Every microphone is a transducer, and the method it uses to turn air into electricity decides everything you hear from it — the transient response, the noise floor, the SPL it survives, and the jobs it is quietly wrong for.
A microphone is a transducer: a device that takes energy in one form and hands it back in another. Air arrives as a moving pattern of pressure, and something inside the microphone has to turn that movement into a voltage that a cable can carry. That is the whole job.
What makes microphones interesting is that there are several genuinely different ways to do it, and none of them is a refinement of the others. They are separate pieces of physics. A moving-coil microphone and a condenser microphone are not the same idea at different price points — they have almost nothing mechanically in common, and every practical difference you notice between them follows from that.
This matters because it makes microphone choice predictable instead of superstitious. Once you know what is physically moving inside a mic and how heavy it is, you can predict how it will behave on a source before you plug it in.
A moving-coil microphone — almost always just called a dynamic — works by electromagnetic induction, the same effect that runs a power station. Move a conductor through a magnetic field and a voltage appears across that conductor. Nothing else is required.
Inside, a thin plastic diaphragm is bonded to a coil of very fine wire. That coil sits in the narrow circular gap of a permanent magnet, with an iron yoke shaping the field so that as much of it as possible crosses the gap where the coil actually is. Sound pressure pushes the diaphragm, the diaphragm drags the coil through the field, and the coil generates a small voltage that follows the movement. There is no electronics in the signal path at all. The microphone is a generator.
Everything good about a dynamic follows from that simplicity. It needs no power, because it makes its own. There is nothing inside to overload, so it survives sound pressure that would ruin other designs — a snare drum at point-blank range, a guitar cabinet being driven hard, a kick drum from inside the shell. It tolerates humidity, temperature, being dropped, and being handled by people who are not being careful. It is the microphone you can hand to a stranger.
Everything limiting about a dynamic follows from the same place. The diaphragm is not moving alone — it is dragging a coil of copper with it, and copper has mass. Mass resists acceleration. When a sound has a fast attack, the diaphragm has to change direction very quickly, and the coil's inertia means it cannot quite keep up. The result is a softened transient and a rolled-off top end, because high frequencies are exactly the ones asking the diaphragm to reverse direction most often.
It is worth being precise about what that means, because it is usually described as a flaw and it is not. A dynamic does not fail to reproduce a loud aggressive source — it rounds the sharpest edge off it, which on a source that has too much edge is the entire reason you reached for it. The same rounding on a fingerpicked acoustic guitar or a brushed snare removes the detail that was the point. The mechanism does not change; only whether you wanted its effect.
A condenser microphone abandons magnetism entirely and uses electrostatics instead. Its capsule is a capacitor: two conductive plates separated by a very small air gap. One plate is fixed. The other is an extremely thin diaphragm, often a few microns of metallised plastic, and it is free to move.
A capacitor's capacitance depends on the distance between its plates. Hold a fixed electrical charge on that capacitor and change the spacing, and the voltage across it changes in step. That is the transduction: sound moves the diaphragm, the spacing changes, the voltage changes. There is no coil, no magnet, and crucially almost no mass — the only thing being accelerated is the diaphragm itself.
That is why condensers sound the way they do. With so little mass to move, the diaphragm follows fast changes almost exactly, so transients arrive intact and the high frequencies extend further and more evenly. The same sensitivity means a much stronger output for a given sound pressure, which means the preamp downstream has to add less gain, which means less of the preamp's own noise ends up in your recording.
The cost is that a condenser cannot work unaided. The capsule needs a fixed charge to hold, and the signal it produces is at an impedance far too high to travel down a cable — hand it straight to a mixer and it would be swamped. So every condenser has electronics inside it: an impedance converter sitting immediately behind the capsule, converting that fragile high-impedance signal into one that can survive the journey. That circuit needs power, and that is what phantom power is for.
A conventional condenser is polarised by an external voltage supplied to the capsule. An electret capsule instead carries a permanently embedded charge, fixed into a layer of the capsule during manufacture, which holds for decades without any supply at all.
This does not eliminate the need for power — the impedance converter still has to be fed — but it eliminates the need for a high polarising voltage, which means the whole circuit can run on very little. That is why electrets dominate everywhere a microphone has to be small and self-contained: lavaliers, headset mics, measurement mics, the microphones in phones and laptops. Early electrets deserved their poor reputation. Modern ones do not, and a good electret capsule is not a compromised condenser, just a differently charged one.
The impedance converter behind the capsule can be built around a field-effect transistor or a small vacuum tube, and this is where a real part of a condenser's character comes from — not from the capsule at all.
A FET stage is small, efficient, runs cool and can be made very clean. A tube stage runs hot, needs more power and more space, and is never as linear. That non-linearity is the point: driven hard, a tube adds harmonics in a pattern most people find flattering, and it compresses gently as it approaches its limit rather than clipping abruptly. What people describe as a tube microphone's warmth is largely that behaviour, arriving before anything downstream has had a chance to act.
It is worth knowing that this is a colour, not a quality. A tube microphone on a source that is already thick makes it thicker, which is sometimes exactly wrong.
