R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 3 [All]   Go Down

Author Topic: Original AKG CK12 Capsules: Sound, Lifespan and Repair  (Read 26277 times)

mike zietsman

  • Newbie
  • *
  • Offline Offline
  • Posts: 19
  • Real Full Name: mike zietsman
Original AKG CK12 Capsules: Sound, Lifespan and Repair
« on: November 23, 2012, 02:35:38 PM »

I thought I would post about a topic that comes up fairly often and with which I have had some recent experiences.

Out of the mics that I have had access to the akg c414 has always been one of my preferred mics for my own vocals - I have one of those voices that deals terribly with a u87 (but keep one around because it works 'respectably' on so many voices. )

I have had three versions of the c414 which I have used extensively - namely the buls, the eb p48 and the silver eb with the brass ring ck12 (with the brass ringed ck12 being the most recent acquisition).

The two versions that I have owned the longest always worked very well but I have always had several constant issues to do with their sound.

The three main issues that I have had with them are:

1: Almost universally I found myself having to apply quite heavy cuts in the 120 - 230hz region to compensate for a very obvious resonance there that would otherwise act to blur a lot of higher frequencies and make voices sound obviously muddy.

2: Sibilance (when present) was often 'smeary' and difficult to isolate as it would occur at several harmonics making harshness a problem - it almost seams counterintuitive but this harshness often made it difficult to bring 'airiness' and 'detail' into voices. You would almost expect a harsh mic to have detail but I often found myself thinking that vocals sounded harsh and lacking detail.

3: I found the midrange difficult to sculpt.

Upon using the eb with the brass capsule I noticed an immediate difference for the better in almost all regards.

The 120 - 230ish resonance was completely gone in my room. The midrange was more forward and when I have dealt with sibiliance it has been much easier to deal with and more musical (there is also a great deal more air around the top end that doesn't interfere with anything or sound harsh).

I know that this isn't news to a lot of people on this board but I just thought i would share my experience. I didn't think that the sound difference between two mics in a series could be so drastic. The buls and the ebp48 (barring the level difference) were near identical in sound (and at a quality level that I would rank as being a step or two lower than the u87) whereas the OG silver eb was another level of microphone and one I am glad that I purchased!

This forum was also a great resource in establishing the condition of the capsule (using Klaus's  Figure of 8 technique with the grill removed and power applied I couldn't get the diaphragm to suck to the backplate at all for longer than a millisecond). I feel it is only fair to share my experiences in return.

Thank you to everyone who shares their knowledge. I hope this is useful to someone!
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: 414eb with brass ring ck12 vs c414eb p48
« Reply #1 on: November 23, 2012, 04:20:34 PM »

As an owner familiar with three different C414 models, performing an additional test would be fun and quite revealing:
would the original CK12 (brass) capsule make a difference in sound if you were to temporarily transplant it to one of the other two mics?

My guess (i.e. MY experience): you would get about 70% of the EB's sound with the original CK12 capsule placed in the more recent models. The remaining 30% being the electronics/transformer of the P48/BULS.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mike zietsman

  • Newbie
  • *
  • Offline Offline
  • Posts: 19
  • Real Full Name: mike zietsman
Re: 414eb with brass ring ck12 vs c414eb p48
« Reply #2 on: November 23, 2012, 04:46:41 PM »

I considered trying just that but decided to leave well enough alone. After using the mics together for a while I decided I was getting everything I liked about a 414 with way less that I didn't out of the silver eb and sold the other two (I generally do mono vocal recordings). I think mic auditions are vital for learning and trying out new mics, plus the gearhead in me really enjoys them - but after a while I have to force myself to make/record some music! The process certainly made me very eager to hear more mics that used the original brass ringed capsule.

Doing the shootout over a bit of a longer period also taught me a lot about the differences in in real world use and how they aren't just academic at all. Seemingly small differences at the initial recording stage lead to much more tangible differences at the mixing stage. (ie. I found the difference in quality of the microphone to become more significant throughout the process of mixing).

