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Klaus Heyne's Mic Lab / How to (Re-)Mount Badges on Microphone Bodies
« Last post by klaus on April 21, 2018, 10:47:22 pm »
Comes a time when a badge fell off the precious U47, or was never there on the used KM84 you bought. You may have bought an overpriced badge on eBay and now want to be absolutely sure to not waste the effort and expense.
Years of trials and mess-ups have taught me how to (re-)mount badges on Neumann, Telefunken and other mics, and I herewith share my tips.

1. Initial Check
Check the radius of the badge against that of the body tube. For a flush fit, both must be the same. If necessary, you can bend and flatten or arch the badge a tiny bit, but do not try to fit a badge made for a different body radius: the body holes may not line up. KM8x badges will not fit U87 housing tubes and vice versa. M49 badges need to be re-bent to fit a U47 housing tube, and vice versa. Once the same radius of badge and housing tube has been confirmed, hold the badge over the correct position and check that the holes for inserting the rivets will line up.

2. Test-Fit
Insert rivets into badge - thumb pressure only - no tools
With rivets in badge, insert all the way into the housing tube, to check correct rivet length: if rivets stick out on the inside, they are too long and need to be shortened until flush with the inside surface of housing tube: On some Neumann mics there is zero clearance between frame and housing tube during insertion.

To shorten rivets that are too long: insert into badge (best for holding rivet in place) and carefully grind down length with a Dremel diamond wheel or other tool.
If rivet shafts are too thick to go into holes without extreme pressure: use diamond wheel to slender the shafts until only light pressure is necessary to seat them

3. Final Installation
Insert rivets through badge, apply a small dab of Eclectic E6000 styrene glue* to center of badge’s back, and guide badge into correct position by lining up rivet shafts with body holes. Press badge firmly into position, making sure that all edges are flush with body. Thumb pressure is optimal. Finally, use your wooden dowel and gently press the rivets until heads are flush with badge. DO NOT HAMMER.
Do not trust the rivets to hold in the badge. They are primarily for looks. To avoid rivets from falling off: place a drop of Crazy Glue to each of the rivet holes from inside the housing tube.

* Eclectic E6000 is great: firm hold, yet easily removed without residue if necessary. 
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Klaus Heyne's Mic Lab / Re: Silica Bags As Desiccants: Do they work?
« Last post by Noah Scot Snyder on April 21, 2018, 12:22:42 pm »
I use the metal cased rechargeable desiccants with success. The style I use starts orange and turns clear as it absorbs water. Once it is clear you toss it in a 300 degree oven for 3 hours and it dries out ready to be used again. One lives in each of my well sealed mic cases (the style often used for camera equipment). 
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Glad it went so well, and glad to hear you're working on the historical end of the convention -- you have to know where you've been before you can figure out where you're going!!

Let's talk closer to October... I have no idea what my travel schedule will be [I go Oktoberfest in München every year] until later in the summer.

Peace
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Hi Fletcher,

Thank you for the well-wishes and help last October, sorry for the delay in replying. It did go well, there was an attentive audience for the big talk and several had been there and shared their memories.

The talk went so well that it gave me some credibility with the powers-that-be and this year I'll be in charge of the Historical Track (track = sequence of talks/papers on a given overall subject; there are many tracks).

The Convention is October 17-20 in New York City at the Javits; if anyone has an historical subject which they are knowledgeable about and want to share and can get themselves to NYC at that time, please PM me and I'll tell you how to get into my Track.

It could be a panel discussion, a solo or duo presentation, or something different. It should involve history of that audio subject.

Thanks again for having me at your place in October; it was a fun time. I'll be doing another version of my presentation, both expanded and contracted, at the Convention and Tom Fine will be in my track with his History of Commercial Stereophony series.

If you wanted to, I'd be happy to come to Suffern again so that people who are not going to the Convention could still get together. That Sunday afternoon is a very fond memory.

PS It took me quite a while to process all that happened at the Convention and my talks, and I honestly avoided the subject altogether for many months which is why it's taken so long to post a followup.
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Klaus Heyne's Mic Lab / Re: Capsule Diaphragms: Nickel vs. Gold
« Last post by Marik on April 16, 2018, 08:15:07 pm »
Using as low tension as possible is a quote from Schoeps's chief engineer Mr. Wutke with whoom I had close contact. I even tested a prototype mic for them at that time. Schoeps is located in my hometown.

Kai,

As always, the evil is in details. In order to compensate for high frequency loss (as a result of diaphragm' lower tension) Schoeps uses resonator system, which is just another way of implementing and making it work...


Specially on fig. of eight mic's the low frequency response is of major concern, as the pressure gradient (the pressure difference between front and backside of the capsule / diaphrag) gets lower with frequency.
The stiffer the diaphrag the less it will follow the air movement.
Most REAL (single diaphragm, not double-cardiod) fig. of eight condensors roll off below 200Hz or even higher because of this.

The single diaphragm fig8 condenser is very specialized capsule and there were only a few more or less successful models on the market. Of course, I was talking about cardioid capsules.

In general, to make a fig8 single diaphragm we need a mass controlled system, so the diaphragm is tuned to a very low frequency. In this case the sensitivity will drop with rate of 6dB per octave going up. On the other hand, the pressure gradient forces on the diaphragm will increase twice per each octave. That's how we will get a linear frequency response. That's why ribbon microphones naturally have a linear response up to the point of cancellation on the top extreme, where the front to back distance is equal to the frequency of wave length and pressure gradient is 360 degree out of phase.

Condenser single diaphragm works as mass controlled only above the frequency of tuning resonance. Below it is a resistance controlled system. In order to make a flat response we need to introduce acoustical resistance. The lower the tuning resonance, the less acoustical resistance we need, the more output such capsule will have for a given linearity. But of course, as you rightly mentioned, here we are faced with diaphragm stability problems, which is the main limiting factor.

