mediocreplayer wrote: ↑Sat Oct 14, 2023 6:05 pm
øøøøøøø wrote: ↑Thu Oct 12, 2023 6:52 pm
In the real world, the biggest distinctions between superior and inferior mics tend to reveal themselves in things like pattern uniformity.
Can you explain further what this means? Is it whether the mic responds to off-axis sounds as it should (depending on its pattern)? Or is there more to it than that?
It’d be easy to look at microphone documentation and assume it “does what it says on the tin.” Inconveniently, real life is much more complex.
You may know that graphs of frequency response behavior are averaged, or “smoothed,” such that very narrow-band anomalies don’t display (there’s no industry standard for exactly how this is done, by the way).
But graphs of polar response are even more…approximate.
One important consideration is that these polar patterns are 3-dimensional in the real world, and the 2D illustrations of various patterns don’t often convey a good intuitive sense of what’s actually going on. A cardioid isn’t so much “heart shaped” as it is “tomato-shaped,” with the rear null being where the stem would be (for one example).
But the bigger consideration (for purposes of your question) is that these patterns are generally NOT uniform at all frequencies.
A cardioid will morph into omni at low frequencies (the exact transition point depends on the design) and its pattern will become extremely narrow—and usually sprout a rear lobe—at very high frequencies (critical frequency here depends on diaphragm diameter). This is just one common scenario. In real-world mics things generally get a lot stranger.
If a microphone is damaged, poorly-manufactured or flawed in its design, more-idiosyncratic pattern anomalies can occur—but even a properly-working and well-conceived mic can have some very strange things going on off-axis. These are things that won’t really show up on typical documentation.
To truly comprehend this, it’s required to have at least a little understanding about how mics achieve their patterns.
A ribbon is “natively” figure-eight. A moving coil or single-membrane condenser is “natively” omni (if sealed at the rear). A moving coil can also be natively figure-8 if its rear is open (rare: think Beyerdynamic M380) and it’s designed properly.
Any other pattern is made by a series of engineering contrivances, and that’s where things start to get weird.
Mathematically, cardioid is achieved by a 1:1 sum of omni and fig 8, so the first cardioids (e.g. STC 4033, Western Electric 639b) actually combined a ribbon and a moving coil.
But this was cumbersome.
Later it was figured out that by leaking some sound to the rear of a moving coil or condenser capsule, you could cause *just enough* phase cancellation to create a cardioid… but the methods still in use for this are hilariously low-tech.
Thinking of this YouTuber’s favorite mic (the SM57), you’ll notice little side grilles. These are crucial to forming the mic’s pattern (if you were to gaff tape over them, the mic would become an omni)
There are also various mechanical and acoustic resonators inside an SM57 (including a big Helmholtz chamber behind the diaphragm). These resonators seek to counterbalance the diaphragm’s own natural resonance, and can also interact with the pattern-generating acoustical labyrinth.
This means the off-axis can… get weird. Peaky resonances can abound (think of taking a mid-band EQ, turning the “Q” all the way narrow, and cranking boost or cut…). Remember that these patterns are being achieved by phase-shift using building blocks that are resonant by definition and highly non-linear…
Similar things are achieved with condenser capsules, but through radically-different means. There, things get even stranger as the tolerances of backplate machining become critically-important (the AKG CK12 is so hard to get right that almost nobody will make a *true* clone).
Multi-pattern condensers usually rely on multiple diaphragms and careful engineering of backplate geometry (with a series of through-holes and blind holes to tune response and pattern).
There are always trade-offs when dealing with real-world physics.
This is already TL;DR but I’ve barely scratched the surface.
Summary: omni dynamics and single-pattern condensers are pretty reliable in their patterns (below a diameter-dependent frequency anyway). So are figure-8 ribbons. Anything else can get really weird, and the amount/acceptability of that weirdness is down to both design and also to manufacturing tolerances/precision.