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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by Jim Williams on September 06, 2018, 11:42:52 am »
I have done some tests that exposed the reflection effects. It was so audible the capsule had to be raised up 5 mm to overcome it. It was on a Rode NT-2 that I designed for Rode back in the mid 1990's.

No, I didn't bother with frequency sweeps as I don't have the anechoic room to do that here.
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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by klaus on September 05, 2018, 05:38:47 pm »
That (shape of mounting base) will affect the response.
Whether or not, or if, how much the shape of the base affects the sound of the mic is probably hard, if not impossible, to listeners. Unless all that is done, the statement is speculation.

Quote
I noticed in similar mics with a domed mount that the shape does create reflections, resonances and some nulls too.
Again, speculation, unless proven. I could as well argue (and probably trace) the exact opposite: parallel surfaces - here, a flat base plate, flat capsule sides, flat top of basket- may create standing waves of a higher audible magnitude than the somewhat random reflections off a curved surface (as with the old base).

But the reason I mentioned only the capsule-height differences in my review, and not any acoustical effects of the U87Ai base used in the Reissue vs. the old U67/87 curved one: I did not hear any. And what I heard was the focus of my review.
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Mounting the capsule a few mm higher can overcome some of those reflections
How would you know? It might as easily affect just the wavelength of the reflection, with little decrease in its volume, or may result in nothing audible at all. For me, it was the latter. So I left it out of the review.
Quote
A complete frequency response plot with the differences would also be informative but that isn't likely to happen here.
No, indeed, "here" we listen to detect subtly of sounds, rather than running test tones or protocols.

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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by Jim Williams on September 05, 2018, 11:22:43 am »
That will affect the response. I noticed in similar mics with a domed mount that the shape does create reflections, resonances and some nulls too.

Mounting the capsule a few mm higher can overcome some of those reflections. A complete frequency response plot with the differences would also be informative but that isn't likely to happen here.
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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by RuudNL on September 04, 2018, 01:30:30 pm »
I was a bit surprised that I didn't read a word about the change in shape of the base below the microphone capsule.
In the 'old' U67 there was a dome shaped piece just below the capsule itself.
In the 'new' U67 the capsule sits higher in the headbasket, but the base where the capsule is mounted on, is flat.
IMHO this could influence the sound. Any opinions?
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Any comments?

Opacheco.
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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by brucekaphan on September 03, 2018, 03:41:00 pm »
Klaus, THANK YOU for doing such a thorough job of analyzing and interpreting the U67 reissue—I have to say I would have expected no less, but that doesn't change my appreciation for the obvious amount of time, energy, and thought you put into your analysis. And I am a big fan of using all of one's senses, not just one's intellect, when it comes to judging anything having to do with music/recording. Not being a spring chicken myself, I know how hard fought the battle is to learn how to deeply hear, and even more so to learn to deeply hear and be able to make useful judgements based on hearing deeply. I was one of those foolish folks who bought into the M149 release, before it had been tested and (dis-) proven both by experts such as yourself, and by the marketplace. I wasn't going to make that mistake again! There's a lot of food for thought that you've served up here—so very helpful! Thank you!!!!!
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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by uwe ret on September 02, 2018, 01:09:11 pm »
A few good measurements will always trump multiple opinions...
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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by Jim Williams on September 02, 2018, 12:46:24 pm »
An objective analysis will tell "the rest of the story". Load effects on frequency response, THD effects from various loads, peaking of the response and other effects can then be easily documented for those without the time nor test gear to do their own research. This, like many other audio subjects is crying out for answers that can easily be obtained with sufficient effort.
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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by soapfoot on September 02, 2018, 09:02:09 am »
Thanks, David!

And at risk of continuing the topic drift just a bit too long--what, in your mind, are some practical means of addressing (or circumnavigating) this issue in a methodical, but not-overly-technical way?

Let's say there are several recordists at a studio who have great ears and make great recordings, but whose background is more musical than technical (i.e. they have music degrees, and not EE degrees). How might they be made aware of this problem in a way they might grasp intuitively, and how might they test or control for it if they sense that it's becoming a factor with a given signal chain?

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Klaus Heyne's Mic Lab / Re: Neumann U67 Reissue: Complete Tear Down and Analysis
« Last post by David Satz on September 01, 2018, 01:56:14 pm »
soapfoot, this board has always seemed to tolerate small amounts of "topic drift" as long as it doesn't get out of hand. Ultimately it's up to Klaus, of course. So I'll just post this one, tiny message (like all my postings), and then we can all return to the topic, OK?

The easy part first: Impedance matching (source impedance = transmission line impedance = load impedance) simply isn't relevant here. Leave that for RF circuitry, where it maximizes power transfer. As you said, we want to maximize voltage transfer, so a bridging approach is called for (with the load impedance at least an order of magnitude greater than the source impedance).

The technical problem is that real-world microphones and real-world preamps--especially where transformers are used on one or both sides--don't have purely resistive impedances. Thus their interactions can lead to audible frequency response variations and other problems. It seems misleading to specify impedance as a single number in such cases; a curve, or at least a numeric range, would be far more appropriate IMO. (Note that there are also microphones where the problem goes the opposite way--e.g. some ribbons have impedance curves that exceed 1 kOhm around their primary resonance. Those microphones are as "preamp sensitive" as microphones with very low impedance.)

The human side of the problem is that circuit designers test their work under certain practical conditions, and can't know whether their designs remain valid under other conditions or not. Langevin, for example, may have tested the preamp shown in Temmer's paper only with dynamic microphones, which were far more prevalent in American broadcasting at the time. American studios back then tried to keep equipment running for as long as they could--so in the 1960s, consoles from the 1950s were still in widespread use, with circuit designs based on microphones prevalent in U.S. studios even earlier.

There's a fundamental problem in evaluating anything that interacts with other things. Say you're a studio engineer, and you've always liked the sound of a certain preamp that you have. A client brings his or her own favorite microphone to a session and you plug it in, never having used that particular type of microphone before. Say it sounds harsh or muffled, or whatever--but not as good as people say that it's supposed to sound. You would normally think that you had just heard "what the microphone sounds like." You might never suspect that your impression was based on an impedance interaction like the ones we're talking about--essentially a malfunction in your trusty preamp. If you're an audiophile, and particularly if the preamp is very expensive, you might even think, "My preamp is so great, it lets me 'resolve' differences between microphones that other people don't hear with their inferior, 'lower-resolution' preamps." Both reactions are unconsciously biased but completely honest, and the experience will probably be very convincing for the person who has it.

This is what I think may be going on when people say that the 200 Ohm setting of a microphone sounds different (qualitatively) from the 50- or 150-Ohm setting. Basically, if any such qualitative difference is perceived, alarm bells should go off in people's minds, rather than stopping there and drawing conclusions about the "sound" of one impedance setting or another; such conclusions may not be generally valid.

--Back to practical solutions: If your preamp's frequency response depends on the microphone's output impedance as Temmer's paper shows, you might try to find out or figure out what kind of load the secondary winding of the input transformer is "working into" (driving). Those frequency response variations can sometimes be tamed by placing a shunt resistance, or possibly a parallel RC network, across the secondary. Or if you can't (or don't want to) get into the preamp circuitry, you can do what Hardy does when you're going to use a very-low-impedance microphone. That "pads down" the signals coming from the microphone, but not too severely, and it reduces the microphone's self-noise as well as any noise due to interference in the cable, exactly as much as it reduces the wanted signal. So unless your preamp is rather noisy, it won't harm the signal-to-noise ratio of the recording, and it may also help avoid preamp overload.

--best regards
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