Quote
You are right with cardiods, they present a complex system using a combination of even more then the mentioned accoustic effects, needing to be properly tuned to each other.
Still, low tension is desirable here if you need to cover the full range.
Klaus prefers the lower tensioned specimen of the Neumann capsules e.g., for their fuller bodied sound.

This low tension close to the possible is one of the main reasons for cardiod capsule failure, there is no big margin like with higher tensioned omnis.

As I mentioned before, the diaphragm tensioning depends on the desired voicing and very much depends on entire system it is part of. In general, all the capsules are tuned differently. For example K47 is considerably low, K67 quite a bit higher. On the other hand, CK12 way higher than either. The reason being the first two are aperiodic designs and introduce quite high acoustical resistance and damping to the diaphragm, while the CK12 is a multi-chambered and rather resonant system.

Best, M
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Klaus Heyne's Mic Lab / Re: Capsule Diaphragms: Nickel vs. Gold
« Last post by Kai on April 16, 2018, 05:24:54 pm »
But with lower tension then you are losing top end response.
In fact you linearize the bass.
Using as low tension as possible is a quote from Schoeps's chief engineer Mr. Wutke with whoom I had close contact. I even tested a prototype mic for them at that time. Schoeps is located in my hometown.

Specially on fig. of eight mic's the low frequency response is of major concern, as the pressure gradient (the pressure difference between front and backside of the capsule / diaphrag) gets lower with frequency.
The stiffer the diaphrag the less it will follow the air movement.
Most REAL (single diaphragm, not double-cardiod) fig. of eight condensors roll off below 200Hz or even higher because of this.

Schoeps CCM8 reaches 50Hz with a soft rolloff to only -6dB (often compensated by the proximity effect when used as spot mic). There is no problem in the high range with this mic, it's ruler flat up to 15kHz and sounds very nice and rounded.
The mic uses mylar sputtered with gold, but in former times Schoeps built mic's with pure nickel diaphragms with comparable accoustic properties.

You are right with cardiods, they present a complex system using a combination of even more then the mentioned accoustic effects, needing to be properly tuned to each other.
Still, low tension is desirable here if you need to cover the full range.
Klaus prefers the lower tensioned specimen of the Neumann capsules e.g., for their fuller bodied sound.

This low tension close to the possible is one of the main reasons for cardiod capsule failure, there is no big margin like with higher tensioned omnis.
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Klaus Heyne's Mic Lab / Re: Capsule Diaphragms: Nickel vs. Gold
« Last post by Marik on April 16, 2018, 02:49:26 pm »
But your claim that a Mylar film twice as thick as nickel would still be more compliant (i.e.flexible) than nickel is something I would like to see proof of. It does not seem logical.

Klaus,

The Young's modulus (i.e. a measure of the stiffness) for Ni is 190x10^6 PSI and for Mylar 1x10^6 PSI. In other words, Mylar is by far more compliant material.

When building a microphone it's not the goal to have as high tension as possible on the diaphrag. In fact the opposite is true, the lowest tension that still gives a stable result is desirable to extend the low frequency response.

Kai,

But with lower tension then you are losing top end response. The carefully chosen optimum tension/tuning frequency for a given capsule is always a part of a system comprised of capsule acoustical chamber parameters, time delay network, resonator system (if any), and desired voicing. It will also affect capsule's sensitivity.

Best, Mark Fouxman
Samar Audio Design
Omni8 Audio
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Klaus Heyne's Mic Lab / Re: Capsule Diaphragms: Nickel vs. Gold
« Last post by Kai on April 13, 2018, 07:36:34 pm »
But compliance comparisons...
When building a microphone it's not the goal to have as high tension as possible on the diaphrag. In fact the opposite is true, the lowest tension that still gives a stable result is desirable to extend the low frequency response.
I once talked to Mr. Wutke from Schoeps here in Karlsruhe, and he told me that is what they do with their figure of eight and cardiod capsules. Omnis are different.
Metal could have a point over Mylar in long-term stability in that regard, but I'm only (educated) guessing here.
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Klaus Heyne's Mic Lab / Re: Capsule Diaphragms: Nickel vs. Gold
« Last post by klaus on April 13, 2018, 06:50:48 pm »
I do to argue with the weight difference between similar-dimensioned nickel and Mylar diaphragms. But your claim that a Mylar film twice as thick as nickel would still be more compliant (i.e.flexible) than nickel is something I would like to see proof of. It does not seem logical.
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Klaus Heyne's Mic Lab / Re: Nickel vs. gold sputtering
« Last post by Marik on April 13, 2018, 04:36:03 pm »
And I can’t imagine a better conductor than gold. Since so little gold is actually deposited on a membrane,  it doesn’t seem like raw material cost would be significant.

Mickey,

The layer of deposited gold is in the range of only 100 Angstroms, so it has pretty low conductivity to start with, which is not a priority here, as it is a very high Z circuit, anyway.

But that may defeat the purpose of using a very thin and agile metal diaphragm instead of a plastic one that usually is twice as thick or thicker than a metal diaphragm.

Klaus,

The effect of thickness here can be quite deceiving. The density of Ni is 8.9g/cm^3, and of Mylar only 1.38g/cm^3. That means that twice as thick Mylar will still be more than 3 times lighter than Ni counterpart (and more compliant). On the other hand, there will be other factors such as mass of loading air (which is moved along with the diaphragm and which is frequency dependent) and also stiffness of the air trapped between diaphragm and backplate, which works as a spring, effectively damping the diaphragm. Those may (or may not) negate all those mass and compliance differences.

Best, Mark Fouxman
Samar Audio Design
Omni8 Audio
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