I'd been asked recently what the real differences are between a handcrafted boutique capsule and one that is mass produced, for larger scale companies that sell more affordable gear. It's a great question; because its a complex and nuanced thing to answer. It's really complex, in fact; because some boutique capsules actually do utilize some pretty heavy mass production technology, and some overseas-made capsules are actually made in small batches using some of the more hobby-shop techniques.
Let's start by what I would call mass production. I call mass production making 1000 pieces at a time. You could say 500; but sometimes when a really large factory overseas is fulfilling an order for 500 retail units they will still prep up 1000 or 2000 capsules in a single run. 797 Audio (PRC) do this. They make capsules for MANY brands of microphones known in the US, Asia, and Europe. They use the same capsules in many different mics. Even though they make capsules that may cost all of $10 each in bulk; some of them wind up in some rather pricey mic brands that sell for four figures (no, I won't say who, but several). Alctron Audio and some of the other really large scale microphone mills who make for many different brands do similarly. I would not say that any of these are examples of particularly good capsules. I've sampled them. The types of things I see in these are often ripples in the mylar from either poor termination or components shifting in transit, and sometimes de-burring residue rattling around behind the diaphragm. This is from the brasswork not being properly cleaned and the work not being done in as clean of a clean-room as one should. Crooked screw-holes, cheap wire, loose terminations, and other tolerance issues are not uncommon.
From a sonic perspective, what you see in these types of capsules sometimes is too much sibilance, not enough bass due to tensioning or poor design, over-presence in the form of a too-high 10k bump, and over-sensitivity. Over-sensitivity is when a capsule essentially picks up microphonics and resonance from the mic body itself and anything attached to it, almost a stethoscope-like effect. Yes, microphonics even in a microphone can be bad. A mic will always be prone to vibration and handling noise; but should always at least have some semblance of detachment from its environment. It's one of those things you have to catch before you fully understand it. Really Really cheap China mics do this. In general, really really cheap capsules can be bright, harsh, have obnoxious peaks and valleys, poor bass, and just generally a poor tonal balance. All the tubes and transformers and capacitors in the world won't fix this, though you can bet that cheaper manufacturers will keep trying.
There's another thing going on that is really hard to quantify, and that's a sense of realism that you get with a really nice boutique capsule. You get the sense that a clone of you is speaking into your ears from in front of you... Like its another you and not an electro-acoustic reproduction. I've only heard this on really well made capsules. They can sound not just life-like, but larger than life. The science-person in me is sure that this boils down to THD measurements and micro-dynamics, or maybe have a smoother frequency plot without as many abrupt peaks and valleys... but this is the listener's point of view of what is happening. The very high end capsule sounds like one layer has been taken off of the veil between real and reproduction. It seems to have a soul. And there are some capsule designs which have thus far eluded Asia's ability to mass produce. AKG's CK12 is one good example. The true, chambered capsule is an enigma to build. Everything you see coming out of China is a look-alike, made by edge-terminating a K67 style backplate; and can sound good but not really the same.
Now that being said, I do feel that the gap between the two worlds continues to close in. 20 years ago, Asian capsules didn't even use Dupont Mylar or Japanese PET film, and the industrial Mylar would deteriorate over time, causing capsule stiffness and failure. This isn't so much true anymore, and you'll see most Asian manufacturers using decent Mylar to skin their capsules. And some makers are far better than the larger mills. I think that the elusive Frank He does some decent work; though not to a level where I would use his capsules just yet. Though I think they are a bit scooped (think smiley face EQ), he makes a fairly decent capsule. His work is seen in the M-Audio and Sterling line of microphones, among others. Part of why I mod the Sterling mics (and remove that tuning baffle from his capsule with extreme prejudice) is because I think there's at least something decent there to be had there once the proper corrections are made.
And application should play a part in these things... If you are putting a mic in front of a kick drum, it may not be as important for that mic to 'have a soul' as if you are going to be singing your heart out into it for the single that is going to be your breakout hit. Although the handcrafted capsule will sure make that kick sound great as an outer kick mic FET 47. :)
The Baseline edition mics that I make use an imported capsule, from a very small shop in mainland China. I've known the owner for years and worked with him across 3 different companies. I have them made to my exact needs, and I measure and test them here. I measure their capacitance and side to side differential, backplate isolation, etc, before ever even putting them in. They're almost always fine. They cost me far less than handcrafted parts (as reflected in the price of the mic); but cost about 5x that of a poor quality Asian capsule as well. They are made in very small batches of about six at a time, truly almost straddling the fence between mass production and boutique. They use NOS Japanese PET film (lab-grade Mylar), gold sputtering, good brass, well tuned up CNC machines, and a clean-room environment, with measurements taken in an anechoic chamber. They have better equipment to make and measure capsules on than most of the boutique makers. This shop makes capsules for several other brands, all of whom charge a good bit more than I do for many of their products and DO market them as being fully high end capsules. Mine are custom made for me, however. I think they sound darn good, esp the K47, which is my favorite. It almost splits the difference between what people expect an M7 and K47 to sound like. Its warmer, rounder, with still a hint of the mid-forward newer Neumann sound. They're very consistent as well. That being said, I can still tell they are 'manufactured' rather than handmade. And I cannot even truly verbalize or quantify the why or the how that I know this; only that I can tell there's a difference. Maybe its that the handcrafted capsules have a slightly more vibrant midrange and that elusive life-like presence instead of sounding like a very good reproduction. It could be that or just the physical differences of technique.
But one very interesting observation though, that even though I have convinced myself that I only hear that mysterious 'soul' on the uber-expensive handcrafted parts; I do hear a 'soul' when these mics go out there, get used on records, and I hear them played back on my system (when people are kind enough to share some tracks!). The soul seems to be put in them by the artists, and I then hear that 'soul' in the form of a delayed response. Esp with a blues recording that was done here in Louisiana with some really legendary folks up there in age; it just about brought a tear to my eye. So it may be that we convince ourselves of things based on our expectations and based on what we pay for certain parts, etc. It will be interesting to see how this plays out in the future; if the true artistry of handcrafted parts has a place out there. I certainly do hope it does. If anything else, it helps some people who can afford it know that they have something unique, that was made one at a time, that others will not have. That's something that all great producers and engineers try to have in their tool belts.