Logged

Peller

  • Newbie
  • *
  • Offline Offline
  • Posts: 30
Re: 414eb with brass ring ck12 vs c414eb p48
« Reply #3 on: November 26, 2012, 10:27:07 AM »

Klaus, could I beg you to share some of your experience regarding membrane tension in these capsules? I have two 414EBs with CK12s. One is fine, while the other is suffering from some tension loss, and can get sucked onto the backplate, especially in fig-8. Is there anything that can be done for it other than a re-skin?
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: 414eb with brass ring ck12 vs c414eb p48
« Reply #4 on: November 26, 2012, 03:57:40 PM »

In my experience, a significant amount of original AKG CK12, made from 1953 through 1976, suffer from gradual or complete loss of diaphragm tension. The reduced tension often seems unrelated to use or abuse.

Tension loss may be due to several factors:

* the CK12 diaphragm is rather large and unsupported  in its center, unlike similar-sized Neumann capsules with center lead-out screw

* stand-off nipples mounted into backplates, which prevent electrostatic collapse on most Neumann capsules, are not present on CK12

*Styroflex membrane material seems to be more prone to fatigue than polyester/Mylar/PE

Remedies are, in order of my preference:

1. reverse the capsule, and hope that the diaphragm tension on the rear side is still ok. Then forfit patterns other than cardioid for that mic

2. Replace defective  diaphragm with healthy original CK12 diaphragm from same era

3. Replace entire CK12 with healthy CK12 (both AKG products, of course!)

4. Send capsule to Tim Campbell in Denmark, and have him replace both diaphragms
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Peller

  • Newbie
  • *
  • Offline Offline
  • Posts: 30
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #5 on: November 29, 2012, 09:02:55 AM »

Thank you Klaus,

That is absolutely the clearest statement on the topic I've ever read!

In your experience, how much of an impact does the gradual tension loss have on sound quality, S/N ratio and so on in the early stages, before it becomes significant enough to cause collapse?
Logged

Nob Turner

  • Newbie
  • *
  • Online Online
  • Posts: 40
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #6 on: November 29, 2012, 11:19:29 AM »

a friend asked me last night what the result might be of putting a brass ck12 in a 414B-ULS. is the circuitry significantly different, such that it wouldn't sound similar to an original 414EB?

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #7 on: November 29, 2012, 02:09:14 PM »

Coincidentally, I received an email inquiry from Germany with the same question two days ago, to which I responded (in part):

"in these mics, the capsule contributes about 70% (as if one could assign a number to sensual impressions!) to their overall sound. Installing an original CK12 from the 1970s will therefore have a noticeable impact, but the remaining sound-shaping components of the transplant patient will either augment that new experience or partially negate it. The level of either can only be assessed by the listener's astuteness."

An original CK12 "brass" (as if they weren't all delivered with brass surround!) is an expensive proposition these days, so it may be questionable to invest more than the mic was worth in the first place.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Jim Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 599
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #8 on: November 30, 2012, 11:50:30 AM »

Many of the older EB capsules have been removed and used in other mics. One fellow in California a decade ago bought all he could find and placed them into those AKG "The Tube" mics he bought used for about $500. The remainders are privatly held or are suffering from age and use. It's sort of rare to find clean good condition "c-12" capsules these days. New aftermarket solutions may be the best scenerio.
Logged

Pasarski

  • Newbie
  • *
  • Offline Offline
  • Posts: 4
  • Real Full Name: Pasi Siitonen
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #9 on: December 21, 2012, 01:59:48 PM »

FYI: AKG has started to offer re-skinning of brass CK12's. I got this Information from Mr. Michael Amon of AKG Vienna/Austria who is the technician doing the re-skinning.
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #10 on: December 23, 2012, 02:49:43 PM »

Thanks for the info. I will chat with Michael, and report back.

Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #11 on: January 07, 2013, 08:32:00 PM »

Update:
Corresponded with Michael Amon, and he confirms: he personally re-diaphragms CK12 (old style, with diaphragm screws) with current crop of AKG polyester skins.

