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Author Topic: Geffel UM70S needs repair.  (Read 9749 times)

John Willett

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Re: Geffel UM70S needs repair.
« Reply #15 on: July 20, 2012, 07:40:36 AM »

Gefell do vigorously deny this, of course, and say that nothing has changed at all in the manufacture of the M7 capsule and it's the same as it has always been.

Kai

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Re: Geffel UM70S needs repair.
« Reply #16 on: July 20, 2012, 10:20:44 AM »

... the current PVC capsules MG manufactures are hardly recognizable as the same thing they produced up to 7-8 years ago...
Is this still the case, did you have the chance to compare M7s currently manufatured with older ones?

Might be that MG reacted on this lately?

Something like lack of bass should be easy to measure if you had both types for comparison.

You could even send me files recorded from two capsules placed side by side (or one after the other, exactly placed at the same point), at two different distances 30cm and 100cm from the source.
No need for an unechoic chamber, and any broadband sound will do as source.
I can do an objective comparison (measurment) here and post the result.

Regards
Kai
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klaus

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Re: Geffel UM70S needs repair.
« Reply #17 on: July 20, 2012, 11:30:17 AM »

A few years back I was making a prototype for a new microphone to be issued as flagship model for Microtech Gefell. The bottleneck in the development was the then-current M7 PVC capsule, which, compared to the PVC capsules made until about 10 years ago, had changed dramatically, I thought. 

After I complained about the, in my opinion, considerable degradation of the current capsules' frequency balance and low end, I provided running production samples to MG, about seven years ago. Objective measurements were then made by MG in its anechoic chamber by the head of capsule development, for the purpose of proving or disproving my subjective experience.

While an average loss was measured between 2 and 4dB @50Hz in the capsules I sent, the drop-off was deemed insignificant and within specs by the MG employee, in an email to me. That effectively stopped any further development of the microphone, as I was not willing to put my name on a product with what I regarded as an unsatisfactory sounding capsule.

I have no indication that either more of the original, now obsolete, PVC material which MG used for decades, has been found since the measurements were done, or that the original specialist in charge of M7 PVC manufacture has been un-retired, and his extensive skills revived by the current staff.

I am always eager to alert the public if things have changed, and welcome any information you may have that would point to an improvement of MG's PVC capsules.

Postscript: This morning I received an email from MG threatening me with a lawsuit unless I immediately retract my opinion. (I will start a new thread on the subject of manufacturers' intimidation of free speech, and the corrosive effect this has on the exchange of information and improvement of microphones.)

I feel honored that my opinions are taken that seriously.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

David Satz

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Re: Geffel UM70S needs repair.
« Reply #18 on: July 21, 2012, 12:35:49 PM »

> While an average loss was measured between 2 and 4dB @50Hz in the capsules I sent, the drop-off was deemed insignificant and within specs by the MG employee, in an email to me.

Klaus, just to clarify: Do you mean that the 50 Hz sensitivity of these capsules was 2 to 4 dB less than that of some reference M 7 capsule(s) that you'd agreed upon? Or do you mean that these capsules were 2 to 4 dB less sensitive at 50 Hz than they were at 1 kHz?

The former might be news, but the latter would not.

--best regards
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Oliver Archut

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Re: Geffel UM70S needs repair.
« Reply #19 on: July 21, 2012, 12:41:00 PM »

Quote
but I would *only* have a Gefell mic. repaired by Gefell at the factory in Germany

Hey John,
That is wishful thinking here in the US and any other countries outside the EU. And, even for the EU your statement might be right for current productions, but for everything before MTG (the "peoples owned" times) there are several techs that will do a better job than Gefell can do today. (That point has been covered numerous times in the past in the old forum.)

Regarding Gefell M7 PVC.
Gefell knows about those problems, Klaus points out from several others techs including myself. You are right that they deny it. I bought several new Gefell capsules and they re-worked several original Neumann capsules for me, and at first everything seems fine but at one point about 5 years ago, the quality changed. All my inquiries were returned by Gefell that nothing had changed, but after some digging and talking with former/retired Gefell workers, the picture was quite different. It appears that some personal changes happened around the time the issue started.
All my dealing with Gefell did not come to a point that was acceptable, I had been stranded with 5 capsules that had been delivered and died within 8 months, and all showed the same problems, the other ones that did not rapture were not useable at all. After their unwillingness to even take my point seriously, I wrote off the costs and moved on. In the last three years my company bought over 100 PVC capsules from Mr. Thiersch, and only one had some problems, Mr. Thiersch exchanged it with no questions asked.

Regarding Gefell's statement that the M7 PVC has not changed: The original PVC substrate developed and manufactured by IG Farben (before WWII) called "Igelit" was outlawed in Western Germany in 1958, because of its toxicity. In the Eastern German VEB Bitterfeld company (formally IG Farben) the same "Igelit" material was produced to about 1990, but with the German reunion, it was discontinued. Gefell changed diaphragm material after they ran out, [and since use] an alternative PVC material (source: Gefell). If they deny that today, that is probably due to marketing.

Best regards,

Oliver
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Oliver Archut
www.tab-funkenwerk.com

We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.

klaus

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Re: Geffel UM70S needs repair.
« Reply #20 on: July 21, 2012, 06:43:50 PM »


Klaus, just to clarify: Do you mean that the 50 Hz sensitivity of these capsules was 2 to 4 dB less than that of some reference M 7 capsule(s) that you'd agreed upon? Or do you mean that these capsules were 2 to 4 dB less sensitive at 50 Hz than they were at 1 kHz?

The former might be news, but the latter would not.

--best regards

The former. And in direct comparison with MG capsules from previous generations that I own.

There may be more than just bass response discrepancies that account for the distinctly different sound produced by the two MG capsule periods. I have recently seen 3-D imaging of moving capsules that, for the first time, seem to correlate timbre to diaphragm material, whereas even similar frequency responses of differing diaphragm materials produce audibly different oscillations (and, anecdotally, audible variations.)
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com
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