved by just realign it. if it was pressed down by magnetic dust, it doesn't work to recenter it, because the diaphragm is always to close to the motor.
And also: Yes: I said the same to the OP: standard tranny, standard bass chamber: the lack of low end has nothing to do with this. In most cases the D12 doesn't sound right it is a diaphragm problem. The magnet is so strong, the diaphragm so thin and so big, every bit of magnetic dust leaves a big impact on it. And all of the ones I opened had magnetic dust on them. On other mics as a Shure 57 or 545, also on Sennheisers (421, 409) the impact of magentic dust isn't that of a problem, but on a lot of AKG's it is.
And yes: to repair it it is very very difficult. So the man for the job is @panman !
StereoSteve
Member
I don't think your suggestions are contradictory and i get the point that it has to do something with the diaphragm. I managed to get distortion free tones till 60 Hz or so, below that the sound is so faint that it's difficult to interpret.
Made a new measurement - yellow. Not enough bass.
Then i thought maybe the published freq response of the D12 is measured with more proximity. In my setup the mic is some1.6 meters away from any source. I measured a MD441 ( pink) in the same position and bang, lots of bass.
So either the diaphragm is still restrained somewhere, or maybe there is something else.
I.e. is it necessary that the diaphragm placement is airtight? Maybe if there is a leak in the shims the bass chamber resonating effect could be diminished or diaphragm cancellation effects occur?
Made a new measurement - yellow. Not enough bass.
Then i thought maybe the published freq response of the D12 is measured with more proximity. In my setup the mic is some1.6 meters away from any source. I measured a MD441 ( pink) in the same position and bang, lots of bass.
So either the diaphragm is still restrained somewhere, or maybe there is something else.
I.e. is it necessary that the diaphragm placement is airtight? Maybe if there is a leak in the shims the bass chamber resonating effect could be diminished or diaphragm cancellation effects occur?
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dmp
Well-known member
Strange, on a good one you'll be able to clearly hear the sound down to 20-30 Hz.
If you turn down the level can you hear it? Maybe at low frequencies the travel is hitting something.
Yeah, and if you hook the signal generator up to the MD441 you'll see what I mean - you'll clearly hear the sound down to 20 Hz
I don't think so, you just want the diaphragm to be able to move freely. You do need to tighten the screws holding the diaphragm down.
How many times have you loosened, adjusted, tightened and tested with the signal gen?
StereoSteve
Member
Good suggestion in comparing with the md441! Sounds totally clean down to 30 Hz.
Restarted the procedure and managed to get result with the d12, clean to the bottom. But this doesn't result in more subs...
So i imagine something else is at play still, notice the mid bump too...
I'm checking my options, is there a way to PM @panman to discuss this matter? Panman if you read this, you can contact me
Restarted the procedure and managed to get result with the d12, clean to the bottom. But this doesn't result in more subs...
So i imagine something else is at play still, notice the mid bump too...
I'm checking my options, is there a way to PM @panman to discuss this matter? Panman if you read this, you can contact me
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I have a D12E thats been suffering for a bit now, wondering if anyone has some good instructions on disassembly of the capsule, it seems really convoluted in here and the felt is just EVERYWHERE inside..
never mind... i freed the capsule from the suspension figured i couldnt do anything with it and just checked the screws around the diaphragm (which mine has a weird felt thing over)... all the screws were VERY loose. I tightened them up and the mic now picks up below 30hz again.... whats that about?!
never mind... i freed the capsule from the suspension figured i couldnt do anything with it and just checked the screws around the diaphragm (which mine has a weird felt thing over)... all the screws were VERY loose. I tightened them up and the mic now picks up below 30hz again.... whats that about?!
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raketenmann
Well-known member
I don't know what all the dirt should be inside your mic?
Over the diaphragm is a resonator that has (depending on the model) sometimes has a piece of felt or some sort of fabric over it. This is a 2nd pop filter, resonator and dust cap in one piece.
whatever the felt like substance is inside the mesh is just weird. never felt (uh the pun) anything like it Just really strange. And yes, its like a black piece of cloth thats shaped over where the capsule should be. This seems to almost have its own ring with some golden paint or glue holding it on and then theres this grey paint or glue holding the second layer on (along with the screws). I dont think im gonna mess with it too much now that it seems like the mic is actually picking up correctly.