I will report back, once I have the information as to shipping and payment logistics (re-diaphragming price per side: €150, or €300 for the whole capsule), and, most importantly: quality of work.

I probably will send him and Tim Campbell each an ELA M 251 capsule, and then compare the outcome.

Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Tim Campbell

  • Newbie
  • *
  • Offline Offline
  • Posts: 26
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #12 on: January 09, 2013, 10:21:39 AM »

Since we're mentioning prices here mine are listed on my webpage. 1100 danish kroner (147.50 euro) for 1 membrane, 1500 danish kroner (201.50 euro)  for both. Shipping is 100 danish kroner (14.00 euro)by Fedex.
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #13 on: January 09, 2013, 01:52:14 PM »

Appreciated! And an exception I've made on this forum, because of the extreme rarity of the service, and the high demand for it.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mike zietsman

  • Newbie
  • *
  • Offline Offline
  • Posts: 19
  • Real Full Name: mike zietsman
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #14 on: February 17, 2013, 04:44:12 AM »

Does anybody know if motorboating (low frequency self oscillation) is ever associated with tension loss in the ck12 capsules in the akg c414eb models?

I replaced all of the tantalum capacitors on mine which made it much better but not perfect?

What are the signs of a ck12 capsule on the way out?

Thanks,
Mike
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #15 on: February 17, 2013, 02:34:26 PM »

Motorboating CAN be a sign of capsule deterioration- most often it's moisture discharges, due to diaphragm contamination.
Injuries to diaphragms can also cause momentary shorting to the backplate, with the same symptom of motor boating.

Unfortunately, electronic component deterioration sometimes also shows up through motorboating discharges.

Signs of capsule deterioration always include audible artifacts to the signal. So I would not be concerned if the sound of the mic is as it normally would be.

Here are some of the audible signs of capsule deterioration:

* excess distortion,
* gross frequency response aberration (on CK12 usually a severe drop-off in low frequencies, or, worse, telephone-like response 
   with pronounced mids and not much else), and, most often,
* discharge noises, like background thundering, slow farting sounds and other odd, irregular discharge sounds

In all of the above cases, the cause for the noise may also be an electric or electronic one, so additional steps of confirmation (f. ex. can the noise be triggered or altered through close breathing onto the capsule?) need to be done.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mike zietsman

  • Newbie
  • *
  • Offline Offline
  • Posts: 19
  • Real Full Name: mike zietsman
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #16 on: February 17, 2013, 07:15:32 PM »

As always, thanks for your help Klaus.

Strangely enough mine sounds fine (I think it sounds quite good and definitely emits a full frequency response that is free of obvious distortion) Breathing on the capsule gives maybe half a second of static, sending a short sharp plosive into the capsule gives a short sharp click (no doubt the sound of the capsule bottoming out?) but the mic recovers immediately in all patterns. (I don't do any of these tests often! Only after the motorboating became evident)

However tapping the side of the mic makes the motor boating become worse, as does tipping the mic on it's side.
(this happened in two locations and it is not just the mic picking up stray mechanical noises)
If i recall correctly it is worst in figure 8.

The only solution that I could find online to the motorboating was to change the tantalums. My tech changed the tantulum capacitors which made it much better (and made the mic usable again) but it is still slightly intermittent (whereas before it was constantly present and intermittently got worse).

I found one suggestion online (on another forum - to someone else with a similar problem) to replace the three diodes on the dc converter board but my electronics knowledge is insufficient to know if this is a good idea and my tech said that they were unlikely to go bad or cause motorboating. (aside from the fact that I am not a huge fan of just replacing parts in things "just incase" because of an anonymous message on the internet).


In the next couple of weeks a friend in a different part of the country is giving me a 414eb with a broken capsule and (as far as he knows) functioning electronics. changing the capsule into this mic should be a revealing process.

In the meantime I am going to use the mic in non-critical applications to discern if it is actually giving real world problems.

If anybody has anything that might point me in the right direction it would be greatly appreciated - I fear that I have a capsule arriving at the beggining of it's end (though reading Klaus's last post eases my fears a great deal).

failing that I will report back on anything that I find out.

