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[aremos]

Of course we're all looking for Klaus's review! But have been using it for months now & it's really a great mic, to say the least & in it's own right. Is it exactly & a replica of V.1 (or 2)? We'll wait for Klaus on that aspect of it.

[aremos]

Klaus,
You stated: " ... a brand-new K870 (build date late 2012), and my jaw dropped: Both sides of the capsule are lush ... and are extraordinarily musical. Only the very best K67 from the mid 1960s (the famous 'fibre board' model) could hold a candle to this one ... I am hoping and praying that this is a trend, and will report what the next new K870 capsule portends."

I guess that the hope of it becoming a trend didn't live up - after reading your review of the U67 Reissue?

[klaus]

Ernie Black, PSW's Webmaster Extraordinaire, is currently formatting my review for this forum. It should be up and live soon!

[RuudNL]

Very interesting review! So again, the tensioning of the capsule membranes is the biggest problem.
Could you unveil a little how it is possible to relax the tensioning of the membranes?
(Not that I am even thinking about doing this myself!!!)
As far as I remember, the membranes were glued to the tensioning rings.
(Anyway, that is what I saw when I took a damaged Neumann U87 capsule apart.)

[klaus]

The membranes on large diaphragm, Neumann capsules are not glued, but held in place through clamping tension.

I cannot share how I relax the diaphragms, except I am working on a device that makes my previous efforts more predictable and easier to repeat and to dial in more precisely.

[RuudNL]

Interesting. I remember I once removed the 'good' membrane from a damaged U87 capsule and used it to repair another U87 capsule. In this case, the membrane was definitely glued to the tensioning ring. (Otherwise I would never have been able to reuse it again!) The repaired microphone sounded good after this 'transplantation'.
Anyway: the owner of the microphone was very happy with the result.
Although the capsule looked as an original Neumann one, there is of course a chance that it had been replaced with a third party one. Or could it be that after many years of use the membrane just sticks to the tensioning ring? (I would be surprised if this happens.)

[mikezietsman]

It is quite easy to unscrew the two halves of a k87/k870 capsule but if you touch even a single screw that is holding the diaphragm in place, you will ruin the tension in the diaphram.

Source: I took apart a diaphragm that had been ruined by an amateur cleaning attempt.

I can say with a certain authority that these diaphragms are both tougher and more fragile than most people realise. I imagine it is a thing of working with them a lot that helps you to understand in which ways they are tough and in which ways they are fragile.

I experimented on two completely ruined diaphragms... Had I experimented on a two working diaphragms, I would have ended up with two non-working diaphragms...

Interesting. I remember I once removed the 'good' membrane from a damaged U87 capsule and used it to repair another U87 capsule. In this case, the membrane was definitely glued to the tensioning ring. (Otherwise I would never have been able to reuse it again!) The repaired microphone sounded good after this 'transplantation'.
Anyway: the owner of the microphone was very happy with the result.
Although the capsule looked as an original Neumann one, there is of course a chance that it had been replaced with a third party one. Or could it be that after many years of use the membrane just sticks to the tensioning ring? (I would be surprised if this happens.)

[RuudNL]

Yes, I have seen many capsules that were destroyed by people who had attempted to 'clean' the membranes!
Gold wiped off, holes in the membranes etc.
Once I got a capsule that was cleaned so thorougly, that all the gold was gone...
The owner asked if I didn't have a spraycan, so I could apply a new layer of gold. 
I explained to him that it didn't work this way...

[gtoledo3]

Very interesting review! So again, the tensioning of the capsule membranes is the biggest problem.
Could you unveil a little how it is possible to relax the tensioning of the membranes?
(Not that I am even thinking about doing this myself!!!)
As far as I remember, the membranes were glued to the tensioning rings.
(Anyway, that is what I saw when I took a damaged Neumann U87 capsule apart.)

Heat could possibly decrease Mylar tension, but the problem in this case that is that it has gold bonded to it.

Any sort of pre-age/stress like heat would be best done before application of the gold, because with heating after the fact the gold and Mylar will not respond in the same way to heat, which may theoretically cause abberations in the bond, at least according to research.

That said, it’s hard to think of other approaches to tweak the tension of an assembled capsule.

[gtoledo3]

Klaus, did you consider variability of the caps for the high frequency shunts as another thing to examine in differences of new vs vintage? (Not naysaying your point about the tension!)

It was occurring to me that what happens with the top end there, can also really pop out to the ear.

[klaus]

Heat could possibly decrease Mylar tension, but the problem in this case that is that it has gold bonded to it.

Heat does the opposite to Mylar: it tightens it. That's why drum shops apply heat to dented Mylar heads; the dents come out that way.

[gtoledo3]

When you have a drum head under tension and heat it, a dimple stretches and the Mylar thins. You can then tighten the drum head up more, heat again. Rinse and repeat. Until the drum head gets so thin that it’s shot or breaks.

I thought the pitch relaxed when it thins out on the head, with it being under tension. But it goes up more like shrink wrap? Interesting. I have some timbale heads here that I’ll do that to soon, and pay close attention.

[Kai]

Heat could possibly decrease Mylar tension ...

Mylar is pre-tensioned or stetched during manufacturing. Depending on the tension used in the capsule it's more likely that heat will increase the tensioning.
But - we do not know how Neumann treats the mylar in the manufacturing process.

[gtoledo3]

Mylar is pre-tensioned or stetched during manufacturing. Depending on the tension used in the capsule it's more likely that heat will increase the tensioning.
But - we do not know how Neumann treats the mylar in the manufacturing process.

More than you ever wanted to know about Mylar:

http://usa.dupontteijinfilms.com/wp-content/uploads/2017/01/Mylar_Physical_Properties.pdf

The long story short is that it appears that tensile strength goes down with heat increases and elongation goes UP. At extremes it finally becomes brittle.

Mylar can be preheated, which will serve to condition it, but up to that heating point, not above. I also read another abstract about UV exposure pretreatment fwiw.

I still haven’t done the test on the timbales :-) Recovering from a slip and fall, which probably accounts for more than half of the time I spent chattering about this. (Sorry Klaus!)

[klaus]

Figures 3 and 4 of your linked article shows increasing shrinkage of Mylar with increased heat, in all cases. What am I not getting here about your counter argument?

Besides, I've tested this with Mylar® capsules repeatedly: resonance frequency goes up with heat applied to the tensioned diaphragms.

Get well soon!
KH