A ribbon microphone is a moving-conductor design like a dynamic, but it removes the coil entirely. Instead, a strip of aluminium foil — corrugated so it can flex without tearing, and only a couple of microns thick — is suspended directly between the poles of a magnet. The foil is the diaphragm and the conductor at once.
Because nothing is attached to it, the moving mass is lower than in any other mechanical design, and ribbons follow transients extremely accurately. What they do not do is extend far at the top: the foil is large relative to short wavelengths and the response falls away in the upper register. This is why ribbons are described as dark. They are not filtering the highs out — they simply stop responding, and the effect is smooth rather than abrupt, which is why it tends to sound natural rather than muffled.
A ribbon is also inherently figure-8. Both faces of the foil are open to the air, so it responds to the pressure difference across itself, which makes it equally sensitive front and back and almost deaf at the sides. That is not a design choice layered on top; it falls out of the construction, and the next lesson explains why.
Then the warning, which is the one genuinely dangerous fact in this lesson. A ribbon is a tiny piece of foil under almost no tension. A strong gust of air can stretch or tear it — which means no plosives without protection, no moving one through a room facing forward, and never in front of a kick drum unless it was specifically built for it. Worse, a miswired cable carrying phantom power can destroy a vintage ribbon instantly. On a correctly wired balanced cable, phantom power appears equally on both conductors and the ribbon never sees a voltage across it. On a cable with a fault, or one wired to a different standard, it does see one — and a large current through a two-micron foil is a heater. Modern ribbons are usually protected; older ones are not, and there is no repairing it afterwards.
Three designs sit outside the main families but turn up often enough to be worth knowing.
Piezoelectric. Certain crystals and ceramics generate a voltage when they are physically deformed. Couple something to one and its movement becomes a signal directly — no magnet, no capacitor, no power. Piezo elements are cheap, robust and have a high output, but their response is uneven and their impedance is awkwardly high. Their real home is contact pickups: taped to an instrument body, they hear structural vibration rather than air, which is why a piezo on an acoustic guitar sounds nothing like a microphone in front of it.
Carbon granule. A chamber of carbon granules behind a diaphragm changes electrical resistance as the granules are compressed. It is noisy, distorted and narrow-band, and it is obsolete — but it powered telephones for the better part of a century, and its sound is so specific that it is still imitated deliberately when something needs to sound like it came down a phone line.
Boundary layer, or PZM. This one is a genuinely clever application of something you already know. A microphone in open air hears the direct sound and then, a moment later, its reflection from a nearby hard surface — and those two arrivals comb-filter each other. Mount the capsule flush against that surface instead, facing into it across a gap of a millimetre or two, and the direct and reflected sound arrive together. The comb filtering cannot happen because there is no delay between them to cause it. You also get the pressure doubling that occurs at any boundary, worth around 6 dB of free output. A boundary mic on a table for a panel discussion, taped to the lid of a piano, or on a stage floor solves a problem no amount of repositioning a conventional mic can.
Two condensers can use identical electronics and sound completely different because of one thing the family name never mentions: how big the diaphragm is. The split is conventionally drawn at about 3/4 of an inch — above it a large-diaphragm condenser, below it a small-diaphragm one — and the trade between them is real physics rather than marketing.
A large diaphragm intercepts more sound energy, so it produces more output for the same pressure, which means better sensitivity and a lower noise floor. That is why large-diaphragm condensers dominate vocal recording, where the source is often quiet and the noise floor is what limits you.
But a large diaphragm is also large compared to a short wavelength, and that has consequences it cannot escape. Off-axis sound arrives at different parts of the surface at slightly different times and partially cancels, so the polar pattern narrows unevenly at high frequencies and the off-axis response becomes less consistent. The diaphragm also has more mass and more area to flex, which introduces resonances of its own. Much of what people describe as a large-diaphragm microphone having character is this — not a flaw exactly, but not accuracy either.
A small diaphragm reverses every term. Less output and a higher noise floor, but a far more consistent polar pattern across frequency, better off-axis behaviour, and a more accurate transient response because there is less to move. This is why small-diaphragm condensers are the standard choice for acoustic instruments, cymbals, orchestral work and any stereo pair, where what happens off axis matters as much as what happens in front.
The practical shorthand: reach for a large diaphragm when the source is quiet and you want flattery, and a small one when the source is detailed and you want the truth — including the truth about the room around it.
Ask what the source is doing to the air, not what the microphone costs. If the source is loud and blunt and you want its edge softened, the mass of a moving coil is a feature. If the source is quiet or delicate and you need what it actually did, a condenser's low mass is the only thing that will get it. If the top end needs to be smooth and the source sits in front of the mic with something behind it you want gone, a ribbon's figure-8 and natural roll-off do both jobs at once. And if the problem is a reflective surface you cannot move, put the microphone on it.
Pick the transducer for the job, not the price. A dynamic on a screaming amp is not a compromise, it is the right answer — and a condenser there is not an upgrade, it is a repair bill.
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