Thanks,
Mike
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #17 on: February 17, 2013, 08:18:13 PM »

I agree with your tech: the diodes are unlikely culprits.

But you seem to have something that is repeatable: positioning or mechanical pressure on one side of the mic.

Do this: remove the square housing and then plug the mic back in. With a fiddlestick (a non-conductive stalk) poke around the area that triggered the motorboating while the housing was still on. Despite the increased hum, due to the lack of shielding from the missing housing, you should be able to hear any changes in motorboating.

Likewise, if all motorboating has stopped with the housing off, maybe there was intermittent contact between an electronic component or wiring and the (conductive) housing? Probe around for possible tight spaces in the amp compartment, and possible contact/shorting between components and housing.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

GYMusic

  • Newbie
  • *
  • Offline Offline
  • Posts: 36
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #18 on: February 18, 2013, 07:16:31 PM »

The three main issues that I have had with them are:

1: Almost universally I found myself having to apply quite heavy cuts in the 120 - 230hz region to compensate for a very obvious resonance there that would otherwise act to blur a lot of higher frequencies and make voices sound obviously muddy.

2: Sibilance (when present) was often 'smeary' and difficult to isolate as it would occur at several harmonics making harshness a problem - it almost seams counterintuitive but this harshness often made it difficult to bring 'airiness' and 'detail' into voices. You would almost expect a harsh mic to have detail but I often found myself thinking that vocals sounded harsh and lacking detail.

3: I found the midrange difficult to sculpt.

I have a 414 B-ULS and a Tl-II.  I have noticed the same issues when using as a vocal mics.  I recently tried recording with the filter engaged for 150 Hz.  That really helped with the bottom end sitting better in the mix with little other post EQ.  I also use a Shure KSM-44 for vocals and they seem to exhibit the same tendencies as you point out (around 200-500 Hz), but I like the top end a bit more with the 44.  I couldn't help but chime in when I read of the issues we shared.

GY 

usattler

  • Newbie
  • *
  • Offline Offline
  • Posts: 49
  • Real Full Name: Uwe Sattler
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #19 on: February 19, 2013, 04:29:12 PM »

What ever happened to the simplest and reliable method to determine whether crackling is caused by the capsule or a component in the electronic interface (amplifier)? Disconnect the capsule and substitute with a quality (styrene, mica or good ceramic) capacitor of aproximately the same capacitance value and listen to the microphone output after placing it back into its housing to avoid masking by hum.

For dual diaphragm microphones this may require two capacitors, and using this substitution one side at the time even allows to identfy which side may be the cause.
Logged
Uwe Sattler
Technical Director - Neumann|USA (retired)

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #20 on: February 19, 2013, 05:38:15 PM »

Still a good testing method.

But some mic owners get nervous when their shaky fingers get close to a 6µ thin membrane that costs several hundred dollars to replace if they slip. So the breath test is a decent fallback.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

usattler

  • Newbie
  • *
  • Offline Offline
  • Posts: 49
  • Real Full Name: Uwe Sattler
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #21 on: February 20, 2013, 08:44:43 AM »

The breath test does provide for a quick check without disassembly of the microphone, but is often limited value beyond revealing more than the presence of rogue static bias discharge through hygroscopic contamination. Working on and inside a valuable studio microphone should not be for anyone with shaky hands to begin with. No reasonable technician should attempt soldering at the leads close to the diaphragm, but rather at their far end...
Logged
Uwe Sattler
Technical Director - Neumann|USA (retired)

Jim Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 599
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #22 on: February 20, 2013, 11:51:50 AM »

Use that pad to determine where the problems lie. If the problems are attenuated by the use of the pad switch, (-20 db in a B-ULS) then it's located in the head amp before the filter section. That does locate the problem on one of the two pcb's.

