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Author Topic: Audible effect of capsule wires and head basket shapes?  (Read 11396 times)

klaus

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The parallel surfaces between the inside wall of the cylindrical head basket and the diaphragm plane of the U47 present an opportunity for standing waves to develop. Irregularly zig-zagged lead out wire minimizes the transmission to the capsule of these resonances.
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Klaus Heyne
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Uwe

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To the best of my knowledge standing waves would require parallel solid surfaces. In the microphones in question there is only ONE flat surface, namely the capsule diaphragm. The 'opposing' surface is everything but flat or solid. I cannot imagine the acoustically transparent wire mesh of the basket to reflect any acoustic energy back to the diaphragm! Not only are the wires of the mesh as well as the electrical capsule connections much too small relative to the acoustic wavelength, but looking at the individual wires shows them to be round, further dispersing any possible reflected energy randomly in all directions. BTW, it would be utterly impossible with such a short conductor to create an inductance affecting any imaginable audio frequency, no matter how it is coiled! The only reason to make a large spiral or dressing the capsule connection in a zig-zag pattern would be to attenuate potential structure borne mechanical disturbances.
Objective review of the governing physics force me to conclude any claim of audible effects to be more psychological than logical ...
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klaus

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Uwe, I am surprised by your answer.
Reducing reflections between the interior basket surface and the diaphragms through a wedge, rather than cylindrical, head shape was behind the NWDR design improvement developed for the M49/M50, and then assigned to Neumann for serial production. Lessons were obviously learned since introduction of the U47, a few short years earlier.

Neumann then patented the wedge-shaped head design of its first large diaphragm in-house developed mic since the U47: the U67 avoids stranding waves and uncontrolled reflections in a much smaller head with its otherwise even more critical reflective propensities in the mid and upper frequency range.

For decades the reflection-killing basket shape patent of the U67/87 was defended repeatedly and aggressively by Neumann against copy attempts.

But a mic head with reflective properties can be a happy accident, sometimes: the U47's basket size and its distance from the diaphragm add an acoustic component to the overall sound of the mic. Anyone who has ever experimented by fitting a differently shaped and sized head basket on a U47 will attest to it.
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Klaus Heyne
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David Satz

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Klaus, I've read most of Neumann's product literature especially from the 1950s and later, but have never seen any claims of acoustical benefits for the U 67's head basket design. The U 67 was introduced with considerable fanfare, and several pieces of literature were published extolling its technical virtues, including an eight-page bulletin full of graphs and equations. But the outward form of the microphone is referred to only in passing, and is described as attractive-looking with no mention of any functional significance, while a great deal of ink is spent extolling the advanced low-cut filter, the three selectable patterns, the built-in pad switch and so on.

I have a fairly good collection of patent filings from the major microphone manufacturers, and am fairly certain that the patent to which you refer is a design patent. That's a type of protection based purely on the ornamental aspect of an item of trade, not its functionality. Defending such patents doesn't involve any discussion of technical pros and cons, which would be irrelevant.

Coca-Cola once took out a design patent on the shape of their bottles, for example--but this didn't involve any showing that the shape led to any practical benefit other than brand recognition. Wikipedia says that the Statue of Liberty was the subject of a design patent at one time, apparently in the hopes of curtailing the sales of unauthorized replicas--and that, I think is also what Neumann's design patent for the U 87's outward form was about. I say U 87 because if I'm not mistaken, that design patent was taken out decades after the introduction of the U 67, when far Eastern lookalikes (and in some cases, outright counterfeits) were already a factor in the marketplace.

I also just re-read the NWDR (Grosskopf) patent 927 037, which describes the M 49 design; it says nothing about the head basket's acoustics. It does mention the practical advantage of making the microphone smaller in general, so that it can fit in more places, though. And Grosskopf's two articles in FTZ from that period of time, which describe the M 49 and M 50 designs, don't mention the head basket, either.

While the head basket clearly has some sonic influence, I just don't see any evidence that this was a theme of discussion in the literature by (or around) Neumann at the time. Where there is discussion of acoustics, in the material I've seen, it is always in connection with the capsule design. Do you have any specific citations handy?

