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[Trahern]

Hi Klaus,

I recently acquired a sequential pair of 1973 U87s in nice cosmetic shape. However, the sound was a little off so I sent them to Germany (because I know you're really busy) and the original capsules got reskinned.

Unfortunately, for my needs, you are correct in your statements about reskinned k87 capsules sounding different than Neumann capsules. Not only is their tone different but they behave differently to EQ as well and respond to reverb in a different way.

Your probably thinking "just replace the capsules with genuine Neumanns and you'll be all set". However, here is the problem:

About a year ago I sent another U87 in to Sennheiser in CT to replace a bad capsule. The capsule they put in it sounds REALLY similar to how the U87AI sounds. It has a "hard" sound to it as you have stated several times about the current run of k87 capsules. This capsule doesn't sound "right" to me either. The K87 capsule should be open, spacious, natural sounding. The new one that I received from Sennheiser did not have any of these qualities.

Here's my question: How am I to get these 2 mics up to tip top shape without having to put sub-par capsules in them?

[klaus]

I am grateful for your post.

It adds yet another confirmation to what I have tried to express before, about the problems of current-generation K87/870, and the dilemma U87 owners face when trying to restore the sound of their mic by sending the capsule to have it re-diaphragmed ("reskinned"). And it hopefully adds to the conversation how we could get Neumann to make K87/870 replacement capsules available again, which have the full bottom end and lower mids they used to have until recent years.

There may be a proper place for the changed acoustics of the current-edition U87 capsule, but customers who wish to restore their increasingly pricey older mics to their original sound could and should also be accommodated.

[soapfoot]

Klaus,

Do you notice the same issue with the new K47 capsules as well, or do those still perform as-expected?

Apologies if this is slightly off-topic but it seemed like a decent time to pose the question.

[klaus]

Neumann Replacement K47 come through here relatively rarely, because of their high price, and because many owners of vintage U47/M49 etc. choose to send their capsules to Siegfried Thiersch for re-diaphragming.

The last K47/49 specimens I installed, which were manufactured about five years ago, were every bit as excellent as they've always been.

I will report how current production specimens sound, once I had a chance to install one.

[J.J. Blair]

I concur with Klaus' K47 assessment.

[muzikhead]

Hi Klaus and friends,

My 70's U87 capsule started to acting up, periodically getting muted when it gets some humidity from the human in front of it and recovering after a few seconds. I took it to a tech and he discovered a tiny hole in the capsule, so it looks like I'll need to replace my original capsule.

I was wondering if you guys have any experience with the current crop of Neumann k87 capsule production or if there's a decent replacement available?

Many thanks!

-Nir

[klaus]

Your "tech" gave you an opinion that may be based on ignorance. The "tiny hole has nothing to do with the moisture back-down you experience, but is added by Neumann on purpose: It serves as pressure equalizer for the atmospheric pressure between capsule cavity and ambient air pressure, which changes, depending on weather and altitude. The pressure differential inside the capsule would affect the movement of the diaphragm, if it were not allowed to equalize with its surrounding air pressure.

The moisture backdown is caused by capsule contamination which lowers the capacitance of the capsule's two capacitor plates (diaphragm and backplate) to the point that it no longer holds the charge and stops delivering sound. I would probably look for a qualified, experienced microphone specialist to have the capsule professionally cleaned and restored to factory specs. Usually, that takes care of the problem, and saves a bundle over purchasing a new capsule.

And: No, there is no decent replacement for a K87 available from anyone anywhere. I look forward for that to change some day. In the meantime, customers with truly defective capsules (probably not yours) need to purchase a new Neumann K87/67 to keep their mic's sound as original as is possible today.

[muzikhead]

Thank you Klaus! that's a big stone off my chest, I just love the way my 87 sounds and it would have been sad to lose that sound.

I'll be in NYC for the AES at the end of October, any specialist there you can recommend?

Kind regards,

-Nir

[soapfoot]

Nir,

I'd recommend PMing our host here; I bet he can steer you correctly (but is most likely reluctant to do any commerce on the open forum itself, as per his own rules).

[Kai]

The "tiny hole... serves as pressure equalizer for the atmospheric pressure between capsule cavity and ambient air pressure, which changes, depending on weather and altitude....

This is not only for atmospheric pressure changes, but more important, to give the capsule a defined lower limit of it's frequency response.
It's necessary to prevent subsonic frequencies from entering the recording.
Band limit is best done directly in the capsule to cut away unwanted frequencies before they disturb the mic's electronic or maybe even saturate the output transformer.

Once you have recorded with mic's that have a far lower tuned acoustic cut, specially omnis like the transformerless Bruel&Kjaer / DPA 4003's, you know how much subsonic energy is present in a normal environment. Even distant doorslams can cause problems with quiet sources.
On the other hand - the low frequency impulse response is greatly improved, recording low tuned drums is really fun.

Regards
Kai

[klaus]

Kai,
Do you have any Neumann documentation for the claim of sub-sonic wave control from the pressure relief hole? It is so tiny and, as far as I can see, done with a rather imprecise and varying thickness needle prick, that I cannot imagine a significant, calibrated low frequency equalizing of the diaphragm's inner pressure from such a tiny port, within a very fast response time.

What also speaks against this theory: On some K87 diaphragms, Neumann forgot the pinpricks, on others (K870) the total area of the port is a multiple of that of the pinprick's, due to Neumann using a wider slot between the two backplates, i.e. in an entirely different area of the capsule.

In none of these pressure equalization varieties (or lack of any) have I ever detected any difference in low frequency response of K87/870 capsules.

[Kai]

 I don't have any documentation from Neumann.
The only well documented microphones I know are Bruel&Kjaer ones made for measurement.
Here the port is built into the housing and factory tuned by partly filling it with different sizes of very tiny wires.
 I can only guess: it might be that Neumann is using the pinholes for tuning the capsules too.
 This would be an explaination for the different sized pinholes.
 I don't see any other reason for the pinholes at all, because the cardiod microphone's port on the back serves for atmospheric pressure equalization anyway.

Regards
Kai

[klaus]

You may be in error here: Neumann dual-membrane LD capsules have no tuning port, it's a hermetically sealed system, hence the pressure relief hole. So, your example of fine-tuning measurement capsules via calibrated porting may not be applicable to Neumann, AKG or similar LD capsules.