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Vintage AKG C414 BE, how much is it worth? Modular Synthesizers
Old 5th October 2008
  #31
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BOWIE's Avatar
Quote:
Originally Posted by Klaus View Post
I guess no matter how I respond I will disappoint one of the two posters. Here is an explanation of what I meant:

Most if not all CK12 capsules are prone to lose tension over time.
It is unclear to me whether, in addition to the ravages of abuse (both in terms of high SPL and temperatur extremes), there is also a deteriorating factor in these skins that is out of the owner's control, one that can be attributed to 'aging' whatever that means on a molecular level. There are perfectly intact, clean looking capsules that are 50 years old, then there are CK12s from the 1970s which are shot.

Yes, I overstated (or at minimum sloppily explained) the percentage of CK12s I encounter which have catastrophic tension loss - return of the collapsed diaphragm to normal takes longer than 2 seconds - but I know from experience and post-mortem testing of CK12s that a large majority of those capsules that don't fall under the category defined above no longer has the diaphragm tension that they had when they were new. This condition expresses itself in a tubby, mushy low end, and/or in a grossly uneven frequency response lacking in the famous high frequency 'sheen' the capsule usually possesses. These two types of defects add up to to a good 60-75% of all remaining CK12 capsules one encounters in 2008, in my experience.

The bottom line:
It is always self-evident to the ears whether a CK12 is defective. In catastrophic cases, the capsule's diaphragm gets sucked in by the back plate's polarization voltage- just by itself, when you turn on the mic, or with a little help from popping a 'P' with your the lips right in front of the capsule- and then the low end is completely gone, with the output down by at least 15 dB. In less than catastrophic cases of tension loss, when the capsule is gradually on its way out, it sounds less than flattering at the extremes of the response curve.

By the way: there is no correlation between tension loss/sucking in of diaphragms and contamination, regardless of the ill effects that contamination (lowering of the impedance between the two capacitor plates) has. With other words: cleaning a diaphragm will not improve its tension.
That's for the detailed explanation Klaus.
Old 6th October 2008
  #32
Gear Maniac
 

two cents worth

1) the deal you got on the 414 was excellent. if you can sell it for 2000. , i suggest you grab the dough.
2) i think a 414 is a barely acceptable mic in any case , but yours is better than one that has the plastic ring capsule.
3) If the mic sounds good, it sounds good....
4) i think a cloth bag is a better idea than a plastic one, and if the foam in your mic box is old and falling apart , do replace it with a new piece of foam . A single edged razor will cut the spaces you need in the foam.
5)arizona is a better environment for mics than ny...moisture is one of the things that helps gunk build up on the capsule. dry is good....capsules dont "dry out " except perhaps old neumann pvc diaphragms .
6) if your capsule starts making spitting weird noises when you blow an "h" or "ha" sound directly into it, then its "moisture sensative" which may be correctable by proper cleaning. DO NOT attempt to clean it yourself. do not EVER touch the capsule with a q tip.....Ill clean it for you for $150. if you like. or there are numerous other guys around who have done it for many years.

as for the tensioning issue, there are lots of ck12s around that are still working well; certainly we've all seen ones that werent.
7)ALWAYS use a windscreen on vocals or horns, and dont take the mic into the bathtub......
Old 6th October 2008
  #33
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jjblair's Avatar
Klaus, I was wondering when you would stop lurking! Thanks for jumping in to educate us both. I always appreciate the knowledge you share.

Let me clarify something I think I stated unclearly: in the case where you cleaned a capsule that was collapsing, and in the case where toby foster did the same, the capsules stopped collapsing. I did not mean to suggest that cleaning fixed a loss of tension. I am simply saying that implies that the loss of capacitance seemed to me due to contamination rather than tension loss. Please correct me if my interpretation is wrong.

Secondly, given what I have learned about the stability of Mylar, even if the failure rate is as high as you say, would it not seem as logical to you as it does to me that a capsule that has already survived this long is not the ticking time bomb that was inferred?

My objection was simply to the advice dispensed, based on what I considered a misunderstanding of your post. Even though i had always understood from you that rejection rates were very high, and that failure rates on the aggregate were quite high, I never once got the impression from you that any remaining functioning CK12s are destined to fail, like M7s are.
Old 6th October 2008
  #34
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Klaus's Avatar
 

J.J.:

"Collapsing" can be interpreted in two ways:

One, the capsule's capacitance collapses electrically, due to lowered impedance, as a result of contamination.
The other, the diaphragm physical collapses into the backplate, due to mechanical tension loss.

As I mentioned, the former problem can often be repaired on a CK12, the latter never.

What makes the CK12 inherently more unstable over time than, let's say, a Neumann K87 capsule are two factors:

One, the diaphragm is not supported in the center, and tensioning such large diameter sufficiently without losing low frequencies requires a balancing act by the manufacturer: ideally, the diaphragm is barely tensioned enough to withstand the electrostatic suck of the back plate yet retain bass balance.

Two, Neumann, unlike AKG's CK12, utilizes small non-conductive nipples cast into the backplate surface which act as additional electrical charge repellant, which is a much more efficient means to keep the diaphragm away from the attractive backplate than AKG's method of oxidizing or layering the brass surface of the backplate with low conductive layer.

In sum, the time a CK12 diaphragm spends pressed against the backplate accrues to the point of stressing the plastic film and stretching it gradually over the years. Leaving aside the problems with the CK12 Styroflex diaphragms AKG used in its early years, I do not believe that there are "self-aging" factors of the polyester diaphragm material that need to be considered.
I believe the trouble with original CK12s is a combination of sloppy and inconsistent diaphragm assembly and length of exposure to polarization voltage and high SPLs.

Preventative measures for a healthy CK12 then, would consist of avoiding high SPLs, not storing the mic in a car's trunk in the summer or winter, and, as Dan Alexander wisely mentioned, always storing the mic in a suitable dust barrier bag when it is not in immediate use.

Best regards,
Klaus Heyne
Old 7th October 2008
  #35
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jjblair's Avatar
Thanks for clearing that up, Klaus. Always appreciated.
Old 8th October 2008
  #36
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Jim Kerr's Avatar
 

Quote:
Originally Posted by dan alexander View Post
1) the deal you got on the 414 was excellent. if you can sell it for 2000. , i suggest you grab the dough.
2) i think a 414 is a barely acceptable mic in any case , but yours is better than one that has the plastic ring capsule.
3) If the mic sounds good, it sounds good....
4) i think a cloth bag is a better idea than a plastic one, and if the foam in your mic box is old and falling apart , do replace it with a new piece of foam . A single edged razor will cut the spaces you need in the foam.
5)arizona is a better environment for mics than ny...moisture is one of the things that helps gunk build up on the capsule. dry is good....capsules dont "dry out " except perhaps old neumann pvc diaphragms .
6) if your capsule starts making spitting weird noises when you blow an "h" or "ha" sound directly into it, then its "moisture sensative" which may be correctable by proper cleaning. DO NOT attempt to clean it yourself. do not EVER touch the capsule with a q tip.....Ill clean it for you for $150. if you like. or there are numerous other guys around who have done it for many years.

as for the tensioning issue, there are lots of ck12s around that are still working well; certainly we've all seen ones that werent.
7)ALWAYS use a windscreen on vocals or horns, and dont take the mic into the bathtub......

Dan, thanks for the tip (5 & 6)! Hey I met you in Hollywood, Wardbeck!!! Been building....and writing.

Klaus, the engineering and appreciation that encompasses these little devices that we all use is amazing and remarkable. It's especially cool having a peak at how and why. Thanks for that.
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