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[AusTex64]

Interested in learning how one goes about choosing which side of LDC capsules is the "better one". Do you just speak into one side or the other with headphones and it becomes obvious, or do you use musical sounds like an acoustic guitar, or both? Do you record the results or do it live? Or is this something I simply need to try and learn about by doing? Any tips for how other mic builders and repair people go about it will be appreciated. Thank you!

[klaus]

I speak into the capsule, up close, then reverse it and speak again. I have done this for very long time, always on the same equipment (preamp, isolating transformer headphones, cable...). But because of the familiarity with the system, I can deduct quite reliably which side will have the better linearity (if that is desired) or musicality (which is always desired) even from just speaking into it.

It sometimes also depends on the application for the mic, which of the sides one should choose in front. I may choose a different side for certain instruments than for certain voices. But that is the exception. Typically it becomes quite apparent, quite soon, which of the two sides has the greater sex appeal.

[AusTex64]

Klaus, thank you for that reply. I will try your approach with just speaking into the mic with headphones to start. I just took my first modification job (friend's Gefell UM92.1) after building and modifying several mics of my own. Doing the Oliver mods and will also audition the capsule and wire it with the most desireable side of the capsule for cardioid. Will report back on how it goes.

[Uwe]

For a new dual diaphragm capsule this question is superfluous, as by design both sides are equal within extremely tight tolerance.  Preference selection of one side over the other for capsules of unknown pedigree can be made through listening tests, but preferrably NOT with your own voice and headphones. Depending on the phase relationship though the entire set-up you may get strange effects from the interference of hearing your own voice through internal pathways from vocal chord to eardrum and external from the headphones. If you are limited like that for your evaluation, you will get less ambiguous results when using a different sound source, such as someone elses voice, or better yet, some familiar instrument or even inter-station FM-noise.

[klaus]

For a new dual diaphragm capsule this question is superfluous, as by design both sides are equal within extremely tight tolerance.

Not close enough for a discriminating ear: Neumann specifies a ±2dB tolerance in frequency response for its most popular mics, like the U87. Almost all of this spread is due to capsule manufacturing tolerances (Neumann has been very good at reigning in mic amp response variations: I rarely measure more than 1/4 dB!)
That means a maximum spread in capsule response variation of almost 4dB from one point on the frequency spectrum to another. Translation: I have rarely encountered a new Neumann capsule whose sides sounded close enough to one another that I could not hear a distinct timbre and response from each side. It's often even more pronounced with capsule brands from other manufacturers with less tight manufacturing tolerances than Neumann.

Preference selection of one side over the other for capsules of unknown pedigree can be made through listening tests, but preferably NOT with your own voice and headphones.

Though I made it clear that I use this method successfully, I am all for listening education, even for beginners, and would encourage listening to one's capsule sides and their different responses front to back, before using any other methodology.

You mention playing recorded music through the mic, to test its capsule sides for fidelity/best sound. I never understood what that is supposed to accomplish: adding unpredictable artifacts (music source, playback equipment, mic placement, room sound, etc.) when a mic's original purpose is not that. I agree with your observation that live listening tests (voice to mic to headphones) should only be done if: 1. the listener is intimately familiar with the headphones used, and 2. listens at moderate listening levels, to prevent additional artifacts caused by subtle feedback between mic and 'phones.

[David Satz]

Klaus, I think you're confusing two different tolerance limits here. The ±2 dB limit is the maximum divergence from the 0° "Sollkurve" or norm for the microphone type, relative to its 1 kHz sensitivity. But if the front and back halves of any capsule were to differ in their 0° sensitivity by as much as 4 dB, the figure-8 pattern produced by that capsule wouldn't have adequate symmetry. Neumann doesn't publish their tolerance limit for that aspect of symmetry, but logically it must be tighter.

Thinking back to 1959-60 when the U 60 was being created, the aim was to offer a single microphone model as replacement for both the U 47 and the U 48. One innovation toward that end was to manufacture "half capsules" that could be individually tested and sorted by sensitivity into some number of bins. Complete capsules could then be selected and assembled into complete capsules by drawing both halves from the same bin of "half capsules."

In that way, all finished capsules of the type that eventually became known as the K 67 were ready for use in all microphones of the type that eventually became known as the U 67. This contrasted with the situation of the U 48, which required special, additional selection of capsules for front/back symmetry after the capsules were completely assembled. For the K 67 the control of symmetry was effectively built into the assembly process in a way that couldn't be done with a shared-backplate design.

--best regards

[klaus]

Klaus, I think you're confusing two different tolerance limits here. The ±2 dB limit is the maximum divergence from the 0° "Sollkurve" or norm for the microphone type, relative to its 1 kHz sensitivity. But if the front and back halves of any capsule were to differ in their 0° sensitivity by as much as 4 dB, the figure-8 pattern produced by that capsule wouldn't have adequate symmetry. Neumann doesn't publish their tolerance limit for that aspect of symmetry, but logically it must be tighter.

No, I do not think that I confused anything. Granted, figure-of-eight would be a mess, if front and rear were off by 4dB in critical frequency bands, but the fact remains, that Neumann's 'Sollkurve' allows for a deviation of 2dB either way from 0 = 4dB spread. What is interesting, though: in the 1960s, Neumann specified the front of K49 spare capsules with a "0". We can speculate what they measured between the two capsules, and why one would be more ideal as front.

[AusTex64]

Thanks for all these learned comments. This is a great forum!!

It will be easy enough for me to record the test. And would be interesting to see if my choice would be the same if I were not speaking at the same time, only listening. And I might try my Collings acoustic as well as dialog, since the fellow that owns the mic uses it for that purpose a lot. I am real curious to see if my hearing is that discerning....

[boz6906]

All the test methods discussed have some validity.

I do think that humans are most sensitive to differences in the human voice, it's just a matter of evolutionary benefit...

I've been thinking along these same lines as I have a USM69 that seemed to "lean" to one side when used in M/S.

I think a rigid test jig that will let me accurately turn the mic 180 degrees would allow one to use a single test source with valid results.

I do favor a good studio monitor as a test source, either pink noise or music as the mic's ability to respond to frequencies far beyond speech is important.