My experience with these mics is the most likely components to fail are the tantalum caps in the power supply circuits. Always check the power rails first on these mics first or you may be following a false trail.
Logged

mike zietsman

  • Newbie
  • *
  • Offline Offline
  • Posts: 19
  • Real Full Name: mike zietsman
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #23 on: February 28, 2013, 10:14:28 AM »


My experience with these mics is the most likely components to fail are the tantalum caps in the power supply circuits. Always check the power rails first on these mics first or you may be following a false trail.


After replacing all of the tantalum capacitors in my eb I am still getting a reduced voltage to the capsule (I think it was about 40v instead of 60v) which my tech suspects might be because of his multi meter not being able to measure accurately in the part of the circuit that has such a high impedance - does that sound logical?

Also - I am getting a lower output from my eb than I am from a friends eb p48 - about 6 or so db and I would have thought it would be the other way around because of the relatively lower voltages being fed to the capsule on the eb p48. Is that normal?


Thanks,
Mike
Logged

Jim Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 599
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #24 on: February 28, 2013, 10:48:16 AM »

Measure the oscillator output before the series resistors, those are large values and will attenuate the voltage from a high impedance. Most DVM's are 20 meg ohms or less input impedance so they will show a lower reading if you measure after those series resistors on the output of the oscillator.
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #25 on: February 28, 2013, 01:52:24 PM »

Measure the oscillator output before the series resistors, those are large values and will attenuate the voltage from a high impedance. Most DVM's are 20 meg ohms or less input impedance so they will show a lower reading if you measure after those series resistors on the output of the oscillator.
This is good advice for measuring polarization voltage in high impedance sections of ALL condenser mics, not just this model.

These super-high-value resistors (up to 1gig or more) rarely fail, so measuring at their input, i.e. right before them, is a reasonably good way to ascertain that the proper polarization voltage gets into the section.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

J.J. Blair

  • Full Member
  • ***
  • Offline Offline
  • Posts: 130
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #26 on: March 04, 2013, 12:49:25 PM »

I would like to report that Harman/AKG does indeed do legacy repairs on 414EBs at their Northridge, CA location.  I just had two of mine of them fixed there (bad switches and one blown preamp), and they did a fantastic job.  They do not do capsule work, but options for that have already been discussed in this thread.
Logged

Jim Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 599
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #27 on: March 05, 2013, 11:52:52 AM »


I am getting a lower output from my eb than I am from a friends eb p48 - about 6 or so db and I would have thought it would be the other way around because of the relatively lower voltages being fed to the capsule on the eb p48. Is that normal?


Thanks,
Mike

No, that suggests a reduced polarization voltage. The P-48 model has no oscillator, it's like an original U-87 taking the phantom voltage to the capsule, at a reduced level. Usually it's around 42 volts or so after all the series resistors and such. That is why the P-48 414 is about 5 db less output than an older 414 EB. Those use the internal oscillator to raise the polarization voltage to 60~62 volts.
Logged

mike zietsman

  • Newbie
  • *
  • Offline Offline
  • Posts: 19
  • Real Full Name: mike zietsman
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #28 on: March 13, 2013, 05:39:33 PM »

No, that suggests a reduced polarization voltage. The P-48 model has no oscillator, it's like an original U-87 taking the phantom voltage to the capsule, at a reduced level. Usually it's around 42 volts or so after all the series resistors and such. That is why the P-48 414 is about 5 db less output than an older 414 EB. Those use the internal oscillator to raise the polarization voltage to 60~62 volts.

Hmmm.... after replacing every tantalum cap in the mic I am still getting a reduced voltage in my older eb (about 46volts measured just before the resistors before the capsule). Any other ideas about where I might look?

as always - thank you so much!

Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #29 on: March 13, 2013, 06:50:19 PM »

Do you get the same voltage (as a minus voltage) for the rear side (Figure eight)?
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

usattler

  • Newbie
  • *
  • Offline Offline
  • Posts: 49
  • Real Full Name: Uwe Sattler
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #30 on: March 14, 2013, 09:11:52 AM »

Quote
(Quote inserted by K.H., assuming that this was the subject of Uwe's response)

that suggests a reduced polarization voltage. The P-48 model has no oscillator, it's like an original U-87 taking the phantom voltage to the capsule, at a reduced level. Usually it's around 42 volts or so after all the series resistors and such. That is why the P-48 414 is about 5 db less output than an older 414 EB. Those use the internal oscillator to raise the polarization voltage to 60~62 volts.