--best regards
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boz6906

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In my opinion, it's not so much about standing waves but rather comb-filtering caused by the constructive/destructive interferences as the acoustic pressure waves are reflected between the capsule surface and the grille structure.

The wedge-shaped M49/U67 grille should be better than the (mostly) parallel U47 design because the angled grille doesn't reinforce a particular frequency but rather a wide band of Frequencies based on the wavelength's relationship to the varying grille-to-capsule distance.

Yes, standing waves due occur within the space but they would be stationary.
I think the bumpy response of the comb filtering would have a greater effect on the sound.

In any case one would think the reflections from any wire grille structure would be insignificant.

I'd theorize the mechanical resonance of the body/framework/diaphragm and the resonating cavities of the mic itself would be a much greater factor in the overall sound.

Here again the angled body of the U67/87 would offer advantages over the cylindrical body of the U47.
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klaus

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While the head basket clearly has some sonic influence, I just don't see any evidence that this was a theme of discussion in the literature by (or around) Neumann at the time. Where there is discussion of acoustics, in the material I've seen, it is always in connection with the capsule design. Do you have any specific citations handy?
I remember a Neumann-source mentioning the sonic properties of the wedge shape. I will research (may take me a while) and then post my findings.

In the meantime, there is NO discussion to be had in my opinion of the fact that the shape and properties of the head basket of a condenser mic form an acoustic cavity around the capsule, with distinct sonic properties. I have a few "reverse weave" U67 (the three-weave mesh- fine, medium, course- was reversed on early U67) where I can clearly hear a sonic difference by just replacing the basket on the same mic with that of the later version. I was so impressed with the difference in reflective and diffractive properties of placing the course weave on the outside, that I adopted that principle of weave order (course outside, fine inside) to the head of the Brauner KHE.
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Klaus Heyne
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Piedpiper

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What specifically did you notice between the two orders of head basket layering? I would think the coarse weave on the inside would break up the modes more than the finer weave on the inside.

I know Michael Joly has talked about head basket changes quite a bit but he prefers a single layer coarse weave and states that it reduces standing waves and improves transient response. Of course, it can also then require more attention to a pop filter on vocals. My preference would be to in the position of choice when necessary. In my experience, removing the finer layers can remove important shielding causing audible hum problems.
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klaus

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What specifically did you notice between the two orders of head basket layering? I would think the coarse weave on the inside would break up the modes more than the finer weave on the inside.
The opposite: the coarse weave on the outside makes the sound less opaque. I have no scientific explanation. After all, one could claim that, if the same three layers are present, the sequence does not matter. But it clearly does.

One possible explanation is that the diffraction/reflection of sound waves arriving at the first, coarse weave is different, maybe allowing more shorter wave lengths getting through the consecutive layers, arriving at the capsule with higher velocity than if they were already weakened and deflected by a very fine outer weave?

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In my experience, removing the finer layers can remove important shielding causing audible hum problems.
The good shielding properties of the C12's single, very coarse weave would contradict that hypothesis.
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Klaus Heyne
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Piedpiper

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The opposite: the coarse weave on the outside makes the sound less opaque. I have no scientific explanation. After all, one could claim that, if the same three layers are present, the sequence does not matter. But it clearly does.

One possible explanation is that the diffraction/reflection of sound waves arriving at the first, coarse weave is different, maybe allowing more shorter wave lengths getting through the consecutive layers, arriving at the capsule with higher velocity than if they were already weakened and deflected by a very fine outer weave?
The good shielding properties of the C12's single, very coarse weave would contradict that hypothesis.

Interesting...

Re: the shielding issue, my experience is with removing the inner fine mesh on a Peluso VTB and running into intermittent hum issues until I put it back in the rear of the basket.
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M Stage

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Back to the original question about wiring a capsule Klaus. Does anyone know the brand of wire that Neumann is currently using or the number of strands as it must be less than the GAC-3 96 strand? Also Klaus is "leaded silver" solder, as you wrote before, necessary? Or can pure silver solder without lead be used? For health reasons I would prefer to not use lead in any application, but for sound reasons I just might have to use the "leaded" if it is necessary.
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boz6906

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This coarse vs. fine discussion is quite interesting.