All other things being equal, the difference in sensitivity resulting from the bias voltage change for a condenser capsule from 42 to 62 V would be 20 log (62/42), or barely 3.4 dB!
Logged
Uwe Sattler
Technical Director - Neumann|USA (retired)

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #31 on: March 14, 2013, 03:13:40 PM »

Uwe, and others:
There are of course tonal differences, due to the different electrostatic attraction forces, between "properly" polarized LD polyester capsules (around 60VDC) and those that are under-polarized.

But, what about headroom considerations when under-polarizing? How is headroom affected? Seems to me, on one end, under polarizing puts less stress on the FET's limited input capacity (gate). But I often find that robustly polarized capsules perform better, with more robust dynamics.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

mike zietsman

  • Newbie
  • *
  • Offline Offline
  • Posts: 19
  • Real Full Name: mike zietsman
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #32 on: March 15, 2013, 04:35:04 AM »

Do you get the same voltage (as a minus voltage) for the rear side (Figure eight)?

I vaguely remember the voltage being the same - the mic was set in cardoid though - would that affect anything?. I will double check asap and report back...
Logged

Jim Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 599
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #33 on: March 15, 2013, 12:20:03 PM »

All other things being equal, the difference in sensitivity resulting from the bias voltage change for a condenser capsule from 42 to 62 V would be 20 log (62/42), or barely 3.4 dB!

"Being Equal" is the key. This assumes capsule sensitivity is linear or pure log with voltage applied. I've never done this but I suspect the capsule output does not follow a linear voltage vs sensitivity curve. One could test this by measuring capsule sensitivity at various polarization voltage levels. The chart plotted from this would be interesting. I wouldn't be suprized if some bumps occured in the plot.
Logged

usattler

  • Newbie
  • *
  • Offline Offline
  • Posts: 49
  • Real Full Name: Uwe Sattler
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #34 on: March 18, 2013, 02:31:42 PM »

Within the operational range of a capacitive transducer its sensitivity is directly proportional to the polarization voltage:

         e(t) = Eo*c(t)/Co,     where

e(t) is the output voltage,
Eo is the DC-bias voltage,
c(t) is the change in capacity due to diaphragm movement,
Co is the transducer capacitance at rest without sound input, and
t is time

The operational range is limited at both ends by the distance between the fixed electrode (back plate) and diaphragm, and to a lesser degree by the diaphragm tension. Too much DC-bias and/or too little distance may lead to arc-over or 'fatal' attraction, too little of either will reduce sensitivity and signal-to-noise ratio.
 
I can neither see any reasonable explanation or physical cause for non-linearity in sensitivity or any frequency dependency due to changes in the polarization voltage, nor have I ever experienced, heard or measured such behavior. This independence is actually used in many condensator studio microphones to control the sensitivity through adjusting the bias voltage of the transducer, and with dual diaphragm capsules enables the creation of multi pattern microphones.
Logged
Uwe Sattler
Technical Director - Neumann|USA (retired)

Tim Campbell

  • Newbie
  • *
  • Offline Offline
  • Posts: 26
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #35 on: March 19, 2013, 09:00:41 AM »

Uwe, like you, I haven't noticed this non-linearity. During construction of capsules I use variable polarization voltage to measure some parameters. I will say that different types of capsules react uniquely to changes in dampning and polarization. Because these two forces aren't interdependent I could imagine a situation where dampning may be able to overcome additional attraction when the membrane is closest to the backplate but not when it is farthest away or the opposite and this might possibly translate into slight non-linearity. Also in a capsule type where you have one membrane sandwiched between two backplates of equal attraction you may find a limit to output gain with greater polarization.
Logged

usattler

  • Newbie
  • *
  • Offline Offline
  • Posts: 49
  • Real Full Name: Uwe Sattler
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #36 on: March 19, 2013, 11:41:46 AM »