II bremember first learning of the inportance of the wavelenght to apeture ratio at a JBL sound system design seminar in Chicago about 1978.
JBL used the ratio to design the 2305 perforated plate lens for their mid-freq drivers (also known as the 'potato-masher').

The wire mesh is actually like a wire grid polarizer based on Bragg diffraction:

"Diffraction occurs when a wave runs into an obstacle and must avoid the obstacle. Therefore, diffraction describes the apparent bending of waves around objects and the spreading of waves when passing through a small hole. The pattern in which diffraction occurs is due to constructive and destructive wave interference which leads to either a larger or smaller amplitude wave respectively. Diffraction patterns can yield information about the arrangement of the lattice points where diffraction occurs."

http://simple.wikipedia.org/wiki/Bragg_Diffraction

The important relationship is the wavelenght-to-apeture ratio, this can determine pass freq and polarization.

While engineers often talk of polarization at RF I don't know what the effect might be at audio freqs...

Based on these principles I would think changing the size/sequence of mesh sizes could easily change the transfer characteristics.

BTW, this same relationship would apply to hum pickup. you need an aperture sized to block 50-60Hz energy.
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klaus

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Re: the shielding issue, my experience is with removing the inner fine mesh on a Peluso VTB and running into intermittent hum issues until I put it back in the rear of the basket.
I would check with a sensitive ohm-meter all body/housing transitions: between basket and housing tube, and housing tube and bottom bell/connector housing: if you measure even a fraction of an ohm, the total shielding property of the mic is compromised (and of course you already attended to the shield/ground terminations of the mic cable on both ends, correct?)
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Klaus Heyne
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klaus

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Back to the original question about wiring a capsule Klaus. Does anyone know the brand of wire that Neumann is currently using or the number of strands as it must be less than the GAC-3 96 strand?
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I don't but if you really want to try it, I have lots of it lying around.

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Also Klaus is "leaded silver" solder, as you wrote before, necessary? Or can pure silver solder without lead be used? For health reasons I would prefer to not use lead in any application, but for sound reasons I just might have to use the "leaded" if it is necessary.
I understand agree with the lead caution (or why else has the majority of seasoned microphone technicians died before their time?)

But I see no way around it if you really want good connections: molten lead in a 40/60 lead/tin mix covers best, and allows for the most perfect connections between components, especially when a few percent silver is added (silver alone cannot be used, because of its high melting point. It would melt or destroy parts).
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Klaus Heyne
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Uwe

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Re: Audible effect of capsule wires and head basket shapes?
« Reply #28 on: April 12, 2015, 05:53:53 pm »

Where are the parallel opposing surfaces supposedly causing standing waves between the flat capsule diaphragm and the circular basket in the U 47? The only reflections I have seen mentioned in connection with microphone design were concerning the base of the microphone head. Even though the acoustic wavelength limits such effects primarily to the very high frequencies where such reflections may influence frequency response aberrations and mess with the directional pick-up pattern, such observations have lead to various alternatives to the flat shaped bases and other means to ameliorate such effects. The different densities of the wire mesh layers of the head basket are there to break up turbulent air flow which causes popping with plosive consonants. Since they do present also frequency dependent acoustic resistance they will affect the high frequency response. However most of these effects can be compensated in the capsule design or through complimentary electronic equalization.
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M Stage

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I understand agree with the lead caution (or why else has the majority of seasoned microphone technicians died before their time?)

But I see no way around it if you really want good connections: molten lead in a 40/60 lead/tin mix covers best, and allows for the most perfect connections between components, especially when a few percent silver is added (silver alone cannot be used, because of its high melting point. It would melt or destroy parts).

Hi Klaus, there seem to be plenty of "lead free" alternatives for solder. Look at the wiki for Lead Free solder, see if you might try any of those listed.  http://en.wikipedia.org/wiki/Solder#Lead-free_solder

And a company like this seems to sell a variety of lead free solder. Not sure if any of these are suitable.
http://www.indium.com/solder-paste-and-powders/lead-free/

I do not know what would be a good replacement for the lead/tin mix you fancy, but I do believe it is in your best interest to find a replacement, as it should be the interest of everyone on this thread that frequently uses solder.
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