Simply put: Why speculate what happens when pushing the past the limits of the intended operational range? For such applications a different transducer would have to be defined...
Logged
Uwe Sattler
Technical Director - Neumann|USA (retired)

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #37 on: March 24, 2013, 04:13:14 AM »

I can neither see any reasonable explanation or physical cause for non-linearity in sensitivity or any frequency dependency due to changes in the polarization voltage, nor have I ever experienced, heard or measured such behavior. This independence is actually used in many condensator studio microphones to control the sensitivity through adjusting the bias voltage of the transducer, and with dual diaphragm capsules enables the creation of multi pattern microphones.

Unlike you, Uwe, I experience frequently what happens when too much capsule bias voltage is applied:
There is a microphone modifier (who shall remain nameless), who specializes in "quieting down" tube mics by adding 20 volts of polarization voltage beyond the nominal amount traditionally applied to Mylar® LD capsules (around 60VDC).
The mics sound like hell, to put it politely; hard, honky and grainy. The sound immediately returns to its former sweetness once I reduce the voltage back to normal.

It's pretty obvious to me what goes on: too much electrostatic backplate attraction from the over-voltage freezes up the diaphragm movement.

So, in a perverse sense, what is gained in S/N and gain is lost in linear response, especially when complex musical sources are processed. I am sure you guys in Connecticut or maybe in Berlin have some fancy chamber and sensitive enough instruments, where it can be shown what happens to complex waveforms when a backplate is bombarded with too much voltage.

Quote
this independence (from a set capsule bias voltage) is actually used in many condensator studio microphones to control the sensitivity through adjusting the bias voltage of the transducer
But only within reason.  I know of no situation where more than ±60 volts are pulling on a diaphragm.

Quote
... and with dual diaphragm capsules (a variable bias voltage) enables the creation of multi pattern microphones.

Again, never are more than 60 volts electrostatic attraction present; even when the rear pattern control pumps 120VDC into the back diaphragm, the voltage differential between plates never exceeds 60VDC static pull.



Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Tim Campbell

  • Newbie
  • *
  • Offline Offline
  • Posts: 26
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #38 on: March 24, 2013, 07:59:41 AM »

Just to add a little info, Brüel & Kjęr commonly uses 200v polarization voltage. Their capsules are omni with metal diaphrams and a large spacing between membrane and backplate.
Logged

klaus

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2084
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #39 on: March 24, 2013, 02:35:25 PM »

That's why I specified LF mylar diaphragms which usually use ± 40µ spacing.  There's likely no sonic penalty to push as high as 200V if the diaphragm is small enough and its proportion of tension to backplate gap is properly chosen to withstand the effects of electrostatic suck.
Logged
Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

usattler

  • Newbie
  • *
  • Offline Offline
  • Posts: 49
  • Real Full Name: Uwe Sattler
Re: Original AKG CK12 Capsules: Sound, Lifespan and Repair
« Reply #40 on: April 01, 2013, 08:34:13 AM »

The operative words are: "WITHIN THE OPERATIONAL RANGE OF A CAPACITIVE TRANSDUCER" - that shouls exclude any abnormal biasing beyond this range, Some transducers are specifically designed for higher or lower polarization voltages than the 60 V common for large diaphragm Neumann capsules (and many clones). Due to their typically greater diaphragm tension pure pressure transducers (dedicated omni) often can tolerate higher bias than pressure gradient (bi-directional and cardioid) transducers with their low tensioned diaphragms. Diaphragm size and spacing to the stationary backplate are other determining factors for the proper bias. In any case, within the operational range the relationship between bias and sensitivity is strictly linear! Once any deviation from this physical law is encountered, the designed for operational range has been left behind, either by excess bias or (far less likely) excess SPL.
Logged
Uwe Sattler
Technical Director - Neumann|USA (retired)
Pages: 1 2 3 [All]   Go Up
 



Site Hosted By Ashdown Technologies, Inc.

Page created in 0.034 seconds with 19 queries.